γ-Heteroatom directed stereocontrolled Staudinger cycloaddition reaction of vinylketenes and imines

Vinylketenes possessing a γ-heteroatom, on Staudinger cycloaddition reaction with imines, gave trans-3-vinyl-β-lactams in very good yields. The vinyl side chain stereoselectively adopts the Z-configuration in the transition state to stabilize the vinylketene and produces, exclusively, trans-3-vinyl-β-lactams.