Meerwein‐type Bromoarylation with Arylthianthrenium Salts

Abstract

Herein, we report a photocatalyzed Meerwein‐type bromoarylation of alkenes with stable arylthianthrenium salts, formed by site‐selective C−H thianthrenation. This protocol can be applied to late‐stage functionalization of a variety of biomolecules that are difficult to access by other aryl coupling reagents. Halogen introduction allows for a variety of follow‐up transformations, affording numerous biologically active skeletons.

Photoinduced Copper-Catalyzed Late-Stage Azidoarylation of Alkenes via Arylthianthrenium Salts

“…Complex arylthianthrenium salts are readily accessible from arenes and arylboron compounds and can provide reactivity that goes beyond that of conventional aryl halides and pseudohalides . As part of our ongoing endeavors on alkene arylfunctionalizations, we explored the application of arylthianthrenium salts in the direct three-component late-stage azidoethylation. Our previously reported Meerwein bromoarylation of arylthianthrenium salts is not able to directly access the arylethylamino core, possibly due to the inefficient radical trapping of a nitrogen radical donor in the presence of the phenothiazine photocatalyst.…”

“…As part of our ongoing endeavors on alkene arylfunctionalizations, we explored the application of arylthianthrenium salts in the direct three-component late-stage azidoethylation. Our previously reported Meerwein bromoarylation of arylthianthrenium salts is not able to directly access the arylethylamino core, possibly due to the inefficient radical trapping of a nitrogen radical donor in the presence of the phenothiazine photocatalyst. Moreover, the Meerwein bromoarylation only proceeds with electron-poor alkenes, while in the transformation reported here, the substrate scope is not limited to a special class of alkenes.…”

“…Moreover, the Meerwein bromoarylation only proceeds with electron-poor alkenes, while in the transformation reported here, the substrate scope is not limited to a special class of alkenes. The increased substrate scope when compared to Meerwein bromoarylation and the mechanistically distinct approach to Gaunt’s azidoarylation make the azidoarylation reported here a conceptual advance to approach the significant challenge in the three-component aminoarylation of alkenes and grant expedient access to complex acyclic arylethylamine precursors. , We propose that the conceptual novelty is enabled by identifying an appropriate copper catalyst that can both promote the generation of aryl radicals from arylthianthrenium salts and facilitate C–N bond formation through radical abstraction from a Cu­(II) azide catalyst as depicted in Figure C. Use of a single transition-metal catalyst, such as the copper catalyst used here, both as photoredox and as redox catalyst can be beneficial over the use of combinations of independent photosensitizer and metal catalyst .…”

Organothianthrenium salts: synthesis and utilization

“…In 2022, Ritter and co-workers reported a synthesis of C α -tetrasubstituted α - and β -amino acid analogues through the reaction of trifluoromethyl thianthrenium salts with Michael acceptors and acetonitrile ( Scheme 36 ). 98 a TT–CF 3 + BF 4 − generated CF 3 radical and thianthrene radical cations (TT˙ + ) via light induced homolysis. Radical addition of the CF 3 radical to acrylate forms a carboxyl α -carbon radical.…”

Preparation of Alkyl Di(p-tolyl)sulfonium Salts and Their Application in Metal-Free C(sp3)–C(sp3) and C(sp3)–C(sp2) Bond Formations

“…They explained that the stabilization at the oxidative addition intermediate by the back-donation effect between the sulfur atom and the transition metal is the key to success of the reaction. Recently, Ritter and co-workers have reported site-selective thianthrenation to provide aryl sulfonium salts and their application in cross-coupling and photocatalytic reactions using transition metal catalysts (Scheme a) . Therefore, the sulfonium salts have garnered recent attention as unique species for C–C bond formation, accompanied by their easy preparation .…”