C-2-symmetric bis-sulfoxide: A novel chiral auxiliary for asymmetric desymmetrization of cyclic meso-1,2-diols

A new heterocyclic compound, C-2-symmetric bis-sulfoxide 1, has been found to be an efficient chiral auxiliary for asymmetric desymmetrization of cycl ic meso 1,2-diols via diastereoselective acetal fission. Both (R,R)- and (S ,S)-1 are readily synthesized with high optical purity via asymmetric oxida tion of 1,5-benzodithiepan-3-one (2). After acetalization of meso-1,2-diols 6a-e and a mono-TMS ether 6f with this chiral auxiliary 1, the resulting a cetals 7a-f were subjected to base-promoted acetal fission upon treatment w ith potassium hexamethyldisilazide (KHMDS) followed by acetylation or:benzy lation to give the desymmetrized diol derivatives 8a-f with high diastereos electivity. The chiral auxiliary 1 is readily removed by acid-promoted hydr olysis and can be recovered without a loss in enantiomeric excess.