Visible light induced 6π electrocyclization: divergent synthesis of seven membered ring derivatives

We report the first visible light-induced 6π electrocyclic reaction for the divergent synthesis of seven-membered ring derivatives. When BHT was employed, the indole skeletons bearing seven-membered rings underwent a 6π/4π cyclization to form [7–4–5] tricyclic systems fused with indoles. In contrast, the use of TBAI enabled the conversion of the same starting materials into [7–7] bicyclic scaffolds tethered with indoles via an electron donor–acceptor (EDA) complex. Notably, this reaction has significant advantages such as high atom economy and carbon efficiency, as well as the absence of external photocatalysts.