Efficient and Divergent Synthesis of Fully Substituted 1H-Pyrazoles and Isoxazoles from Cyclopropyl Oximes

Efficient and divergent one-pot synthesis of fully substituted 1H-pyrazoles and isoxazoles from cyclopropyl oximes based on reaction conditions selection is reported. Under Vilsmeier conditions (POCl₃/DMF), substituted 1H-pyrazoles were synthesized from 1-carbamoyl, 1-oximyl cyclopropanes via sequential ring-opening, chlorovinylation, and intramolecular aza-cyclization. In the presence of POCl₃/CH₂Cl₂, substituted isoxazoles were obtained from the cyclopropyl oximes via ring-opening and intramolecular nucleophilic vinylic substitution (S_NV) reactions.