Substitution Reactions on Iodine and Bromine: Mechanisms for Facile Halogenations of Heterocycles

Gas-phase techniques were used to examine the halogenation of deprotonated heterocycles by perfluoroaryl and perfluoroalkyl halides. The results indicate that SN2@Br and SN2@I reactions can be very facile and are effective means of halogenating heterocycles. 2-Iodoheptafluoropropane is exceptionally selective for SN2@I reactions with yields upward of 90%. The results also provide evidence counter to the recent suggestion that t-butoxide-induced halogenations of heterocycles proceed via a radical mechanism