Hydride transfer reactions of substituted adamantyl cations

Abstract

In 98% sulphuric acid at 0°, 2-methyladamantan-2-ol gives mainly 2-methyladamantane and an equilibrium mixture of 2-methyladamantan-1-ol and syn- and anti-4-methyladamantan-1-ol; at 50° the major products are 1-methyladamantane and 3-methyladamantan-1-ol; and at higher temperatures the only volatile products are 5-methyladamantan-2-one and 1-methyladamantan-2-one. The structures of the new alcohols were confirmed by comparison with the products obtained by bromination of 2-methyladamantane and hydrolysis of the mixture of bridgehead monobromides produced. 2,2-Dichloro- and 2,2-dibromo-adamantane rearrange in the presence of the appropriate aluminium halide to give 1,4- and 1,3-disubstituted products. The bromination of 2-methyl-adamantane and these rearrangements, which involve hydride transfer reactions, are discussed in terms of the relative stabilities of intermediate cations and of the appropriate products.