Organoboron compounds: CDV. Bromination of 2-isopropyl-2-boraadamantane

Bromination of 2-isopropyl-2-boraadamantane in CH₂Cl₂ proceeds simultaneously by both radical and electrophilic mechanisms. The first involves elimination of HBr and formation of 2-(2-bromo-2-propyl)-2-boraadamantane; this rearranges, under the action of nucleophilic reagents, to a derivative of 4-borahomoadamantane, which converts, on oxidation, to 3α-hydroxy-7α-(2-hydroxy-2-propyl)bicyclo3.3.1]-nonane. The second direction includes cleavage of a BC(isopropyl) bond with formation of i-PrBr and 2-bromo-2-boraadamantane, oxidation of which leads to 3α, 7α-dihydroxybicyclo3.3.1]nonane. In the presence of H₂O, a solvated Br⁺ also takes part in the bromination, which results in formation of hydroxy (3-noradamantyl)isopropylborane, which is oxidized to 3-noradamantanol. Depending on the reaction conditions one of the three possible directions may predominate.