Umpolung Difunctionalization of Carbonyls via Visible-Light Photoredox Catalytic Radical-Carbanion Relay

Abstract

The combination of photoredox catalysis with the Wolff–Kishner (WK) reaction allows the difunctionalization of carbonyl groups by a radical-carbanion relay sequence (photo-Wolff–Kishner reaction). Photoredox initiated radical addition to N-sulfonylhydrazones yields α-functionalized carbanions following the WK-type mechanism. With sulfur-centered radicals, the carbanions are further functionalized by reaction with electrophiles including CO2 and aldehydes, whereas CF3 radical addition furnishes a wide range of gem-difluoroalkenes through β-fluoride elimination of the generated α-CF3 carbanions. More than 80 substrate examples demonstrate the broad applicability of this reaction sequence. A series of investigations including radical inhibition, deuterium labeling, fluorescence quenching, cyclic voltammetry, and control experiments support the proposed radical-carbanion relay mechanism.

Visible-Light-Driven Anti-Markovnikov Hydrocarboxylation of Acrylates and Styrenes with CO 2

“…24 Recently, in addition to UV-light photocatalysis, 16,[25][26][27] visible-light photocatalysis has emerged as an intriguing strategy to realize novel organic transformations with CO 2 . 17,18,22,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] Notably, Iwasawa pioneered this strategy by realizing the hydrocarboxylation of alkenes with Markovnikov regioselectivity via visible-light photoredox/Rh dual catalysis. 27,41 Besides Markovnikov selectivity, König et al 35 also realized a novel hydrocarboxylation of styrenes with anti-Markovnikov regioselectivity 26,[43][44][45] via photoredox/ nickel dual catalysis.…”

Visible Light as the Key for the Formation of Carbon–Sulfur Bonds in Sulfones, Thioethers, and Sulfonamides: An Update

“…This process produced α-functionalized alkyl carbanions which coupled with several electrophiles, among them thiols, produced thiocarboxylic acids and hydroxyfunctionalized sulfides with broad substrate scope and good yields. 81 Thioethers 169 were prepared from anilines 17 and thiols 162 under blue LED irradiation at room temperature without a photocatalyst, under solvent-and transition metal-free conditions, in the presence of tert-butylnitrite (tert-BuONO, 168). 82 Reaction was also applied to the synthesis of selenides.…”

Spirocyclizative Remote Arylcarboxylation of Non-Activated Arenes with CO2 via Visible-Light-Induced Reductive Dearomatization

“…More recently, our group reported the reductive arylcarboxylation of styrenes with CO2 via a radical-polar crossover cascade (RPCC), which was initiated by highly reactive aryl radicals that were generated from the reduction of readily available aryl halides. 75 We wondered whether this RPCC process [75][76][77][78][79][80][81][82][83][84][85][86][87][88][89] could be applied for dearomative di-functionalization of non-activated arenes with CO2. Notably, during our investigation, the Yu group reported the 2,3-arylcarboxylation of indoles, a class of well-studied electron-rich heteroarene in dearomatization reactions, via 5-exo-trig cyclization (Scheme 1b).…”