Divergent Construction of Cyclobutane-Fused Pentacyclic Scaffolds via Double Dearomative Photocycloaddition

Cyclobutane-fused polycyclic scaffolds are structurally interesting cores in natural product synthesis and drug discovery. The construction of these skeletons often requires elaborate synthetic effort and gives low efficiency. We herein demonstrated the divergent construction of various cyclobutane-fused 2D/3D pentacyclic scaffolds by a photocatalytic intermolecular double dearomative cycloaddition of arenes. These skeletons, typically unattainable under thermal conditions, could be accessed with exclusive diastereoselectivity under mild photochemical conditions. Combined experimental and computational mechanistic studies elucidate that the reaction proceeds through a cascade sequence involving photocatalytic 1,4-hydroalkylation, alkene isomerization, and [2 + 2] cycloaddition via an intertwined single electron transfer (SET)/energy transfer (EnT) nature. This protocol provided a divergent synthetic approach for constructing (pseudo)-dimeric cyclobutane-fused 2D/3D pentacyclic scaffolds. The visible light induced intermolecular double dearomative cycloaddition between naphthalenes and benzothiophenes was also realized, providing indispensable methods for unprecedented structurally diverse polycyclic molecules that were difficult to access by conventional transformations.