Synthesis electrochemical generation

The synthesis of metalloporphyrins which contain a metal-carbon a-bond can be accomplished by a number of different methods(l,2). One common synthetic method involves reaction of a Grignardreagent or alkyl(aryl) lithium with (P)MX or (PMX)2 where P is the dianion of a porphyrin macrocycle and X is a halide or pseudohalide. Another common synthetic technique involves reaction of a chemically or electrochemically generated low valent metalloporphyrin with an alkyl or aryl halide. This latter technique is similar to methods described in this paper for electrosynthesis of cobalt and rhodium a-bonded complexes. However, the prevailing mechanisms and the chemical reactions... 

We chose to study the generation of alkoxycarbenium ion 26 from thioacetal 28. The electrochemically generated ArS(ArSSAr)+, 37 which was well characterized by CSI-MS, was found to be quite effective for the generation of alkoxycarbenium ions, presumably because of its high thiophilicity (Scheme 17). The conversion of 28 to 26 requires 5 min at -78 °C. The alkoxycarbenium ion pool 26 thus obtained exhibited similar stability and reactivity to that obtained with the direct electrochemical method. The indirect cation pool method serves a powerful tool not only for mechanistic studies on highly reactive cations but also for rapid parallel synthesis. 

The electrochemical generation of fulleride anions can also be used to synthesize covalent organofullerene derivatives by quenching the anions with electrophiles. This was exemplified in the synthesis of dimethyldihydro[60]fuUerene, the simplest dialkyl derivative of [87]. For this purpose benzonitrile solutions of Cjq and tetra-tert-butylammonium perchlorate (TBACIO4) where exhaustively electroreduced in a dry-box to yield a dark red solution of Treatment of this solution with an... 

SCHEME 7. Synthesis of hydroperoxides from electrochemically generated superoxide and alkyl halides... 

The use of controlled potential electrolysis of fullerenes has thus far been used as a synthetic tool in two general ways. One method has involved the preparation of fullerene derivatives from the reaction of electrochemically generated anions of the pristine cages with electrophiles. The second method has involved an electrochemically induced retro-synthetic reaction of fullerene derivatives, which results in a number of different products, some of which have not been achieved by chemical synthesis. Both methods are described in the following, but special... 

Tremendous effects have been made in studying the possibilities for the electrochemical generation and regeneration of inorganic redox agents like Cr(VI) V(V), Mn(III) Ce(IV) , and Co(in) and their application in the oxidation of aromatics. These studies are mainly performed by means of three types of reactions side-chain oxidations to form benzaldehydes, side-chain oxidations to generate benzoic acids, and nuclear oxidations for the synthesis of quinones (Scheme 1). 

Already very early it was proposed to apply electrochemically generated and regenerated Mn(III) and Ce(IV) as oxygen carriers for the synthesis of benzal-... 

The indirect electrochemical generation of propylene oxide via propylene chloro- or bromohydrin using anodically generated hypochlorite or hypobromite has been studied very intensively. The reason is the lack of a technically useful process for the synthesis of propylene oxide by way of heterogeneous catalysis. The propylene halohydrins are saponified using the cathodically generated sodium hydroxide (Eqs. (42)-(47)) (Table 4. No. 12-15)... 

Electrochemical Generation of Fluorinated Active Species - a New Approach to the Synthesis of Organofluorine Compounds ... 

Recently, a general synthesis of a-formyloxycarbonyl compounds was reported. Yields ranging from 35-90% were achieved via electrochemical generation of enol carbonate cation radicals in DMF156. The cation radicals are trapped by the solvent, and the resulting formiminium ion is hydrolyzed during workup. The mechanism is shown in Scheme 62. 

Challenging applications, such as the synthesis of P-peptides [30] or examples of flash chemistry (like the reaction of electrochemically generated reactive cation pools [31]) have been successfully realized using microreactors. 

The reaction with a, -epoxy carbonyl compounds 12 leads to the corresponding reductive ring-opened products, -hydroxy carbonyl compounds 13, in good yields (Scheme 22). Electrochemically generated benzeneselenolate [21,22] and sodium phenylseleno(triethoxy)borate (1) [35, 36], have been applied for this type of reaction as a nucleophilic selenolate. In the latter case, the reaction mechanism was suggested as shown in Scheme 23 [36]. Reaction of 1 with 12 first produces the ring-opened adduct 14, which is then reacted with an excess amount of 1 to produce the final product 13. This method is important as a simple synthetic procedure to aldols and -hydroxy esters that are rather difficult to obtain by other methods. The reactions have been extended to the reduction of more functionalized a, -epoxy carbonyl compounds [37] and have been successfully applied for the synthesis of several natural products [38]. 

Another approach to the anthracycline antibiotics is exemplified by the synthesis of a-citromycinone (244) see Scheme 20 [57,58]. In this instance the electrochemically generated brominated quinone monoketal 240 was converted to the lithiated species 241. Its reaction with ketal 242, a rather remarkable synthon for the 1,4-dipole 243 [60,61], proceeded smoothly to afford, after sequential treatment with aqueous acid and boron tribromide, a 60% yield of a-citromycinone (244). 

RTILs in the double role of green solvents and parents of electrochemically generated intermediates (bases and catalysts) to trigger a prefixed reaction of synthesis must be evaluated. 

For microreactor synthesis using electrochemically generated reactive species, see Yoshida, J. (2005) Chem. Commun., 4509. 

Pathways (la) and (Id) are the most frequent routes employed for the electrochemical generation of radicals. The radicals can be used in homocoupling, heterocoupling and addition reactions. In some cases these reactions have to compete with further oxidation or reduction of the radicals (see Sections 2.6.3.5 and 2.6.4.3). Electrogenerated radical ions (lb), (le), (If), cations (Ic) and anions (Ig) have been very efficiently used in electroorganic synthesis, e.g. for cathodic hydrodimerization, anodic dehydrodimerization, anodic substitution, cathodic cleavage or ring closure reactions [2, 5, 6]. These conversions are not treated in this review. 

Inoue K, Ishikawa Y, Nishiyama S (2010) Synthesis of tetrahydropyrroloiminoquinone alkaloids based on electrochemically generated hypervalent iodine oxidative cyclization. Org Lett 12 436-439... 

Amano Y, Nishiyama S (2006) Oxidative synthesis of azacyclic derivatives through the nitrenium ion application of a hypervalent iodine species electrochemically generated from iodobenzene. Tetrahedron Lett 47 6505-6507... 

Electrochemical Gewald synthesis has been developed. Thus, when a mixture of powdered graphite and sulfur is used as the cathode at a working potential of about — 0.9 V in DMF, the nucleophilic is generated and reacts with a,j3-unsaturated nitriles (296) to give 2-aminothiophenes (297) yields of the products are sometimes better than those of the Gewald synthesis (Equation (51)) <92SR405>. 

The oxidation of alkenes has attracted interest over decades as a route for organic electro-synthesis. This has included attempts to cany out direct anodic oxidation to eliminate problems associated with the in situ use of electrochemically generated oxidants. A sparged packed bed electrode reactor (SPBER), with propylene oxidation separated from the generation of hydrogen was used... 

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