The structures and ultraviolet spectra of the bromination products of 6,6-diphenylfulvene

Bromination of 6,6-diphenylfulvene 1 gives trans-trans-trans-1,2,3,4-tetrabromo-1,2,3,4-tetrahydro-6,6-diphenylfulvene 3 via trans-1,2-dibromo-1,2-dihydro-6,6-diphenylfulvene 2. Compound 3 in cyclohexane or carbon tetrachloride is converted by heating or exposure to sunlight to its trans-cis-trans stereoisomer 4. The structures of 3 and 4 have been established by X-ray crystallography. Compound 3 is converted to a third stereoisomer 5 on standing in chloroform or dichloromethane solution. Anomalies in the ultraviolet spectra of 3–5 can be interpreted in terms of an interaction of the π system with the bromine atoms at C(1) and C(4). The formation of addition products from 1 is indicative of its olefinic rather than aromatic character.