Rearrangement of thiazolo[3,2-a]pyrimidines into triazolo[4,3-a]pyrimidines induced by C=N bond reduction

Abstract

Triazolo[4,3-a]pyrimidines were prepared by the reduction of 5,6,7-trisubstituted 2-(arylhydrazinylidene)-5H-[1,3]thiazolo[3,2-a]- pyrimidin-3(2H)-ones with NaBH4 in the presence of V2O5 at room temperature. The structure of ethyl 3-(hydroxymethyl)- 5-(4-methoxyphenyl)-7-methyl-1-phenyl-1,5-dihydro[1,2,4]triazolo[4,3-a]pyrimidine-6-carboxylate was proven by the single crystal X-ray diffraction data. The mechanism of the reaction including transition cage structure is discussed.