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 alpha,beta-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.

Automated summary

A facile synthesis of 1,2,3,4-tetrahydroquinolines was achieved by a photoinduced formal [4+2] cycloaddition reaction, with a new Ir-III complex photosensitizer, a thiourea, and an oxidant acting cooperatively. The reaction enables the synthesis of a wide variety of tetrahydroquinolines with high trans/cis diastereoselectivity (>99:1) and constructing contiguous stereogenic centers, while demonstrating a chemoselective cleavage of an acyclic imide auxiliary.