Polyfluoroheterocyclic compounds. Part XXI. Thermal rearrangement of perfluoropyridazine and perfluoroalkylpyridazines to pyrimidines

Abstract

Pyrolysis of tetrafluoropyridazine near 800° gives tetrafluoropyrimidine in 50% yield, together with small amounts of tetrafluoropyrazine and secondary products. Similarly 3,6-difluoro-4,5-bisheptafluoroisopropylpyridazine rearranges at 580° to 4,6-difluoro-2,5-bisheptafluoroisopropylpyrimidine, together with 2,5-difluoro-3,6-bisheptafluoroisopropylpyrazine. A preliminary suggestion that the 2,5-substituted pyrimidine arises by nucleophilic rearrangement of a primary pyrolysis product has been disproved by trapping experiments with ammonia. A mechanism involving the formation and sigmatropic rearrangement of intermediate diazabenzvalenes is put forward to rationalise the results.