Synthesis of halo-fluoro-substituted adamantanes by electrophilic transannular cyclization of bicyclo[3.3.1]nonane dienes

3,7-Dimethylenebicyclo[3.3.1]nonane and its derivatives with a methyl or phenyl substituent in a methylene group react, with N-halosuccinimides NXS (X=Cl, Br, I) in dichloromethane in the presence of tetrabutylammonium dihydrotrifluoride or polyfluorinated alcohols via a transannular cyclization leading to the corresponding 1-fluoro- or 1-polyfluoroalkoxy-3-halomethyladamantanes. The reaction of the dienes with NXS and Bu4N+H2F3− conducted in THF, oxetane or ethylene oxide runs through a cascade addition of electrophiles (positively charged halogen atoms) and external nucleophiles (solvent molecules and halide anions) to the starting diene substrate and intermediate adamantyl carbocation.