Synthesis of [1,3,4]thiadiazolo[3,2‐<i>a</i>]pyrimidines in the presence of formic acid

Abstract

Abstract Formic acid‐phosphorus pentoxide was effective for the preparation of 5,7‐dimethyl[1,3,4]thiadiazolo‐ and ‐[1,3]thiazolo[3,2‐ a ]pyrimidin‐4‐ium salts. Further, the pyrimidine ring transformation and the isocyanation of 5imino‐6 H ‐[1,3,4]thiadiazolo‐ and ‐[1,3]thiazolo[3,2‐ a ]pyrimidin‐7‐ones were carried out in the presence of formic acid and triethyl orthoformate, respectively.