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

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posted on 07.07.2005, 00:00 by Wei-Dong Z. Li, Yu-Rong Yang
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.