Diamantane. II. Preparation of Derivatives of Diamantane

Methods have been developed for the conversion of diamantane (I) to the three possible types of monofunctional derivatives: 1- (medial), 3- (secondary), and 4- (apical). The 1-diamantyl cation is the most stable and most readily generated by hydride abstraction. Kinetically controlled nucleophilic attack on this cation can be made to give 1-bromodiamantane (III) and 1-diamantanecarboxylic acid (V) in liquid bromine and under Koch-Haaf conditions, respectively. Sulfuric acid oxidation of I affords 3-diamantanone (X), a convenient source of other 3-diamantyl derivatives. The secondary 3-diamantyl tosylate (XII) solvolyzes about 3.5 times faster than 2-adamantyl tosylate. Under equilibrium conditions apical adamantyl derivatives are favored by enthalpy over their medial isomers, but the entropy effect is opposite. The enthalpy term for relatively large groups such as methyl dominates. Thus, 4-methyldiamantane (XXIII) can be synthesized by isomerization of the other methyldiamantanes or of other pentacyclotetradecanes, such as XXII, XXV, or XXVI. The equilibrium is less one-sided for smaller substituents, e.g., halide and alcohols, and preparations of apical products require chromatographic separation since they are seriously contaminated by their medial isomers. ¹H nmr chemical shifts of the various types of diamantane derivatives can be predicted satisfactorily by using additivity increments obtained from similarly constituted adamantanes.