Photo‐induced Desulfurative Processes for Carbon Radical Generation

Abstract

Thiols constitute an important family among sulfur‐containing compounds, with well‐established applications in various fields ranging from medicine to material science. For instance, thiol residues are good hydrogen donors which reduce radical species in biological or chemical processes. However, even though the S‐H bond activation of thiols for providing access to thiyl radicals has been largely studied, desulfurative processes affording carbon‐based radicals by C‐S bond activation have been less explored. In recent years, photoredox catalysis has become the prevalent method for the generation of radicals under soft reaction conditions from readily available starting materials under visible light. In this context, recent studies have been devoted to the development of photocatalytic procedures aiming at the desulfurization of thiol derivatives leading to new C‐H, C‐C or C‐Het bond formation reactions. This review will cover the synthetic methodologies and strategies for photo‐mediated desulfurization of native thiols, thioethers, sulfonium salts and xanthates to access new organic compounds. This emerging field is especially interesting for new transformations of cysteine and peptide derivatives.

Peptide macrocyclisation via intramolecular interception of visible-light-mediated desulfurisation

“…Several methods for the desulfurisation of Cys residues have been reported in the literature, these include; photo-induced desulfurisation 69 using a ruthenium PC, 60 photo-desulfurisation in flow, 61 accelerated desulfurisation using tetraethylborate (NaBEt 4 ), 63 desulfurative borylation, 64 and the exploitation of phosphite 66 and phosphine-dependent pathways. 65 We attempted to adapt and explore two appropriate examples.…”

Photoinduced Radical Desulfurative C(sp3)–C(sp2) Coupling via Electron Donor–Acceptor Complexes

“…Thiols are an important class of compounds that can be readily synthesized in various ways from haloalkanes, alcohols, or their derivatives. According to previous works, the thiols can be used as the precursor of alkyl radical and hydrogen atom donor to further react with alkenes to form a C­(sp 3 )–C­(sp 3 ) bond (Figure c) . The strategy is carried out by combining desulfurization and C–C coupling by using thermal or photochemical conditions.…”