SYNTHESES OF SUBSTITUTED-OXAZOLO-1,3,4-THIADIAZOLES, 1,3,4-OXADIAZOLES, AND 1,2,4-TRIAZOLES

Starting from readily available methyl 5-methyloxazole-4-carboxylate (1) and 4-metfiyl-5-oxazolylcarboxylic acid hydrazide (11) the title compounds were prepared. The reaction of compound 1 with hydrazine hydrate afforded the corresponding hydrazide 2. The reaction of compound 2 with formic acid yielded 1-formyl-2-(5-methyloxazole-4-carboxyl)hydrazine (3). Refluxing of the latter with phosphorus pentasulfide in xylene gave compound 5 in 62% yield. The reaction of compound 3 with phosphorus pentoxide afforded compound 4. Starting from hydrazide 11, compounds 13 and 14 were prepared similarly. Reaction of compound 2 with substituted isothiocyanate yielded compound 9 which was cyclized in basic medium to 4-alkyl-5-(5-methyl-4-oxazolyl)-2,4-dihydro-3H-1,2,4-triazole-3-thione (10). The isomer 19 was prepared similarly. Methylation and subsequent oxidation of compound 19 gave compound 21. Reaction of the acid 7 with thio semicarbazide in the presence of phosphorus oxychloride gave 2-amino-5-(5-methyl-4-oxazolyl)1,3,4-thiadiazole (8). 2-Amino-5-(4-methyl-5-oxazolyl)-1,3,4-thiadiazole (17) was prepared from acyl chloride 15 by the usual method.