Chiral Guanidine/Copper Catalyzed Asymmetric Azide-Alkyne Cycloaddition/[2+2] Cascade Reaction.

We report the development of a chiral guanidine-based copper(I) catalyst for the asymmetric azide-alkyne cycloaddition/[2+2] cascade reaction. Optically active spiroazetidinimine oxindoles were constructed by trapping the ketenimine species under mild reaction conditions. High level of enantioinduction and excellent isolated yields were achieved in the three-component reaction of various isatin-derived ketimines, sulfonyl azides, and terminal alkynes. Control experiments and X-ray crystallography were used to probe into the interaction of chiral guanidinium salt with copper salt.