Synthesis of substituted dihydro-1H-pyrazoles and 1H-pyrazoles via formal [4+1] annulation of α-arylhydrazonoketones and dimethyl sulfonium methylides

A formal [4+1] annulation of readily available α-arylhydrazonoketones and dimethyl sulfonium methylides is described, which involving tandem ylide-mediated addition and nucleophilic cyclization reactions. This transformation features mild reaction conditions, simple execution, good to high yields, and provides straightforward synthesis of substituted dihydro-1H-pyrazoles and 1H-pyrazoles via C-C and C-N bond formation.