Kinetically controlled optical resolution of racemic norbornene aldehyde derivatives

A new method for obtaining optically pure 5-norbornene 2-endo-aldehyde derivatives was developed. The reaction of a diastereomeric mixture of the ene acetals 2 and 2′, derived from racemic norbornene aldehydes (±)-1 and chiral nonracemic (S,S)-hydrobenzoin 7, with NBS (0.5–0.6 eq.) in the presence of H2O proceeded in a kinetically controlled manner to give the optically pure hydroxy aldehydes 3 along with the intact ene acetals 2′. Both compounds 3 and 2′ were converted into the optically pure norbornene aldehydes 1 and ent-1, respectively. This method opens the way to produce various types of 5-norbornene 2-endo-aldehydes with 3-exo- or 3-endo-substituents in optically pure forms. Chirality 15:60–67, 2003. © 2002 Wiley-Liss, Inc.