Visible-Light-Driven Solventylation Strategy for Olefin Functionalization

Abstract

Amphiphilic aryl radicals generated upon visible light irradiation of arylazo sulfones have been exploited in the development of a solventylation strategy via hydrogen atom transfer (HAT). The present protocol succeeded in the versatile functionalization of various olefins with carbon-centered radicals deriving from acetone, acetonitrile, chloroform, methylene chloride, nitromethane, methyl acetate, and methyl formate under metal- and photocatalyst-free conditions. The direct addition of the aryl radicals onto the olefin substrates was suppressed under high dilution conditions.

Arylazo sulfones: multifaceted photochemical reagents and beyond

“…The reactions were carried out in extremely dilute conditions to suppress the direct addition of aryl radicals 4 onto the olefin substrates 65 . 67…”

Visible photons as ideal reagents for the activation of coloured organic compounds

“…126 A wide range of electrophilic carbon-based intermediates including, among the others, a-cyanomethyl, acetonyl radical and dichloromethyl radicals have been generated via hydrogen atom transfer between an aryl radical (in turn generated via visible-light irradiation of an arylazo sulfone) and acetonitrile, acetone and dichloromethane, respectively. 127 The resulting radicals have been applied in the synthesis of indolinones from the corresponding N-aryl acrylamides. 127 The blue light photolysis of a-halo boronic esters (e.g., a-iodo BPin) and the subsequent formation of a-boryl radicals was recently employed for the preparation of allyl boronic esters via reaction with substituted styrenes.…”

Synthetic Applications of Photochemically Generated Radicals from Protic C(sp3)−H Bonds

“…The iodanyl radical (II) may then decompose to an aryl iodide and a highenergy phenyl radical capable of abstracting a hydrogen atom from the acetone solvent. The electron-poor radical III derived from the C(sp 3 )À H acid then adds to the alkene acceptor (45), which undergoes a neophyl rearrangement sequence to give benzylic stabilized ketyl radical VI. This ketyl radical (VI) acts as an electron donor, reducing 4CzIPN * + to close the catalytic cycle.…”

“…In 2022, Protti and Ravelli revisited this HAT strategy by using an arylazosulfone radical precursor to activate a wider range of protic solvent molecules. [45] The increased solubility of this reagent as compared with aryl diazonium salts and the lack of requirement for a reducing photocatalyst made for attractive conditions with a broad scope that could activate acetone, acetonitrile, nitromethane, methyl acetate, methyl formate, and various halogenated solvents. Irradiation of arylazosulfones (I) between 400 and 450 nm promotes photolysis of the NÀ S bond followed by loss of nitrogen gas to give a sulfonyl radical (II) and an aryl radical (III) that acts as an HAT agent towards the solvent (V).…”

“…In 2022, Protti and Ravelli revisited this HAT strategy by using an arylazosulfone radical precursor to activate a wider range of protic solvent molecules [45] . The increased solubility of this reagent as compared with aryl diazonium salts and the lack of requirement for a reducing photocatalyst made for attractive conditions with a broad scope that could activate acetone, acetonitrile, nitromethane, methyl acetate, methyl formate, and various halogenated solvents.…”