Synthesis of Benzo[a]quinolizidines via an Aza‐Michael/Oxidative Mannich Process

The synthesis of substituted benzo[a]quinolizidines via aza‐Michael addition of tetrahydroisoquinolines to alkyl vinyl ketones, followed by oxidative Mannich cyclization, is described. Various Michael adducts are easily prepared, and subsequent DDQ‐mediated oxidations stereoselectively afford the corresponding azacycles efficiently. Furthermore, the one‐pot aza‐Michael/oxidative Mannich process gave benzo[a]quinolizidines, thus providing a metal‐free and practical synthetic route to N‐heterocyclic building blocks. One after another: A sequential or one‐pot synthesis of substituted benzo[a]quinolizidines was developed via an aza‐Michael reaction followed by a DDQ‐mediated oxidative Mannich cyclization.