THERMAL REARRANGEMENT OF 1-SUBSTITUTED SPIRO [ADAMANTANE-2,2'-ADAMANTANE] DERIVATIVES

Tertiary 1-halospiro[adamantane-2,2'-adamantane] derivatives (1-halo[1 ]diadamantanes) have been synthesised by reaction of the 1-[1]diadaman tyl cation with appropriate nucleophiles. Thermolysis of 1-chloro- or 1-bromo-[1]diadamantane, but not the 1-fluoro derivative, gives the co rresponding secondary 4-halo derivative in good yield. By H-1 and C-13 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 degrees, this being the les s strained of the two possible 4-substituted isomers, according to mol ecular mechanics calculations. Possible mechanisms for the rearrangeme nt are discussed.