Double Ring Expansion Strategy for Fused 3‑Benzazepines: Alternative Synthesis of the Dolby–Weinreb Enamine

A double ring expansion strategy for constructing fused 3-benzazepines is described. The oxidative ring expansion of spiroamine compounds with N-chlorosuccinimide and subsequent ring expansion of the resulting ketiminium ion intermediates with trimethylsilyldiazomethane afforded fused 3-benzazepines in a one-pot operation. Importantly, the Dolby–Weinreb enamine, which is a key synthetic intermediate for harringtonine alkaloids, cephalotaxines, can be accessed from commercial materials in only two steps using our developed method.