Visible‐Light‐Induced Synthesis of 1,2,3,4‐Tetrahydroquinolines through Formal [4+2] Cycloaddition of Acyclic α,β‐Unsaturated Amides and Imides with N , N ‐Dialkylanilines

1,2,3,4‐Tetrahydroquinolines should be applicable to the development of new pharmaceutical agents. A facile synthesis of 1,2,3,4‐tetrahydroquinolines that is achieved by a photoinduced formal [4+2] cycloaddition reaction of acyclic α,β‐unsaturated amides and imides with N , N ‐dialkylanilines under visible‐light irradiation, in which a new Ir III complex photosensitizer, a thiourea, and an oxidant act cooperatively in promoting the reaction, is reported. The photoreaction enables the synthesis of a wide variety of 1,2,3,4‐tetrahydroquinolines, while controlling the trans / cis diastereoselectivity (>99:1) and constructing contiguous stereogenic centers. A chemoselective cleavage of an acyclic imide auxiliary is demonstrated.