Stereoselective synthesis of trans β-lactams via palladium/N-heterocyclic carbene-catalyzed carbonylative [2+2] cycloaddition

The carbonylative [2+2] cycloaddition of benzyl chlorides and allyl derivatives with imines and CO for synthesis of β-lactam is effectively catalyzed by palladium/N-heterocyclic carbene complex. The desired β-lactam could be obtained in good to excellent yields (61-96%) with excellent regioselectivities (trans/cis > 95:5) and chiral lactams could be obtained with moderate diastereoselectivities. The KIE experimental studies have revealed that the C-H cleavage is most likely to be the rate-limiting step for the carbonylative cycloaddition.