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.
Highlights
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
The reactivity of sulfonium salts is determined by the positive charge that they contain, which is mainly located at the sulfur atom
Enzymes catalyzing the generation of alkyl radicals from sulfonium salts known to date all belong to the radical S-adenosylmethionine (SAM) superfamily (Fig. 1a)[11,12,13,14,15]
Summary
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. 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 Procter group explored a one-pot strategy for the facile construction of (hetero)biaryl motifs with intermediate S-(aryl) dibenzothiophenium salts enabled by organic photoredox catalysts[27] Despite these advances, the vast majority of the sulfonium salts that undergo SET process have been limited to form aryl radicals; The generation of alkyl radicals, especially the nonstabilized ones from sulfonium salts is synthetically challenging. A significant observation of the reactivity of these compounds is that diverse non-stabilized alkyl radicals can be effectively generated as key intermediates in these transformations
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