Allylic Acetal as 3C Synthon in Rh(III)-Catalyzed Divergent C–H Activation/[4 + 3] Annulation: Easy Access to Benzodiazepines

A concise synthesis of benzodiazepines via Rh(III) catalyzed C-H activation/ [4 + 3] annulation of easily available 1-arylpyrazolidinones with allylic acetal has been developed. The allylic acetal was employed as a novel 3C synthon in this transformation. Benzodiazepines were built under mild reaction conditions with high efficiency and chemoselectivity. The high atom-economy and easily accessible substrates reveal potential application.