N-S Cleavage Is Faster Than Homolytic Ring Opening in Single-Electron Transfer to Some N-Sulfonylaziridines. Competition between SN2 and SET

Article abstract of DOI:10.1021/jo00024a028

The radical anions of the N-sulfonylaziridines, 1a,b and 3 undergo N-S cleavage in place of homolytic ring opening as is demonstrated by reactions with anthracenide A^*-.Nucleophilic ring opening of the sulfonylaziridines 1a,b and 3 by the carbanions AH^-, X^-, and Fl^- of dihydroanthracene, xanthene, and fluorene, respectively, proceeds with the expected regioselectivity and is slow enough to allow some competition by a single-electron transfer (SET) initiated N-S cleavage, which provides the desulfonated aziridines and bixanthenyl X-X or bifluorenyl Fl-Fl, respectively.The SET path is favored by light.The competition is in favor of SET to the exclusion of the nucleophilic opening when trityl anion reacts with 1a.The twice-found byproducts 11 and 12 require the azirine intermediate 15, which is, at least formally, generated by elimination of TsH from 1a in a non-SET reaction.