The Stereochemistry of the Reaction of Hydrogen Bromide with Cyclohexene and 1-Methylcyclohexene in the Presence of Oxygen

The reaction of hydrogen bromide with cyclohexene or 1-methylcyclohexene in the presence of oxygen, followed by reduction with lithium aluminium hydride afforded trans-2-bromocyclohexanol or t-2-bromo-1-methyl-r-1-cyclohexanol. These findings show that oxygen attacks intermediate bromocyclohexyl radicals formed by addition of a bromine atom to a double bond exclusively on the side opposite to the bromine substituent. Mechanistic implications are discussed.