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Enzyme‐Catalyzed Reactions, 71). – Enantioselective Esterification of Racemic Cyanohydrins and Enantioselective Hydrolysis or Transesterification of Cyanohydrin Esters by Lipases Pure cyanohydrin enantiomers (S)‐1/(R)‐1 and their O‐acyl derivatives (R)‐3/(S)‐3 are obtained from three different lipasecatalyzed reactions: i) enantioselective hydrolysis of aliphatic and aromatic racemic cyanohydrin esters 3, ii) enantioselective acylation of racemic cyanohydrins 1, iii) enantioselective transesterification of 3 with primary alcohols. Both the cyanohydrin esters and the free cyanohydrins (which are prone to racemization) are isolated as enantiomers with high optical purity on a preparative scale. Hydrolysis of the racemic butyrates 3b, e with Candida cylindracea lipase and pseudomonas sp. lipase, respectively, for example, affords the free (S)‐cyanohydrins (S)‐2‐hydroxypentanenitril [(S)‐1a] and (S)‐mandelonitrile [(S)‐1b)] in high yield with 97 and 96% ee, respectively. (S)‐1a is obtained with the same optical purity by candida sp. lipase‐catalyzed transesterification of 3b with 1‐octanol.

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Enzyme‐Catalyzed Reactions, 8. – Stereoselective Synthesis of 2‐Amino Alcohols from (R)‐ and (S)‐Cyanohydrins erythro‐2‐Amino alcohols (1R,2S)‐ and (1S,2R)‐4 may be synthesized stereoselectively by addition of Grignard compounds to cyanohydrins (R)‐, (S)‐1 and their O‐trimethylsilyl derivatives 3, respectively, followed by hydrogenation. The threo‐2‐amino alcohols (1S,2S)‐ and (1R,2R)‐4 are easily accessible by inversion at C‐1 of the (1R,2S) and (1S,2R) compounds.

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