Preparation by yeast reduction and determination of the sense of chirality of enantiomerically pure ethyl (−)‐4,4,4‐trichloro‐3‐hydroxy‐ and (+)‐4,4,4‐trifluoro‐3‐hydroxybutanoate

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Abstract
Reduction of ethyl 4,4,4‐trichloro‐ and 4,4,4‐trifluoro‐3‐oxobutanoate by fermenting baker's yeast (Saccharomyces cerevisiae) on a preparative scale (20–50 g in ca. 3 1 of H2O) gave 70–80% yields of the trichloro‐ [(−)‐(S)‐1a] and trifluoro‐hydroxyesters [(+)‐(R)2a] of ca. 85 and 45% ee, respectively. Both, (−)‐1a and (+)‐2a could be obtained in > 98% ee by subsequent crystallization (of(−)‐1, (+)‐2a or the 3,5‐dinitrobenzoate (+)‐2b. The absolute configuration of both hydroxyesters was determined (a) by chemical correlation ((−)‐1a), (b) from the melting diagrams and mixed melting points (differential‐scanning calorimetry Fig. 1) of the dinitrobenzoates of the CF3‐derivative (+)‐2a and its CH3‐analogue 8, and c) by X‐ray analysis of the ester 2f from (+)‐2a and (−)‐camphanoyl chloride (Fig. 2 and 3).

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