Chiral Polycyclic Ketones via Desymmetrization of Dihaloolefins

3-Chloronorbornenone (R)-1a (98% ee) was obtained from trichloronorbornene 5 in two steps by the in situ generation of dichloronorbornadiene 2a with t-BuOK and desymmetrization with (−)-ephedrine, followed by hydrolysis with PPTS. The generality of this desymmetrization with (−)-ephedrine was tested with dibromonorbornadiene 2c and other substituted dichloronorbornadienes.