Single-electron transfer-initiated thermal reactions of arylmethyl halides. Part 8. The reaction of 2-halogeno-NN-dimethyl-2,2-diphenylacetamides with sodium methoxide in 2,2-dimethoxypropane. The effects of added acetone, temperature elevation, and of the nature of the halogen. Refinement of the reaction mechanism

Abstract

In addition to the previously isolated products (1c) and (2a), trimeric (2b) and oligomeric products (2c) were shown to result from the title reaction. The reactions leading to all these products are initiated by single-electron transfer (SET) to the halogenoacetamides (1a and b). The operation of chain processes is established (Scheme 4). Acetone enolate is shown to be a more effective single-electron donor towards compound (1a) than methoxide. In the absence of acetone enolate SN reactions with methoxide compete with SET-initiated reactions of compound (1a) at room temperature. Temperature elevation favours SET over SN reactions. The mechanism of trimer (2b) and oligomer (2c) formation is discussed and, in addition to the radical recombination mechanism, the carbanionic mechanism of dimer (2a) formation is established. The chloro derivative (1b) is shown to be less reactive in the title reaction than the bromo analogue (1a).