The electrochemical asymmetric reduction of prochiral carbonyl compounds, oximes, and a ecm-dihalide was examined by using a poly-L-valine-coated graphite electrode.The highest asymmetric yield (16.6%) was obtained in the reduction of 1,1-dibromo-2,2-diphenylcyclopropane to the corresponding monobromocyclopropane.As summarized by Tilborg and Smit,2) four methods, except for intramolecular asymmetric induction, for electrochemical asymmetric reduction have been reported: The use of (a) chiral solvents, Although the methods (a) and (b) gave 6%3) and 20%4) of asymmetric yields, respectively, in each best case in the reduction of acetophenone, these methods inherently need large amounts of optically-active materials as asymmetry-inducing reagents.In contrast, the other two methods need extremely smaller amounts of the inducing reagents. Moreover, the method (c) gave high asymmetric yields as 47.5%5) and 44.3%6, 7) in the reduction of 2-acetylpyridine (in the presence of 0.5 mmol•dm-3 strychinine) and 1,1-dibromo-2,2-diphenylcyclopropane (9) (in the presence of 3.4 mmol•dm-3 emetine), respectively.However The highest asymmetric yield of 43% was obtained using a poly-L-valine-coated graphite electrode in the reduction of 4-methylcoumarin,11)while the highest asymmetric yield (54%) in the oxidation was found in the electrolysis of phenyl cyclohexyl sulfide on a platinum electrode coated with poly-L-valine.12)
Influence of a number of electrolytic conditions on the asymmetric yield of methylsuccinic acid (2) formed in the electrochemical reduction of citraconic acid (1) on poly(amino acid)-coated electrodes was examined. The asymmetric yield was greatly affected by the conditions, while the absolute configuration of an excess enantiomer((S)-(−)-2) remained unchanged even when a polymer with the reversed configuration of the monomer unit was used. The configuration of the excess enantiomer was also unchanged in the asymetric reduction of mesaconic acid which is the geometrical isomer of 1.
Aromatic polyamide‐esters of moderately high molecular weight were prepared from various combinations of three aminophenols (m‐ and p‐aminophenol, and 4‐(4′‐aminophenoxy) phenol) and two aromatic diacid chlorides (isophthaloyl and terephthaloyl) by interfacial polycondensation in a cyclohexanone/water system and two‐phase polycondensation in a dichloromethane/water system with phase‐transfer catalysts. The solution polycondensation in dichloromethane/N,N‐dimethylacetamide was also successful for the production of high‐molecular‐weight polymers. The solubility of the aromatic polyamide‐esters varied markedly with polymer structure. Except for two polyamide‐esters derived from terephthaloyl chloride, all the other polymers were almost amorphous. These polymers had glass transition temperatures at around 200°C and showed 10% weight losses at about 400°C in both air and nitrogen atmospheres.
Graphite electrodes modified chemically with poly(l-valine) and poly(N-acryloyl-l-valine methyl ester) were prepared. They were remarkably more durable than the corresponding dip-coated electrodes when used repeatedly in the electrochemical asymmetric reduction of citraconic acid.
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