Protonation-Enhanced Reactivity of Triplet State in Dearomative Photocycloaddition of Quinolines to Olefins.

The intermolecular dearomative cycloaddition of acidified bicyclic azaarenes with olefins was recently reported. We report here the crucial role of the acid in the dearomative photocycloaddition of quinolines to olefins. Experimental and theoretical results show that the key role of the protonation of quinolines is not to promote the energy transfer but to enhance the reactivity of the triplet state of quinolines toward olefins.