Reactivity and reaction pathways of alkylalkoxybenzene radical cations. Part 2. Effects of 2-alkyl substituents on the relative importance of deprotonation over de-tert-butylation of 2-alkyl-5-tert-butyl-1,4-dimethoxybenzene radical cations

Abstract

The 2-alkyl-5-tert-butyl-1,4-dimethoxybenzene radical cations 1+·a–e (2-alkyl = Me, Et, i-Pr, c-PrCH2 and PhCH2) generated in one-electron oxidation of their parent compounds 1a–e by pentafluorobenzoyl peroxide or cerium(IV) sulfate were characterized by EPR spectrometry. The product analysis shows that under certain conditions 1+·a–e may collapse through two competitive pathways, i.e. deprotonation and de-tert-butylation. The deprotonation of 1+·a–e is further assured by EPR observations of the corresponding benzyl radical intermediates. The relative importance of the two pathways is greatly dependent on the structure of the alkyl substituents, the nature of the solvents and the reaction temperature. For deprotonation, the reactivity order is found to be c-PrCH2 >Me >PhCH2 >Et ≫ i-Pr. Copyright © 1999 John Wiley & Sons, Ltd.