Norbornanoid Chiral Ketones by Desymmetrization of Dibromoalkenes

New optically active polycyclic ketones 6a-6d, amenable to a large variety of synthetic applications, have been prepared from readily available 2,3-dibromonorbornene and analogs (Scheme 2) via desymmetrization with (-)-ephedrine, followed by hydrolysis under mild acidic conditions. At variance with substrates 4a-4d, the sterically hindered norbornene derivative 4e reacts with the solvent N-methylpyrrolidin-2-one (NMP) leading to the formation of the unusual cyclopropanoid products 8a and 8b.