Free Radical Cyclizations, Xvii. Mechanistic Studies

Free radical cyclizations of the 4-phenylbutyl radical and analogues carrying naphthyl and vinyl groups instead of phenyl have been studied. A typical reaction scheme is given below involving closures to fiveand six-membered rings. Competition rate studies for the various types of ring closure were performed with deuterated analogues. The results can be used as an efficient mechanistic tool for other radical processes, as exemplified for the Kornblurn reaction between x-substituted p-nitrobenzyl chlorides with the anion of benzylcyanide in a two.phase system. The nature of (cyclic) byproducts supports and confirms the radical chain mechanism for such substitutions. (1) MECHANISM OF FREE RADICAL CYCLIZATION THROUGH AROMATIC SUBSTITUTION The large amount of information produced by several groups of investigators has led to some understanding of the mechanism of free radical cyclizations through addition'. The problem of the size of the ring which is formed arose early: we began these investigations with heavily substituted resonancestabilized radicals (cyanoesters) which gave