Benzimidazolium Naphthoxide Betaine Is a Visible Light Promoted Organic Photoredox Catalyst

Benzimidazolium naphthoxide (⁻ONap-BI⁺) was first synthesized and utilized as an unprecedented betaine photoredox catalyst. Photoexcited state of ^–ONap-BI⁺ generated by visible light irradiation catalyzes the reductive deiodination as well as desulfonylation reactions in which 1,3-dimethyl-2-phenylbenzimidazoline (Ph-BIH) cooperates with as an electron and hydrogen atom donor. Significant solvent effects on the reaction progress were discovered, and specific solvation toward imidazolium and naphthoxide moieties of ^–ONap-BI⁺ was proposed

Visible Light and Hydroxynaphthylbenzimidazoline Promoted Transition-Metal-Catalyst-Free Desulfonylation of <i>N-</i>Sulfonylamides and <i>N-</i>Sulfonylamines

A visible light promoted process for desulfonylation of <i>N-</i>sulfonylamides and -amines has been developed, in which 1,3-dimethyl-2-hydroxynaphthyl­benzimidazoline (HONap-BIH) serves as a light absorbing, electron and hydrogen atom donor, and a household white light-emitting diode serves as a light source. The process transforms various <i>N-</i>sulfonylamide and -amine substrates to desulfonylated products in moderate to excellent yields. The observation that the fluorescence of 1-methyl-2-naphthoxy anion is efficiently quenched by the substrates suggests that the mechanism for the photoinduced desulfonylation reaction begins with photoexcitation of the naphthoxide chromophore in HONap-BIH, which generates an excited species via intramolecular proton transfer between the HONap and BIH moieties. This process triggers single electron transfer to the substrate, which promotes loss of the sulfonyl group to form the free amide or amine. The results of studies employing radical probe substrates as well as DFT calculations suggest that selective nitrogen–sulfur bond cleavage of the substrate radical anion generates either a pair of an amide or amine anion and a sulfonyl radical or that of an amidyl or aminyl radical and sulfinate anion, depending on the nature of the <i>N-</i>substituent on the substrate. An intermolecular version of this protocol, in which 1-methyl-2-naphthol and 1,3-dimethyl-2-phenyl­benzimidazoline are used concomitantly, was also examined