BiBr3-catalyzed benzylation of alcohols. Stereochemistry and mechanistic investigations

Article abstract of DOI:10.1016/S0040-4020(01)00014-X

We have investigated the benzylation of optically active aliphatic alcohols (octan-2-ol and butan-2-ol) as well as cis and trans 2-methylcyclohexanol or (S)-(-)-menthol, catalyzed by bismuth (III) bromide in the presence of (-) or (±)-1-phenylethanol (PeOH). Under mild conditions, aliphatic alcohols provided an equimolar mixture of diastereomeric ethers while alicyclic alcohols gave rise to ethers with retention of configuration. To explain these results, we assumed that BiBr₃, acting as Lewis acid, would lead to the formation of a 6-fold coordinated bismuth intermediate involving two molecules of 1-phenylethanol and one molecule of aliphatic alcohol. We have proposed a mechanism to explain these BiBr₃-promoted etherification reactions.