Reactivities of Stable Rotamers. XXIII. Some Addition Reactions toward the Vinyl Group in 9-(2-Vinyl-1-naphthyl)fluorene Rotamers

Abstract

Abstract Addition reactions to the vinyl group of the ap and the sp rotamers of 9-(2-vinyl-1-naphthyl)fluorene were carried out. Whereas action of sulfuric acid on the sp rotamer caused a cyclization reaction, the ap isomer was recovered under the conditions. While addition of bromine afforded normal products for both the isomers, reaction of chlorine afforded chlorine-substituted products (chloro olefins) in addition to the normal adduct, the formation of the former being predominant, in the sp form. The slightly enhanced reactivity of the sp form relative to the ap in bromination together with the formation of the chloro olefin and the behavior of the sp form in the treatment with sulfuric acid are attributed to the stabilization of the intermediates by the π-participation of the fluorene ring. Other addition reactions, epoxidation, hydrogenation, hydroboration, osmium tetraoxide oxidation, chlorination with (dichloroiodo)benzene, and diimide reduction, which are believed to proceed through a cyclic transition state, have also been studied to show that the rates of the reactions of one isomer are not much different from those of another. Spectroscopic data suggest that the conformation of the vinylnaphthalene portion in both isomers are similar. Little difference in the reaction rates of the two rotamers are attributed to the possible transition state conformation which may not be affected by the steric hindrance of the fluorene ring.