Photoinduced Electron Donor-Acceptor Complex-Mediated Radical Cascade Involving -(Acyloxy)phthalimides: Synthesis of Tetrahydroquinolines.

We conceptualized a novel disconnection approach for the synthesis of fused tetrahydroquinolines that exploits a visible light-mediated radical (4 + 2) annulation between alkyl -(acyloxy)phthalimides and -substituted maleimides in the presence of DIPEA as an additive. The reaction proceeds through the formation of a photoactivated electron donor-acceptor complex between alkyl NHPI esters and DIPEA, and the final tetrahydroquinolines were obtained in a complete regioselective fashion. The methodology features a broad scope and good functional group tolerance and operates under metal- and catalyst-free reaction conditions. Detailed mechanistic investigations including density functional theory studies provide insight into the reaction pathway.