Ruthenium‐Catalyzed Oxidative Formal Aza‐Diels–Alder Reaction: Enantioselective Synthesis of Benzo[a]quinolizine‐2‐ones

A method for the preparation of thermodynamic (4R,11bS)‐benzo[a]quinolizine‐2‐one derivatives in good enantio‐ and diastereoselectivity by a one‐pot oxidative formal aza‐Diels–Alder reaction of 1,2,3,4‐tetrahydroisoquinolines and α,β‐unsaturated ketones is described. The reaction proceeds via tandem ruthenium‐catalyzed amine dehydrogenation using tert‐butyl hydroperoxide (TBHP) as the oxidant and a chiral thiourea‐catalyzed formal aza‐[4+2] cycloaddition, providing a step‐economical strategy for the synthesis of these valuable heterocyclic products.