Photoinduced radical cascade brominative addition/spirocyclization of N-arylpropiolamides and CBr4 with O2 as oxidant

A visible-light-induced brominated spirocyclization of N-arylpropiolamides and CBr₄ for the synthesis of 3-bromo-azaspiro[4,5]trienones is reported here. This process allows the formation of C-Br, C-C, and C=O bonds in a single reaction via a cascade radical addition/ipso-cyclization/oxidative dearomatization sequence. This protocol also features high functional group tolerance, operational simplicity and the use of molecular oxygen as an oxidant as well as sustainable photocatalyst- and additive-free reaction conditions at room temperature. Meanwhile, the presented straightforward and sustainable strategy has also been applied to the synthesis of several biologically active compounds.