Redox Mediators in Visible Light Photocatalysis: Photocatalytic Radical Thiol–Ene Additions

Abstract

Synthetically useful radical thiol–ene reactions can be initiated by visible light irradiation in the presence of transition metal polypyridyl photocatalysts. The success of this method relies upon the use of p-toluidine as an essential additive. Using these conditions, high-yielding thiol–ene reactions of cysteine-containing biomolecules can be accomplished using biocompatibile wavelengths of visible light, under aqueous conditions, and with the thiol component as the limiting reagent. We present evidence that p-toluidine serves as a redox mediator that is capable of catalyzing the otherwise inefficient photooxidation of thiols to the key thiyl radical intermediate. Thus, we show that co-catalytic oxidants can be important in the design of synthetic reactions involving visible light photoredox catalysis.

Proton-Coupled Electron Transfer in Organic Synthesis: Fundamentals, Applications, and Opportunities

“…In synthetic contexts, thiyl radicals are known to engage in a number of useful reactions [191][192][193][194][195][196][197][198], including C-H bond abstraction [197,[199][200][201][202][203]. Recently, MacMillan has demonstrated the capacity of catalytically generated thiyl radicals to cleave the C-H bond of benzylic ethers for radical coupling reactions ( Figure 27) to form diaryl methanols (a) [204] or β-amino ethers (b) [205].…”

Recent advances in sulfur- and phosphorous-centered radical reactions for the formation of S–C and P–C bonds

“…55 The same photocatalyst was used for the reaction of glutathione 32 in the synthesis of 33 (Scheme 20). 56 The Stephenson group used Ru(bpy) 3 Cl 2 as a photocatalyst for the hydrothiolation of olefins to form 34 (Scheme 21). 57…”

Keggin-type Polyoxometalates as Bidirectional Redox Mediators for Rechargeable Batteries

“…Redox mediators (RMs) have long been used in electrochemical studies [1][2][3][4] and in devices such as biosensors, 5 solar cells, 6 photocatalysis, 7 and batteries. [8][9][10][11][12][13][14][15] They facilitate the electrochemical reactions of redox compounds that are located away from the electrodes and are not electrically connected to them.…”