The One-electron Reduction of Carbonium Ions. VI. The Trapping of the Cycloheptatrienyl Radical with 2-Methyl-2-nitrosopropane in the Course of the Zinc Reduction of the Tropylium Ion

Abstract

Abstract The zinc reduction of the tropylium ion was carried out in the presence of 2-methyl-2-nitrosopropane (a radical scavenger) in H2O–THF (7:3 by volume) at room temperature. In the reaction mixture with a short reaction time (5 min), t-butyl tropyl nitroxide (II) (a radical-trapping product) was identified by the ESR analysis. α-Phenyl-N-t-butylnitrone (I), which was isolated from the reaction mixture during a prolonged reaction time (30 min), was proved to be derived from the nitroxide II through the hydrogen abstraction by t-butyl nitroxide, which was itself formed from 2-methyl-2-nitrosopropane in situ in the acidic reaction mixture in the presence of zinc powder. The hydrogenation (on Pd/C) of the product mixture for a short reaction time (1 min) gave N-t-butyl-N-cycloheptylhydroxylamine and bicycloheptyl. On the basis of these observations, it is concluded that the primary product of the zinc reduction of the tropylium ion must be the tropyl radical.