Synthesis of tetracyclic dibenzo[ b , f ][1,4]oxazepine-fused β-lactams via visible-light-induced Staudinger annulation.

An efficient visible-light-induced Staudinger [2 + 2] annulation reaction between α-diazo ketones and dibenzo[ b , f ][1,4]oxazepine/thiazepine-imines under catalyst-free conditions has been developed. This protocol provides a facile method to synthesize tetracyclic dibenzo[ b , f ][1,4]oxazepine/thiazepine-fused β-lactams bearing a quaternary carbon center with a broad substrate scope and high efficiency (37 examples, up to >99% yield).