Electron transfer reactions. Reaction of Δ2-oxazoline-5-ones and related substrates with potassium

Abstract

The reaction of several Δ2-oxazolin-5-ones (1a–c, 12) and bioxazolinones (17, 26) with potassium in THF has been investigated. Treatment of 1a with potassium in THF gave a mixture of dibenzamide (11a), N-benzoyl-C-phenylglycine (6a), and C-phenylglycine (10a). A higher yield of 11a was obtained, together with benzoic acid (9), when the reaction of 1a was carried out in THF saturated with oxygen. The reaction of 1b gave a mixture of β-phenylalanine (10b) and 9, whereas 1c gave a mixture of N-benzoyl-C,C-diphenylglycine (6c) and N-benzoyl-C,C-diphenylmethylamine (5c). Similarly, the reaction of 12 gave a mixture of α-benzamidocinnamic acid (15) and 9. The reaction of the bioxazolinone 17 with potassium gave a mixture of 11a, 6a, and 10a, along with an appreciable yield of 2,3,5,6-tetraphenylpyrazine (25), whereas 26 under analogous conditions gave a mixture of 15, 6b, and benzamide (29). Reasonable mechanisms, involving the initial formation of radical anion intermediates and their subsequent transformation to give the observed products, have been suggested. Potassium superoxide oxidation of some of these substrates gives similar product mixtures. Cyclic voltammetric studies have been carried out to measure the reduction potentials of 1a–c, 12, 17, and 26 in the generation of their radical anions. The radical anions of these substrates were also generated pulse radiolytically in methanol and their spectra showed absorption maxima in the region 295–350 nm.