Metallaphotoredox processes have emerged as powerful methods for CÀ C bond formations. The Ni-photoredox catalyzed desulfurative cross-coupling of thiol derivatives with aryl bromides has now been established. This procedure provides access to simple and complex unsymmetrical diarylmethane molecules under mild reaction conditions with a broad functional group tolerance. The key steps of the reaction involve a silane-mediated halogen-atom transfer (XAT) and a subsequent intramolecular homolytic substitution (S H ), forming C-centered radicals from various thiol derivatives as shown by mechanistic studies. This study paves the way for new transformations of abundant, naturally occurring thiols.
The first photo‐mediated process enabling the generation of halide radicals by Halogen‐Atom Transfer (XAT) is described. Contrary to radical transformations involving XAT reactivity, which exploit stable carbon radicals, this unique approach uses 1,2‐dihaloethanes for the generation of unstable carbon radicals by XAT. These transient radicals then undergo β‐scission with release of ethylene and formation of more stable halide radicals which have been used in selective hydrohalogenations of a large number of unsaturated hydrocarbons, including Michael acceptors, unactivated alkenes and alkynes. This hydrohalogenation is tolerant of a broad range of functionalities and is believed to proceed through a radical‐chain manifold that propagates by the use of silane derivatives.
CF3-containing molecules are frequently encountered in many best-selling pharmaceutical drugs. Consequently, a large number of methods have been developed for introducing a CF3 group into organic compounds. However, innovative protocols enabling direct access to alkyl-CF3 moieties are still sought after. In this context, we report a visible-light-induced formal trifluoropropanation of various alkyl and aryl halide derivatives using the 2-Bromo-3,3,3-trifluoro-1-propene (BTP) as a readily available building block. Our strategy relies on the use of a catalytic system merging a catalytic amount of supersilane and NaBH4 as an additional reductant. These mild reaction conditions are compatible with a large range of functional groups. Finally, double deuterium incorporation was obtained upon replacement of NaBH4 with NaBD4 under these catalytic conditions, leading to the formation of hitherto unknown α,α-d 2-CF3 compounds.
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.
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