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

Abstract

Sulfur(VI) fluoride exchange (SuFEx) gives rise to a plethora of high-valent sulfur linkages; however, the availability of (aliphatic) sulfonyl fluoride manifolds lag behind, owing to the limited sources of introducing the SO2F moiety via a classical two-electron approach. Recently, radical-based methodologies have emerged as a complementary strategy to increase the diversity of accessible click partners. In this work, synthesis of a bench-stable sulfamoyl fluoride reagent is presented, which may undergo sigma-bond homolysis upon visible-light-induced sensitization to form protected β-amino sulfonyl fluorides from alkene feedstocks. Notably, this offers an appealing strategy to access various building blocks for peptido sulfonyl fluorides, relevant in a medicinal chemistry context, as well as an intriguing entry to β-ammonium sulfonates and β-sultams, from alkenes. Densely functionalized 1,3-sultones were obtained by employing allyl alcohols as substrates. Surprisingly, allyl chloride-derived β-imino sulfonyl fluoride underwent S–O bond formation and ring closure to yield rigid cyclopropyl β-imino sulfonate ester under SuFEx conditions. Furthermore, by engaging a thiol-based hydrogen atom donor in the reaction, the reactivity of the same reagent can be tuned toward the direct synthesis of aliphatic sulfonyl fluorides. Mechanistic experiments indicate an energy transfer (EnT)-mediated process. The transient sulfonyl fluoride radical adds to the alkene and product formation occurs upon either radical–radical coupling or hydrogen atom transfer (HAT), respectively.

Photochemical Alkene Trifluoromethylimination Enabled by Trifluoromethylsulfonylamide as a Bifunctional Reagent

“…On the basis of these observations and previous reports, a possible mechanism is proposed (Scheme d). Initially, the photosensitizer absorbed the light to form the triplet exited benzophone * .…”

Photochemical and Atom-Economical Sulfonylimination of Alkenes with Bifunctional N-Sulfonyl Ketimine

“…For example, Luo and Willis recently demonstrated that N -sulfonyl imines could be utilized as a sulfonyl radical source in the monofunctionalization of alkenes through energy transfer catalysis. To our knowledge, the utilization of sulfonamides as bifunctional reagents in organic synthesis remains rare (Figure b) …”

Visible-light-driven reactions for the synthesis of sulfur dioxide-inserted compounds: generation of S–F, S–O, and S–N bonds

“…Recently, Glorious and co-workers developed a novel method to synthesize β-amino sulfonyl fluorides through addition of both amine and SO 2 F groups into alkenes using (diphenylmethylene)sulfamoyl fluoride as a novel reagent for imino-fluorosulfonylation ( Scheme 26 ). 86 Reactions were carried out in a single step by treatment of alkenes with (diphenylmethylene)sulfamoyl fluoride in the presence of thioxanthone as a photocatalyst in DMC under blue LED irradiation at room temperature for 24 hours. Styrenes containing various functional groups were tolerated with this process to give the corresponding di-substitutes product 93a in good yield.…”