Thermal rearrangement of 1-substituted spiro[adamantane-2,2′-adamantane] derivatives

Abstract

Tertiary 1-halospiro[adamantane-2,2′-adamantane] derivatives (1-halo[1]diadamantanes) have been synthesised by reaction of the 1-[1] diadamantyl cation with appropriate nucleophiles. Thermolysis of 1-chloro- or 1-bromo-[1]diadamantane, but not the 1-fluoro derivative, gives the corresponding secondary 4-halo derivative in good yield. By ¹H and ¹³C NMR spectroscopy and by X-ray crystallography it has been established that the 4-bromo [1]diadamantane isolated is the anti isomer, with the Br–C–C–C_spiro torsion angle close to 170°, this being the less strained of the two possible 4-substituted isomers, according to molecular mechanics calculations. Possible mechanisms for the rearrangement are discussed.