ELECTROPHILIC REACTIONS AT SINGLE BONDS .25. NITRATION OF ADAMANTANE AND DIAMANTANE WITH NITRONIUM TETRAFLUOROBORATE

The slow reaction of adamantane with nitronium tetrafluoroborate at room temperature in purified, nitrile-free nitromethane or in nitroethane gives 1-nitroadamantane in 66% and 74% isolated yield, respectively. Similar reaction of diamantane gives 62% 1- and 5% 4-nitrodiamantane. Initial reaction upon aqueous workup gives 1-adamantanol with 1-fluoroadamantane, 3-fluoro-1-adamantanol, and adamantanone as byproducts. Upon prolonged reaction 1-nitroadamantane is formed in good yield. The experimental data are in accord with intermediate formation of the 1-adamantyl cation (by hydride abstraction or cleavage of initially formed 1-nitroadamantane) followed by reaction with HNO2 or NO2- formed in the reaction, giving 1-adamantyl nitrite, which then undergoes cleavage-rearrangement to give 1-nitroadamantane. A small kinetic hydrogen isotope effect of k(H)/k(D) = 1.2-1.3 is indicative of a nonlinear highly unsymmetrical transition state in the rate-determining step of the reaction.