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

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 H 2 O) 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 CF 3 ‐derivative (+)‐ 2a and its CH 3 ‐analogue 8 , and c ) by X‐ray analysis of the ester 2f from (+)‐ 2a and (−)‐camphanoyl chloride ( Fig. 2 and 3 ).