Asymmetric Synthesis of Bicyclic Amidines via Rhodium-Catalyzed [2+2+2] Cycloaddition of Carbodiimides

A highly enantioselective rhodium-catalyzed [2+2+2] cycloaddition of terminal alkynes and alkenyl carbodiimides has been developed. This reaction demonstrates the feasibility of olefin insertion into carbodiimide-derived metalacycles and provides a new class of chiral bicyclic amidines as the major products. An isonitrile migration process responsible for the formation of the minor cycloadduct can be observed and is highly sensitive to the electronics of alkynyl substrates.