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

• Published in: Chemistry : a European journal 2021-03, Vol.27 (16), p.5171-5179
• Main Authors: Itoh, Kennosuke, Nagao, Shun‐ichi, Tokunaga, Ken, Hirayama, Shigeto, Karaki, Fumika, Mizuguchi, Takaaki, Nagai, Kenichiro, Sato, Noriko, Suzuki, Mitsuaki, Hashimoto, Masashi, Fujii, Hideaki
• Format: Article
• Language: English
• Subjects: Amides; aromatic substitution; Chemistry; conjugate addition; Cycloaddition; Imides; Irradiation; Light irradiation; nitrogen heterocycles; Oxidants; Oxidizing agents; photochemistry; radical reactions; Stereoselectivity
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202004186

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 IrIII 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. Coming together: The cooperative action of an IrIII complex photosensitizer, a thiourea, and an azo compound enables the visible‐light‐induced formal [4+2] cycloaddition of acyclic α,β‐unsaturated amides and imides with N,N‐dialkylanilines to synthesize structurally diverse 1,2,3,4‐tetrahydroquinolines possessing contiguous stereogenic centers in a highly diastereoselective manner. The chemoselective removal of the auxiliary can be achieved.