Aminofluorosulfonylation of β,γ-Unsaturated Hydrazones with Sulfur Dioxide and N-Fluorobenzenesulfonimide: Accessing Pyrazoline-Functionalized Aliphatic Sulfonyl Fluorides

Abstract

An efficient aminofluorosulfonylation strategy was developed for the synthesis of various pyrazoline-functionalized aliphatic sulfonyl fluorides using β,γ-unsaturated hydrazones with sulfur dioxide and NFSI as the starting materials under mild conditions. The sulfonyl fluoride products could be successfully transformed into the corresponding sulfonate esters and amides via the sulfur(VI) fluoride exchange (SuFEx) click reactions. Preliminary mechanistic investigations demonstrate that the reaction operates through a radical cyclization/SO 2 insertion/fluorination cascade process.

Radical Cyclization-Initiated Difunctionalization Reactions of Alkenes and Alkynes

“…Wang and coworkers reported a similar reaction of unsaturated hydrazones for the synthesis of SO 2 F-functionalized pyrazolines. The reaction of β , γ -unsaturated hydrazones 455 , DABSO and NFSI in the presence of 2,4,6-collidine, EtOH under Ar at 25 °C for 24 h gave products 456 in good to excellent yields ( Scheme 91 ) [ 115 ]. Products 456 could be further transformed into sulfonate esters and amides.…”

Recent Advances in Developing Radical Methods for the Synthesis of Aliphatic Sulfonyl Fluorides

“…Wang and co-workers recently reported an efficient method for the amino-fluorosulfonylation of β, γ-unsaturated hydrazones with DABSO and NFSI as the corresponding SO 2 and F source in the absence of photocatalysts, which provided a facile access to diverse pyrazoline-functionalized aliphatic sulfonyl fluorides (Scheme 32). [49] The starting β, γ-unsaturated hydrazine are supposed to be deprotonated first and then oxidized by NFSI (or together with base) via single electron transfer to generate the N-centered radicals, followed by an intramolecular 5-exo-trig cyclization to afford the key alkyl radical intermediates.…”

Radical Cyclization-initiated Difunctionalization Reactions of Alkenes and Alkynes

“…Wang and coworkers reported a similar reaction of unsaturated hydrazones for the synthesis of SO2F-functionalized pyrazolines. The reaction of β,γunsaturated hydrazones 455, DABSO and NFSI in the presence of 2,4,6-collidine, EtOH under Ar at 25 °C for 24 h gave products 456 in good to excellent yields (Scheme 91) [115]. Products 456 could be further transformed to sulfonate esters and amides.…”