Pyrimidine derivatives and related compounds. Part 45. Synthesis of 4-allophanoylpyrazoles via a pyrimidine-to-pyrazole ring transformation

Abstract

Reaction of the 5-formyluracil derivatives (1a–f) with hydrazines in the presence of acetic acid produced a ring contraction to give the corresponding 4-allophanoylpyrazoles (2a–h). Further treatment of these pyrazoles (2a–h) with sodium methoxide afforded methyl pyrazole-4-carboxylate (3a). Conceivable mechanisms for the present pyrimidine-to-pyrazole transformation were discussed.