Catalytic Asymmetric Synthesis of Aza-β-Lactams

Significance

This work describes the first catalytic asymmetric synthesis of aza-β-lactams through [2+2] cycloaddition of ketenes with azo compounds. A catalytic amount of planar-chiral 4-pyrrolidino pyridine (PPY) derivative (-)-1 accomplishes the formation of the desired heterocyclic products in good yields and enantioselectivities. A range of aryl alkyl ketenes is tolerated among which those bearing a secondary alkyl group gave superior results. Moreover, concise synthetic routes to the corresponding α-amino ­acids and hydantoins starting from the aza-β-lactams are presented (S. Bräse and co-workers Eur. J. Org. Chem. 2007, 266).