Cyclocondensations of Substituted Thiosemicarbazides with 2-Bromo- 1,2-diphenylethan-1-one

Abstract

The cyclocondensation of 4-methylthiosemicarbazide with 2-bromo-1,2-diphenylethan-1-one in ethanol afforded isomeric 2-methylamino-5,6-diphenyl-6H-3,4-thiadiazine and 2-hydrazono-3- methyl-4,5-diphenyl-2,3-dihydro-1,3-thiazole. A pyrazole was obtained by cyclocondensation and subsequent desulfurization of the thiadiazine when the reaction was carried out in concentrated hydrochloric acid. A chemical proof of the structures has been provided. The product distribution of the cyclizations strongly depends on the substitution pattern of the starting materials, and the cyclizations of methylthiosemicarbazide with 2-bromo-1,2-diphenylethan-1-one behaved considerably different from that of the analogous reactions of α-bromoacetophenone.