Catalytic Decarboxylative Fluorosulfonylation Enabled by Energy-Transfer-Mediated Photocatalysis

Abstract

Sulfonyl fluorides are useful building blocks in a wide array of fields. Herein, we report a catalytic decarboxylative fluorosulfonylation approach for converting abundant aliphatic carboxylic acids to the corresponding sulfonyl fluorides. This transformation is enabled by simple preactivation as aldoxime esters and energy-transfer-mediated photocatalysis. This operationally simple method proceeds with high functional-group tolerance under mild and redox-neutral conditions.

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

“…Weng and co-workers formed carbon-centered radicals by proton-coupled electron transfer (PCET) to amides and intramolecular 5-exo-trig cyclization with alkenes 28 or by energy transfer (EnT)mediated decarboxylation of oxime esters. 29 These can then be trapped by SO 2 and "F + " equivalents to enable the intramolecular 1,2-amido-fluorosulfonylation of alkenes and decarboxylative fluorosulfonylation of oxime esters, respectively. Larionov and co-workers applied the same strategy for the direct synthesis of aliphatic sulfonyl fluorides from carboxylic acids.…”

“…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 . These can then be trapped by SO 2 and “F + ” equivalents to enable the intramolecular 1,2-amido-fluorosulfonylation of alkenes and decarboxylative fluorosulfonylation of oxime esters, respectively.…”

N–O Bond Activation by Energy Transfer Photocatalysis

“…Careful selection of the substrate and photocatalyst in terms of compatible triplet energies and mismatched redox potentials is a prerequisite for the success of the EnT process. Figure shows substrates and photocatalysts used in N–O bond activation by selective EnT, including oximes (aryl oximes, − oxime esters, ,− oxime carbonates, , and oxime (gly)­oxalates), 1,2,4-oxadiazolines, , phthalimide enolates, N -indolyl carbonates, N -benzoyloxy carbamates, and N -enoxybenzotriazoles, with a disclosure of their triplet excited state energies. Our laboratory (often in collaboration with the You and Shin groups) utilized a diverse range of substrates such as 1,2,4-oxadiazolines, oxime esters, N -indolyl carbonates, and N -enoxybenzotriazoles.…”

Photocatalytic fluorosulfonylation of aliphatic carboxylic acid NHPI esters

“…16 Unsurprisingly, it can also be used to synthesize aliphatic sulfonyl fluorides. 17 For example, the Willis group reported a radical approach toward primary and secondary alkylsulfonyl derivatives via donor–acceptor activation of pyridinium salts which were trapped by DABSO to generate sulfonyl radicals (Scheme 1, II, A). 18 Hence, the SO 2 radical insertion/fluorination strategy became a popular method for the construction of the fluorosulfonyl group, with special synthetic advantages in the direct synthesis of sulfonyl fluorides via C–SO 2 F bond formation.…”