Anthraquinones as Photoredox Catalysts for the Reductive Activation of Aryl Halides

Abstract

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

Micellized Tris(bipyridine)ruthenium Catalysts Affording Preparative Amounts of Hydrated Electrons with a Green Light‐Emitting Diode

“…As trapping reagents that avoid the formation of several cross‐coupling products, we selected mesitylacetate MesAc and N ‐methylpyrrole‐2‐carboxylate NMPCA. With the former, all ring positions except meta are occupied; with the latter, it is well known that the addition of radicals to pyrroles almost exclusively occurs at the ring position adjacent to the nitrogen atom . Proof of principle for the viability of our approach is obtained from the NMR spectra in SI‐5.3.…”

Electron Donor‐Acceptor Complexes in Perfluoroalkylation Reactions

“…On the other hand, the strong chromophoric character of organic dyes,, being inexpensive, nontoxic, readily available and the fact that can be easily separated/extracted from the reaction mixtures render them excellent environmentally superior alternatives to metal complexes. To that effect, organic dyes such as Rose Bengal, Eosin Y, Red Nile, anthraquinone‐2‐carboxylic, anthraquinone‐2‐sulfonic acids and others have successfully been employed in the production of carbon‐centered radicals triggered by visible light irradiation. Moreover, photocatalysts absorbing in the red region of the electromagnetic spectrum have allowed even lower energy irradiation sources to be used capable of effecting reductive quenching cycles (Figure ).…”

Photochemical Functionalization of Helicenes

“…Photochemical reactions in the presence of heteroarenes such as substituted pyrroles, indoles, thiophenes, and furan gave the desired heteroarylated- [7]helicene products in moderate to very good isolated yields (examples 6 a-g, Figure 2). Note that the CÀBr bond in the indole moiety remains intact in the functionalized product 6 e. Heteroarenes, such as thiophene and furan, which were reported to be relatively inert in trapping (hetero)arene radicals under reductive photoredox reaction conditions, [35,44] can be installed onto the [7]helicene scaffold under our photochemical conditions albeit in moderate yields. Photochemical reactions in the presence of triethylphosphite, bis(pinacolato)diboron, and dimethyl disulfide gave the desired products 6 h-j, which were isolated in 45-92 % yields.…”