Visible‐Light‐Mediated Intramolecular Dearomatization of Naphthalene and Anthracene with Bicyclo[1.1.0]butanes Through Energy Transfer Catalysis

Cyclization of bicyclo[1.1.0]butanes (BCBs) is an effective way to construct saturated polycyclic 3D structures. Herein we report a visible-light-induced intramolecular dearomative reaction to forge bicyclo[4.1.1] frameworks through (1,3)-cyclization of BCBs. Moreover, the unprecedented (1,2,3)-cyclization of BCBs through 1,4-hydrogen atom transfer (HAT) process was also realized along with the further transformations. The mechanistic studies revealed that the reaction was initially carried out by an energy transfer (EnT) process and the key open-shell singlet biradical intermediate may undergo [4π + 2σ] cycloaddition or 1,4-HAT process leading to the formation of two products and we found that the selectivity of product is related to the substituents at the BCBs bridgehead position. Our findings are supported by control experiments, deuterium labeling and kinetic studies, cyclic voltammetry, Stern-Volmer experiments, as well as density functional theory (DFT) calculations.