Synthesis of unique 1,2-diazepine-fused b-lactams via Staudinger-type [2+2] cyclization

Herein, we report a one-pot sequence to prepare 1,2-diazepine fused b-lactams under photochemical irradiation. Hence, a-diazoketones are readily converted to corresponding ketenes in an additive-free Wolff rearrangement. The operative mechanism follows the rules of the Staudinger [2+2] synthesis and involves a 4 p conrotatory ring closure. Key factors, both steric and electronic, governing the diastereoselectivity were identified. Post-modification of the substrates, including a Diels-Alder reaction on the residual diene, showcase the synthetic utility of the present work. Finally, the divergent reactivity of acyl ketenes, yielding oxazinone-fused 1,2-diazepines was also established.