Visible‐Light‐Catalyzed Formal [3+2] Annulation‐Aromatization of Amidines with Isoquinolinium N‐Ylides: Access to Imidazo[2,1‐a]isoquinolines

Abstract

A visible‐light‐catalyzed formal [3 + 2] annulation‐aromatization reaction for the synthesis of various substituted imidazo[2,1‐a]isoquinolines from amidines with stabilized isoquinolinium N‐ylides in the presence of bases is developed. The procedure reported here involves a direct C‐H activation and the formation of C‐C/C‐N bonds in one‐pot. The reaction mechanism is probed by radical‐trapping experiment, fluorescence quenching, and light on/off experiments. The late‐stage modification experiments provide the potential applications in the field of organic and medicinal chemistry for chemists.

Base-Mediated Cascade Lactonization/1,3-Dipolar Cycloaddition Pathway for the One-Pot Assembly of Coumarin-Functionalized Pyrrolo[2,1-a]isoquinolines

“…Based on the preliminary mechanistic experiments and previous reports, a plausible mechanism for this cascade reaction is proposed in Scheme . Initially, propargylamine 1a produces the alkynyl o -quinone methide ( o -AQM) intermediate [detected by high resolution mass spectra (HRMS), m / z [M + H] + 207.0810] via the elimination of piperidine under basic conditions as the reported literature .…”

Visible Light Mediated Chemoselective Hydroxylation of Benzylic Methylenes

“…Ethan-1-one (2). The residue was purified by column chromatography (Hex/EA = 3/1) on silica gel and collected as off-white solid (53.2 mg, 91% yield with 99% conversion of raw material).…”

“…1 Secondary alcohols are commonly synthesized by the nucleophilic addition or reduction of carbonyl compounds. 2 These synthetic procedures are tedious and suffer from limitations such as sensitivity to air and moisture, toxicity of the organometallic reagents, poor functional group tolerance, and harsh reaction conditions. The oxyfunctionalization of benzylic C−H bond to corresponding alcohol was a competitive method, but there are only a few examples of selective oxidation of benzylic compounds by enzymatic, 3 polymeric, 4 and core−shell catalysis.…”

“…However, the application of this strategy to oxidize benzylic C–H bonds was predominantly resulted in the isolation of ketone rather than benzyl alcohol, primarily due to the aforementioned challenges. With our interest in the photochemical reactions, in this paper, we developed a method for the oxidation of benzylic methylenes to benzyl alcohols utilizing eosin Y as photocatalyst under visible light irradiation. The methodology presented herein offers a robust solution to chemoselective hydroxylate benzylic C–H bonds and it is expected to inform future efforts toward natural product synthesis and derivatization.…”