NHC-Catalyzed β-Lactam Synthesis

Significance

Carbene catalysis has been applied to the highly enantio- and diastereoselective synthesis of bicyclic β-lactams. 3-Alkyl or 3-aryl enals 1 and chalcone-derived N-sulfonyl imines 2 are used as starting materials. Chiral tri­azolium precatalyst 3 (10 mol%) together with either DBU (for aliphatic enals) or DMAP (for aromatic enals) as catalytic base were sufficient to afford cyclopentyl-fused β-lactams 4 in good yields and with excellent enantioselectivities. In the case of 3-alkyl enals 1, only a single diastereomer was formed. The authors propose a tandem crossed-aza-benzoin/oxy-Cope reaction as the key bond-forming step.