Enantioselective Synthesis of Dihydropyrazoles by Formal [4+1] Cycloaddition of in Situ-Derived Azoalkenes and Sulfur Ylides

Abstract

An unprecedented strategy to access highly enantioenriched dihydropyrazoles is described. It involves formal [4+1] cycloadditions of in situ-derived azoalkenes and sulfur ylides catalyzed by a chiral copper/Tol-BINAP complex. A variety of synthetically and biologically important dihydropyrazoles have been obtained with high enantioselectivities (up to 97:3 er) in good yields (83-97%).