A new continuous production process has been developed for optically active pure (2R,5R)-hexanediol. The process uses resting whole cells of Lactobacillus kefir DSM 20587 as a biocatalyst. The reduction of (2,5)-hexanedione to (2R,5R)-hexanediol was carried out in a 2-L continuously operated membrane reactor. Conversion of (2,5)-hexanedione was nearly quantitative and the selectivity between product and intermediate was 78% for the product. Enantioselectivity and diastereoselectivity were >99% for the whole period. The productivity of L. kefir could be increased by factor 30. (2R,5R)-Hexanediol was continuously produced over 5 days with a space−time yield of 64 g·L-1·d-1.

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An improved synthesis of (R,R)‐ and (S,S)‐hexane‐2,5‐diol is presented. The (S,S)‐derivative was converted into a cyclic sulfate, which on treatment with NaPH2 in liquid ammonia ultimately gave the secondary (R,R)‐2,5‐dimethylphospholane. This phospholane can be introduced into the side chain of chiral tricarbonylchromium and ferrocene derivatives to give new bidentate ligands of the Josiphos and Daniphos type. Both the ferrocene‐ and tricarbonylchromium‐based diphosphanes have been characterized by X‐ray diffraction analysis. A discussion of their structural features is included. The new ligands were successfully applied to the enantioselective hydrogenation of itaconic acid esters. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

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