SCOPE AND MECHANISM OF THE ELECTRON-TRANSFER PHOTOINDUCED ALKYLATION OF AN AROMATIC NITRILE

The photoinduced alkylation of 1,2,4,5-tetracyanobenzene in the presence of tetralkylsilane or stannane derivatives as well of 2,2-dialkyldioxolanes has been studied using substrates containing rearranging radicals (5-hexenyl and cyclopropylmethyl). The quantum yield of the rearranged and non rearranged alkyltricyanobenzenes has been determined in acetonitrile, ethyl acetate and in the presence of radical traps, protic and nucleophylic agents, a cosensitizer (biphenyl) and various salts. The results support unimolecular fragmentation of the donor radical cation followed by radical - radical anion combination for the case of stannane and silane derivatives, while with the dioxolanes a S(N)2-like mechanism has an important role. This study allows some predictions about the use of photoinduced electron transfer for synthetic reactions via radicals.