Cation-pool reduction

Next, we examined the reduction of cation pools in the presence of radical acceptors. The radical that is formed by one-electron reduction of the cation is expected to add to a carbon-carbon double bond. The electrochemical reduction of 2 in the presence of methyl acrylate gave the expected addition product 16 (Scheme 9). A mechanism involving addition of radical 14 to the acrylate to generate radical 17 followed by subsequent reduction of anion 18, which is protonated to give 16 has been suggested. 

The use of cation pools as precursors of carbon radicals solves the problem, because carbocations are more easily oxidized than carbon radicals in many cases. In fact, it is well known that one-electron reduction of a carbocation leads to the formation of the corresponding carbon radical. Therefore, the reduction of cation pools should lead to the formation of carbon radicals (Scheme 5.26). 

Carbon radicals can be generated by the reduction of cation pools and this method might serve as an effective method for the generation of... 

A divided cell equipped with a sintered glass separator, a carbon fiber anode, and a platinum cathode is used in order to avoid the electrochemical reduction of anodically generated carbocations. Tetrabutylammonium tetrafluoroborate is usually used as supporting electrolyte, and dichloromethane is in most cases suitable as solvent because of less nucleo-philicity and low viscosity at low temperature. Two equivalent of TfOH (trifluoromethane-sulfonic acid) to a cation precursor is added in the cathodic chamber to facilitate the reduction of protons in the cathodic process. The constant current electrolysis (20 mA) was then carried out at —78 °C with magnetic stirring until 2.0-2.5 F/mol of electricity was consumed to give a cation pool. Carbamates (oc-silyl carbamate) (Scheme 2a) [3], a-silyl ethers (Scheme 2b) [4], diarylmethanes (silylated diary Imethanes) (Scheme 2c) [5] can be... 

The radical mediated carbon-carbon bond formation can be performed based on the reduction of a cation pool (Scheme 3) [7]. 

Cation-Pool Method, Scheme 3 Reduction of cation pool... 

Suga S, Suzuki S, Yoshida J (2002) Reduction of a cation pool . A new approach to radical mediated C-C bond formation. J Am Chem Soc 124 30-31... 

The electrochemical reduction of W-acyliminium ion pool 2 gave rise to the formation of the corresponding homo-coupling product 13 (Scheme 8).23 Presumably, a radical intermediate 14 was generated by one electron reduction of 2 and homo-coupling of the radical led to the formation of the dimer 13. However, a mechanism involving two-electron reduction to give anion 15 followed by the reaction with cation 2 cannot be ruled out. 

Volume 75 concludes with six procedures for the preparation of valuable building blocks. The first, 6,7-DIHYDROCYCLOPENTA-l,3-DIOXIN-5(4H)-ONE, serves as an effective /3-keto vinyl cation equivalent when subjected to reductive and alkylative 1,3-carbonyl transpositions. 3-CYCLOPENTENE-l-CARBOXYLIC ACID, the second procedure in this series, is prepared via the reaction of dimethyl malonate and cis-l,4-dichloro-2-butene, followed by hydrolysis and decarboxylation. The use of tetrahaloarenes as diaryne equivalents for the potential construction of molecular belts, collars, and strips is demonstrated with the preparation of anti- and syn-l,4,5,8-TETRAHYDROANTHRACENE 1,4 5,8-DIEPOXIDES. Also of potential interest to the organic materials community is 8,8-DICYANOHEPTAFULVENE, prepared by the condensation of cycloheptatrienylium tetrafluoroborate with bromomalononitrile. The preparation of 2-PHENYL-l-PYRROLINE, an important heterocycle for the synthesis of a variety of alkaloids and pyrroloisoquinoline antidepressants, illustrates the utility of the inexpensive N-vinylpyrrolidin-2-one as an effective 3-aminopropyl carbanion equivalent. The final preparation in Volume 75, cis-4a(S), 8a(R)-PERHYDRO-6(2H)-ISOQUINOLINONES, il lustrates the conversion of quinine via oxidative degradation to meroquinene esters that are subsequently cyclized to N-acylated cis-perhydroisoquinolones and as such represent attractive building blocks now readily available in the pool of chiral substrates. 

The cationic species also affects the CO2 reduction at metal electrodes. Paik et al. studied electroreduction of CO2 to HCOO at a Hg pool electrode in Li , Na and (C2H5)4N hydrogen-carbonate solutions. The electrode potential at a constant current increases in the positive direction with the sequence of Li < Na < (C2H s)4N . The results were discussed in connection with the vari-... 

It is well known that corrosion processes are enhanced if there are high levels of impurities in the water. Therefore, to keep the level of impurities low, an ion exchange purification system has been employed since startup in the MIR reactor coohng pool. This system includes a heat exchanger, a pump, two filters with a total capacity of 800 L, a flowmeter, shut-off valves and other fittings. The filters are filled with Russian made nuclear grade ion exchange resins KU-2-8 (cationic) and AV-17-8 (anionic) in the ratio of 2 1. This system provides reduction of the specific p activity by more than a factor of 10. When this index drops to a factor of 2, the resin is replaced otherwise, as a rule, it is replaced once a year. 

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