Sulfonium Salts as Acceptors in Electron Donor-Acceptor Complexes

Abstract

The photoactivation of electron donor-acceptor complexes has emerged as a sustainable, selective and versatile strategy for the generation of radical species. Electron donor-acceptor (EDA) complexation, however, imposes electronic constraints on the donor and acceptor components and this can limit the range of radicals that can be generated using the approach. New EDA complexation strategies exploiting sulfonium salts allow radicals to be generated from native functionality. For example, aryl sulfonium salts, formed by the activation of arenes, can serve as the acceptor components in EDA complexes due to their electron-deficient nature. This "sulfonium tag" approach relaxes the electronic constraints on the parent substrate and dramatically expands the range of radicals that can be generated using EDA complexation. In this review, these new applications of sulfonium salts will be introduced and the areas of chemical space rendered accessible through this innovation will be highlighted.

Keywords: Aryl Radical; Arylation; Charge Transfer; EDA Complex; Sulfonium Salt.

Scheme 1

General molecular orbital comparison between direct photoexcitation and the excitation of an EDA complex.

Scheme 2

Sulfonium salt EDA complexation leading to radical release. An illustrative system involving aryl radical generation from in situ generated aryl sulfonium salts.

Scheme 3

In situ formation and exploitation of aryl sulfonium salts in EDA complexes with triaryl amine donors; application in a formal C−H alkylation to give α‐aryl ketones. 1,2 DCE=1,2‐Dichloroethane, DBT S‐oxide=Dibenzothiophene S‐oxide, 1‐Np=1‐Naphthyl.

Scheme 4

In situ formation and exploitation of aryl sulfonium salts in EDA complexes with triaryl amine donors; application in a formal C−H cyanation.

Scheme 5

Exploitation of aryl sulfonium salts in EDA complexes with amine donors; application in aryl radical heteroarylation. DABCO=1,4‐Diazabicyclo[2.2.2]octane.

Scheme 6

Exploitation of aryl sulfonium salts in EDA complexes with thiolate donors; application in aryl radical thiolation.

Scheme 7

Exploitation of aryl sulfonium salts in EDA complexes with sulfinate donors; application in aryl radical sulfonylation.[ ²⁵ , ²⁶ ]

Scheme 8

Exploitation of aryl sulfonium salts in EDA complexes with dithioate donors; application in the synthesis of aryl xanthates and aryl dithiocarbamates.

Scheme 9

Exploitation of aryl sulfonium salts in EDA complexes with a B₂cat₂⋅DMF adduct as donor; application in aryl radical borylation.

Scheme 10

Exploitation of alkyl sulfonium salts in EDA complexes with a B₂cat₂⋅DMA adduct as donor; application in alkyl radical borylation. DMA=Dimethylacetamide.