Unusual Cyclopropanation of 9-Bromocamphor Derivatives: A Novel Formal C(1)−C(7) Bond Cleavage of Camphor

An unusual cyclopropanation of 9-bromocamphor derivatives 1 to a 7-spiro-cyclopropyl camphor derivative 3 was effected by the action of
potassium tert-butoxide (or sodium hydride) in warm DMSO. The exo-hydroxy group and a non-hydrogen endo-substituent at C(2) have proven
to be essential structural elements, and the solvent DMSO has proven to be the sole effective reaction medium. Tricyclic compound 3 undergoes
a facile tandem Wagner−Meerwein rearrangement−cyclopropyl ring-opening under mild acidic conditions, leading to norbornenyl derivative 12
and subsequent Meinwald rearrangement of bicyclic epoxide 13 to a formal C(1)−C(7) bond cleavage product 14.