Stereoselective Synthesis of Benzo[ a ]quinolizidines via Aerobic DDQ-Catalyzed Allylation and Reductive Cyclization.

Stereoselective synthesis of C 4 -substituted benzo[ a ]quinolizidines via redox-controlled catalytic C-C-bond-forming reactions was carried out. Aerobic DDQ-catalyzed allylation of N -Cbz tetrahydroisoquinolines efficiently provided α-allylated products 5 , which were transformed to enones 6 via cross-metathesis reactions using the second-generation Hoveyda-Grubbs catalyst. Palladium-catalyzed hydrogenation of 6 prompted alkene reduction, protecting group removal, and intramolecular reductive amination in one step to afford the desired benzo[ a ]quinolizidines 7 as single diastereomers.