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.