Selective synthesis of 4-(sulfonyl)-methyl-1H-pyrazoles and (E)-4,5-dihydro-1H-pyrazoles from N-allenic sulfonylhydrazones.

Selective synthesis of 4-(sulfonyl)-methyl-1H-pyrazoles and (E)-4,5-dihydro-1H-pyrazoles from N-allenic sulfonylhydrazones with sulfonyl group migrations has been developed. A key feature of these reactions is that the migrations of the sulfonyl groups to different positions can be controlled by changing the Lewis acids.