Electrogenerated bases synthesis

Application of Electrogenerated Bases to Fluoro Organic Synthesis... 

Quite recently, Troupel et al. have developed an effective synthesis of gem-difluoro-/ -oxonitriles using an electrogenerated base derived from phenyl bromide and a sacrificial magnesium anode together with a nickel cathode coated with a small deposit of cadmium as shown in Scheme 4.5 [34]. 

Amputch MA, Little RD (1991) Tetrahedron 47 383. Utley JHP, (1987) Electrogenerated bases. In Steckhan E (ed) Topics in current chemistry. Springer, Berlin Heidelberg New York, p 133 Little RD, Sowell CG (1991) Stereoselection in electroreductive cyclization. Construction of a Corey lactone precurser. In Little RD, Weinberg NL (eds) Electroorganic synthesis, festschrift for Manuel M. Baizer. Dekker, New York, p 323 Shono T, Mitani M (1971) J. Am. Chem. Soc. 93 5284... 

In situ Wittig synthesis through an electrogenerated base has been carried out in a divided cell at a mercury pool cathode in an inert atmosphere the potential of the cathode is controlled at the peak value of the corresponding probase as given in Table 2. 

Reductive formation of a carbanion, either by reduction of a C-halogen bond or by removal of a proton by an electrogenerated base, followed by an intermolecular nucleophilic substitution, has been used in the synthesis of substituted lactams [11]. A similar reaction is used for the formation of quinolizidine and indolizidine derivatives from... 

If a mercury cathode is expected to be necessary, the aprotic solvent-alkali-metal salt system appears to be inconvenient since many compounds are cathodically cleaved, reduced, or/and deprotected at potentials beyond that of alkali-metal amalgam formation. nevertheless, in certain cases the use of lithium salts as an electrolyte possessing strong electrophilic properties appears necessary in order to avoid the possibility of a Hofmann degradation of the tetraalkylammonium ion by electrogenerated bases. Under such experimental conditions, the cathodic synthesis of some aza and aza-oxa ligands [31] has been successfully achieved from the corresponding and readily obtained poly-... 

Scheme 16.13 Synthesis of P-lactams, via deprotonation of bromoamides by electrogenerated bases, in RTILs and in VOCs (Reprinted from Ref. [113] with kind permission of Elsevier)...

Casadei MA, Cesa S, Rossi L (2000) Electrogenerated base-promoted synthesis of organic carbonates from alcohols and carbon dioxide. Eur J Org Chem 13 2445-2448... 

APPLICATION OF ELECTROGENERATED BASES TO FLUORO-ORCANIC SYNTHESIS... 

In electroorganic synthesis, radical ions preponderate as useful intermediates (Scheme la). Radical cations can, in subsequent deprotonations and further electron transfers (ET), be transformed into carbocations or vice versa as radical anions can be converted by protonation and further reduction into carbanions. Carbanions can also be generated by reductive cleavage of R-X (X = Cl, Br, I, OTos), and subsequent reduction of the intermediate radical R (Scheme Id). Radical anions can also be used as electrogenerated bases (EGBs, see Chapter 14) for the deprotonation of C-H bonds to form carbanions. 

Advances have been achieved in recent years, such as the use of CL reagents as labels to derivatize and sensitively determine analytes containing amine, carboxyl, hydroxy, thiol, and other functional groups and their application in HPLC and CE [35, 36], the synthesis and application of new acridinium esters [37], the development of enhanced CL detection of horseradish peroxidase (HRP) labels [38], the use of immobilization techniques for developing CL-based sensors [39-42], some developments of luminol-based CL in relation to its application to time-resolved or solid-surface analysis [43], and the analytical application of electrogenerated CL (ECL) [44-47], among others. 

Bonafoux, D. Bordeau, M. Biran, C. Cazeau, P. Dunogues, J. Regio- and stereoselective synthesis of silyl enol ethers using a new base electrogenerated from HN(SiMe3)2. J. Org. Chem. 1996, 63, 5532-5536. 

A new approach for the synthesis of functionalized 4-alkylquinolines was developed utilizing electrogenerated carbanions <07SL1031>. The desired 4-alkylquinolines 83 were synthesized through a sequential alkylation/heterocyclization of p-(2-aminophenyl)-a,p-ynones 84 and the electrogenerated carbanions of nitroalkanes 85. This novel approach avoided metal and base catalysts and is performed under solvent free conditions. 

Nanocrystalline cerium (IV) oxide powders with an average particle size of 10 -14 nm have been prepared by the cathodic base electrogeneration method.The nanocrystallinc CeO powders are prepared in the cathode compartment of a divided electrochemical cell. The cathode is a platinum wire and the anode is a platinum mesh electrode. The cathode compartment in the divided cell contained 0.5 mol T cerium (HI) nitrate and 0.5 moM ammonium niu-ate, and the anode compartment contained 0.5 mol I ammonium nitrate. The two compartments are separated with a medium porosity glass frit. The electrochemical synthesis is run in the galvanostatic mode at a current density of I A cm and the particle size is controlled by adjusting the solution temperature. 

The most traditional approach for the electrodeposition of metal oxides and hydroxides is based on the cathodic electrogeneration of base [6]. Depending upon the deposition potential, choice of the anion and the pH of the solution, various reactions take place at the cathode, such as the reduction of nitrate ions in aqueous solutions. These reduction reactions cause a local pH increase in vicinity of the cathode either by the consumption of protons or by the generation of hydroxide ions as in the case of nitrate reduction, which subsequently leads to the precipitation of metal hydroxides. The best known application of this technique is the synthesis of nickel hydroxide by the electroreduction of aqueous nickel nitrate solutions. Depending on the metal and deposition conditions, this cathodic technique often yields hydroxides rather than oxides, making a post-deposition calcination for the transformation of the hydroxide to the oxide necessary. Unfortunately, the deposited amorphous hydroxides are often metastable. Other cathodic electrodeposition methods involve the direct reduction of the oxidation state of the metal cation and deposition of the oxide onto the electrode [9]. 

Thus, the role of strong acidic moieties in the stability of the 0 02 redox couple in [PeeewlCl has been studied via addition of hydrochloric acid, (a common side product in phosphonium-based ILs synthesis) [31] by cyclic voltammetry. Figure 18.11 depicts that in the presence of HCl the reduction process for oxygen is irreversible [28] as opposed to the pure [PeeewlCl where chemical reversibility of the electrogenerated superoxide anion is observed which exemplify of the detrimental effect of HCl on the reversibility of the O2 reductimi process. 

---