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Anthraquinones as Photoredox Catalysts for the Reductive Activation of Aryl Halides
Author(s) -
Bardagi Javier I.,
Ghosh Indrajit,
Schmalzbauer Matthias,
Ghosh Tamal,
König Burkhard
Publication year - 2018
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201701461
Subject(s) - chemistry , photochemistry , semiquinone , aryl , photoredox catalysis , protonation , aryl radical , hydrogen atom abstraction , redox , radical , catalysis , electron transfer , radical ion , halide , quinone , photocatalysis , ion , inorganic chemistry , organic chemistry , alkyl
Quinones are ubiquitous in nature as structural motifs in natural products and redox mediators in biological electron‐transfer processes. Although their oxidation properties have already been used widely in chemical and photochemical reactions, the applications of quinones in reductive photoredox catalysis are less explored. We report the visible‐light photoreduction of aryl halides (Ar–X; X = Cl, Br, I) by 1,8‐dihydroxyanthraquinone. The resulting aryl radical anions fragment into halide anions and aryl radicals, which react through hydrogen abstraction or C–C bond‐forming reactions. The active photocatalyst is generated from 1,8‐dihydroxyanthraquinone by photoinduced single‐electron reduction to the radical anion or subsequent protonation and further reduction (or vice versa) to the semiquinone anion. Subsequent visible‐light excitation of the anthraquinone radical anion or semiquinone anion converts them into very potent single‐electron donors. A plausible mechanism for the reaction is proposed on the basis of control experiments and spectroscopic investigations.