Organothianthrenium salts: synthesis and utilization

Abstract

Organothianthrenium salts are a class of compounds containing a positive charged sulfur atom and a neutral sulfur atom. Over the past years, organothianthrenium salts have been emerging as attractive precursors...

Selective Fluorosulfonylation of Thianthrenium Salts Enabled by Electrochemistry

“…Such an electrochemical activation strategy might afford new advances in thianthrenium salt chemistry, and the tunable redox ability of the electrochemical strategy should be able to reduce both aryl and alkyl thianthrenium salts, to form the corresponding aryl and nonstabilized alkyl radicals, respectively. This is different from previous processes in which thianthrenium salts have been mainly explored as the aryl radical source, with limited applications of challengeable primary alkyl radical sources. , To our delight, after extensive exploration, an electrochemically driven fluorosulfonylation of thianthrenium salts has been successfully developed (Figure C). Herein, we report our preliminary results.…”

“…On the basis of the results presented above and the related literature, , two plausible pathways have been proposed [using 1a as the model substrate (Figure )]. Initially, it was postulated that 1a could be reduced to form p - tert -butylphenyl radical A at the cathode.…”

“…On the contrary, by employing the good site-selective prethianthrenation of aromatic C–H bonds, pioneered by the groups of Ritter and Wang, a variety of elegant coupling reactions have recently been developed . Although these protocols show excellent applications, they mainly rely on the use of transition metal catalysis or photoredox catalysis to activate thianthrenium salts (Figure B). − Broadening the synthetic applicability with the new activation model remains underdeveloped .…”

“…On the contrary, by employing the good site-selective prethianthrenation of aromatic C–H bonds, pioneered by the groups of Ritter and Wang, a variety of elegant coupling reactions have recently been developed . Although these protocols show excellent applications, they mainly rely on the use of transition metal catalysis or photoredox catalysis to activate thianthrenium salts (Figure B). − Broadening the synthetic applicability with the new activation model remains underdeveloped . In this context, considering that the reductive potential of stable and easy-to-handle aryl thianthrenium salts (TT) is around −1.5 V (vs SCE) and driven by the intrinsic advantage of electrosynthesis using electron as a green redox reagent to activate substrates under mild reaction conditions, we envisioned that thianthrenium salts should be facilely reduced to form the carbon-based radicals at the cathode under a suitable voltage, based on our previous works .…”

“…To further demonstrate the synthetic value of this electrochemical fluorosulfonylation protocol, we attempted to apply the protocol for the modification of drug or its derivative. As depicted in Scheme C, in combination with excellent regioselectivity toward C–H thianthrenation of aromatics, two selected drug-derived thianthrenium salts, 1ah and 1ai , containing an ester or alkyl ketone moiety can be smoothly transformed into the desired sulfonyl fluoride 4 or 5 , respectively, in 42–80% yields under the optimal reaction conditions.…”