Copper-Catalyzed Diastereo- and Enantioselective 1,3-Dipolar Cycloaddition of Imino Lactones with Ylidene-Pyrazolones

Abstract

A Cu(MeCN)₄BF₄/Fesulphos complex successfully catalyzes the asymmetric 1,3-dipolar cycloaddition (1,3-DC) of imino lactones with 4-ylidene-pyrazol-5-ones to afford bis-spirocyclic pyrrolidines in good yields with high diastereo- and enantioselectivities (up to >20:1 dr, 99% ee). In addition, exo'-(2,5-trans-4,5-trans)-pyrrolidine scaffolds are exclusively produced as single diastereomers. A wide variety of imino lactones bearing electron-donating and electron-withdrawing groups on the phenyl groups and heteroaryl substrates is employed in this reaction. The substrate scope of ylidene-pyrazol-5-ones is investigated, and the substituents on the phenyl ring have limited effect on the product yields and stereoselectivity of the reaction.