Functionalization of diamantane dimers

Aim. To develop preparative methods for functionalization of diamantane dimers. Results and discussion. The reaction of 1,1′-bisdiamantane with bromine and the subsequent hydrolysis gives 6-hydroxy-1,1′-bіsdіamantane with a yield of 56 %. The reactions of 4,4′-bisdiamantane with nitric acid or liquid bromine followed by hydrolysis leads to a mixture of hydroxy derivatives and 1,1′-dihydroxy-4,4′-bisdiamantane after isomerization in sulfuric acid (with a yield of 73 %). Thus, the reactivity of bisdiamantanes with electrophiles is determined by the higher stability of the carbocations in the medial positions of the cages as shown by DFT computations. Whereas medial bridgehead substitutions dominate in reactions of 4,4′-bisdiamantane with electrophiles, the arylation with benzene in the presence of tert-butyl bromide and aluminum chloride gives bis-apical derivative – 9,9’-diphenyl-4,4’-bisdiamantane. Experimental part. The structure of 6-hydroxy-1,1′-bіsdіamantane was confirmed by X-ray diffraction analysis. The substitution pattern in 1,1′-dihydroxy-4,4′-bisdamantane was confirmed by 2D-NMR spectra. The arylation of 4,4′-bisdiamantane with benzene proceeds as bis-apical substitution to give highly symmetric 9,9’-diphenyl-4,4’-bisdiamantane in 47 %. Conclusions. It has been shown that the medial bridgehead substitution dominates in the reactions of bisdiamantanes with strong electrophiles, and only the arylation of 4,4′-bisdiamantane proceeds as a bis-apical substitution.