Rh-Catalyzed Enantioselective 2 + 2 Cycloaddition of Alkynyl Esters and Norbornene Derivatives

reaction: see text The enantioselective 2 + 2 cycloaddition of alkynes possessing an ester functionality and norbornene derivatives proceeded efficiently using a chiral rhodium catalyst. The chiral tri- and tetracyclic cyclobutenes were obtained in moderate to high ee.