| The geometrical dependance for an aryl bromide-alkyllithium exchange reaction has been investigated by use of the endocyclic restriction test.;There have been four mechanistic alternatives presented for the aryl bromide-alkyllithium exchange reaction: a four-centered transition structure mechanism; a single-electron mediated mechanism; an S;Through double double-label experiments, we have determined that the aryl bromide-alkyllithium exchange of 52 to 53 proceeds intermolecularly in systems in which an intramolecular exchange through a five-, six-, and eight-membered endocyclic ring is available. The exchange will proceed intramolecularly through an eighteen-membered endocyclic ring. This is the first determination of a geometrical dependance for an aryl bromide-alkyllithium exchange.;Through these results, we have ruled out the four-center mechanism, which should proceed intramolecularly though the smaller endocyclic ring systems. The observation of a geometrical dependance also rules out the single-electron transfer mechanism. The mechanistic alternatives which involve large C-Br-C transition structure angles, the S... |
