Enantioselective, NHC-Catalyzed bicyclo-β-lactam formation via direct annulations of enals and unsaturated N-sulfonyl ketimines

A wide range of alpha,beta-unsaturated aldehydes induding 3-alkyl derivatives undergo N-heterocyclic carbene (NHC)-catalyzed annulations with N-sulfonyl ketimines under mild condition, to provide bicyclo[3.2.0]lactams with outstanding diastereo- and enantioselectivity. This concise route to beta-lactams established four new chiral centers in a single operation. Although this process could occur via the intermediacy of a catalytically generated homoenolate equivalent, the stereochemical outcome supports a tandem or concerted aza-Benzoin/oxy-Cope reaction as the key bond forming step.