Phosphine-Catalyzed [4+2] Cycloadditions of Allenic Ketones: Enantioselective Synthesis of Functionalized Tetrahydropyridines.

Amino-acid-derived phosphine catalyzed [4+2] cycloaddition leading to chiral tetrahydropyridines, making use of α-substituted allenic ketones as "C4 synthons" and N-sulfonyl cyclic ketimines, has been developed. This asymmetric cycloaddition tolerates a wide range of α-substituted allenic ketones. A series of chiral sultam-fused tetrahydropyridines bearing a quaternary stereocenter were obtained in high yields with good enantioselectivities.