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Syntheses of substituted‐oxazolo‐1,3,4‐thiadiazoles, 1,3,4‐oxadiazoles, and 1,2,4‐triazoles

1995; Wiley; Volume: 32; Issue: 4 Linguagem: Inglês

10.1002/jhet.5570320424

1943-5193

Abbas Shafiee, Ebrahim Naimi, P. Mansobi, Alireza Foroumadi, Mohammad Reza Shekari,

Synthesis and Reactivity of Sulfur-Containing Compounds

Abstract Starting from readily available methyl 5‐methyloxazole‐4‐carboxylate ( 1 ) and 4‐methyl‐5‐oxazolylcar‐boxylic 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‐3 H ‐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 thiosemicarbazide 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.