Reactivity and reaction pathways of alkylalkoxybenzene radical cations. Part 3. Effects of 2-alkyl substituents on the relative importance of ring-substitution over deprotonation of 2-alkyl-1,4-dimethoxybenzene radical cations

One-electron oxidation of 2-alkyl-1,4-dimethoxybenzene 1a-f (2-alkyl = Me, Et, i-Pr, cy- C3H5CH2, PhCH2 and t-Bu) by 4-nitrobenzoyl peroxide 2 and pen taflurobenzoyl peroxide 3 was proved by the observation of great accelerati on of decomposition of the peroxides at room temperature, the detection of the corresponding radical cations 1(+.) a-f and product analysis. The produ ct studies have disclosed that under the conditions employed (in acetonitri le at 40 degreesC), the reaction pathways of the radical cations are greatl y dependent on the nature of 2-aIkyl substituents: Ring- 4-nitrobenzoloxyla tion product at C-5 and C-6 were obtained exclusively in the reactions of t he donors with aliphatic 2-alkyl substituents bearing at least one alpha -h ydrogen atom, such as 1a, 1b, 1c and 1d; whereas in the case of 1e (with 2- benzyl group), both ring-substitution at C-5 (4e) and C-6 (5e) and deproton ation/4-nitrobenzoloxylation products 8e were isolated; from the donor with out cc-hydrogen atom, If, de-t-butylation products 12 and t-butyl 4-nitrobe nzoate 13 were incorporated with ring-substitution at C-5 (4f) and C-6 (5f) . Furthermore, the product distribution (4 over 5) is also affected by the bulkiness of 2-alkyl group. For all the electron-transfer reactions, large amounts of the benzoic acid (4-NO2C6H4COOH or C6F5COOH) were generated and trace amounts of de-methylation product (2-alkyl-1,4-benzoqinones 6) were a lso detected by H-1 NMR.