Optical resolution of racemic norbornene aldehydes: kinetically controlled intramolecular haloetherification of ene acetals

Haloetherification reaction of a diastereomeric mixture of the ene acetals 2 and 2′, derived from racemic norbornene aldehydes and chiral non-racemic (S,S)-hydrobenzoin, proceeded in a kinetically controlled manner to give the optically pure aldehydes 3 along with the intact ene acetals 2′. Compounds 3 and 2′ were converted to the optically pure norbornene aldehydes in both enantiomeric forms. Then a new chiral auxiliary for asymmetric desymmetrization of meso-1,2-diols was found.