Cascade cyclization, dipolar cycloaddition of azomethine imines for the synthesis of pyrazolidines

Abstract

A tandem multi-step, one-pot reaction of aldehydes with hydrazines has been used for the preparation of tetrahydropyrazoles and dihydropyrazoles. The chemistry involves condensation then cyclization, followed by inter- or intramolecular dipolar cycloaddition of the resulting azomethine imine intermediates. The intramolecular cycloaddition gives fused tricyclic compounds as single diastereoisomers. The intermolecular cycloaddition was successful with a variety of activated alkene and alkyne dipolarophiles.