BR+ TRANSFER TO REACTIVE ALKENES FROM THE BROMONIUM ION OF ADAMANTYLIDENEADAMANTANE

The transfer of Br+ from the bromonium ion of adamantylideneadamantane (1-Br+/CF3SO3-) to the reactive alkenes cyclohexene, omega-alken-1-ol s, 3a-c, and 4-pentenoic acid, 4, in 1,2-dichloroethane at 25 degrees C has been investigated. H-1 NMR analysis of the reactions of equimola r 1-Br+/CF3SO3- and olefin indicates the products to be the expected c yclic ones in the cases of 3a-c and 4, and trans-2-bromocyclohexyltrif luoromethane sulfonate in the case of cyclohexene, along with adamanty lideneadamantane (Ad=Ad). Detailed kinetic analysis shows that the rea ction rates are suppressed by the addition of free Ad=Ad, suggestive o f a common species rate depression. In the case of certain of the cycl ization reactions such as that of 4-penten-1-ol, 3a, the cyclization r eaction is bimolecular in acceptor olefin. A primary deuterium kinetic isotope effect of 2.0 on the cyclization of 3a-OH relative to 3a-OD e xists. The role of the second molecule appears to be that of a general base in assisting the cyclization of an intermediate omega-hydroxy cy clic bromonium ion. A general mechanistic scheme for Br+ transfer from 1-Br+ to the reactive alkenes is proposed.