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

A Cu(MeCN) 4 BF 4 /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.