Rearrangement of methylenecamphor during electrophilic bromination: remarkably clean access to the unnatural fenchyl (1,3,3-trimethylbicyclo[2.2.1]heptane) system

Treatment of (+)-methylenecamphor (2) with NBS in the presence of pyridine resulted in a rapid and remarkably clean rearrangement to yield a brominated (+)-methylenefenchone (3) in high yield and purity (>96%). The structure of the product was established by X-ray crystallography and the stereochemistry confirmed by both polarimetric and chiral GC analyses. Two transformations of the product were also performed to elucidate the structure.