Isoxazole(isothiazole)-5-carboxamides of the formula ##STR1## where X is oxygen or sulfur, PA1 R.sup.1 is hydrogen, substituted or unsubstituted alkyl, alkoxy, substituted or unsubstituted cycloalkyl, a 5- or 6-membered heterocyclic radical having one or two heteroatoms selected from the group consisting of oxygen, sulfur and nitrogen, and which may be substituted, or substituted or unsubstituted phenyl, or PA1 R.sup.2 is formyl, 4,5-dihydrooxazol-2-yl or a radical of the formula COYR.sup.5 or CONR.sup.6 R.sup.7, where PA2 Y is oxygen or sulfur, PA2 R.sup.5 is PA3 hydrogen, substituted or unsubstituted alkyl, substituted or unsubstituted alkenyl, haloalkenyl, substituted or unsubstituted alkynyl, PA3 cycloalkyl, PA3 cycloalkenyl, PA3 substituted or unsubstituted phenyl, PA3 a 5- or 6-membered heterocyclic radical having one or two heteroatoms selected from the group consisting of oxygen, sulfur and nitrogen, PA3 cycloalkanimino, phthalimido, succinimido, or a radical ##STR2## R.sup.3 and R.sup.4 have the meanings defined herein, or their agriculturally acceptable salts possess herbicidal activity.

The present invention relates to substituted isoxazole- and 
isothiazole-5-carboxamides and their use for controlling undesirable plant 
growth. 
Isoxazole- and isothiazolecarboxylic acids and their derivatives are known. 
These are 5-aminocarbonyl-3-methylisoxazole-4-carboxylic acid, ethyl 
5-aminocarbonyl-3-methylisoxazole-4-carboxylate, 
isothiazole-4,5-dicarboxamide and 5-carbamoylisothiazole-4-carboxylic acid 
(J. Chem. Soc. Perkin Trans. I 1982, 2391; J. Heterocycl. Chem. 22 (1985), 
1561 and J. Chem. Soc. 1959, 3061). Possible uses of these substances are 
not described. 
We have found that isoxazole(isothiazole)-5-carboxamides of the formula Ia 
##STR3## 
where X is oxygen or sulfur, 
R.sup.1 is hydrogen, 
C.sub.1 -C.sub.10 -alkyl which is unsubstituted or substituted by C.sub.1 
-C.sub.3 -alkoxy, C.sub.1 -C.sub.3 -haloalkoxy, halogen, cyano or phenyl 
which may be substituted by halogen, C.sub.1 -C.sub.4 -alkyl, C.sub.1 
-C.sub.4 -haloalkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 
-haloalkoxy, C.sub.1 -C.sub.4 -alklthio, C.sub.1 -C.sub.4 -haloalkylthio, 
cyano or nitro, C.sub.1 -C.sub.4 -alkoxy, 
C.sub.3 -C.sub.8 -cycloalkyl which is unsubstituted or substituted by 
C.sub.1 -C.sub.4 -alkyl or halogen, 
a 5-membered or 6-membered heterocyclic radical having one or two 
heteroatoms selected from the group consisting of oxygen, sulfur and 
nitrogen, which may be substituted by C.sub.1 -C.sub.4 -alkyl, carboxyl or 
C.sub.1 -C.sub.4 -alkoxycarbonyl, 
or phenyl which is unsubstituted or substituted by C.sub.1 -C.sub.6 -alkyl, 
C.sub.1 -C.sub.6 -haloalkyl, C.sub.1 -C.sub.6 -alkoxy, C.sub.1 -C.sub.6 
-haloalkoxy, C.sub.1 -C.sub.8 -alkylthio, C.sub.1 -C.sub.6 -haloalkylthio, 
halogen, nitro or cyano, 
R.sup.2 is formyl, 4,5-dihydrooxazol-2-yl or a radical of the formula 
COYR.sup.5 or CONR.sup.6 R.sup.7, where 
Y is oxygen or sulfur, 
R.sup.5 is hydrogen, 
C.sub.1 -C.sub.8 -alkyl which may be substituted by C.sub.1 -C.sub.4 
-alkoxy, C.sub.1 -C.sub.4 -alkoxy-C.sub.1 -C.sub.4 -alkoxy, halogen, 
cyano, hydroxyl, trimethylsilyl, C.sub.1 -C.sub.4 -alkylthio, C.sub.1 
-C.sub.4 -alkylamino, C.sub.1 -C.sub.4 -dialkylamino, C.sub.1 -C.sub.4 
-alkylsulfinyl, C.sub.1 -C.sub.4 -alkylsulfonyl, carboxyl, C.sub.1 
-C.sub.4 -alkoxycarbonyl, C.sub.1 -C.sub.4 -dialkylaminocarbonyl, C.sub.1 
-C.sub.4 -dialkoxyphosphonyl, alkyliminooxy, benzyloxy, benzoyl which is 
unsubstituted or substituted by C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.3 
-alkoxy or halogen, or phenyl which is unsubstituted by C.sub.1 -C.sub.4 
-alkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -haloalkyl, halogen, 
nitro or cyano, or may be substituted by thienyl, furyl, tetrahydrofuryl, 
phthalimido or pyridyl, 
C.sub.3 -C.sub.8 -alkenyl which is unsubstituted or substituted by phenyl 
which may be substituted by C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 
-alkoxy, C.sub.1 -C.sub.4 -haloalkyl, halogen, nitro or cyano, C.sub.3 
-C.sub.5 -haloalkenyl, 
C.sub.3 -C.sub.8 -alkynyl which is unsubstituted or substituted by hydroxyl 
or C.sub.1 -C.sub.4 -alkoxy, 
C.sub.3 -C.sub.6 -cycloalkyl, 
C.sub.5 - or C.sub.6 -cycloalkenyl, 
phenyl which is unsubstituted or substituted by C.sub.1 -C.sub.4 -alkyl, 
C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -haloalkyl, halogen, nitro, 
cyano, C.sub.1 -C.sub.4 -alkoxycarbonyl or acylamino, 
a 5-membered or 6-membered heterocyclic radical having one or two 
heteroatoms selected from the group consisting of oxygen, sulfur and 
nitrogen or a benzotriazole radical, 
C.sub.6 - or C.sub.7 -cycloalkylimino, phthalimido, succinimido, or a 
radical 
##STR4## 
or one equivalent of a cation from the group consisting of the alkali 
metals, alkaline earth metals, manganese, copper, iron, ammonium and 
substituted ammonium, or a radical 
##STR5## 
where R.sup.8 and R.sup.9 independently of one another are each C.sub.1 
-C.sub.4 -alkyl, C.sub.2 -C.sub.5 -alkoxyalkyl, C.sub.3 -C.sub.8 
-cycloalkyl, phenyl or furyl or together form a methylene chain of the 
formula --(CH.sub.2).sub.m --, where m is from 4 to 7, and R.sup.9 is 
additionally hydrogen, 
R.sup.6 is hydrogen, C.sub.1 -C.sub.8 -alkyl or C.sub.3 -C.sub.8 
-cycloalkyl and 
R.sup.7 is hydrogen or C.sub.1 -C.sub.8 -alkyl, or 
R.sup.6 and R.sup.7 form a methylene chain having 4 or 5 members, 
R.sup.3 is hydrogen, 
C.sub.1 -C.sub.8 -alkyl which is unsubstituted or substituted by hydroxyl, 
halogen, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkylthio or C.sub.1 
-C.sub.4 -dialkylamino 
or C.sub.3 -C.sub.8 -cycloalkyl which is unsubstituted or substituted by 
C.sub.1 -C.sub.4 -alkyl, halogen or C.sub.1 -C.sub.4 -haloalkyl, and 
R.sup.4 is hydrogen, hydroxyl, C.sub.1 -C.sub.4 -alkoxy, 
C.sub.1 -C.sub.10 -alkyl which is unsubstituted or substituted by C.sub.1 
-C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -haloalkoxy, C.sub.1 -C.sub.4 
-alkylthio, C.sub.1 -C.sub.4 -dialkylamino, halogen, C.sub.3 -C.sub.6 
-cycloalkyl or phenyl which may be substituted by halogen, cyano, nitro, 
C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -haloalkyl, C.sub.1 -C.sub.4 
-alkoxy, C.sub.1 -C.sub.4 -haloalkoxy, C.sub.1 -C.sub.4 -alkylthio or 
C.sub.1 -C.sub.4 -halo-alkylthio, 
C.sub.3 -C.sub.10 -alkynyl or 
C.sub.3 -C.sub.10 -alkenyl which is unsubstituted or substituted by halogen 
or C.sub.1 -C.sub.4 -alkoxy, 
C.sub.3 -C.sub.8 -cycloalkyl which is unsubstituted or substituted by 
C.sub.1 -C.sub.6 -alkyl, C.sub.1 -C.sub.6 -haloalkyl, C.sub.1 -C.sub.6 
-alkoxy, C.sub.1 -C.sub.6 -haloalkoxy, C.sub.1 -C.sub.6 -alkylthio, 
C.sub.1 -C.sub.6 -haloalkylthio, halogen, nitro or cyano, 
C.sub.1 -C.sub.4 -dialkylamino, a 3-membered to 6-membered heterocyclic 
radical which is unsubstituted or substituted by C.sub.1 -C.sub.6 -alkyl, 
C.sub.1 -C.sub.6 -haloalkyl or halogen and has one or two heteroatoms 
selected from the group consisting of oxygen, sulfur and unsubstituted or 
methylsubstituted nitrogen, naphthyl, or phenyl which is unsubstituted or 
substituted by C.sub.1 -C.sub.6 -alkyl, C.sub.1 -C.sub.6 -haloalkyl, 
C.sub.1 -C.sub.6 -alkoxy, C.sub.1 -C.sub.6 -haloalkoxy, C.sub.1 -C.sub.6 
-alkylthio, C.sub.1 -C.sub.6 -haloalkylthio, halogen, nitrogen, cyano, 
formyl, C.sub.1 -C.sub.6 -alkanoyl or C.sub.1 -C.sub.6 -haloalkanoyl, 
or R.sup.3 and R.sup.4 together form a radical of the structure 
--(CH.sub.2).sub.n --Y.sub.p --(CH.sub.2).sub.q --, where n and q are each 
1, 2 or 3, p is 0 or 1 and Y is oxygen, sulfur or N-methyl, or the radical 
of the formula 
EQU --(CH.sub.2).sub.2 --CO-- 
and their agriculturally acceptable salts possess herbicidal activity. 
The methyl, alkoxy, alkenyl and alkynyl radicals R.sup.1, R.sup.3, R.sup.4, 
R.sup.5, R.sup.6 and R.sup.7 may be straight-chain or branched and are 
preferably of 1 to 4 carbon atoms. The same applies to the alkyl radicals 
which may be present as substituents in the radicals R.sup.1, R.sup.3, 
R.sup.4, R.sup.5, R.sup.6 and R.sup.7, and to the alkyl groups in the 
haloalkyl, alkoxy, haloalkoxy, alkylthio, haloalkylthio, dialkylamino, 
alkanoyl, haloalkanoyl and alkoxycarbonyl radicals. 
Preferred halogen substituents are chlorine substituents. 
The heterocyclic radicals R.sup.1 are saturated or unsaturated. Suitable 
examples are tetrahydropyranyl, tetrahydrofuryl, pyrazolyl, thienyl, 
furyl, pyridyl and tetrahydrofuryl. These radicals may be substituted by 
C.sub.1 -C.sub.4 -alkyl, carboxyl or C.sub.1 -C.sub.4 -alkylcarbonyl. 
The heterocyclic radicals R.sup.5 may be saturated or unsaturated. Suitable 
radicals are thienyl, furyl, tetrahydrofuryl, triazolyl, imidazolyl, 
tetrahydropyranyl, pyridyl, morpholino and piperidino. 
Saturated or unsaturated heterocyclic radicals R.sup.4 are, for example, 
tetrahydropyranyl, tetrahydrofuryl, thiazolyl, pyridyl, morpholino, 
piperidino and pyrimidyl. 
The novel compounds I can form addition salts, for example with inorganic 
and organic acids or with alkyl halides, or, if one of the substituents 
has acidic properties, they can be reacted with inorganic and organic 
bases to give salts. The present invention also relates to such salts, to 
the extent that they are agriculturally acceptable. 
Isoxazole(isothiazole)-5-carboxamides which are preferred herbicidal active 
ingredients are those of the formula Ia, where R.sup.3 is hydrogen. 
Other compounds of the formula Ia which are preferred active ingredients 
are those in which X is oxygen or sulfur, R.sup.1 is hydrogen or C.sub.1 
-C.sub.4 -alkyl, R.sup.2 is COYR.sup.5, R.sup.3 is hydrogen and R.sup.4 is 
C.sub.1 -C.sub.4 -alkyl or C.sub.3 -C.sub.8 -cycloalkyl. In these 
compounds, R.sup.5 is preferably hydrogen, C.sub.1 -C.sub.4 -alkyl, or 
phenyl which is unsubstituted or substituted by C.sub.1 -C.sub.4 -alkyl, 
C.sub.1 -C.sub.4 -haloalkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 
-alkylthio or halogen, or a radical 
##STR6## 
where R.sup.8 and R.sup.9 in turn are preferably each C.sub.1 -C.sub.4 
-alkyl. 
Isoxazole(isothiazole)-5-carboxamides of the formula 
##STR7## 
where X, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 have the meanings stated 
for formula Ia, with the proviso that X is sulfur when R.sup.1 is 
CH.sub.3, R.sup.2 is COOH or COOC.sub.2 H.sub.5 and R.sup.3 and R.sup.4 
are each hydrogen, and that X is oxygen when R.sup.1 is hydrogen, R.sup.2 
is COOH or CONH.sub.2 and R.sup.3 and R.sup.4 are each hydrogen, are 
novel. 
The isoxazole(isothiazole)-5-carboxamides of the formula I or Ia can be 
prepared by the following methods: 
1. A process for the preparation of compounds of the formula Ib and Ia, 
where R.sup.2 is COOR.sup.5 and R.sup.3 is hydrogen or C.sub.1 -C.sub.8 
-alkyl (cf. Scheme 1), is based on the reaction of a dialkyl isoxazole- or 
isothiazole-4,5-dicarboxylate II (R.sup.8 =C.sub.1 -C.sub.8 -alkyl) with 
an aqueous base and subsequent reaction with a mineral acid to give a 
carboxylic acid III. Particularly suitable dicarboxylates II are lower 
alkyl esters (R.sup.5 =R.sup.8 =C.sub.1 -C.sub.4 -alkyl), dimethyl and 
diethyl esters being particularly preferred. 
The reaction is carried out by treating a dialkyl dicarboxylate II with a 
strong base for example NaOH, KOH or Ca(OH).sub.2, at from about 0.degree. 
to 80.degree. C., preferably from 0.degree. to 50.degree. C., in an 
organic solvent, e.g. methanol or ethanol. In general, about one 
equivalent of the strong base is used in aqueous solution. When the 
reaction is complete, the mixture is cooled and acidified with a strong 
mineral acid, for example hydrochloric acid or sulfuric acid. The 
resulting carboxylic acid III can be isolated in a conventional manner, 
for example by filtration under suction or by extraction with an organic 
solvent. 
To convert the carboxylic acid III into the carbonyl halide IV, the acid 
III is reacted in a conventional manner with an inorganic acid halide, 
such as thionyl chloride, a phosphorus trihalide or a phosphorus 
pentahalide, the chlorides being preferred. Advantageously, the inorganic 
acid halide is used in a n amount of from 1 to 5, preferably from 1 to 2, 
molar equivalents. The reaction can be carried out in the absence of a 
solvent or in the presence of an inert organic solvent, for example 
benzene or toluene, at from room temperature to the boiling point of the 
inorganic acid halide or of the inert organic solvent. In some cases, the 
addition of a catalyst, such as dimethylformamide or 
4-dimethylaminopyridine, may be advantageous. When the reaction is 
complete, the acyl halide IV can be isolated in a conventional, manner, 
for example by distilling off the excess inorganic acid halide and the 
organic solvent and then distilling the acyl chloride IV under atmospheric 
or reduced pressure. 
The carboxamides Ib are obtained from the carbonyl halides by reaction with 
an amine V. For this purpose, it is advantageous if the carbonyl halide, 
in an inert organic solvent, such as dichloroethane, or an ether, such as 
diethyl ether or methyl tert-butyl ether, is reacted with an amine V, 
likewise dissolved in an organic solvent. The amine V is advantageously 
used in from 2 to 5, preferably from 2 to 3, times the molar amount in 
order to bind the resulting hydrogen halide. The reaction may also be 
carried out in the presence of an auxiliary base, such as a tertiary 
amine, e.g. triethylamine. In this case, from 1 to 1.5 molar equivalents 
of amine V are sufficient. The reaction temperature may be from 0.degree. 
to 50.degree. C., preferably from 0.degree. to 20.degree. C. The reaction 
is generally complete after from 1 to 12 hours. The mixture can be worked 
up in a conventional manner, for example by hydrolysis with water and 
extraction of the product of the formula Ib with an organic solvent and 
evaporation of the organic solvent. The product of the formula Ib can be 
purified, for example, by recrystallization or chromatography. 
The 4-alkoxycarbonylisoxazole-5-carboxamides or 
4-alkoxycarbonylisothiazole-5-carboxamides Ib can be converted into the 
free carboxylic acids Ic by reaction with an aqueous base followed by 
reaction with a mineral acid. The reaction is carried out by treating the 
esters Ib, in an organic solvent, e.g. methanol or ethanol, with a base, 
e.g. NaOH, KOH or Ca(OH).sub.2, at from 0.degree. to 80.degree. C., 
preferably from 0.degree. to 50.degree. C. In general, about 1-3, 
preferably 1-1.5, equivalents of the strong base are used in aqueous 
solution. When the reaction is complete, the mixture is acidified with a 
strong mineral acid, for example hydro-chloric acid or sulfuric acid, 
while cooling. The resulting carboxylic acids Ic can be isolated by 
filtration under suction or by extraction with an organic solvent and 
evaporation of this organic solvent. The acids Ic may be further purified 
by recrystallizing or chromatographing them. 
##STR8## 
The dialkyl isoxazole- and isothiazole-4,5-dicarboxylates II required as 
starting materials for this process are known from the literature (J. Org. 
Chem. 43 (1978), 3736; Chem. Pharm. Bull. 28 (1980), 3296; Tetrahedron 30 
(1974), 1365); those which are unknown can be prepared by methods 
generally known from the literature. 
2. A further process for the preparation of the compounds Id is based on 
the reaction of an isoxazole- or isothiazole-5-carbonyl halide VI with an 
amine V. Preferred carbonyl halides VI are the chlorides. In this 
procedure, it is advantageous to react the carbonyl halide, in an inert 
organic solvent, such as dichloromethane, or an ether, such as diethyl 
ether or methyl tert-butyl ether, with an amine V, likewise dissolved in 
an organic solvent. The amine V is advantageously used in from 2 to 5, 
preferably from 2 to 3, times the molar amount in order to bind the 
resulting hydrogen halide. The reaction may also be carried out in the 
presence of an auxiliary base, for example a tertiary amine 
(triethylamine). In this case, from 1 to 1.5 molar equivalents of amine V 
are sufficient. The reaction temperature may be from 0.degree. to 
50.degree. C., preferably from 0.degree. to 20.degree. C. The reaction is 
generally complete after from 1 to 12 hours. The mixture can be worked up 
in a conventional manner, for example by hydrolysis with water and 
extraction of the product VII with an organic solvent and evaporation of 
the organic solvent. 
The isoxazole- or isothiazolecarboxamides VII are converted into the 
5-aminocarbonylisoxazole-4-carboxylic acids or 
5-aminocarbonylisothiazole-4-carboxylic acids of the formula Id by 
reaction with an alkyllithium, preferably with the addition of a solvent 
which is inert under the reaction conditions, such as diethyl ether or 
tetrahydrofuran. As a rule, the reaction is carried out under a nitrogen 
atmosphere at from -70.degree. C. -80.degree. C. In this process, the 
alkyllithium compound is generally used in from 2 to 3 times the molar 
amount, based on amide of the formula VII used. When the reaction is 
complete, the mixture is treated with carbon dioxide, preferably in an 
inert solvent, such as diethyl ether or, for example, tetrahydrofuran, the 
desired products of the formula Id, where R.sup.2 is carboxyl, being 
obtained. 
Using the same process, it is also possible to obtain isoxazole- and 
isothiazolecarboxamides of the formula, Id, where R.sup.2 is formyl, if 
dimethylformamide is used instead of the carbon dioxide. Working up in a 
conventional manner gives substituted 4-formylisoxazole-5-carboxamides or 
4-formylisothiazole-5-carboxamides of the formula Id. 
##STR9## 
The isoxazole- and isothiazole-5-carbonyl halides VI required as starting 
materials for this process are known from the literature. Those which are 
unknown can be prepared from the corresponding carboxylic acids VIII in a 
conventional manner, as described above. 
##STR10## 
The carboxylic acids VIII required for this purpose are likewise known from 
the literature (Chem. Ber. 106 (1973), 3345, J. Chem. Soc. 1959, 3061, J. 
Chem. Soc. 1963, 2032, Adv. in Heterocyclic Chem. 14 (1972), 1); those 
which are unknown can be prepared by methods generally known from the 
literature, for example from the corresponding alcohols or aldehydes by 
oxidation or from the corresponding nitriles by hydrolysis. 
3. Another process leads to compounds Ie, in which R.sup.2 is COOR.sup.5 
and R.sup.5 is C.sub.1 -C.sub.8 -alkyl which is unsubstituted or 
substituted by C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -alkoxy-C.sub.1 
-C.sub.4 -alkoxy, halogen, C.sub.1 -C.sub.4 -alkylthio, C.sub.1 -C.sub.4 
-alkylsulfinyl, C.sub.1 -C.sub.4 -alkylsulfonyl, C.sub.1 -C.sub.4 
-alkoxycarbonyl or benzyloxy or by phenyl which may be substituted by 
C.sub.1 -C.sub.4 -alkyl, C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 
-haloalkyl, halogen, nitro or cyano, or R.sup.5 is C.sub.3 -C.sub.6 
-cycloalkyl or is C.sub.3 -C.sub.8 -alkenyl which is unsubstituted or 
substituted by phenyl which may be substituted by C.sub.1 -C.sub.4 -alkyl, 
C.sub.1 -C.sub.4 -alkoxy, C.sub.1 -C.sub.4 -haloalkyl, halogen, nitro or 
cyano, or R.sup.5 is C.sub.3 -C.sub.8 -alkynyl, C.sub.6 - or C.sub.7 
-cycloalkylimino, succinimido or a radical of the formula 
##STR11## 
by reaction of an acid Ic with a corresponding alcohol IX in the presence 
of a strong mineral acid, for example hydrochloric acid or sulfuric acid, 
at from 0.degree. to 100.degree. C. preferably from 20.degree. to 
50.degree. C. As a rule, an excess of the alcohol IX is used, but it is 
also possible to employ an inert solvent. 
##STR12## 
4. In a further process for the preparation of the compounds of the formula 
Ie, an acid Ic is reacted with an alcohol or thiol IX in the presence of a 
dehydrating agent (e.g. dicyclohexylcarbodiimide (DCC)) at from 
-20.degree. to 50.degree. C., preferably from 0.degree. to 30.degree. C. 
As a rule, the starting materials are used for the reaction in a roughly 
stoichiometric amount. The reaction is preferably carried out in the 
presence of an inert solvent, for example tetrahydrofuran, dichloromethane 
or toluene. 
##STR13## 
(where Y is O or S). 
5. Another process for the preparation of the compounds Ic is based on the 
reaction of an alkyl carboxylate If with an alkali metal alkoxide X, such 
as sodium alkoxide or potassium alkoxide, with a corresponding alcohol IX 
in a conventional manner at from 20.degree. C. to the boiling point of the 
selected alcohol IX. 
##STR14## 
(R.sup.9 =methyl or ethyl) 
6. Compounds of the formula Ig, where R.sup.2 is COOR.sup.2 and R.sup.5 is 
a salt-forming cation, for example an alkali metal, alkaline earth metal, 
ammonium or substituted ammonium ion, are obtained by reacting a 
substituted isoxazole- or isothiazole-4-carboxylic acid Ic with one 
equivalent of the salt-forming cation. If the cation in question is an 
inorganic cation, for example sodium, potassium or calcium, the acid Ic is 
advantageously dissolved or suspended in water or in a lower alcohol or a 
mixture of these, and one equivalent of the salt-forming cation is added. 
The salt-forming cation may be used, for example, in the form of its 
hydroxide, carbonate or bicarbonate, preferably in the form of its 
hydroxide. The reaction is generally complete after a few minutes, and the 
mixture can be worked up in a conventional manner, for example by 
precipitation and filtration under suction or by evaporation of the 
solvent. To prepare compounds Ig in which B.sup..sym. is ammonium or 
organic ammonium, the acid Ic is dissolved or suspended in an organic 
solvent, e.g. diethyl ether, tetrahydrofuran or dioxane, and the mixture 
is treated with one equivalent of ammonia, an amine or a 
tetraalkylammonium hydroxide. 
Among the amines which may be used, the following should be mentioned: 
methylamine, ethylamine, n-propylamine, isopropylamine, n-butylamine, 
isobutylamine, sec-butylamine, n-amylamine, isoamylamine, hexylamine, 
heptylamine, octylamine, nonylamine, decylamine, undecylamine, 
dodecylamine, tridecylamine, tetradecylamine, pentadecylamine, 
hexadecylamine, heptadecylamine, octadecylamine, methylethylamine, 
methylisopropylamine, methylhexylamine, methylnonylamine, 
methylpentadecylamine, methyloctadecylamine, ethylbutylamine, 
ethylheptylamine, ethyloctylamine, hexylheptylamine, hexyloctylamine, 
dimethylamine, diethylamine, di-n-propylamine, diisopropylamine, 
di-n-amylamine, diisoamylamine, dihexylamine, diheptylamine, dioctylamine, 
trimethylamine, triethylamine, tri-n-propylamine, triisopropylamine, 
tri-n-butylamine, triisobutylamine, tri-sec-butylamine, tri-n-amylamine, 
ethanolamines, n-propanolamine, isopropanolamine, diethanolamine, 
N,N-diethylethanolamine, N-ethylpropanolamine, N-butylethanolamine, 
allylamine, n-buten-2-ylamine, n-penten-2-ylamine, 
2,3-dimethylbuten-2-ylamine, dibuten-2-ylamine, n-hexen-2-ylamine, 
propylenediamine, tallowamine, cyclopentylamine, cyclohexylamine, 
dicyclohexylamine, piperidine, morpholine and pyrrolidine. 
In the case of tetraalkylammonium hydroxides, for example, tetramethyl-, 
tetraethyl- or trimethylbenzylammonium hydroxide may be used. As a rule, 
the ammonium salt or organic ammonium salt is precipitated from the 
solution and can be isolated by a conventional method. Alternatively, the 
salt of the formula Ig can also be obtained by evaporating the solvent. 
##STR15## 
7. Another process leads to compounds Ih in which R.sup.2 is CONR.sup.6 
R.sup.7. It consists in reacting an ester Ib with a primary or secondary 
amine XI. The process is carried out by reacting an ester Ib with from 1 
to 50 times the molar amount of amine XI, in the presence or absence of an 
organic solvent, at from room temperature to the boiling point of the 
amine or of the organic solvent. Preferred esters Ib are lower alkyl 
esters, particularly the methyl and ethyl esters. The reaction products Ih 
can be isolated in a conventional manner, for example by filtration under 
suction or evaporation of the solution and, if required, can be further 
purified by recrystallization or chromatography. 
##STR16## 
8. In another process for the synthesis of the compounds Ib, a dialkyl 
isoxazole- or isothiazole-4,5-dicarboxylate II is reacted with an amine V. 
Particularly suitable dialkyl esters II are lower alkyl esters, preferably 
dimethyl esters or diethyl esters. The reaction is carried out by treating 
a dialkyl dicraboxylate II with about one equivalent of a primary or 
secondary amine V at from 0.degree. to 100.degree. C., preferably from 
50.degree. to 80.degree. C., in an organic solvent, for example an 
alcohol, such as methanol or ethanol. When the reaction is complete, the 
mixture is cooled and filtered under suction or evaporated down. The 
resulting product of the formula Ib can be further purified by a 
conventional standard method, such as recrystallization or chromatography. 
##STR17## 
9. Compounds of the formula Ii can be obtained by reacting a substituted 
isothiazole-4,5-dicarboxylic anhydride XII with an amine V. The reaction 
is advantageously carried out by initially taking the anhydride XII in an 
inert solvent, such as an ether or a halohydrocarbon, and adding dropwise 
about a molar amount of an amine V, if necessary likewise dissolved in an 
inert solvent. After the reaction is complete, the reaction product is 
filtered off under suction or isolated by evaporating the solvent used. In 
some case, the isomeric amides XIII may be formed in this process, the 
amide Ii generally being the preferred ones. 
##STR18## 
The isothiazole-4,5-dicarboxylic anhydrides XII required as starting 
materials for this process are known form the literature (J. Chem. Soc. 
1959, 3061); those which are unknown can be synthesised by methods which 
are generally known from the literature. 
10. In another process for the preparation of compounds of the formula Ik, 
an acid Ic is reacted with an alcohol or thiol XIV in the presence of a 
1-methyl-2-halopyridinium iodide at from 20.degree. to 80.degree. C., 
preferably from 30.degree. to 40.degree. C. The reaction is carried out in 
the presence of an inert solvent, e.g. dichloromethane or toluene. The 
process is known in principle from the literature (Chem. Lett. 1045 
(1975); ibid. 13 (1976); ibid. 49 (1976)).