Examining the Bromination of Benzobicyclooctadiene by ab Initio Methods.

The bromination of 5.8-diacetoxy-1,4-dihydro-1,4-ethanonaphthalene was reported several years ago to yield a single stereospecificly formed dibromide. Given related cases from the literature, the result was interpreted as indicating a significant interaction between the aryl and olefin pi-electron systems. This paper reports an ab initio study of the mechanism of the bromination of benzobicyclooctadiene. It is proposed that the stereochemistry is best accommodated by an asynchronous concerted electrophilic addition of bromine across carbons 1 and 3, and that it proceeds via an ion pair transition structure in which the Wagner-Meerwein portion of the reaction has already occurred. All final results were calculated at the Becke3LYP/6-31G level.