Synthesis of hydroxypyrazoles and 1-methyl-3-isoxazolones via haloform reactions

The synthesis of a new series of hydroxypyrazoles (2a–f) and 2-methyl-3-isoxazolones (3a–d) from the cyclocondensation reaction of trichloromethyl-substituted 1,3-dielectrophiles (1a–f) with dry hydrazine and N-methylhydroxylamine is reported. The regiospecific cyclocondensation took place with the elimination of the trichloromethyl group in a haloform type reaction when acetonitrile under basic medium was used. The structure of compounds 2 and 3 were determined mainly by 1H and 13C NMR spectroscopy.