Stereoselective Access to 1,3-Diols by Diastereoselective Reduction

Substituted 1,3-diols are valuable intermediates in the synthesis of drugs and natural products [18]. Starting from the regio- and enantioselective enzymatic reduction of diketo esters described above, various methods to obtain enantio-merically pure 3,5-dihydroxy esters were developed. 

Diastereoselective reduction by chemical methods For the preparation of both enantiomers of dihydroxy ester sy -5a Prasad s [19] sy -selective borohydride reduction was applied, giving dihydroxy esters syn-5a in a diastereomeric ratio of dFsy a ti = 28 1 to 45 1. The enantiomers of dihydroxy ester anti-Sa were synthesized according to Evans method [20], which resulted in dr = 14 1 to 18 1 

Advantageously, the diastereomeric ratios could be raised to approximately 200 1 and more for all dihydroxy esters 5a by a single crystallization step affording enantiopure diols 5a on a gram scale [11]. Enantiopure syn-(3R,SS)-5a was prepared on a 200 g scale, enabling various applications in natural product total 

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