Citraconic acid, reduction

Subsequently, a number of reactions at poly-L-valine coated carbon electrodes 237-243) gj.g reported to yield optically active products. Reductions, e.g. of citraconic acid or l,l-dibromo-2,2-diphenylcyclopropane as well as the oxidation of aryl-alkyl sulfides proceeded with chiral induction at such electrodes... 

The results cited in this section indeed appear very promising and encouraging, but there are still many problems to solve. Chemical and optical yields are extremely sensitive to experimental conditions such as current density and electrolyte composition Some experimental details in the asymmetric reduction of citraconic acid are indeed puzzling, such as a temperature maximum of the optical yield, and the fact the same product enantiomer is formed regardless if D or l polyvaline was used... 

Nonaka et al. 62) examined the asymmetric reduction of open-chain olefins in the presence of optically active amino acids. In the best case (R)-methylsuccinic acid (23) was formed in 2.4 % and 53 % optical and chemical yields, respectively, from citraconic acid (24) in the presence of (R)-cysteine. 

Reduction of 25 mmole of citraconic acid gave a mixture of saturated acid (27%) and starting material. The optical rotation was not taken. 

Cinnamic acid, starch ester, I, 303 Cinnamaldehyde, phytochemical reduction of, IV, 79, 91 Cinnamyl alcohol, IV, 91 phytochemical reduction of, IV, 92 Citraconic acid, IV, 327 Citral, phytochemical reduction of, IV, 79... 

On a poly-L-valine-coated graphite electrode, the asymmetric reduction of the C=C bond in 2-methylcoumarin and in citraconic acid produced ee s of 43% and 25%, respectively Earlier, methyldihydrocoumarin was obtained only with an ee of 18.6% using spartein as an asymmetric inductor... 

Now if one of the protons of maleic (or fumaric) acid is replaced by a methyl group to form citraconic acid and this dibasic acid is electrochemically reduced, the product is expected to be methyl succinic acid. This acid now contains an asymmetric center, so that it may be possible to form an optically active product under conditions of electrolytic reduction citraconic acid would be expected to yield the racemic mixture ... 

Methylsuccinic acid has been prepared by the pyrolysis of tartaric acid from 1,2-dibromopropane or allyl halides by the action of potassium cyanide followed by hydrolysis by reduction of itaconic, citraconic, and mesaconic acids by hydrolysis of ketovalerolactonecarboxylic acid by decarboxylation of 1,1,2-propane tricarboxylic acid by oxidation of /3-methylcyclo-hexanone by fusion of gamboge with alkali by hydrog. nation and condensation of sodium lactate over nickel oxide from acetoacetic ester by successive alkylation with a methyl halide and a monohaloacetic ester by hydrolysis of oi-methyl-o -oxalosuccinic ester or a-methyl-a -acetosuccinic ester by action of hot, concentrated potassium hydroxide upon methyl-succinaldehyde dioxime from the ammonium salt of a-methyl-butyric acid by oxidation with. hydrogen peroxide from /9-methyllevulinic acid by oxidation with dilute nitric acid or hypobromite from /J-methyladipic acid and from the decomposition products of glyceric acid and pyruvic acid. The method described above is a modification of that of Higginbotham and Lapworth. ... 

Another route involving 1,3-dipoIar addition was next attempted (54). The key feature of this route is a cycloaddition of nitrile oxide (55) 88 with citraconate 87 (Scheme 16). Treatment of 89 prepared from 3-bromopropanol with phenyl isocyanate produced the nitrile oxide 88 which was then subjected to cycloaddition with dimethyl citraconate 87 to afford the adducts 86a and 86b as a 1 1 mixture. In this reaction, as expected, 86a, in which the less hindered oxygen is substituted at the quaternary carbon, was the major product (56). Conveniently, however, the undesired adduct 86b could be separated in the following dehydration step. These adducts were next subjected to various reduction conditions (57) in order to obtain intermediate 85 (eq.9). Unfortunately, we could not obtain any of the desired compound even under Curran s conditions (Raney-Ni (W-2), boric acid) which are mild enough to suppress undesired side reactions. All compounds produced in this reduction were retro-aldol products 90-93 probably derived from 85 or its imine form. This... 

Nonaka, T., Abe, S. and Fuchigami, T. (1983) Part 2. Electrochemical asymmetric reduction of citraconic and mesaconic acids on optically-ac-tive polyamino acid-coated electrodes. Bull. Chem. Soc. Jpn, 56, 2778-2783. 

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