Enantioselective Synthesis of Indolizidines Bearing Quaternary Substituted Stereocenters via Rhodium-Catalyzed [2 + 2 + 2] Cycloaddition of Alkenyl Isocyanates and Terminal Alkynes

An enantioselective synthesis of indolizidines bearing quaternary substituted stereocenters by way of a rhodium-catalyzed [2 + 2 + 2] cycloaddition of substituted alkenyl isocyanates and terminal alkynes is described. The reaction provides lactam products using aliphatic alkynes, whereas aryl alkynes give rise to vinylogous amide products. Through modification of the phosphoramidite ligand, high levels of enantioselectivity, regioselectivity, and product selectivity are obtained for both products.