An enantioconvergent halogenophilic nucleophilic substitution (S_N2X) reaction

Bimolecular nucleophilic substitution (S_N2) plays a central role in organic chemistry. In the conventionally accepted mechanism, the nucleophile displaces a carbon-bound leaving group X, often a halogen, by attacking the carbon face opposite the C-X bond. A less common variant, the halogenophilic S_N2X reaction, involves initial nucleophilic attack of the X group from the front and as such is less sensitive to backside steric hindrance. Herein, we report an enantioconvergent substitution reaction of activated tertiary bromides by thiocarboxylates or azides that, on the basis of experimental and computational mechanistic studies, appears to proceed via the unusual S_N2X pathway. The proposed electrophilic intermediates, benzoylsulfenyl bromide and bromine azide, were independently synthesized and shown to be effective.