Intramolecular Dearomative [2 + 2] Cycloadditions of (Hetero)arenes Utilizing an Energy-Transfer Organic Photocatalyst

Abstract Expanding the application scope of organic photoredox catalysts is of considerable importance in photocatalysis. Herein, we report an energy transfer (EnT)-mediated intramolecular dearomative [2+2] cycloaddition of N-substituted-N-(2-arylallyl)-2-naphthamides, N-acryloyl-N-substituted α/β-naphthamides, and benzoheterocycles using an easily accessible phenothiazine-derived organic photocatalyst. This transformation proceeds under mild conditions and provides efficient access to structurally complex polycyclic frameworks. DFT studies reveal that the photocatalyst plays a pivotal role in facilitating the reaction through the formation of a triplet exciplex between the substrate and the triplet-state photocatalyst.