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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%).
Chen et al. (Fri,) studied this question.