3-Aryl-4-Isoxazolecarboxylic Acids as Plant Growth Regulants

The invention relates to the use of 3-aryl-4-isothiazolecarboxylic acids, 3-aryl-4-isoxazolecarboxylic acids and derivatives thereof as plant growth regulants. More specifically, the invention is directed to the application of certain chemicals compounds to leguminous plants in order to regulate the growth of said plants.

The novel carboxylic acids and their derivatives may be requested by the formula ##STR1## wherein E is oxygen or sulfur; X and Y are independently selected from the group consisting of hydrogen, lower alkyl, lower alkoxy, trifluoromethyl, halogen, cyano and nitro; n is zero or one provided that when n is zero, Z is selected from the group consisting of chloro and NR.sub.1 R.sub.2 wherein R.sub.1 and R.sub.2 are independently selected from the group consisting of hydrogen and lower alkyl; when n is one, Z is selected from the group consisting of hydrogen, alkyl having up to 12 carbon atoms inclusive, haloalkyl, benzyl, lower alkoxy, lower alkyl, allyl, monochlorinated allyl, dichlorinated allyl, ##STR2## and agriculturally acceptable cations; wherein R.sub.1 and R.sub.2 are as previously defined, R.sub.3 is hydrogen or methyl and R.sub.4 is lower alkyl.

As used herein, the term "lower alkyl" and "lower alkoxy" is understood to include those alkyl and alkoxy groups having up to 5 carbon atoms, inclusive. The term "haloalkyl" is understood to mean those lower alkyl groups which have been substituted with from 1 to 3 halogen atoms, inclusive. The term "agriculturally acceptable cations" is understood to mean those cations that are commonly used to form the salt of the free acid. Such cations include, but are not limited to, alkali metal, alkaline earth, substituted amine and ammonium cations. The term "alkyl" includes primary, secondary and tertiary alkyls.

The carboxylic acids and their derivatives of the foregoing formula may be prepared by a number of different procedures. Scheme A, summarized below, illustrates a procedure for preparing 3-aryl-4-isothiazolecarboxylic acids as well as esters thereof. ##STR3##

In accordance with Scheme A, 1.25 - 1.50 equivalents of chlorocarbonylsulfenyl chloride prepared in accordance with British Pat. No. 1,079,348 is dissolved in a suitable solvent, such as toluene, along with the appropriate benzamide. The solution is stirred and heated at approximately 100 .degree. C. until gas evolution has nearly ceased and/or until an infrared spectrum has revealed the absence of residual amide. Up to 5.0 equivalents of chlorocarbonylsulfenyl chloride can be employed with less reactive amides. Concentration of the reaction mixture under vacuum and crystallization of the residue from an appropriate solvent results in a 5-aryl-1,3,4-oxathiazol-2-one.

A solution of 0.10 moles of the oxathiazolone and 0.20 moles of dimethyl acetylenedicarboxylate in 60 ml of an appropriate solvent, such as chlorobenzene, is stirred at reflux until CO.sub.2 evolution ceases. After removal of the solvent and the excess dimethyl acetylenedicarboxylate, the dimethyl 4,5-isothiazoledicarboxylate is crystallized from an appropriate solvent.

The dicarboxylate is then hydrolyzed by first treating the dimethyl 4,5-isothiazoledicarboxylate with an excess of sodium hydroxide in water. For very insoluble esters, a small amount of dioxane may be added to the reaction mixture. The resultant solution may then be acidified to a pH of less than 1.0 with an excess of concentrated hydrochloric acid and then extracted several times with ether. The ether layers are combined, dried (CaSO.sub.4), and concentrated under vacuum.

3-Aryl-4-isothiazolecarboxylic acid may then be prepared by monodecarboxylation of the 4,5-isothiazoledicarboxylic acids effected by heating said diacid in an appropriate solvent, such as o-dichlorobenzene at reflux. The solution is then allowed to cool and the solid product collected, washed and recrystallized.

Esters of the isothiazole-4-carboxylic acid may then be obtained by heating said acid with an excess of thionyl chloride at reflux. The resultant solution is concentrated under vacuum and heated at reflux with the appropriate alcohol. The solution may then be concentrated to give pure ester or in the case of solids, the solid may then be recrystallized.

In order to illustrate the preparation of 3-aryl-4-isothiazolecarboxylates by the methods of Scheme A, the following examples are presented.

All examples presented herein are only for purposes of illustration and are not intended as a limitation in the scope of the invention. All temperatures are understood to be Centigrade.

5-Aryl-1,3,4-oxathiazol-2-ones may be prepared in accordance with Examples 1-5.

Chlorocarbonylsulfenyl chloride was prepared by a literature procedure. A mixture of 784.9 g (4.22 mol) of trichloromethanesulfenyl chloride and 76 g (4.22 mol) of water dissolved in 886 ml of concentrated H.sub.2 SO.sub.4 was stirred at 45.degree.-50.degree. for 1 hour in a 51. flask, at which time the initially-copious HC1 evolution had ceased. (Foaming presented problems in the beginning.) The mixture was transferred to a separatory funnel, and after 15 minutes, the layers were separated. The top, fluid layer, which amounted to 404.3 g (3.08 mol, 73% yield) of fairly pure chlorocarbonylsulfenyl chloride, was added to 373 g (3.08 mol) of benzamide in 1 1. of toluene in a 5 1. flask fitted with stirrer and reflux condenser. The mixture was stirred vigorously and was heated gently to 58.degree.. A mildly exothermic reaction carried the temperature to 65.degree. with foaming and vigorous gas evolution. The mixture was heated at 65.degree. for 20 minutes, at 70.degree. for 8 hours, at 70.degree.-110.degree. for 0.5 hours, and at 110.degree. for 0.75 hours, at which time gas evolution had ceased. The reaction mixture was concentrated under vacuum to 1.5 mm and 90.degree.. The residue was heated with 650 ml of methylcyclohexane; the mixture was treated with charcoal, filtered, and allowed to cool. The resultant solid was recrystallized from 650 ml of methylcyclohexane, heated to 75 (charcoal treatment and filtration) to give 375 g of very pale yellow solid, 5-phenyl-1,3,4 -oxathiazol-2-one, m.p. 64.degree.-67.degree.. An additional 27.2 g of product, m.p. 64.degree.-67.degree., was obtained from the filtrates. The total yield, 412.2 g, corresponds to 75% of the theoretical amount.

m-Toluamide (116 g, 0.86 mol) and chlorocarbonylsulfenyl chloride (144 g, 1.1 mol, 28% excess) were heated to 100.degree. C. in 400 ml of toluene, with stirring, for 5.5 hours. Cooling resulted in an orange solid. The solid, isolated by filtration, was dissolved in hot methylcyclohexane and decolorized. The light yellow product was recrystallized once from methyl-cyclohexane to give 76.05 g (45.8%) of white solid, m.p. 82. 5.degree.-84.degree..

Anal. Calc'd. for C.sub.9 H.sub.7 NO.sub.2 S: C, 55.94; H, 3.65.

Found: C, 56.07; H, 3.59.

Preparation of 5-(m-Chlorophenyl)-1,3,4-Oxathiazol-2-One. m-Chlorobenzamide (75 g. 0.48 mol) and chlorocarbonylsulfenyl chloride (79 g, 0.6 mol, 25% excess) were reacted as described in Example 2 for 1.5 hours. Volatile components were removed under reduced pressure. The dark brown oil was taken up in hot cyclohexane, and the mixture was filtered. Cooling resulted in separation of a dark orange solid. The solid, recrystallized twice from hot ethyl acetate, gave 64.21 g (0.316 mol, 65.8%) of off-white slid, m.p. 83.degree.-84.5.degree..

Anal. Calc'd. for C.sub.8 H.sub.4 ClNO.sub.2 S: C, 44.97; H, 1.89. Found: C, 44.92; H, 1.62.

Preparation of 5-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-1,3,4-Oxathiazol-2-One. .alpha.,.alpha.,.alpha.-Trifluoro-m-toluamide (82.7 g, 0.437 mol) and chlorocarbonylsulfenyl chloride (86 g, 0.667 mol, 53% excess) were reacted under the conditions of Example 2 for 0.5 hours. The light yellow residue was dissolved in ethyl acetate and cooled to -78.degree.. The white precipitate was filtered and washed with hexane to yield 93.14 g (0.377 mol, 86.2%) of white solid, m.p. 85.degree.-86.5.degree..

Anal. Calc'd. for C.sub.9 H.sub.4 F.sub.3 NO.sub.2 S: C, 43.73; H, 1.63. Found: C, 43.66; H, 1.58.

Preparation of 5-(.alpha.,.alpha.,.alpha.,.alpha.',.alpha.',.alpha.'-Hexafluoro-3,5- Xylyl)-1,3,4-Oxathiazol-2-One. 3,5-Bis(trifluoromethyl)benzamide (60.5 g, 0.235 mol) and five equivalents of chlorocarbonylsulfenyl chloride (154 g, 1.175 mol) were heated in 600 ml of toluene at reflux, with stirring, for 12 hours. The crude product, a dark brown oil, weighed 77.5 g. After decolorization in hexane, the material was taken up in methanol and recrystallized three times to give 22.0 g (0.0699 mol, 29.75%) of pale gold solid, m.p. 61.degree.-62.5.degree..

Anal. Calc'd. for C.sub.10 H.sub.3 F.sub.6 NO.sub.2 S: C, 38.11; H, 0.96. Found: C, 38.22; H, 0.90.

Additionally, the following compounds may be prepared in accordance with Examples 1-5.

5-(3',4'-dimethoxyphenyl)-1,3,4-oxathiazol-2-one, m.p. 143.degree.-144.5.degree..

5-(3',4'-dichlorophenyl)-1,3,4-oxathiazol-2-one, m.p. 130.5.degree.-131.5.degree..

5-(p-cyanopheny)-1,3,4-oxathiazol-2-one, m.p. 173.degree. with decomposition.

5-(p-nitrophenyl)-1,3,4-oxathiazol-2-one, m.p. 168.degree.-169.degree. with decomposition.

5-(p-chlorophenyl)-1,3,4-oxathiazol-2-one, m.p. 129.degree.-131.degree..

5-(m-nitrophenyl)-1,3,4-oxathiazol-2-one, m.p. 95.degree.-96.5.degree..

The dicarboxylate may be prepared in accordance with Examples 6-13.

Preparation of Diethyl 3-Phenyl-4,5-Isothiazoledicarboxylate. A solution of 412.2 g (2.3 mol) of 5-phenyl-1,3,4-oxathiazol-2-one, 662.7 g (4.66 mol) of dimethyl acetylenedicarboxylate, and 1 l. of chlorobenzene was heated at 135.degree. for 6.5 hours, at which time CO.sub.2 evolution became very slow. Infrared and gas chromatography assays also indicated that the reaction was complete. The reaction mixture was concentrated under vacuum to 0.2 mm and 90.degree.. The 680 g of pot residue was crystallized from about 700 ml of methanol to give 393 g of solid dimethyl 3-phenyl-4,5-isothiazoledicarboxylate, m.p. 70.degree.-71.5.degree.. An additional 69.9 g of solid, m.p. 70.degree.-72.degree., was obtained from the filtrate. The total of 462.9 g amounted to a 72.7% yield.

Preparation of Dimethyl 3-(.alpha.,.alpha.,.alpha.,.alpha.',.alpha.',.alpha.'-Hexafluoro-3,5-Xylyl )-4,5-Isothiazoledicarboxylate. A solution of 20.7 g (0.0657 mol) of 5-(.alpha.,.alpha.,.alpha.,.alpha.',.alpha.',.alpha.'-hexafluoro-3,5-xylyl )-1,3,4-oxathiazol-2-one and 18.7 g (0.131 mol) of dimethyl acetylenedicarboxylate in 52 g of o-dichlorobenzene was held at reflux for 10 hours (gas chromatography assay revealed the product had formed in 77% yield) and was concentrated under vacuum to 90.degree. at 0.5 torr. The residue was crystallized from methanol to give 17.9 g of solid, m.p. 71.degree.-74.degree.. The solid was recrystallized to give 14.3 g (53% yield) of white solid, m.p. 73.degree.-75.degree..

Anal. Calc'd. for C.sub.15 H.sub.9 F.sub.6 NO.sub.4 S: C, 43.59; H, 2.19. Found: C, 43.77; H, 2.13.

Preparation of Dimethyl 3-(3,4-Dimethoxyphenyl)-4,5-Isothiazoledicarboxylate. 5-(3,4-Dimethoxyphenyl)-1,3,4-oxathiazol-2-one (58 g, 0.24 mol) and dimethyl acetylenedicarboxylate (70 g, 0.49 mol) were heated at reflux in 120 ml of chlorobenzene for 43 hours. The residue crystallized from methanol at -29.degree., was recrystallized once from methanol, twice from ethyl acetate, and twice from methylcyclohexane to yield 59.07 g (0.175 mol, 73.0%) of pale yellow solid, m.p. 113.5-114.5.degree..

Anal. Calc'd. for C.sub.15 H.sub.15 NO.sub.6 S: C, 53.41; H, 4.48. Found: C, 53.03; H, 4.46.

Preparation of Dimethyl 3-(3,4-Dichlorophenyl)-4,5-Isothiazoledicarboxylate 5-(3,4-Dichlorophenyl)-1,3,4-oxathiazol-2-one (99.2 g, 0.4 mol) and dimethyl acetylenedicarboxylate (113.5 g, 0.8 mol) were heated in 240 ml of chlorobenzene at reflux for 47 hours. The product, from hot methanol, was recrystallized twice from hot methanol to give 97.8 g (0.283 mol, 70.7%) of white solid, m.p. 105.degree.-107.degree..

Anal. Calc'd. for C.sub.13 H.sub.9 Cl.sub.2 NO.sub.4 S: C, 45.10; H, 2.62. Found: C, 45.12; H, 2.58.

Preparation of Dimethyl 3-(p-Cyanophenyl)-4,5-Isothiazoledicarboxylate. Dimethyl acetylenedicarboxylate (42.63 g, 0.4 mol) and 5-(p-cyanophenyl)-1,3,4-oxathiazol-2-one (20.42 g, 0.1 mol) were heated at reflux in o-dichlorobenzene for 10 hours. Volatile materials were removed under reduced pressure (1 mm). The red-brown residue contained at least three contaminants (g.c.) which were removed by crystallization from methanol. Four recrystallizations resulted in 18.1 g (0.0598 mol, 59%) of light yellow solid, m.p. 134.degree.-135.degree..

Anal. Calc'd. for C.sub.14 H.sub.10 N.sub.2 O.sub.4 S: C, 55.62; H, 3.33. Found: C, 55.55; H, 3.23.

Preparation of Dimethyl 3-(p-Nitrophenyl)-4,5-Isothiazoledicarboxylate. Dimethyl acetylenedicarboxylate (85.26 g, 0.6 mol) and 5-(p-nitrophenyl)-1,3,4-oxathiazol-2-one (33.63 g, 0.15 mol) were heated as given above for 15 hours. Crystallization of the brown solid from methanol (2X) gave little improvement in purity. The brown solid as decolorized in ethyl acetate solution and recrystallized (3X) to give 12.2 g (0.0378 mol, 25.2%) of dark gold solid, m.p. 142.degree.-143.degree..

Anal. Calc'd. for C.sub.13 H.sub.10 N.sub.2 O.sub.6 S: C, 48.45; H, 3.13. Found: C, 48.76; H, 3.18.

Preparation of Dimethyl 3-(m-Tolyl)-4,5-Isothiazoledicarboxylate. 5-m-Tolyl-1,3,4-oxathiazol-2-one (19.32 g, 0.1 mol) and dimethyl acetylenedicarboxylate (28.42 g, 0.2 mol) were heated at reflux in 60 ml of chlorobenzene as given above. After the initial crystallization from cold methanol, three recrystallization from diethyl ether/petroleum ether gave 15.18 g (0.0522 mol, 52.2%) of white solid, m.p. 53.degree.-54.5.degree..

Anal. Calc'd. for C.sub.14 H.sub.13 NO.sub.4 S: C, 57.72; H, 4.50. Found: C, 57.79; H, 4.20.

Preparation of Dimethyl 3-(m-Chlorophenyl)-4,5-Isothiazoledicarboxylate. 5-(m-Chlorophenyl)-1,3,4-oxathiazol-2-one (21.37 g, 0.1 mol) and dimethyl acetylenedicarboxylate (28.42 g, 0.2 mol) were heated in 60 ml of chlorobenzene at reflux as above for 32 hours. After crystallization once from methanol and twice from diethyl ether/petroleum ether, 16.11 g (0.0517 mol, 51.7%) of pale yellow solid was obtained, m.p. 69.degree.-70.degree..

Anal. Calc'd. for C.sub.13 H.sub.10 ClNO.sub.4 S: C, 50.09; H, 3.23. Found: C, 50.24; H, 3.42.

Hydrolysis of the dicarboxylate is illustrated by Examples 14-19.

Preparation of 3-(.alpha.,.alpha.,.alpha.,.alpha.',.alpha.', .alpha.'-Hexafluoro-3,5-Xylyl)-4,5-Isothiazoledicarboxylic Acid. A mixture of 14.7 g (0.0356 mol) of dimethyl 3-(.alpha.,.alpha.,.alpha.,.alpha.',.alpha.',.alpha.'-hexafluoro-3,5-xylyl )-4,5-isothiazoledicarboxylate, 7.2 g (0.18 mol) of NaOH, and 45 ml of water was held at reflux for 2 hours, was cooled, extracted twice with ether, and acidified with 30 ml (0.36 mol) of concentrated HCl The resultant mixture was extracted three times with ether; these ether extracts were combined, dried (CaSO.sub.4), and concentrated under vacuum to 12.8 g (93.4%) of white solid, m.p 193.degree.-193.5.degree. with decomposition.

Anal. Calc'd. for C.sub.13 H.sub.5 F.sub.6 NO.sub.4 S: C, 40.53; H, 1.31. Found: C, 40.31; H, 1.18.

Preparation of 3-(3,4-Dimethoxyphenyl)-4,5-Isothiazoledicarboxylic Acid. The diester was hydrolyzed with five equivalents of NaOH in aqueous dioxane at reflux for 3 hours. The mixture was cooled, acidified with concentrated HCl, and extracted several times with ether (total volume = 3 l.) and with 1.5 l. of 1:1 ether-THF. The organic layers were combined, dried (CaSO.sub.4), and concentrated to give 45.06 g of crude product. A sample was recrystallized twice from 90% aqueous ethanol to give a hydrated product, m.p. 190.5.degree.-191.5.degree. with decomposition (fast), m.p. 216.degree.-217.degree. with decomposition (slow; monoacid).

Anal. Calc'd. for C.sub.13 H.sub.11 NO.sub.6 S.multidot.0.7 H.sub.2 O: C, 48.50; H, 3.88. Found: C, 48.73; H, 4.10.

Preparation of 3-(3,4- Dichlorophenyl)-4,5-Isothiazoledicarboxylic Acid. A mixture of 51.9 g (0.15 mol) of dimethyl 3-(3,4-dichlorophenyl)-4,5-isothiazoledicarboxylate and 30 g (0.75 mol) of NaOH in 150 ml of water was held at reflux for 2 hours, was cooled, acidified with HCl, and was extracted with ether several times (total ether volume equals 1300 ml). The ether solution was dried (CaSO.sub.4) and concentrated to give 46.12 g of solid. A small sample was recrystallized twice from water and once from ether-dichloroethane to give pure product, m.p. 187.5 -188.5.degree. with decomposition (fast).

Anal. Calc'd. for C.sub.11 H.sub.5 Cl.sub.2 NO.sub.4 S: C, 41.53; H, 1.58. Found: C, 41.56; H, 1.60.

Preparation of 3-(m-Tolyl)-4,5-Isothiazoledicarboxylic Acid. Dimethyl 3-(m-tolyl)-4,5-isothiazoledicarboxylate (14.03 g, 0.0548 mol) was hydrolyzed in NaOH (10.96 g, 0.274 mol) and 50 ml H.sub.2 O for 0.5 hours at reflux. Acidification with HCl, extraction with ether and recrystallization gave a light yellow solid, m.p. 166.5.degree.-167.degree. with decomposition.

Anal. Calc'd. for C.sub.12 H.sub.9 NO.sub.4 S: C, 54.75; H, 3.45. Found: C, 54.54; H, 3.63.

Preparation of 3-(m-Chlorophenyl)-4,5-Isothiazoledicarboxylic Acid. Dimethyl 3-(m-chlorophenyl)-4,5-isothiazoledicarboxylate (14.51 g. 0.0504 mol) was hydrolyzed as given above with NaOH (10.08 g. 0.252 mol) and then acidified with HCl. The purified yellow solid had m.p. 185.degree.-6.degree. with decomposition (rapid heating of the sample produced normal decomposition in this temperature range; slow heating caused a color change to red and m.p. 217.5.degree.-218.5.degree. with decomposition. Infrared of material heated slowly to 190.degree. showed that it was 3-(m-chlorophenyl)-4-isothiazolecarboxylic acid).

Anal. Calc'd. for C.sub.11 H.sub.6 ClNO.sub.4 S: C, 46.57; H, 2.13. Found: C, 46.50; H, 2.17.

Prepared of 3-(-Chlorophenyl)-4,5-Isothiazoledicarboxylic Acid. Dimethyl 3-(p-chlorophenyl)-4,5-isothiazoledicarboxylate (35.0 g, 0.112 mol) was hydrolyzed in NaOH (22.6 g, 0.56 mol) as stated above. Acidification with HCl and the usual workup as in Example 14 gave a purified pale yellow solid which had m.p. 177.degree.-177.5.degree. with decomposition.

Anal. Calc'd, for C.sub.11 H.sub.6 ClNO.sub.4 S: C, 46.57; H, 2./3. Found: C, 46.22; H, 2.26.

Decarboxylation of the dicarboxylic acids to the corresponding monoacid is illustrated by Examples 20-25.

Preparation of 3-(m-Tolyl)-4-Isothiazolecarboxylic Acid. 3-(m-Tolyl)-4,5-isothiazoledicarboxylic acid (7.98 g, 0.0303 mol) was heated in 25 ml of o-dichlorobenzene at vigorous reflux for 15 minutes and cooled. Hexane was added and the resultant precipitate was filtered off to yield 5.52 g (0.0258 mol, 83.1%) of a light pink solid, m.p. 144.5.degree.-146.degree..

Anal. Calc'd. for C.sub.11 H.sub.9 NO.sub.2 S: C, 60.26; H, 4.14. Found: C, 60.21; H, 4.04.

Preparation of 3-(m-Chlorophenyl)-4-Isothiazole-carboxylic Acid. 3-(m-Chlorophenyl)- 4,5-isothiazoledicarboxylic acid (8.0 g, 0.0282 mol) was reacted as previously stated. The dark tan solid was crystallized from ethylene chloride/acetonitrile solution to give 5.84 g (0.0244 mol, 86.6%) of white solid, m.p. 215.degree.-216.degree..

Anal. Calc'd for C.sub.10 H.sub.6 ClNO.sub.2 S: C, 50.11; H, 2.52. Found: C, 50.32; H, 2.47.

Preparation of 3-(p-Chlorophenyl)-4-Isothiazolecarboxylic Acid. 3-(p-Chlorophenyl)-4,5-isothiazoledicarboxylic acid recrystallization residues were heated at reflux as given above for 0.5 hours. On cooling a tan precipitate formed which was crystallized from acetonitrile and from ethylene chloride to yield a white solid having m.p. 181.5.degree.-182.5.degree..

Preparation of 3-(.alpha.,.alpha.,.alpha., .alpha.', .alpha.', .alpha.'-Hexafluoro-3,5-Xylyl)-4-Isothiazoledicarboxylic Acid. A solution of 11.7 g of diacid in 100 ml of o-dichlorobenzene and 30 ml of ether was heated on a hot plate, and the ether was allowed to distill off. The solution was allowed to boil at 180.degree. for 10 minutes, was cooled, and was filtered to give a solid. This material was recrystallized from heptane to give 5.52 g of white solid, m.p. 152.degree.-154.degree..

Anal. Calc'd for C.sub.12 H.sub.5 F.sub.6 NO.sub.2 S: C, 42.24; H, 1.48. Found: C, 42.13; H, 1.34.

An additional 3.14 g of solid, m.p. 151.degree.-153.5.degree. was obtained by concentration of the o-dichlorobenzene filtrate and crystallization of the residue once from heptane and once from 1,2-dichloroethane.

Preparation of 3-(3,4-Dimethoxyphenyl)(-4-Isothiazolecarboxylic Acid. A 42 g sample of diacid was heated in 100 ml of nitrobenzene at reflux for 15 minutes. The solution was cooled, diluted with 150 ml of hexane, and filtered. The resultant solid was crystallized twice from dioxane and once from 85% aqueous ethanol to give 32.6 g (90%) of solid, m.p. 215.5.degree.-216.degree. with decomposition.

Anal. Calc'd. for C.sub.12 H.sub.11 NO.sub.4 S.0.2 H.sub.2 O: C, 53.60; H, 4.27. Found: C, 53.63; H, 4.20.

A small sample was recrystallized twice from ethyl acetate and dried at 80.degree. (.degree.0.1 torr).

Anal. Calc'd for C.sub.12 H.sub.11 NO.sub.4 S: C, 54.33; H, 4.18. Found: C, 54.32; H, 4.24.

Preparation of 3-(3,4-Dichlorophenyl)-4-Isothiazolecarboxylic Acid. A 19.1 sample of diacid was heated in o-dichlorobenzene at reflux for 15 minutes. Cyclohexane was added to the cooled mixture, and the resultant 14.41 g of solid was recrystallized from 90% aqueous ethanol and from ethertoluene to give pure product, m.p. 247.degree.-247.5.degree. with decomposition.

Anal. Calc'd for C.sub.10 H.sub.5 Cl.sub.2 NO.sub.2 S: C, 43.82; H, 1.84. Found: C, 43.84; H, 1.87.

Additionally, the following compounds have been prepared.

3-phenyl-4-isothiazolecarboxylic acid, m.p. 166.degree.-7.degree. C.

Anal. Calc'd. for C.sub.10 H.sub.7 NO.sub.2 S: C, 58.52; H, 3.44; N, 6.83. Found: C, 58.70; H, 3.40; N, 6.88. 3-(m-trifluoromethylphenyl)-4-isothiazolecarboxylic acid, m.p. 123.degree.-124.5.degree. C.

Anal. Calc'd for C.sub.11 H.sub.6 F.sub.3 NO.sub.2 S: C, 48.71; H, 2.23. Found: C, 48.73; H, 2.26.

3-(p-tolyl)-4-isothiazolecarboxylic acid, m.p. 179.5.degree.-181.degree. C.

Anal. Calc'd, for C.sub.11 H.sub.9 NO.sub.2 S: C, 60.26; H, 4.14. Found: C, 60.49; H, 4.10.

3-(m-nitrophenyl)-4-isothiazolecarboxylic acid, m.p. 234.degree.-235.5.degree. C.

Anal. Calc'd. for C.sub.10 H.sub.6 N.sub.2 O.sub.4 S: C, 48.00; H, 2.42; N, 11.20. Found: C, 48.08; H, 2.38; N, 11.06. 3-(p-nitrophenyl)-4-isothiazolecarboxylic acid, m.p. 264.5.degree.-265.5.degree.C.

Examples 26-45 illustrate the esterification of 3-aryl-4-isothiazolecarboxylic acid by preparing the acid chloride with thionyl chloride and reacting said acid chloride with the appropriate alcohol.

Preparation of Methyl 3-(.alpha.,.alpha., .alpha.,.alpha.', .alpha.', .alpha.40 -Hexafluoro-3,5-Xylyl)-4-Isothiazolecarboxylate. A solution of 7.50 g (0.022 mol) of 3-(.alpha., .alpha., .alpha., .alpha.', .alpha.', .alpha.'-hexafluoro-3,5-xylyl)-4-isothiazolecarboxylic acid and 20 ml (32.8 g, 0.276 mol) of thionyl chloride was held at reflux on a steam bath for 0.5 hours and was concentrated under vacuum to 7.6 g of acid chloride, an oil.

A solution of 2.50 g of acid chloride and 10 ml of methanol was held at reflux for 0.5 hours, filtered, and concentrated to 90.degree. (0.4 torr) to 2.23 g (90% yield) of oil, n.sub.D.sup.23 = 1.4966, that slowly recrystallized; m.p. 45.degree.-46.5.degree..

Anal. Calc'd. for C.sub.13 H.sub.7 F.sub.6 NO.sub.2 S: C, 43.95; H, 1.99. Found: C. 44.12; H, 2.14.

Preparation of Ethyl 3-(.alpha.,.alpha., .alpha., .alpha.',.alpha.', .alpha.'- Hexafluoro-3,5-Xylyl)-4-isothiazolecarboxylate. Use of a similar procedure to that above gave the product in 96% yield as an oil, n.sub.D.sup.23 = 1.4901, that slowly crystallized; m.p. 61.5.degree.-63.degree..

Anal. Calc'd. for C.sub.14 H.sub.9 F.sub.6 NO.sub.2 S: C, 45.53; H, 2.46. Found: C, 45.31; H, 2.51.

Preparation of Propyl 3-(.alpha.,.alpha., .alpha., .alpha.', .alpha.', .alpha. '-Hexafluoro-3,5-Xylyl)-4-Isothiazolecarboxylate. A solution of 2.50 g of acid chloride and 10 ml of 1-propanol was heated on a steam bath for 2 hours, filtered, and concentrated under vacuum to 90.degree. (0.4 Torr) to give 2.52 g (94% yield) of oil, n.sub.D.sup.23 = 1.4875.

Anal. Calc'd. for C.sub.15 H.sub.11 F.sub.6 NO.sub.2 S: C, 47.00; H, 2.89. Found: C, 47.01; H, 2.86.

Preparation of Ethyl 3-(3,4-Dimethoxyphenyl)-4-Isothiazolecarboxylate. A solution of 26.7 g (0.112 mol) of acid and 70.3 g (5equivalents) of thionyl chloride was heated on a steam bath for 0.75 hours, concentrated under vacuum, heated in 50 ml of ethanol at reflux for 45 minutes, concentrated under vacuum, and the residue was crystallized from ethanol-hexane to give 32.05 g (98%) of solid, m.p. 74.degree.-75.5.degree..

Anal. Calc'd. for C.sub.14 H.sub.15 NO.sub.4 S: C, 57.32; H, 5.15. Found: C, 57.36; H, 5.14.

Preparation of Methyl 3-(.alpha.,.alpha., .alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylate. A solution of 2.92 g (0.010 mol) of 3-(.alpha., .alpha., .alpha.-trifluoro-m-tolyl)-4-isothiazolecarbonyl chloride prepared as in Example 29 and 10 ml of methanol was held at reflux for 0.5 hours and was concentrated under vacuum to 80.degree. (0.3 torr) to 2.72 g of oil, n.sub.D.sup.23.4.degree. = 1.5404.

Anal. Calc'd. for C.sub.12 H.sub.8 F.sub.3 NO.sub.2 S: C, 50.17; H, 2.81. Found: C, 50.26; H, 2.88.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Isopropyl Ester. A solution of 2.92 g (0.010 mol) of acid chloride prepared as in Example 29 and 10 ml of isopropyl alcohol was heated on a steam bath for 1.5 hours, filtered, and concentrated under vacuum to 90.degree.0 (0.2 torr) to give 2.95 g of colorless oil, n.sub.D.sup.24 = 1.5225.

Anal. Calc'd. for C.sub.14 H.sub.12 F.sub.3 NO.sub.2 S: C, 53.33; H, 3.84. Found: C, 53.16; H, 3.77.

Preparation of 3-(.alpha.,.alpha., .alpha.-Trifluoro-m-Tolyl)-4-isothiazolecarboxylic Acid. 2,2,2-Trifluoroethyl Ester.

A solution of 2.50 g (0.00856 mol) of 3-(.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl)-4-isothiazolecarbonyl chloride and 50 ml of 2,2,2-trifluorethanol was held at reflux for 40 minutes, was allowed to stand overnight, and was concentrated under vacuum (to 90.degree. at 0.1 torr) to give 2.68 g (88%) of oil, n.sub.D.sup.24 = 1.4976.

Anal. Calc'd. for C.sub.13 H.sub.7 F.sub.6 NO.sub.2 S: C, 43.95; H, 1.99. Found: C, 43.73; H, 1.98.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, 2,2,2-Trichloroethyl Ester. A solution of 2.0 g (0.0069 mol) of 3-(.alpha.,.alpha., .alpha.-trifluoro-m-tolyl-4-isothiazolecarbonyl chloride and 1.22 g (1.18 equivalents) of 2,2,2-trichloroethanol was heated at 70.degree.-140.degree. in an oil bath for 6.5 hours. The reaction mixture was concentrated under vacuum to give 1.78 g of oil, n.sub.D.sup.23 = 1.5499 (yield 63.8%).

Anal. Calc'd. for C.sub.13 H.sub.7 Cl.sub.3 F.sub.3 NO.sub.2 S: C, 38.59; H, 1.74; N, 3.46. Found: C, 38.28; H, 1.69; N, 3.19.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, 2-Chloroethyl Ester. By a procedure similar to that used for Example 33, there was obtained 1.65 g of oil, n.sub.D.sup.23 = 1.5452 (yield 72%).

Anal. Calc'd. for C.sub.13 H.sub.0 ClF.sub.3 NO.sub.2 S: C, 46.51; H, 2.70; N, 4.17. Found: C, 46.54; H, 2.55; N, 4.10.

Preparation of 3-(.alpha.,.alpha., .alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, n-Octyl Ester. A solution of 1.0 g (0.0034 mol) of 3-(.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl-9-4-isothiazolecarbonyl chloride and 0.45 g (1 equivalent) of 1-octanol was heated on a steam bath for 2.0 hours. Threaction mixture was dissolved in ether, dried, filtered, and concentrated under vacuum to give 1.04 g of oil, n.sub.D.sup.23.2 = 1.5107 (yield 78.7%).

Anal. Calc's for C.sub.19 H.sub.22 F.sub.3 NO.sub.2 S: C, 59.21; H, 5.75; N, 3.63. Found: C, 59.06; H, 5.60; N, 3.63.

Preparation of 3-(.alpha.,.alpha., .alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, n-Hexyl Ester. By a procedure similar to that used for Example 35, using excess n-hexanol, there was obtained 0.91 g of oil, n.sub.D.sup.23 = 1.5094 (yield 74.9%).

Anal. Calc'd. for C.sub.17 H.sub.18 F.sub.3 NO.sub.2 S: C, 57.13; H, 5.08; N, 3.92. Found: C, 57.67; H, 5.15; N, 3.68.

Preparation of 3-(.alpha.,.alpha., .alpha.-Trifluoro-m-Tolyl-4-Isothiazolecarboxylic Acid, Allyl Ester. By a procedure similar to that used for Example 35, using excess alcohol, there was obtained 0.55 g of oil, n.sub.D.sup.23 = 1.5360 (yield 51.6%).

Anal. Calc'd for C.sub.14 H.sub.10 F.sub.3 NO.sub.2 S: C, 53.67; H, 3.22; N, 4.47. Found: C, C, 54.00; H, 3.56; N, 4.70.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, 2-Chloroallyl Exter. By a procedure similar to that used for Example 33, there was obtained 0.65 g of an oil, n.sub.D.sup.23.2 = 1.5468 (yield 55%).

Anal. Calc'd. for C.sub.14 H.sub.9 ClF.sub.3 NO.sub.2 S: C, 48.36; H, 2.61; N, 4.03. Found: C, 48.26; H, 2.69; N, 4.06.

Preparation of 3-(m-Nitrophenyl)-4-Isothiazolecarboxylic Acid, Ethyl Ester. A solution of 1.5 (0.006 mol) of the free acid prepared in accordance with Scheme A and excess thionyl chloride was heated on a steam bath for 0.75 hours. The reaction mixture was concentrated under vacuum. A solution of the residue and 15 cc of ethanol was heated on a steam bath for 0.75 hours and cooled to give a solid. The solid was recrystallized twice from ethanol to give 1.0 g solid, m.p. 136.5.degree.-138.degree.. The first filtrate residue was crystallized from ethanol to give 0.2 g solid, m.p. 132.degree.-136.degree.. (Total yield 71.9%).

Anal. Calc'd. for C.sub.12 H.sub.10 N.sub.2 O.sub.4 S: C, 51.79; H, 3.62; N, 10.07. Found: C, 51.85; H, 3.38; N, 10.07.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Propyl Ester. A solution of 2.92 g (0.010 mol) of 3-(.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl)-4-isothiazolecarbonyl chloride and 4 g (0.0667 mol) of 1-propanol was heated on a steam bath for 1 hour and was concentrated under vacuum to 70.degree. (0.5 torr) to give 3.17 g of clear oil, n.sub.D.sup.20.8 = 1.5261, infrared (film) 5.80 .mu..

Anal. Calc'd. for C.sub.14 H.sub.12 F.sub.3 NO.sub.2 S: C, 53.33; H, 3.84. Found: C, 53.67; H, 4.01.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Butyl Ester. A solution of 2.92 g (0.010 mol) of acid chloride and 0.80 g (0.0108 mol) of 1-butanol was heated in an oil bath at 110.degree. for 2 hours and was concentrated under vacuum to 90.degree. (0.4 torr) to give 3.01 g (91%) of oil, n.sub.D.sup.20.5 = 1.5221, infrared (film) 5.80 .mu..

Anal. Calc'd. for C.sub.15 H.sub.14 F.sub.3 NO.sub.2 S: C, 54.70; H, 4.28. Found: C, 54.46; 4.09.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoromethyl-m-Tolyl)-4-Isothiazolecarboxyli c Acid, 2-Butoxyetyl Ester. A solution of 2.92 g (0.010 mol) of acid chloride and 1.22 g (0.0103 mol) of 2-butoxyethanol was heated in an oil bath at 110-115.degree. for 3 hours and was concentrated under vacuum to 90.degree. (0.04 torr) to 3.66 g of oil, n.sub.D.sup.22.4 = 1.5152, infrared (film) 5.80 .mu..

Anal. Calc'd. for C.sub.17 H.sub.18 F.sub.3 NO.sub.3 S: C, 54.68; H, 4.86. Found: C, 54.67; H, 4.80.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, m-Cumenyl Ester. A solution of 2.92 g (0.010 mol) of acid chloride and 1.36 g (0.010 mol) of pure m-isopropylphenol was heated in an oil bath at 115.degree.-120.degree. for 2 hours and was concentrated under vacuum at 90.degree. (0.6 torr) to 3.90 g (100%) of oil, n.sub.D.sup.21 = 1.5611, infrared (film) 5.74 .mu..

Anal. Calc'd. for C.sub.20 H.sub.16 F.sub.3 NO.sub.2 S: C, 61.37; H, 4.12. Found: C, 61.22; H, 3.97.

Preparation of 3-(m-Chlorophenyl)-4-Isothiazolecarboxylic Acid, Ethyl Ester. Utilizing a procedure similar to Example 39, there was obtained a solid, m.p. 66.5.degree.-68.degree..

Anal. Calc'd. for C.sub.12 H.sub.10 ClNO.sub.2 S: C, 53.83; H, 3.76. Found: C, 53,86; H, 3.73.

Preparation of 3-(3',4'-Dichlorophenyl)-4-Isothiazolecarboxylic Acid, Ethyl Ester. Utilizing the procedure of Example 39, there was obtained a solid, m.p. 111.5.degree.-112.degree..

Anal. Calc'd. for C.sub.12 H.sub.9 Cl.sub.2 NO.sub.2 S: C, 47.70; H, 3.00. Found: C, 47.61; H, 3.02.

The 3-aryl-4-isothiazolecarboxylates of the invention may also be prepared by adding aryl Grignard reagent to alkyl cyanoacetate. The resultant .beta.-aminocinnamates are converted to the carboxylate via a Vilsmeir-Haack reaction, thiation and oxidation. For purposes of clarity, Scheme B is provided below. ##STR4##

In accordance with Scheme B, 1.0 mole of alkyl cyanoacetate is treated with two moles of aryl magnesium bromide in ether while stirring at temperatures from -75.degree. to room temperature. The mixture is then heated at reflux until gas chromatographic analysis of hydrolyzed aliquots of the reaction mixture revealed the reaction to be complete. Then, the reaction mixture is cooled to about 10.degree. or below and poured slowly into a 1.7 liter mixture of ice-water containing 2.0 moles of NH.sub.4 Cl. This mixture is shaken with an ice-cold solution of 2.0 moles of HCl in 500 ml of water. The layers are separated and the aqueous layer is then extracted with ether. The ether layers are combined, dried (CaSO.sub.4), and concentrated under vacuum to give crude alkyl .beta.-aminocinnamate.

To a solution of 0.10 moles of the appropriate alkyl .beta.-aminocinnamate in 90 ml of dimethylformamide is added 0.10 moles of phosphorous oxychloride while stirring at -60.degree. under dry N.sub.2. After warming to about 15.degree.-25.degree., the mixture is stirred at about 25.degree. for about ten minutes. The solution is then poured into an ice-cold solution of 0.11 moles of Na.sub.2 S.multidot.9H.sub.2 O in 110 ml of water. The resultant mixture is stirred for about five minutes and extracted with benzene. The benzene layers are dried (CaSO.sub.4) and then 0.1 moles of I.sub.2 in 200 ml of benzene is then added at 20.degree.-30.degree.. The dark benzene solution is then washed with an aqueous K.sub.2 CO.sub.3 solution and an aqueous solution of Na.sub.2 S.sub.2 O.sub.3. A third washing with an aqueous K.sub.2 CO.sub.3 solution, drying (CaSO.sub.4) and concentration under vacuum gives the crude isothiazolecarboxylate.

In order to illustrate the preparation of the 3-aryl-4-isothiazolecarboxylates by the methods of Scheme B, the following examples are presented.

The preparation of .beta.-aminocinnamates is illustrated by Examples 46-50 .

Preparation of Ethyl .beta.-Aminocinnamate. Bromobenzene (235 g, 1.5 mol) in 200 ml of anhydrous ether was added dropwise, with stirring, to 36.5 g of magnesium turnings (1.5 mol) in about 400 ml of ether according to literature methods. When addition was complete, the mixture was heated at reflux for one hour and then cooled to <20.degree.. To the cooled Grignard reagent was added dropwise, with stirring, 0.5 equivalents of ethyl cyanoacetate (84.9 g, 0.75 mol). The temperature was kept below 20.degree. by cooling in ice. During the addition, the formation of a gelatinous solid was noted. On completion of addition of the ester, a 2-ml aliquot of the reaction mixture was hydrolyzed with saturated NH.sub.4 Cl; gas chromatography of the ether layer showed that some product was already present. The reaction mixture was heated to reflux for 19 hours. Hydrolysis of the mixture with 1500 ml of ice-cold saturated NH.sub.4 Cl was exothermic. Extraction of this mixture with ether proved very difficult due to the presence of a persistent gummy emulsion, until it was determined that addition of 2N HCl to just the emulsion in the separatory funnel, only to the point of separation into 2 neat layers, would result in a pH decrease to about 7-7.5 without destroying the desired product. The ether extracts were dried (CaSO.sub.4) and concentrated under reduced pressure to yield 127.7 g of gold-yellow residue, which was vacuum distilled twice to give 86.01 g (60% yield by weight) of pure material, boiling point 110.degree.-112.degree. (0.2 mm).

Preparation of Ethyl .beta.-Amino-m-Trifluoromethylcinnamate. Phenylmagnesium bromide was prepared from 70 g (0.445 mol) of bromobenzene and 11.1 g (0.458 mol) of magnesium in 300 ml of ether. Then, 50.3 g (0.445 mol) of ethyl cyanoacetate was added dropwise with stirring at -55.degree. to -35.degree. (vigorous exothermic reaction after about 20-30% of the ethyl cyanoacetate added, even with Dry ice-acetone bath cooling). A very heavy precipitate formed that prevented stirring. The mixture was allowed to warm to 15.degree..

A solution of m-(trifluoromethyl)phenylmagnesium bromide, prepared from 100 g (0.445 mol) of m-bromobenzotrifluoride and 11.1 g (0.458 mol) of magnesium, in 300 ml of ether was added to the above mixture. The resultant mixture was stirred at reflux for 44 hours and then was cooled. A solution of 53 g (1.0 mol) of NH.sub.4 Cl in 300 ml of water was added slowly with stirring at 10.degree.-20.degree., and then 0.90 mol of 2N HCl was slowly added. The layers were shaken together in a separatory funnel and were separated. The aqueous layer was extracted with two 250-ml portions of ether. The ether layers were combined, dried (CaSO.sub.4), and concentrated under vacuum to 95.7 g of black oil. Gas chromatography assay of this oil on a 10 ft. 5% SE-30 column at 220.degree. showed there was less than 1% (none detected) of ethyl .beta.-aminocinnamate in the ethyl .beta.-amino-m-trifluoromethylcinnamate, which elutes first. Gas chromatography assay of a weighed aliquot of the oil with a weighed quantity of o-dichlorobenzene and use of a calibration mixture revealed that the 95.7 g of oil contained 74.8% product (62% yield). Distillation of the oil gave 72.9 g of 94% pure product (60% yield), boiling point 110-115.degree. (0.05 torr). Redistillation of a small amount of this material gave a 99-100% pure sample, boiling point 106.degree.-107.degree. (0.06 torr).

Anal. Calc'd for C.sub.12 H.sub.12 F.sub.3 NO.sub.2 : C, 55.60; H, 4.67. Found: C, 55.42; H, 4.36.

Preparation of Ethyl .beta.-Amino-p-Trifluoromethylcinnamate. To the Grignard reagent prepared from 98 g (0.436 mol) of p-bromobenzotrifluoride and 10.59 g (0.436 mol) of magnesium in ether was added 24.65 g (0.218 mol) of ethyl cyanoacetate dropwise with stirring and cooling in an ice bath. The resultant mixture was stirred at reflux for 24 hours. The usual workup gave 49.4 g of dark red-brown residue; distillation of this material gave 16.73 g (30%) of product, boiling point 120.degree.-123.degree. (0.15 torr).

Anal. Calc'd. for C.sub.12 H.sub.12 F.sub.3 NO.sub.2 : C, 55.60; H, 4.67. Found: C, 56.67; H, 4.63.

Preparation of Ethyl .beta.-Amino-m-Methylcinnamate. To 202 ml of 2.9 M phenylmagnesium bromide in ether (0.585 mol) was aded 100 ml of ether. Then, 66.1 g (0.585 mol) of ethyl cyanoacetate was added over a few minutes with stirring at -40.degree. to -15.degree.. A heavy, thick precipitate formed that made stirring difficult. The mixture was allowed to warm slowly to 20.degree.. Then, the Grignard reagent prepared from 100 g (0.585 mol) of 3-bromotoluene and 14.4 g (0.593 mol) of magnesium turnings in 300 ml of ether was added. The mixture was stirred at reflux for 4 hours, cooled, and poured slowly with stirring into 1 l. of ice-water mixture in which 62.6 g (1.17 mol) of NH.sub.4 Cl was dissolved. Then, an ice-cold solution of 1.17 mol of HCl in 300 ml of water was added with stirring. The two layers were shaken together and separated. The aqueous layer was extracted with two 200-ml portions of ether. The ether layers were combined, dried (CaSO.sub.4), and concentrated under aspirator vacuum to 112.0 g of oil that contained 78.4 g (65% yield) of product (gas chromatography assay with internal standard). The oil was distilled to give 83.2 g of 89% pure product (62% yield of ester), boiling point 120.degree.-130.degree. (0.08 torr). Redistillation of the product through a fractionating column gave 57.2 g (48%) of 97% pure product, boiling point 118.degree. (0.05 torr). A small sample was redistilled to give 100% pure material, boiling point 118.degree. (0.1 torr).

Anal. Calc'd. for C.sub.12 H.sub.15 NO.sub.2 : C, 70.22; H, 7.37. Found: C, 70.31; H, 7.44.

Preparation of Ethyl .beta.-Amino-m-Isopropylcinnamate. To the Grignard reagent prepared from 39.5 g (0.198 mol) of m-bromocumene and 4.9 g (0.20 mol) of magnesium in 150 ml of ether was added 11.2 g (0.099 mol) of ethyl cyanoacetate dropwise with stirring at 10.degree.. The mixture was stirred at reflux for 22 hours and was allowed to stand at 23.degree. for four days. Then, 10.6 g (0.20 mol) of NH.sub.4 Cl in 60 ml of water was added with stirring at 10.degree.-15.degree., followed by 0.20 mol of 2N HCl at 0.degree.. The layers were separated, and the water layer was extracted with 100 ml of ether. The ether layers were combined, extracted with dilute NaHCO.sub.3 solution, dried (CaSO.sub.4), and distilled to give 4.95 g of 80% pure product, boiling point 139.degree.-142.degree. (0.15 torr) and 0.87 g of about 97% pure product, boiling point 142.degree.-143.degree. (0.15 torr). [Infrared analysis of the lower-boiling impurity indicated it to be bi(m-cumenyl)].

Anal. Calc'd. for 97% C.sub.14 H.sub.19 NO.sub.2 -3% C.sub.18 H.sub.22 ; C, 72.60; H, 8.24; N, 5.82. Found: C, 72.60; H, 8.46; N, 5.84.

Preparation of 3-aryl-4-isothiazolecarboxylates from the .beta.-aminocinnamates is illustrated by Examples 51-55.

Preparation of Ethyl 3-Phenyl-4-Isothiazolecarboxylate. 1.91 g of ethyl .beta.-aminocinnamate (0.01 mol) and 6 ml of dimethyl formamide (5.68 g, 0.073 mol) were cooled to -60.degree., with stirring. Then 1.533 g (0.917 ml, 0.01 mol) of POCl.sub.3 was added and mixture allowed to warm up exothermically to about 25.degree.. It was then poured into an ice-cold solution of 2.40 g Na.sub.2 S nonahydrate (0.01 mol) in 10 ml of H.sub.2 O. This mixture was extracted three times with benzene. The benzene solution was dried (CaSO.sub.4). A mixture of 3.03 g of I.sub.2 in 50 ml of benzene was added to this material, dropwise with stirring; stirring was continued for 10 minutes more. It was extracted twice with 10% Na.sub.2 CO.sub.3 and then twice with 5% Na.sub.2 S.sub.2 O.sub.3. The benzene was dried (CaSO.sub.4), concentrated, and the residue redissolved in about 30 ml benzene plus 6.00 g of o-dichlorobenzene (internal gas chromatography standard) and assayed (gas chromatography) for percent product (best yield, 72.0%).

Preparation of 3-(m-Cumenyl)-4-Isothiazolecarboxylic Acid. To 5.8 g of about 80% pure ethyl .beta.-amino-m-isopropylcinnamate (about 0.02 mol) in 18 ml of DMF was added slowly 2.28 ml (3.82 g, 0.025 mol) of POCl.sub.3 with stirring at -60.degree.. The mixture was allowed to warm; an exothermic reaction carried the temperature to 0.degree.. The mixture was stirred for 10 minutes at 20.degree. and was poured into a cold solution of 7.20 g (0.030 mol) of Na.sub. 2 s.multidot.9H.sub.2 O in 30 ml of water. This mixture was stirred for 5 minutes and was extracted with three 40-ml portions of benzene. The benzene layers were combined, dried (CaSO.sub.4), treated with 6.35 g (0.025 mol) of I.sub.2 in 120 ml of benzene, stirred for 5 minutes, extracted three times with aqueous NaHCO.sub.3 solution and twice with aqueous sodium thiosulfate solution, and concentrated under vacuum to 6.1 g of an oil that was a 16:84 mixture (gas chromatography assay). The oil was heated with 4.0 g (0.10 mol) of NaOH in 80 ml of 50% aqueous ethanol at reflux for 1 hour. The solution was concentrated under vacuum, diluted with 200 ml of water, extracted three times with ether, and acidified with 17 ml of concentrated HCl (0.20 mol). The resultant mixture was extracted three times with ether. These three ether extracts were combined and concentrated under vacuum. The residue was crystallized from aqueous ethanol to give 2.96 g (60%) of solid, m.p. 143.degree.-157.degree.. The solid was recrystallized from 1,2-dichloroethane to give 2.04 g of solid, m.p. 157.degree.-159.degree.. Recrystallization of this material from 1,2-dichloroethaneheptane (charcoal) gave a white solid, m.p. 158.degree.-160.degree..

Example 52 illustrates the preparation of the free acid from which the ester may be prepared as illustrated in Example 53. The acid is prepared as an aid to purification.

Preparation of Ethyl 3-(m-Cumenyl)-4-Isothiazolecarboxylate

A mixture of 1.50 g (0.00608 mol) of 3-(m-cumenyl)-4-isothiazolecarboxylic acid and 5 ml (8.2 g, 0.069 mol) of thionyl chloride was heated at reflux on a steam bath for 30 minutes and was concentrated under vacuum. The residue was heated in 15 ml of ethanol at reflux for 15 minutes; the solution was filtered and concentrated under vacuum to 90.degree. (0.3 torr) to give 1.53 g (92%) of oil, n.sub.D.sup.23.degree. = 1.5693.

Anal. Calc'd. for C.sub.15 H.sub.17 NO.sub.2 S: C, 65.43; H, 6.22. Found: C, 65.46; H, 6.30.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-p-Tolyl)-4-Isothiazolecarboxylic Acid. Using the same procedure of Example 51 but starting with 16.2 g of ethyl .beta.-amino-p-trifluoromethylcinnamate gave 17.09 g of crude ethyl 3-(.alpha.,.alpha.,.alpha.-trifluoro-p-tolyl)-4-isothiazolecarboxylate. This material was heated with five equivalents of NaOH in 50 ml of water at reflux for 5 hours. The solution was cooled, extracted with ether, acidified with HCl, and extracted with ether. The latter ether extract was dried (CaSO.sub.4) and concentrated under vacuum. The residue was crystallized three times from 1,2-dichloroethane to give 4.0 g (23%) of solid, m.p. 195.degree.-196.degree..

Anal. Calc'd. for C.sub.11 H.sub.6 F.sub.3 NO.sub.2 S: C, 48.35; H, 2.21. Found: C, 48.39; H, 2.24.

Preparation of Ethyl 3-(.alpha.,.alpha. ,.alpha.-Trifluoro-p-Tolyl)-4-Isothiazolecarboxylate. A solution of 2.5 g (0.0091 mol) of acid and 5.36 g (five equivalents) of thionyl chloride was heated for 0.5 hours on a steam bath and concentrated under vacuum. The residue was heated in 50 ml of ethanol at reflux for 1 hour. Concentration of the solution and crystallization of the residue from ethanol gave 1.41 g (51%) of solid, m.p. 63.degree.-64.degree..

Anal. Calc'd. for C.sub.13 H.sub.10 F.sub.3 NO.sub.2 S: C, 51.82; H, 3.35. Found: C, 51.77; H, 3.35.

A third route for the preparation involves the thermolysis of the oxathiazol-2-ones prepared in accordance with Examples 1-5 with alkyl propiolate. Scheme C illustrates this method of preparation. ##STR5##

Scheme C is exemplified below in Examples 56-59.

Preparation of Ethyl 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylate. A solution of 12.36 g (0.050 mol) of 5-(.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl)-1,3,4-oxathiazol-2-one and 19.62 g (0.20 mol) of ethyl propiolate in 75.0 g of o-dichlorobenzene was held at reflux under N.sub.2 for 20 hours, at which time analysis by gas chromatography revealed that the reaction was complete and that the 4-carboxylate and the 5-carboxylate had formed in 46% and 39% yields, respectively. Concentration of the solution under vacuum gave 16.4 g of dark oil. Crystallization of the oil from 35 ml of ethanol at -20.degree. gave 5.05 g (34%) of tan solid, m.p. 77.degree.-79.degree., that was about 98% pure 5-carboxylate (gas chromatography assay). Concentration of the filtrate gave 10.8 g of oil. Chromatography of the oil on 550 g of silicic acid with benzene gave 5.2 g of 4-carboxylate that was 97% pure (3% low boilers, no 5 -carboxylate present; gas chromatography analysis); infrared (CHCl.sub.3) 5.83 .mu.; nmr (CDCl.sub.3) .delta. 9.43 (s, 1, 5-H), 8.03 - 7.43 (m, 4, ArH), 4.30 (q, 2, J = 7 Hz, OCH.sub.2 CH.sub.3), 1.23 (t, 3, J = 7 Hz, OCH.sub.2 CH.sub.3).

Anal. Calc'd. for C.sub.13 H.sub.10 F.sub.3 NO.sub.2 S: C, 51.82; H, 3.35. Found: C, 52.09; H, 3.50.

The chromatography also gave 0.31 g (2%) of pure 5-carboxylate, m.p. 80.degree.-81.5.degree.. Recrystallization of the 5.05 g of 5-carboxylate from ethanol gave 4.05 g (27%) of colorless crystals, m.p. 80-81.5.degree.; infrared (CHCl.sub.3) 5.81 .mu.; nmr .delta. 8.20 (s, 1, 4-H), 8.30 - 7.47 (m, 4, ArH), 4.47 (q, 2, J = 7 Hz, OCH.sub.2 CH.sub.3), 1.43 (t, 3, J = 7 Hz, OCH.sub.2 CH.sub.3).

Anal. Calc'd. for C.sub.13 H.sub.10 F.sub.3 NO.sub.2 S: C, 51.82; H, 3.35. Found: C, 51.98; H, 3.39.

Preparation of Ethyl 3-(p-Cyanophenyl)-4-Isothiazolecarboxylate. A solution of 10.2 g (0.050 mol) of 5-(p-cyanophenyl)-1,3,4-oxathiazol-2-one and 19.62 g (0.20 mol) of ethyl propiolate in 75.0 g of o-dichlorobenzene was held at reflux under N.sub.2 for 20 hours, at which time gas chromatography analysis indicated that the 4-carboxylate and the 5-carboxylate had formed in 44% and 46% yields, respectively. Concentration of the reaction mixture under vacuum gave 20.3 g of brown solid. Crystallization of this material from ethanol gave 5.54 g (43%) of 5-carboxylate as a beige solid, m.p. 175.degree.-179.degree.. Crystallization of the solid from ethanol gave 0.1 g of unidentified, fairly insoluble white solid, m.p. 236.degree.-237.degree., infrared (CHCl.sub.3) 4.50, 5.81 .mu.. The residue from the filtrate was chromatographed on silica gel with benzene, and the purest fractions were crystallized from ethanol to give 1.27 g (10%) of 5-carboxylate as a white solid, m.p. 183.degree.- 184.5.degree.; infrared (CHCl.sub.3) 4.50, 5.81 .mu.; nmr (CDCl.sub.3) .delta. 8.17 (s, 1, 4-H), 7.93 AA'BB' m, 4, ArH), 4.43 (g, 2, J = 7 Hz, OCH.sub.2 CH.sub.3), 1.40 (t, 3, J = 7 Hz, OCH.sub.2 CH.sub.3).

Anal.Calc'd. for C.sub.13 H.sub.10 N.sub.2 O.sub.2 S: C, 60.45; H, 3.90. Found: C, 60.49; H, 3.98.

The filtrate from the crystallization of the 20.3 g of brown solid was concentrated under vacuum, and the residue was chromatographed on silica gel with benzene. The 4-carboxylate thus obtained was crystallized from heptane to give 4.06 g (32%) of white solid, m.p. 109.degree.-110.degree.; infrared (CHCl.sub.3) 4.50, 5.81 .mu.; nmr (CDCl.sub.3) .delta. 9.40 (s, 1, 5-H), 7.73 (s, 4, ArH), 4.30 (q, 2, J = 7 Hz, OCH.sub.2 CH.sub.3), 1.27 (t, 3, J = 7 Hz, OCH.sub.2 CH.sub.3).

Anal. Calc'd. for C.sub.13 H.sub.10 N.sub.2 O.sub.2 S: C, 60.45; H, 3.90. Found: C, 60.48; H, 3.96.

Preparation of Ethyl 3-(p-Chlorophenyl)-4-Isothiazolecarboxylate. A solution of 10.68 g (0.050 mol) of 5-(p-chlorophenyl)-1,3,4-oxathiazol-2-one and 19.62 g (0.20 mol) of ethyl propiolate in 75 g of o-dichlorobenzene was held at reflux (150.degree.) under N.sub.2 for 10 hours and was concentrated under vacuum to 90.degree. at 0.2 mm to give 16.0 g of black oil. Dry column chromatography of the oil on silica gel with benzene and crystallizations of the fractions rich in 5-carboxylate gave 3.50 g (26% yield) of pure ethyl 3-(p-chlorophenyl)-5-isothiazolecarboxylate, m.p. 87.5.degree.-89.degree. (from ethanol); nmr (CDCl.sub.3).delta. 8.13 (s, 1, 4-H), 7.7 (m, 4, ClC.sub.6 H.sub.4), 4.47 (q, 2, J = 7 Hz, OCH.sub.2 CH.sub.3), 1.43 (t, 3, J = 7 Hz, OCH.sub.2 CH.sub.3).

Anal. Calc'd. for C.sub.12 H.sub.10 ClNO.sub.2 S: C, 53.83; H, 3.76. Found: C, 53.84; H, 3.64.

Crystallizations of the fractions rich in 4-carboxylate from aqueous ethanol gave 2.45 g (18% yield) of pure ethyl 3-(p-chlorophenyl)-4-isothiazolecarboxylate, m.p. 70.5.degree.-71.5.degree..

Preparation of Ethyl 3-(3,5-Dimethoxyphenyl)-4-Isothiazolecarboxylate. By a procedure similar to that employed above, ethyl 3-(3,5-dimethoxyphenyl)-4-isothiazolecarboxylate was obtained in 25% yield as a white solid, m.p. 71.5.degree.-73.degree. (from ethanol); nmr (CDCl.sub.3).delta. 9.23 (s, 1, 5-H), 6.72 (d, 2, J = 2 Hz, ArH), 6.48 (t, 1, J = 2 Hz, ArH), 4.23 (q, 2, J = 7 Hz, OCH.sub.2 CH.sub.3), 3.78 (s, 6, OCH.sub.3), 1.23 (t, 3, J = 7 Hz, OCH.sub.2 CH.sub.3).

Anal. Calc'd. for C.sub.14 H.sub.15 NO.sub.4 S: C, 57.32; H, 5.15. Found: C, 57.40; H, 5.21.

Ethyl 3-(3,5-dimethoxyphenyl)-5-isothiazolecarboxylate was obtained in 32% yield as a white solid, m.p. 101.degree.-103.degree. (from ethanol), nmr (CDCl.sub.3) 7.98 (s, 1, 4-H), 7.03 (d, 2, J = 2 Hz, ArH), 6.47 (t, 1, J = 2 Hz, ArH), 4.37 (q, 2, J = 7 Hz, OCH.sub.2 CH.sub.3), 3.82 (s, 6, OCH.sub.3), 1.40 (t, 3, J = 7 Hz, OCH.sub.2 CH.sub.3).

Anal. Calc'd. for C.sub.14 H.sub.15 NO.sub.4 S: C, 57.32; H, 5.15. Found: C, 57.50; H, 5.17.

Another preparation of 3-aryl-4-isothiazolecarboxylates involves the reaction of oxathiazol-2-ones with alkyl chloroacrylate as illustrated by Scheme D. ##STR6##

Example 60 is illustrative of the preparation of 3-aryl-4-isothiazolecarboxylates using the method of Scheme D.

Preparation of 3-(p-Chlorophenyl)-4-Isothiazolecarboxylates.

A solution of 40.4 g (0.30 mol) of ethyl 2-chloroacrylate and 2.14 g (0.010 mol) of 5-(p-chlorophenyl)-1,3,4-oxathiazole-2-one in 75 g of o-dichlorobenzene was held at reflux (165.degree.-175.degree.) for 55 minutes, at which time gas chromatography analysis indicated about 70% reaction. The reaction mixture was allowed to cool, and the supernatant was decanted from polymeric ester. Concentration of the supernatant under vacuum, chromatography of the residue on silicic acid, and crystallizations of the various materials thus obtained gave 0.30 g (16%) of ethyl 3-(p-chlorophenyl)-4-isothiazolecarboxylate, m.p. 69.degree.-70.degree., and 0.31 g (17%) of ethyl 3-(p-chlorophenyl)-5-isothiazolecarboxylate, m.p. 87.degree.-89.degree..

Salts of the isoxazole-4-carboxylic acid may be prepared by neutralization of the appropriate acid with the appropriate base. The acid may be prepared in accordance with Scheme A or an ester prepared by any of the other methods may be hydrolyzed to the free acid.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Potassium Salt. A solution of 1.91 g (0.0070 mol) of carboxylic acid and 0.462 g of 85 % KOH (0.0070 mol) in 12 ml of water was concentrated under vacuum to 1.9 g (87%) of white solid, m.p. 276.degree.-277.degree. , infrared (mineral oil mull) 6.30 .mu..

Anal. Calc'd. for C.sub.11 H.sub.5 F.sub.3 KNO.sub.2 S: C, 42.44; H, 1.62.

Found: C, 42.51; H, 1.63.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Isopropylamine Salt. To a solution of 2.73 g (0.010 mol) of carboxylic acid in 30 ml of ether was added 0.59 g (0.010 mol) of isopropylamine with swirling. After several seconds, copious precipitation of a white solid occurred. The solid was collected and washed with ether to give 2.7 g of white solid, m.p. 145.degree.-147.degree. .

Anal. Calc'd. for C.sub.14 H.sub.15 F.sub.3 N.sub.2 O.sub.2 S: C, 50.60; H, 4.55.

Found: C, 50.57; H, 4.63.

Preparation of 3-(.alpha.,.alpha., .alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Dodecylamine Salt. A solution of 2.70 g (0.0099 mol) of carboxylic acid and 1.83 g (0.0099 mol) of dodecylamine in 30 ml of ether was filtered and concentrated under vacuum to 4.53 g of viscous oil that slowly crystallized, m.p. 43.degree.-45.degree. . Anal. Calc'd. for C.sub.23 H.sub.33 F.sub.3 N.sub.2 O.sub.2 S: C, 60.24; H, 7.25.

Found: C, 60.05; H, 7.12.

Preparation of 3-Phenyl-4-Isothiazolecarboxylic Acid, Sodium Salt. A solution of 0.005 moles of the free acid, 5 ml of water and 0.005 moles of NaOH were combined on a steam bath at 15 mm. The residual powder had a melting point above 300.degree. .

Anal. Calc'd. for C.sub.9 H.sub.7 N.sub.2 O.sub.2 SNa: C, 43.9; H, 2.87; N, 11.38;

S, 13.02; Na, 9.34.

Found: C, 42.4; H, 2.81; N, 10.68;

S, 12.44; Na, 11.89.

Additionally, esters have been prepared from the free acid prepared in accordance with Scheme A. These esters have been prepared by various procedures illustrated by Examples 65-68.

Preparation of Ethyl 3-(p-Tolyl)-4-Isothiazolecarboxylate. 3-(p-Tolyl)-4-isothiazolecarboxylic acid (1.5 g, 0.0068 mol), 20 ml of absolute ethanol, and boron trifluoride etherate (4.3 ml, 0.034 mol) were heated at reflux for 24 hours. Volatile materials were removed under reduced pressure. Water (25 ml) was added and the material extracted four times with ether. The ether was back-extracted with 5% NaHCO.sub.3, dried (CaSO.sub.4) and concentrated under reduced pressure to yield 1.51 g (0.0061 mol, 89.9%) of oil, n.sub.D.sup.25 = 1.5671.

Anal. Calc'd. for C.sub.13 H.sub.13 NO.sub.2 S: C, 63.13; H, 5.30.

Found: C, 62.95; H, 5.52.

Preparation of Ethyl 3-(p-Nitrophenyl)-4-Isothiazolecarboxylate. 3-(p-Nitrophenyl)-4-isothiazolecarboxylic acid (1.5 g, 0.006 mol), plus one equivalent (2.51 g) of benzyl trimethylammonium hydroxide (40% in methanol) and excess ethyl iodide were heated just to reflux in hexamethylphoramide. The product was recrystallized twice from ethanol to yield 0.24 g (0.00086 mol, 14.3%) of ester, m.p. 150.5.degree. -152.5.degree. .

Anal. Calc'd. for C.sub.12 H.sub.10 N.sub.2 O.sub.4 S: C, 51.79; H, 3.62.

Found: C, 52.35; H, 3.70.

Preparation of Glycolic Acid, Ethyl Ester, 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylate. To a mixture of 1.36 g (0.0050 mol) of 3-(.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl)-4-isothiazolecarboxylic acid in 10 ml of hexamethylphosphoric triamide was added 0.80 g of 50% NaOH (0.010 mol), followed by 3.1 g (0.0254 mol) of ethyl chloroacetate. The mixture was stirred vigorously for 18 hours, diluted with water, and extracted twice with 40 -ml portions of ether. The combined ether layers were washed twice with water, three times with aqueous K.sub.2 CO.sub.3 solution, again with water, dried (CaSO.sub.4), and concentrated under vacuum to 90.degree. at 0.3 torr to give 1.5 g of 87% pure product as an oil. This oil was chromatographed on 130 g of Woelm silica gel (for dry column chromatography) in a 30 mm diameter column with 30% CHCl.sub.3 in benzene. There was obtained 0.43 g of colorless liquid, n.sub.D.sup.22.8.degree. = 1.5241, that was 100% pure product.

Anal. Calc'd. for C.sub.15 H.sub.12 F.sub.3 NO.sub.4 S: C, 50.14; H, 3.37.

Found: C, 50.06; H, 3.28.

Preparation of Lactic Acid, Ethyl Ester, 3-(.alpha.,.alpha.,.alpha.,-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylate. By a procedure similar to that used for Example 67, there was obtained 1.7 g of oil, n.sub.D.sup.23 = 1.5169 (yield 66.5%).

Anal. Calc'd. for C.sub.16 H.sub.14 F.sub.3 NO.sub.4 S: C, 51.47; H, 3.78; N, 3.75.

Found: C, 51.20; H, 3.48; N, 3.73.

3-Phenyl-4-isothiazolecarbonyl chlorides may be prepared by reaction of the free acid with thionyl chloride as discussed in Scheme A.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarbonyl Chloride. A mixture of 27.3 g (0.10 mol) of 3-(.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl)-4-isothiazolecarboxylic acid and 20 ml (32.8 g, 0.276 mol) of thionyl chloride (purified by distillation from a little triphenyl phosphite) was heated on a steam bath for 40 minutes and then was concentrated under vacuum to remove excess SOCl.sub.2. The resultant 27.3 g of product was crystallized from heptane to give 25.5 g (87%) of white solid, m.p. 76.degree.-77.5.degree., infrared (CH.sub.2 Cl.sub.2) 5.70 .mu..

Anal. Calc'd. for C.sub.11 H.sub.5 ClF.sub.3 NOS: C, 45.30; H, 1.73.

Found: C, 45.41; H, 1.65.

3-Phenyl-4-isothiazolecarboxamides may be prepared by reaction of the acid chloride with ammonia or the appropriate amine.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxamide. A solution of 2.92 g (0.010 mol) of 3-(.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl)-4-isothiazolecarbonyl chloride in 10 ml of THF was added to a solution of excess ammonia gas in THF stirred in a dry ice acetone bath. The mixture was slowly warmed to 23.degree. with stirring. The solid NH.sub.4 Cl was removed by filtration, and the filtrate was concentrated to about 20 ml. Then 100 ml of ether was added, and the solution was extracted with two portions of 10% Na.sub.2 CO.sub.3 solution and once with saturated NaCl solution. The ether layer was dried (CaSO.sub.4 ) and concentrated to 2.25 g (83%) of white solid, m.p. 141.degree.-141.5.degree.; infrared (mineral oil mull) 2.92, 3.11, 6.09, 6.11 .mu..

Anal. Calc'd. for C.sub.11 H.sub.7 F.sub.3 N.sub.2 OS: C, 48.53; H, 2.59.

Found: C, 48.73; H, 2.75.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Lsothiazolecarboxylic Acid, Isopropyl Amide. To a solution of 1.0 g (0.0034 mol) of 3-(.alpha.,.alpha.,.alpha.-trifluoro-m-tolyl)-4-isothiazolecarbonyl chloride and 20 cc of THF was added 0.45 g (2.1 equivalents) of isopropylamine. The reaction mixture was heated on a steam bath for 20 minutes. The isopropylamine hydrochloride was filtered off and the filtrate was concentrated to a solid. The solid was washed with H.sub.2 O, dissolved in THF, dried (CaSO.sub.4), and concentrated under vacuum to give 0.94 g of solid. The solid was recrystallized from EtOAc/hexane to give 0.4 g of white solid, m.p. 166.degree.-167.degree.. The filtrates gave another 0.3 g of white solid, m.p. 166.5.degree.-168.degree.. (Total yield = 88%).

Anal. Calc'd. for C.sub.14 H.sub.13 F.sub.3 N.sub.2 OS: C, 53.50; H, 4.17; N, 8.91.

Found: C, 53.61; H, 4.10; N, 8.92.

Preparation of 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isothiazolecarboxylic Acid, Diethylamide. By a procedure similar to that used for Example 71, there was obtained 0.97 g of a yellow oil, n.sub.D.sup.23 = 1.5383. (yield 86.9%).

Anal. Calc'd. for C.sub.15 H.sub.15 F.sub.3 N.sub.2 OS: C, 54.87; H, 4.60; N, 8.53.

Found: C, 54.93; H, 4.96; N, 8.59.

The isoxazolecarboxylates of the foregoing formula can be prepared by 1,3-dipolar cycloaddition of nitrile oxides, formed in situ from hydroxamoyl chlorides, to alkyl .beta.-pyrrolidinylacrylates. Scheme E illustrates the preparation of said isoxazolecarboxylates. ##STR7##

Alkyl .beta.-pyrrolidinylacrylate may be prepared by the addition of pyrrolidine to alkyl propiolate. Hydroxamoyl chloride may be prepared by the addition of chlorine to the appropriate benzaldoxime.

Examples 73-80 are presented in order to illustrate the preparation of the isoxazolecarboxylates of the invention.

Preparation of Ethyl .beta.-Pyrrolidinylacrylate. A solution of 29.43 g of ethyl propiolate (0.30 mol) in 200 ml of benzene was held at 25.degree. in a water bath with magnetic stirring. A solution of 21.34 g of pyrrolidine in 50 ml of benzene was added dropwise over a period of 45 minutes, during which time the temperature rose to 35.degree.. The clear brown solution was stirred overnight and the solvent under reduced pressure at 55.degree.. The residue was distilled under reduced pressure to give 35.05 g of yellow oil, boiling point 110.degree. (0.4 torr), which crystallized upon standing. The yellow solid was recrystallized from petroleum ether to give 31.36 (62%) of yellowish platelets, m.p. 37.5.degree.-39.5.degree..

Preparation of m-Trifluoromethylbenzohydroxamoyl Chloride. A solution of 15.70 g of m-trifluoromethylbenzaldoxime (0.082 mol) in 40 ml of chloroform was cooled with magnetic stirring to -5.degree. in ice-MeOH. A gentle stream of Cl.sub.2 was passed into the solution, while the temperature was maintained below 0.degree., until addition of more Cl.sub.2 did not produce a green color. The mixture was stirred for two hours and allowed to warm to room temperature. The solvent was removed by evaporation under reduced pressure at 50.degree. and the oily product recrystallized twice from petroleum ether, to give 13.69 g (70%) of tan needles, m.p. 52.5.degree.-54.degree.; infrared (melt) 3400 cm, 1600 (m), 1430 (m), 1325 (s); nmr (CCl.sub.4) .delta. 8.64 (s, 1H) and .delta. 7.3-8.2 (m, 4H).

Anal. Calc'd. for C.sub.8 H.sub.5 ClF.sub.3 NO: C, 42.98; H, 2.25; Cl, 15.86; N, 6.26. Found: C, 42.98; H, 2.32; Cl, 16.13; N, 6.27.

Other hydroxamoyl chlorides prepared by this procedure were: benzohydroxamoyl chloride, m.p. 42.degree.; p-chlorobenzohydroxamoyl chloride, m.p. 82.degree.-84.degree.; m-chlorobenzohydroxamoyl chloride, m.p. 61.degree.-63.degree.; m-nitrobenzohydroxyamoyl chloride, m.p. 98.degree.-101.degree..

Preparation of Ethyl 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isoxazolecarboxylate. A solution of 4.87 g of ethyl .beta.-pyrrolidinylacrylate (0.0288 mol) and 5.0 ml of triethylamine in 60 ml of ethyl ether was cooled to 0.degree.. A solution of 6.43 g of m-trifluoromethylbenzohydroxamoyl chloride in 25 ml of ether was added over a period of 40 minutes with magnetic stirring, during which time a white precipitate of Et.sub.3 N.HCl formed. The mixture was stirred at 0.degree. for 2.5 hours and filtered and the solid washed thoroughly with ether. The combined solutions were washed with 5% HCl and water, dried over MgSO.sub.4, filtered and concentrated to 7.66 g of orange oil; only one peak was observed on GLC. Double distillation through a 4 inch .times. 1/2 inch Vigreux column gave 5.95 g (72% crude), boiling point 98.degree.-100.degree. (0.08 torr), slightly yellow oil, tlc (Silica Gel G, benzene) showed 3 spots, R.sub.f 0.21, 0.46 and 0.61. Chromatography of 5.80 g of the oil on 110 g of dry column silica gel (.about.80 cm long) gave 1.79 g of oil (mixture R.sub.f 0.46 and 0.61, faint), first 120 ml benzene eluent and 3.78 g clear colorless oil in the second 120 ml benzene (pure by tlc, R.sub.f 0.46). The second fraction was distilled giving 2.85 g (34%) of pure product, boiling point 94.degree. (0.045 torr), infrared (neat); 1720 cm.sup.-1 (s), 1340 (s), 1120 (s); nmr (CCl.sub.4) .delta. 1.25 (t, 3H), 4.26 (q, 2 H), 7.4-8.2 (m, 4H) and 9.0 (s, 1H).

Anal. Calc'd. for C.sub.13 H.sub.10 F.sub.3 NO.sub.2 : C, 54.74; H, 3.53; F, 19.98; N, 4.91. Found: C, 54.68; H, 3.39; F, 19.87; N, 5.00.

Preparation of Ethyl 3-(4-Chlorophenyl)-4-Isoxazolecarboxylate. The crude product from the reaction of 4.23 g of ethyl .beta.-pyrrolidinylacrylate (0.025 mol) and the nitrile oxide from 4.75 g p-chlorobenzohydroxamoyl chloride (0.025 mol) and 3.5 ml Et.sub.3 N run as above, gave, after chromatography, 1.27 g (20%) of white solid, m.p. 43.degree.-45.degree.; infrared (melt); 1725 cm.sup.-1 (s), 1290 (s) and 1170 (s); nmr (CCl.sub.4) .delta. 1.35 (t, 3H), 4.30 (q, 2H), 7.4 and 7.8 (ABq, 4H) and 8.95 (s, 1H).

Anal. Calc'd. for C.sub.12 H.sub.10 ClNO.sub.3 : C, 57.27; H, 4.01; Cl, 14.09; N, 5.57. Found: C, 57.29; H, 3.88; Cl, 14.04; N, 5.35.

Preparation of Ethyl 3-(3-Chlorophenyl)-4-Isoxazolecarboxylate. The crude oil from the reaction of 4.23 g of ethyl .beta.-pyrrolidinylacrylate (0.025 mol) and the nitrile oxide from 4.75 g of 3-chlorobenzohydroxamoyl chloride and 3.5 ml of Et.sub.3 N, run as in Example 75, was twice crystallized from petroleum ether to give 2.78 g (44%) of tan powder, m.p. 43.degree.-45.degree.; infrared (melt); 1720 cm.sup.-1 (s), 1550 (s), 1290 (s), 1125 (s); nmr (CCl.sub.4) .delta. 1.35 (t, 3H), 4.25 (q, 2H), 7.2-7.4 and 7.5-7.9 (complex, 4H), 8.95 (s, 1H).

Anal. Calc'd. for C.sub.12 H.sub.10 ClNO.sub.3 : C, 57.27; H, 4.01; Cl, 14.09; N, 5.57. Found: C, 57.07; H, 4.02; Cl, 13.99; N, 5.67.

Preparation of Ethyl 3-(3-Nitrophenyl)-4-Isoxazolecarboxylate. A mixture of 4.23 g (0.025 mol) of ethyl .beta.-pyrrolidinylacrylate and 3.5 ml of triethylamine in 60 ml of anhydrous ether was cooled to -10.degree.. A solution of 5.01 g (0.025 mol) of 3-nitrobenzohydroxamoyl chloride in 20 ml of ether was added dropwise in 30 minutes with rapid magnetic stirring. The mixture was stirred at -10.degree.-0.degree. for 4 hours and allowed to warm to room temperature overnight. The solid was removed by filtration and washed four times with 50 ml of boiling ether. The residues from the evaporation of the ether solutions were recrystallized from hexane and combined to give 3.72 g (58%) of white needles, m.p. 90.degree.-92.degree.; nmr (CCl.sub.4) .delta. 1.30 (t, 3H), 4.27 (q, 2H), 7.47-8.80 (m, 4H) and 9.06 (s, 1H).

Anal. Calc'd. for C.sub.12 H.sub.10 N.sub.2 O.sub.5 : C, 54.97; H, 3.84; N, 10.68. Found: C, 55.07; H, 3.91; N, 10.59.

Preparation of Ethyl 3-(3-Cyanophenyl)-4-Isoxazolecarboxylate. A solution of 8.46 g (0.05 mol) of .beta.-pyrrolidinylacrylate and 9.05 g (0.05 mol) of 3-cyanobenzohydroxamoyl chloride in 175 ml of ether was cooled to -15.degree.. A solution of 7.0 ml of triethylamine in 15 ml of ether was added dropwise with magnetic stirring over 40 minutes. A dense white precipitate formed immediately. The mixture was stirred at 0.degree. for 3 hours and allowed to warm to room temperature overnight. The dense suspension was thoroughly mixed with 400 ml of methylene chloride. The suspension was washed twice with water and twice with 6N HCl. The aqueous solution was back-extracted with four 50-ml portions of methylene chloride. The combined organic solutions were washed with water and dried over anhydrous sodium sulfate, filtered, and concentrated to a nearly white solid. Recrystallization from benzene-hexane gave 9.57 g (79%) of slightly yellow needles, m.p. 135.degree.-7.degree.; infrared (KBr) 2245 cm.sup.-1, nmr (CDCl.sub.3) .delta. 1.37 (t, 3H), 4.40 (q, 2H), 7.6-8.3 (m, 4H) and 9.13 (s, 1H).

Anal. Calc'd. for C.sub.13 H.sub.10 N.sub.2 O.sub.3 : C, 64.46; H, 4.16; N, 11.56. Found: C, 64.49; H, 4.12; N, 11.56.

Preparation of Ethyl 3-Phenyl-4-Isoxazolecarboxylate. Utilizing the procedure of Example 79 with benzohydroxamoyl chloride as a reactant in lieu of 3-cyanobenzohydroxamoyl chloride, ethyl 3-phenyl-4-isoxazolecarboxylate was prepared as a crude oil.

Anal. Calc'd. for C.sub.12 H.sub.11 NO.sub.3 : C, 66.35; H, 5.10; N, 6.45. Found: C, 66.22; H, 5.09; N, 6.55.

Haloalkyl esters may be prepared from the free acid in accordance with Example 81.

Preparation of 2,2,2-Trifluoromethyl 3-(.alpha.,.alpha.,.alpha.-Trifluoro-m-Tolyl)-4-Isoxazolecarboxylate. A solution of 2.85 g ethyl ester prepared by Example 75 in 10 ml glacial acetic acid and 10 ml concentrated HCl was heated at reflux for 4 hours. The solution was cooled and most of the solvent removed by evaporation under reduced pressure. The pasty residue was washed with water and dried giving 2.2 g (85%) of acid, m.p. 115.degree.-118.degree..

A solution of 5.31 g of the acid in 15 ml of thionyl chloride was heated at reflux for 1 hour. The excess thionyl chloride was removed by evaporation under reduced pressure giving 5.70 g of crude acid chloride (nmr showed no acid proton) which was used immediately in the following two reactions.

The crude acid chloride, 1.70 g, was stirred at room temperature with 5 ml of 2,2,2-trifluoroethanol for 1 hour and then heated at reflux for 2 hours. The excess alcohol was removed by evaporation to give a brown oil. The nmr spectrum showed two isoxazole ring protons indicating incomplete reaction. The mixture was dissolved in 5 ml 2,2,2-trifluoroethanol and heated at reflux for two hours and stirred at room temperature overnight. After removal of excess alcohol, the yield was 1.55 g of brown oil which was chromatographed on 25 g silica gel. Elution with 50 ml of 1:1 hexane-ether gave 1.51 g ester. Distillation gave 0.620 g pure ester, boiling point 88.degree. 0.1 torr; nmr (CCl.sub.4) .delta. 4.56 (q, 2H), 7.3-8.2 (m, 4H) and 9.05 (s, 1H).

Anal. Calc'd. for C.sub.13 H.sub.7 F.sub.6 NO.sub.3 : C, 46.03; H, 2.08; 33.61; 33.61. N, 4.13. Found: C, 46.22; H, 2.03; F, 33.86; N, 4.28.

As noted previously, the carboxylic acids and their derivatives are useful in regulating the growth of leguminous plants, e.g. soybeans.

As used herein, the regulation of "plant growth or development" is understood to mean the modification of the normal sequential development of a treated plant to agricultural maturity. Such modifications are most readily observed as changes in size, shape, color or texture of the treated plant or any of its parts. Similarly, changes in the quantity of plant fruit or flowers are also quite apparent from visual inspection. The above changes may be characterized as an accleration or retardation of plant growth, stature reduction, leaf or canopy alteration, increased branching, terminal inhibition, increased flowering, defoliation, increased root growth, increased cold hardiness and the like. While many of these modifications are desirable in and of themselves, most often it is their effect on the economic result that is of most importance. For example, a reduction in stature of the plant permits the growing of more plants per unit area. A darkening of the foliar color may indicate a higher chlorophyll content and be indicative of an improved rate of photosynthesis.

Although phytotoxic amounts of the active ingredient may be employed to exert a herbicidal effect, the regulation of plant growth in accordance with the present invention does not include the total inhibition or killing of such plants. The present invention contemplates the use of an amount of active ingredient which will modify the normal sequential development of the treated plant to agricultural maturity. Such plant growth regulating amounts may vary, not only with the material selected, but also with the modifying effect desired, the species of plant and its stage of development, the plant growth medium and whether a permanent or transitory effect is sought. It is, however, well within the skill of the art to determine the amount of active ingredient required.

Modification of the plants may be accomplished by applying the active ingredient to seeds, emerging seedlings, roots, stems, leaves, flowers, fruits or other plant parts. Such application may be made directly to the plant part, or indirectly by application to the plant growth medium. When operating in accordance with the present invention, effective amounts of the active ingredients are applied to the plant system. By application to the plant system is meant the application of the active ingredient in or on soil or plant growth media and/or applied above-ground portions of plants in any convenient fashion.

By the term "active ingredient" is meant the active isothiazole and isoxazole carboxylic acids and derivatives of the foregoing formula.

In the practice of the invention, the active ingredient can be used alone or in combination with a material referred to in the art as an adjuvant in either liquid or solid form. To prepare plant growth regulating compositions, the active ingredient is admixed with an adjuvant including diluents, extenders, carriers and conditioning agents to provide compositions in the form of finely-divided particulate solids, granules, pellets, wettable powders, dusts, solutions and aqueous dispersions or emulsions. Thus, the active ingredient can be used with an adjuvant such as a finely-divided particulate solid, a solvent liquid of organic origin, water, a wetting agent, dispersing agent or emulsifying agent or any suitable combination of these.

Illustrative finely-divided solid carriers and extenders which are useful in plant growth regulating compositions of this invention include the talcs, clays, pumice, silica, diatomaceous earth, quartz, Fullers earth, sulfur, powdered cork, powdered wood, walnut flour, chalk, tobacco dust, charcoal and the like. Typical liquid diluents include Stoddard solvent, acetone, alcohols, glycols, ethyl acetate, benzene and the like. The plant growth regulating compositions of this invention, particularly liquids and wettable powders, usually contain one or more surface-active agents in amounts sufficient to render a given composition readily dispersible in water or in oil. The term "surface-active agent" is understood to include wetting agents, dispersing agents, suspending agents and emulsifying agents. Such surface-active agents are well-known and reference is made to U.S Pat. No 2,547,724, Columns 3 and 4, for detailed examples of the same.

Generally, the active ingredients are applied in the form of a composition containing one or more adjuvants which aid in the application of a uniform distribution of the active ingredient. The application of liquid and particulate solid compositions of the active ingredient can be carried out by conventional techniques utilizing, for example, spreaders, power dusters, boom and hand sprayers and spray dusters. The composition can also be applied from airplanes as a dust or spray. Should the application of the plant growth composition to the plant growth medium be desired, this is accomplished by incorporating the compositions in the soil or other media in the area where modification of the plants is desired.

The quantity of active ingredient in the plant growth regulating composition varies upon the type of formulation, rate of application, plant to be treated, etc. Compositions of this invention generally contain from about 5 to 95 parts active ingredient, about 1 to 50 parts surface-active agent and about 4 to 94 parts solvent, all parts being by weight based on the total weight of the composition. The specific quantity of active ingredient utilized, however, is well within the skill of the art.

In selecting the appropriate rate of application of the active ingredient, it will be recognized that precise rates will also be dependent upon the mode of application, such as soil incorporation, band application, pre-plant seed treatment and various other factors known to those skilled in the art. In foliar treatment for the regulation of plant growth, the active ingredients are applied in amounts of from about 0.056 to about 11.2 or more kilos per hectare. Preferred are foliar applications of from 0.056 to 3.36 kilos of the active ingredient per hectare. In application to the soil habitat of germinant seeds, emerging seedlings and established vegetation for the regulation of plant growth, the active ingredients are applied in amounts of from 0.0112 to about 22.4 kilos per hectare or more. Foliar application to plants beginning to blossom are preferred over other types of applications.

In accordance with the practice of the invention, several plant growth regulating compositions were formulated utilizing various compounds as the active ingredient. These compositions were formulated so that they could be applied in tests at a rate the equivalent of 302 liters per hectare. Table I illustrates the formulation of the composition for several application rates of active ingredient. In each formulation, the stock solution utilized is one percent of the active ingredient dissolved in acetone.

Utilizing compositions formulated in accordance with Table I, several compounds exhibited unexpected plant growth regulatory properties as illustrated by the test set forth in Example A.

A number of soybean plants, variety Corsoy, are grown from seeds in aluminum pans in the greenhouse for a period of approximately one week to the primary leaf stage. The plants are thinned to three uniform plants in each pan and the height of each plant in the pan is measured to the terminal bud and the average height is noted. One pan containing three soybean plants is used for each chemical treatment and three pans are not treated and used as a control. The composition as formulated in accordance with Table I is then applied to the pan of growing plants by overhead spray at a rate equivalent to the desired rate of active ingredient per acre. The treated pans, along with the control pans, are maintained in a greenhouse and watered from below on a sand bench and fertilized with a uniform portion of a water-soluble balanced fertilizer.

Two weeks after application of the chemical, the average height of the soybean plants in the treated pan is again measured as above and the difference in the average height before and two weeks after application represents the increase in the development of the treated pans. This development in growth to the treated plants is compared to the average increase in growth of the plants in the control pans during the same period of time. A variation of twenty-five percent or more in the development of at least two-thirds of the treated plants when compared to the development of the control plants demonstrates that the chemical is an effective plant regulant. Thus, a chemical is considered active when the treated plants manifest a decrease in growth of at least twenty-five percent less than that of the control plants, i.e., stature reduction, or an increase in growth in excess of twenty-five percent of that of the control plants, i.e. growth stimulation.

Table II below summarizes the results and observations made in accordance with Example A when the compounds of the invention were utilized as the active ingredient at several rates.

Further advantages of this invention are shown in Example B.

Individual soybean plants, variety Corsoy, are grown from seed in 6-inch pots containing a good grade of top soil. Two pots of 6-week old plants (5-6 trifoliate stage) are used for each application of the chemical. An overhead spray of an aqueous composition of the chemical is applied to the pots at an equivalent rate as indicated below. Two to four sets of plants which received no chemical application are included and serve as controls. All of the pots are maintained under good growing conditions and are watered and are fertilized with a uniform amount of a water-soluble balanced fertilizer. Two weeks after the application of the chemical, the growth responses of the treated plants are compared with that of the control plants. The total height of the plant is measured to the tip of the terminal bud. A variation of 15 percent in the average total height of the treated plants, when compared to the average total height of the control plants, demonstrates that the chemical is an effective growth regulator. Observations made utilizing the test procedure of Example B are summarized in Table III.

Many of the isothiazole carboxylates were further tested in accordance with Example C.

A number of soybean plants, variety Williams, were grown from seeds in plastic pots in the greenhouse for a period of one week at which time the plants are thinned to one plant per pot. When the second trifoliate leaf (three weeks) was fully expanded, the plants were treated with a solution of the active ingredient in acetone and water. Aqueous Tween 20 was used as a surfactant.

When the fifth trifoliate leaf (four to five weeks) was fully expanded, the treated plants were compared with the non-treated control plants and the observations recorded. Table IV summarizes the results of those observations.

As illustrated above, the carboxylic acids and their derivatives are effective as plant growth regulants. Preferred are the isothiazolecarboxylic acids and their derivatives especially those isothiazolecarboxylates of Formula I wherein Z is alkyl having up to 8 carbon atoms, especially ethyl.

Although this invention has been described with respect to specific modifications, the details thereof are not to be construed as limitations, for it will be apparent that various equivalents, changes and modifications may be resorted to without departing from the spirit and scope thereof and it is understood that such equivalent embodiments are intended to be included herein.