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.
We present herein a photochemical reaction to synthesize 4-alkyl-and 4-aryl-1-methyl-2-pyrrolidinones through the formal [3+2] photocycloaddition of α,β-unsaturated imides or amide with N,N,N',N'-tetramethyldiaminomethane, where an iridium(III) complex acts as a photosensitizer. The reaction is driven by visible-light-induced single-electron transfer between a photoexcited iridium(III) complex and N,N,N',N'-tetramethyldiaminomethane to generate an α-aminoalkyl radical. The resulting α-aminoalkyl radical is added to α,β-unsaturated imides or amide in a 1,4-fashion to produce conjugate adducts, subsequently causing intramolecular acylation to furnish 4-alkyl-and 4-aryl-1-methyl-2-pyrrolidinones.
Inspired by Greek mythology, Orion is shown in the cover image as a lion‐hearted hunter; he hits acyclic α,β‐unsaturated imides and N,N′‐dialkylanilines with the club to give 1,2,3,4‐tetrahydroquinolines (1,2,3,4‐THQs; the lion fur in the cover image). There are three stars in Orion′s Belt; i.e., ϵ Ori, ζ Ori, and δ Ori, which enhance his toughness. The trio applied to the novel iridium(III) complex photo‐sensitizer, the thiourea, and the azo compound, works cooperatively and powerfully to achieve the photochemical synthesis of structurally diverse 1,2,3,4‐THQs with excellent diastereoselectivity. More information can be found in the Full Paper by K. Itoh, H. Fujii, et al. on page 5171.
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