Stereocontrolled Synthesis of N-Vinyl-, N-(1'-Propenyl)-, and N-Unsubstituted-β-lactams from 2-Aza-1,3-butadienes via the Staudinger Reaction

2-Aza-1,3-butadienes 2 and 5 were synthesized in good yields and on a large scale. Reaction of 2 and 5 with acid chlorides in the presence of triethylamine (Staudinger reaction) resulted in the high-yielding formation of N-vinyl- and N-(l'-propenyl)-β-lactams. Excellent cis-stereoselectivity was observed in the reaction of 2-aza-1,3-butadienes 2 and 5 with Bose-Evans ketenes and Sheehan ketenes, whereas reaction with a Moore ketene gave, as expected, a trans β-lactam. N-Formyl, N-vinyl, and N-(l'-propenyl) groups at the β-lactam nitrogen could be cleaved oxidatively in one step and in good yields by treatment with potassium permanganate. It was also found that the N-vinyl group can be removed successfully under hydrolytic conditions to yield N-unsubstituted-β-lactams.