Skeletal Reorganization of Saturated Six-Membered Aza-cycles to Sulfonated Pyrrolidines under Redox-Neutral Conditions

Ring contraction in skeletal reorganization strategies is one of the most intriguing yet surprisingly challenging transformations. Herein, we report for the first time a ring contraction tandem sulfonation between saturated six-membered N-heterocyclic nitroxides and sulfonyl hydrazides to access sulfonated pyrrolidine derivatives by an electrochemical redox cascade under redox-neutral and metal-free conditions, which is unavailable via conventional synthetic approaches. This benign approach to sulfonated pyrrolidine derivatives has been further demonstrated by gram-scale preparation and pharmaceutical molecule synthesis under mild conditions.