Electron transfer reactions. Reaction of nitrones with potassium

Abstract

Treatment of nitrones (1a–d, 26a,b, 34, 49) with potassium in tetrahydrofuran (THF) gives rise to radical anion (2a–d, 27a,b, 35, 50) and dianion intermediates (3a–d, 28a,b, 36) through electron transfer reactions. These intermediates undergo further transformations to give a variety of products. Thus, the aldehydonitrones (1a–d) give the corresponding aldehydes (10a–c), carboxylic acids (25a–c), and azobenzenes (19a,d), whereas the ketonitrones (26a,b) give deoxygenation products (31a,b). The nitrone 34 gave a mixture of products consisting of benzoic acid (25a), dibenzyl (48), the dimeric product 38, and tetraphenylpyrazine (46), whereas 49 did not give any isolable product. Cyclic voltammetric studies have been employed to measure the reduction potentials for both one-electron and two-electron transfer processes, leading to the radical anions and dianions respectively. These intermediates have been characterized through their electronic spectra and they were quenched by oxygen. Pulse radiolysis of the nitrones 1a–d, 26a,b, 34, and 49 also gave the corresponding radical anions 2a–d, 27a,b, 35, and 50, characterized by their spectra.