Reactivities of Stable Rotamers. XXXI. Bromine Addition to the Olefinic Moiety of Rotameric 1-(9-Fluorenyl)-2-(1-methylethenyl)naphthalenes

Abstract

Abstract Reaction of bromine with the ap form of the title compound afforded a normal addition compound, whereas the same with the sp form did no addition compound but a pair of bromo-olefins and a cyclized product, formation of which can be rationalized by deprotonation from and by attack of the π-system of the fluorene group on the intervening cation. The abnormal reactions of the sp form are the consequence of the steric effects of the fluorene moiety that prohibits the formation of the tetrahedral carbon at the reaction site. The stereochemistry of the cyclized product was determined both by NOE experiments and by X-ray crystallography. The stereoselective formation of only one isomer was rationalized by the structure of the starting material, of which stereodynamics was studied by the dynamic NMR method, and the direction of the attack of the bromine cation. For comparison of the fate of the intervening cation, the adduct from the ap form was treated with silver p-toluenesulfonate. It was found that the ratios of olefin formation were different from one rotamer to another. The results are discussed on the basis of different degree of openness of the intervening bromonium cation with reference to the same reaction for (1,2-dibromo-1-methylethyl)benzene.