15 Bis-dimethylglyoximato Cobalt(II) : 光学活性塩基錯体を触媒とするα-ケトカルボニル化合物の均一系接触不斉還元

概要

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Catalytic asymmetric hydrogenation of benzil was examined by use of bis-dimethylglyoximato cobalt(II)-optically active amine complex. This system gave an extroadinarily high optical yield (50%) never seen before in the case of homogeneous metal complex-catalyzed asymmetric syntheses. The results were summarized as follows. a) Co(DMG)_2 complexes with optically active polyfunctional bases such as quinine, quinidine, cinchonidine, O-acetyl-quinine and brucine resulted in asymmetric hydrogenation, especially amino alcohols were highly effective. However, simple amine could not affect asymmetric induction. b) Increase in the molar ratio of substrate to cobalt or base does not bring about decrease in optical yield, but rather small increase. c) It is worthy to mention that molar equivalent of optically active base is enough to affect asymmetric induction. d) Asymmetric yield increased with increasing polarity of the solvent used. This asymmetric reaction is presumably due to an asymmetry induced on the bis-dimethylglyoxime ring by optically active axial base, provided that this reaction proceeds through the same mechanism as alkyl-Co(DMG)_2B formation from Co(DMG)_2B and olefines under hydrogen atmosphere.
天然有機化合物討論会の論文
1970-10-01