Dicarbonyl compound reductions yeast

Reaction of lithiodithianes with acyl chlorides, esters or nitriles leads to the fOTination 1,2-dicarbonyl compounds in which one of the carbonyl groups is protected as the thioacetal. d76043j44 Optically active amino ketones of type (69) are inepared via acylation of dithiane with an oxazoline-protected (5)-serine methyl ester (Scheme 41). Optically active (5)-2-alkoxy-l-(l,3-dithian-2-yl)-l-propanones were prepaid by the reaction of the corresponding methyl (5)-lactate with 2-lithio-l,3-enantioselective synthesis of (-)-trachelanthic acid. Enantioselective synthesis of L-glyceraldehyde involves the acylation of a dithiane glycolic acid derivative followed by bikers yeast mediated reduction. ... 

The selective enzymatic reduction of 2-substituted / -keto esters or /S-diketones is more interesting than that of unsubstituted compounds since two stereogenic centers can be introduced into the molecule in one step. The observation that baker s yeast reduction of these compounds results in predominantly one of the four possible diastereomeric products has been explained by a keto- enol equilibration of the enantiomeric / -dicarbonyls with the simultaneous removal of one of these substrates by an asymmetric reduction49. 

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