Electrochemical reduction asymmetric

Electrochemical reduction of folic acid is a convenient route to tefrahydrofolic acid. Reaction is performed in an aqueous buffer of triethylamine bicarbonate [98]. Water and buffer salts can then be removed by freeze-drying. The process generates a new asymmetric centre on the tetrahydropyridazine ring and only one of the... 

Electrochemical reduction of 2,8-dinitro- and 2-nitrophenoxatellurines in DMSO produces the corresponding radical anions [77JCS(P2)529]. In the former case, a presence of two interconverting asymmetric conformers in solution was detected by ESR. When 2-nitrophenoxatellurine was re-... 

For the asymmetric reduction of ketone and aldehyde derivates, two electrochemical reduction systems using ADH as catalyst were examined (Fig. 22) [108]. In system A, the reduced coenzymes are regenerated using either FNR for NADPH or DP for NADH. Methyl viologen serves as electron mediator between the electrode and FNR/DP. System B contains ADH as sole enzyme, which catalyzes both reduction of substrates and regeneration of cofactors. Phenylethanol is oxidized by ADH accompanied by reduction of NADP+ to NADPH and its oxidation product acetophenone is reduced electrochemically at a glassy carbon cathode. 

Miscellaneous Physical Chemistry. A kinetic study has been made of the electrochemical reduction of /8-carotene. The photoelectron quantum yield spectrum and photoelectron microscopy of /3-carotene have been described. Second-order rate constants for electron-transfer reactions of radical cations and anions of six carotenoids have been determined. Electronic energy transfer from O2 to carotenoids, e.g. canthaxanthin [/8,/3-carotene-4,4 -dione (192)], has been demonstrated. Several aspects of the physical chemistry of retinal and related compounds have been reported, including studies of electrochemical reduction, the properties of symmetric and asymmetric retinal bilayers, retinal as a source of 02, and the fluorescence lifetimes of retinal. Calculations have been made of photoisomerization quantum yields for 11-cis-retinal and analogues and of the conversion of even-7r-orbital into odd-TT-orbital systems related to retinylidene Schiff bases. ... 

TABLE 6. Asymmetric electrochemical reduction of l-X-2,2-diphenylcyclopropyl bromide" derivatives in the presence of strongly adsorbed alkaloids as inducers ... 

Electrochemical reduction of coumarin [187] affords the meso and ( ) forms of a product hydrodimerized (at C-4) like many other a,)6-unsaturated acid derivatives. In the presence of tertiary amines, which are not destroyed during the process but catalyze the evolution of hydrogen, a transfer of hydrogen takes place from the amine radical to the coumarin radical with formation of 3,4-dihydrocoumarin. Asymmetric amines cause asymmetric induction during the reduction of 4-methylcoumarin, as in Chapter 26 [188]. 

Gourley, R.N., Grimshaw, J. and Millar, P.C. (1967) Electrochemical reduction in the presence of tertiary amines an asymmetric synthesis of 3,4-di-hydro-4-methylcoumarin, J Chem. Soc. Chem. Comm. 1278-1279. 

Bonner, W.A. (1995) The quest for chirality, m. Physical origin of homochirality in life. Conference Proceedings, 379. Santa Monica, Cal., American Institute of Physies Press, Woodbury, N.Y., p. 17-49 Bonner, W.A. (1990) Attempted asymmetric electrochemical reductions in magnetic-fields. Origins of Life and Evolution of Biosphere 20,1-13 Bonner, W.A. (1990) The eleetrochemical reduction of phenylglyoxylic acid in a magnetic-field, Electrochem. Acta 35, 683-684. 

The p -hybridized carbon atom of the carbonyl group has frequently been reduced by asymmetric reagents to yield the 5p -hybridized carbon atom of an optically active alcohol. For example, Horner and Brich have studied electrochemical reduction of acetophenone in the presence of optically active quaternary ammonium salts or crown ethers. The optical purity achieved was low. In contrast, the conversion of the sp -hybridized carbon atom of a carbonyl compound into the sp -hybridized carbon atom of an optically active amine, a process common in Nature, has been exemplified using an artificial pyridoxamine analogue by Kuzuhara et aC Optical yields were moderate. 

Also, reductive desorption of SAMs of such asymmetrical disulfides as butyl hexadecyl disulfide and decyl-2(perifluoro-hexyl)ethyl disulfide has been studied on Au(lll), using CV [168]. Peak potentials corresponding to electrochemical desorption waves of the adsorbed species were different from those obtained for monolayers... 

Unsubstituted NDIs are seen as attractive chromophoric units because of their electronic complementarity to ubiquinones and their ease of formation from commercially available starting materials, forming symmetrical and asymmetric analogues relatively efficiently. Simple aromatic diimides undergo single reversible reduction processes either chemically or electrochemically to yield the corresponding radical anion in high yield (E1 = -1.10V vs. Fc/Fc+) (Fc ferrocene) [20a]. 

There are several disadvantages to potential sweep methods. First, it is difficult to measure multiple, closely spaced redox couples. This lack of resolution is due to the broad asymmetric nature of the oxidation/reduction waves. In addition, the analyte must be relatively concentrated as compared to other electrochemical techniques to obtain measurable data with good signal to noise. This decreased sensitivity is due to a relatively high capacitance current which is a result of ramping the potential linearly with time. Potential sweep methods are easy to perform and provide valuable insight into the electron transfer processes. They are excellent for providing a preliminary evalnation, bnt are best combined with other complementary electrochemical techniqnes. 

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