Arylazo sulfones: multifaceted photochemical reagents and beyond

Abstract

The photochemical action of arylazo sulfones under visible light irradiation has recently gained considerable attention for the construction of carbon-carbon and carbon-heteroatom bonds in organic synthesis. The inherent dyedauxiliary group...

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

“…Arylazo sulfones ( 27.1 , Scheme 27a) are crystalline, coloured (yellow to red) derivatives that bear a dyedauxiliary NN–SO 2 R moiety, capable of imparting both colour and photoreactivity to the starting compound (Scheme 1f). 35,36,141 Accordingly, upon visible-light irradiation, a N–S bond homolytic cleavage occurred from the 1 nπ* singlet excited state of 27.1 , producing a diazenyl radical 27.2 and the sulfonyl radical 27.3 . Aryl radical 27.4 is then released upon nitrogen loss from 27.2 , and such an intermediate has been applied in the development of a plethora of protocols for the formation of both C–C and C–heteroatom bonds.…”

“…An exemplary case is that of arylazo sulfones J (Scheme 1f), obtained in two steps from anilines I and prone to generating several radical intermediates upon photolysis. 35,36 Saying so, the ideal case is the photochemical conversion of a (purposely designed) coloured compound into a valuable product without any additives, as it is the case for α-diazoesters K , which are widely used as precursors of carbenes L (Scheme 1g). 37…”

“…Arylazo sulfones (Scheme 1f) 35,36 and arylazo sulfonates 68 show an absorption band in the 400–450 nm range, arising from a nπ* transition. Irradiating these sulfones with blue light induces the homolytic cleavage of the N–S bond, resulting in the subsequent formation of aryldiazenyl, sulfonyl and aryl radicals, 35 making these compounds ideal candidates for the uncatalyzed formation of C–C bonds.…”

Electroreduction strategy: a sustainable tool for the generation of aryl radicals

“…68 Recent studies have found that arylazo sulfones usually work as effective aryl radical precursors to construct C(sp 2 )–heteroatom bonds. 69 In 2021, Yi et al developed an electroreductive radical thiolation/selenylation using arylazo sulfones as aryl radical donors, providing a transition-metal catalyst and reductant-free synthesis route to produce a series of decorated unsymmetrical thioethers and selenides (Scheme 33). 70 A hydrogenation product was isolated without a radical acceptor in 23% yield, which offered important evidence for the aryl radical mechanism.…”