Ring transformations in reactions of heterocyclic compounds with nucleophiles (XX). Conversion of 5‐nitropyrimidine into 3,5‐dinitropyridine. A novel ring transformation

Heating of 5‐nitropyrimidine with acetic acid in water leads to the formation of 3,5‐dinitro‐pyridine. The mechanism proposed for this novel ring transformation involves a fragmentation of the pyrimidine ring, leading to the formation of a two‐atom and a four‐atom moiety, which on condensation gives the pyridine ring. With hydrazine hydrate, 5‐nitropyrimidine undergoes ring contraction into 4‐nitropyrazole.