Rearrangements and cyclizations—XVI: Ring-opening reactions of 1,1-diacetylcyclopropane with hydrazine and hydroxylamine derivatives as the novel synthesis of β-X-ethyl substituted pyrazoles and isoxazoles

The reactions of 1,1-diacetylcyclopropane (1) with a number of hydrazine and hydroxylamine derivatives proceed via cyclopropane ring opening with incorporation of external nucleophile (solvent) to give the 4-β-X-ethyl derivatives of 3,5-dimethylpyrazoles and -isoxazoles, a novel route to these heterocycles. This ring cleavage occurs especially smoothly in water as a solvent. A rationale for this unusually mild nucleophilic cyclopropane ring opening is discussed.