Photochemical Synthesis of 1,2-Diazepine-Fused β-Lactams via Staudinger-Type [2 + 2] Cyclization

Herein, we report a one-pot sequence to prepare 1,2-diazepine fused β-lactams under photochemical irradiation. Hence, α-diazoketones are readily converted to the corresponding ketenes in an additive-free Wolff rearrangement and react with isolated or in situ generated 1,2-diazepines to yield a rather uncommon β-lactam core. The operative mechanism follows the rules of the Staudinger [2 + 2] synthesis and involves a 4 π conrotatory ring closure. Key factors, both steric and electronic, governing the diastereoselectivity were identified. Postmodification of the substrates, including (hetero) Diels–Alder reactions on the residual diene, showcases the synthetic utility of the present work. Finally, the divergent reactivity of acyl ketenes, yielding oxazinone-fused 1,2-diazepines, was also established.