Photoredox catalytic radical fluorosulfonylation of olefins enabled by a bench-stable redox-active fluorosulfonyl radical precursor

Abstract

Sulfonyl fluorides have attracted considerable and growing research interests from various disciplines, which raises a high demand for novel and effective methods to access this class of compounds. Radical flurosulfonylation is recently emerging as a promising approach for the synthesis of sulfonyl fluorides. However, the scope of applicable substrate and reaction types are severely restricted by limited known radical reagents. Here, we introduce a solid state, redox-active type of fluorosulfonyl radical reagents, 1-fluorosulfonyl 2-aryl benzoimidazolium triflate (FABI) salts, which enable the radical fluorosulfonylation of olefins under photoredox conditions. In comparison with the known radical precursor, gaseous FSO2Cl, FABI salts are bench-stable, easy to handle, affording high yields in the radical fluorosulfonylation of olefins with before challenging substrates. The advantage of FABIs is further demonstrated in the development of an alkoxyl-fluorosulfonyl difunctionalization reaction of olefins, which forges a facile access to useful β-alkoxyl sulfonyl fluorides and related compounds, and would thus benefit the related study in the context of chemical biology and drug discovery in the future.

EnT-Mediated N–S Bond Homolysis of a Bifunctional Reagent Leading to Aliphatic Sulfonyl Fluorides

“…Liao and co-workers applied sulfuryl chloride fluoride under mild photoredox conditions to furnish alkenyl sulfonyl fluorides from alkenes, while alkynes underwent chloro-fluorosulfonylation . Very recently, benzimidazolium-based reagents (Figure A) were simultaneously uncovered by Wang and Liao , group independently to serve as sulfonyl fluoride radical precursors by photoredox catalysis, enabling the synthesis of alkenyl sulfonyl fluorides and β-alkoxy sulfonyl fluorides, among other functionalities. Weng and co-workers formed carbon-centered radicals by proton-coupled electron transfer (PCET) to amides and intramolecular 5- exo -trig cyclization with alkenes or by energy transfer (EnT)-mediated decarboxylation of oxime esters .…”

Photo-organocatalytic Synthesis of β-Keto Sulfonyl Fluorides via Radical Fluorosulfonylation of Vinyl Acetates

“…Based on these results and on related mechanistic studies in the literature, 40,41 we outlined a possible mechanism in Scheme 3C. Under irradiation with blue LEDs, the organic photocatalyst (ODA) is excited (E 1/2 (ODA * /ODA •+ ) = −1.76 V vs. SCE) 42 and then acts as a reductant to reduce the redox-active radical precursor FABI 2 (E 1/2 = −1.07 V vs. SCE) 38 via a singleelectron transfer (SET). In contrast, Eosin Y-Na 2 and Rhodamine 6G gave trace amounts of products only (Table 1), probably due to their weak reducing power.…”

Sulfur(vi) fluorides as tools in biomolecular and medicinal chemistry

“…33 In addition to two-electron strategies, an emerging field in S(VI) fluoride synthesis has centered around electrochemical and photochemical strategies to prepare sulfonyl fluorides. [34][35][36][37][38][39][40] One of the first examples of an electrochemical strategy toward sulfonyl fluorides was reported by Noël and coworkers. 34 This method involves an oxidant-free, direct conversion of thiols and disulfides to aryl and alkyl sulfonyl fluorides using electrochemical synthesis employing potassium fluoride as a cheap fluoride source.…”

“…6 ). Complementary to electrochemical methods, photochemical strategies have also been employed toward sulfonyl fluorides using aryl diazonium salts, 38 carboxylic acids, 39 as well as alkenes 40 as precursors ( Fig. 7 ).…”