Rh-catalyzed enantioselective [2+2] cycloaddition of alkynyl esters and norbornene derivatives

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.