Substituted 1H-Pyrazoles and Isoxazoles from Cyclopropyl Oximes

Significance

Reported here is a synthesis of substituted 1H-pyrazoles and isoxazoles from the oximes of 1-acyl and 1-carbamyl cyclopropanes under mild reaction conditions. The synthesis of the pyrazoles was achieved under Vilsmeier conditions (DMF/POCl₃) via ring opening and chloro­vinylation followed by intramolecular cyclization. When DMF was replaced with CH₂Cl₂, the same substrates afforded isoxazoles via ring opening followed by an intramolecular vinylic substitution reaction. In some cases, the yields for 1H-pyrazoles were very low and the reactions furnished inseparable and uncharacterizable mixtures.