Competitive Desulfonylative Reduction and Oxidation of α-Sulfonylketones Promoted by Photoinduced Electron Transfer with 2-Hydroxyaryl-1,3-dimethylbenzimidazolines under Air

Abstract

Desulfonylation reactions of α-sulfonylketones promoted by photoinduced electron transfer with 2-hydroxyarylbenzimidazolines (BIH-ArOH) were investigated. Under aerobic conditions, photoexcited 2hydroxynaphthylbenzimidazoline (BIH-NapOH) promotes competitive reduction (forming alkylketones) and oxidation (producing α-hydroxyketones) of sulfonylketones through pathways involving the intermediacy of α-ketoalkyl radicals. The results of an examination of the effects of solvents, radical trapping reagents, substituents of sulfonylketones, and a variety of hydroxyaryl-and aryl-benzimidazolines (BIH-ArOH and BIH-Ar) suggest that the oxidation products are produced by dissociation of α-ketoalkyl radicals from the initially formed solvent-caged radical ion pairs followed by reaction with molecular oxygen. In addition, the observations indicate that the reduction products are generated by proton or hydrogen atom transfer in solvent-caged radical ion pairs derived from benzimidazolines and sulfonylketones. The results also suggest that arylsulfinate anions arising by carbon-sulfur bond cleavage of sulfonylketone radical anions act as reductants in the oxidation pathway to convert initially formed α-hydroperoxyketones to α-hydroxyketones. Finally, density functional theory calculations were performed to explore the structures and properties of radical ions of sulfonylketones as well as BIH-NapOH.

Photocatalytic turnover of CO2 under visible light by [Re(CO)3(1-(1,10) phenanthroline-5-(4-nitro-naphthalimide))Cl] in tandem with the sacrificial donor BIH

“…To explain the cause of this activity, we noted a literature report of BIH forming a radical cation in the presence of atmospheric O 2 without irradiation. 24 Under blue light irradiation, BIH alone, in MeOH/DCM (1 : 9 v/v), was able to reduce CO 2 to formate with a low turnover of 5.7 (TN = [formate]/[BIH]). Given the sizable difference in TN from 5.7 to 533, we conclude that any BIH-only mechanism is overridden in the presence of 1 by the hydride mechanism.…”

Photoredox-Mediated Desulfonylative Radical Reactions: An Excellent Approach Towards C–C and C–Heteroatom Bond Formation

“…In 2021, they introduced a similar work under aerobic conditions (Scheme 12b) using the active species directly in a stoichiometric amount and concluded with both the oxidation and reduction product. 28 Mechanistically (Scheme 12c), both the works were of similar…”

“…In the following year, they have introduced a similar work in aerobic condition (scheme 12b) using the active species directly in stoichiometric amount and concluded with both the oxidation and reduction product. 28 Mechanistically, both the works were of similar types where the active photocatalyst 44a in its excited state transfers an electron to the substrate 40, 42 or 45, followed by the desulfonylative fragmentation of the substrate. Then oxidation or reduction occurs depending on the reaction conditions.…”

Desulfonylation via Radical Process: Recent Developments in Organic Synthesis

“…Other efforts had shown that a neutral organic electron donor tetraazaalkene ( 84 - 1 ) seemed to be suitable for the reductive cleavage of aryl sulfones (ArSO 2 R), which afforded radical cations and dications stabilized by aromaticity upon oxidation . Nonetheless, details of some representative examples will be omitted and not be listed in the present section …”

“…296 Nonetheless, details of some representative examples will be omitted and not be listed in the present section. 297 2.6.2. Alkyl Sulfones as Alkylated Reagents.…”