Generation of non-stabilized alkyl radicals from thianthrenium salts for C–B and C–C bond formation

Abstract

Sulfonium salts bearing a positively charged sulfur atom with three organic substituents have intrigued chemists for more than a century for their unusual structures and high chemical reactivity. These compounds are known to undergo facile single-electron reduction to emerge as a valuable and alternative source of aryl radicals for organic synthesis. However, the generation of non-stabilized alkyl radicals from sulfonium salts has been a challenge for several decades. Here we report the treatment of S-(alkyl) thianthrenium salts to generate non-stabilized alkyl radicals as key intermediates granting the controlled and selective outcome of the ensuing reactions under mild photoredox conditions. The value of these reagents has been demonstrated through the efficient construction of alkylboronates and other transformations, including heteroarylation, alkylation, alkenylation, and alkynylation. The developed method is practical, and provides the opportunity to convert C–OH bond to C–B and C–C bonds.

Electrochemical Synthesis of Allylic Amines from Terminal Alkenes and Secondary Amines

“…We recently developed an electrochemical strategy to engage oxidatively sensitive nucleophiles in net oxidative alkene difunctionalization reactions . Our approach draws inspiration from Yoshida’s pioneering cation pool work − and contributes to a rapidly growing body of literature exploiting oxidized thianthrene derivatives as synthetic intermediates. − Specifically, we leveraged electrochemistry to cleanly generate dicationic adducts between unactivated alkenes and thianthrene ( TT ), , a safe and inexpensive reagent. This strategy circumvents the need for oxidatively stable coupling partners in net oxidative alkene functionalization reactions; the oxidative alkene activation event is decoupled from nucleophilic substitution.…”

Photocatalytic C(sp3) radical generationviaC–H, C–C, and C–X bond cleavage

“…Alkyl sulfonium salt can be easily synthesised from alkyl halides, thiols and alcohols. [164][165][166][167][168] Upon receiving an electron, such a trivalent species undergoes R-S cleavage to release an Rc and a thioether. In 2018, MacMillan et al disclosed a Cu(II)/Ir(III) dual photocatalytic system to couple aryl bromides and tri-uoromethylsulfonium salt in the presence of a supersilanol (Scheme 41A).…”

Visible-light-catalyzed C–H arylation of (hetero)arenes via arylselenonium salts

“…[22][23][24][25] Sulfonium salts are provided with photosensitivity, thereby generating aryl radicals. [26][27][28][29][30] In 2019, Ritter and coworkers extended the application of thiophene salts as precursors to the coupling of C-O, C-N and trifluoromethane with a wide range of functional groups (Scheme 1a), [31][32][33] laying the foundation for the late-stage highly selective functionalization of small molecules. Then Huang et al reported that by using visible light as a green energy source, redox-neutral borylation of aryl sulfonium salts via C-S activation could be achieved with moderate to good yields.…”