STEREODIVERGENT SYNTHESIS OF OPTICALLY-ACTIVE ALPHA-HYDROXY ACIDS VIA DIASTEREOSELECTIVE REDUCTION OF ALPHA-KETO ESTERS DERIVED FROM L-QUEBRACHITOL

Reduction of an alpha-keto ester derived from chiral cyclitol, readily available from L-quebrachitol, with K-Selectride proceeded via re-face attack of the ketone with high diastereoselectivity to obtain the alpha-hydroxy ester in 92% de. On the other hand, reduction of the alpha-keto ester with K-Selectride in the presence of 18-Crown-6 took place via si-face attack of the ketone to furnish the corresponding alpha-hydroxy ester in 92% de. Thus both enantiomers of mandelic acid were obtained in optically pure form.