REACTIONS WITH AZIRIDINES .55. N-S CLEAVAGE IS FASTER THAN HOMOLYTIC RING-OPENING IN SINGLE-ELECTRON TRANSFER TO SOME N-SULFONYLAZIRIDINES - COMPETITION BETWEEN SN2 AND SET

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.