Electroreduction

The allylstannane 474 is prepared by the reaction of allylic acetates or phosphates with tributyltin chloride and Sml2[286,308] or electroreduction[309]. Bu-iSnAlEt2 prepared in situ is used for the preparation of the allylstannane 475. These reactions correspond to inversion of an allyl cation to an allyl anion[3l0. 311], The reaction has been applied to the reductive cyclization of the alkenyl bromide in 476 with the allylic acetate to yield 477[312]. Intramolecular coupling of the allylic acetate in 478 with aryl bromide proceeds using BuiSnAlEti (479) by in situ formation of the allylstannane 480 and its reaction with the aryl bromide via transmetallation. (Another mechanistic possibility is the formation of an arylstannane and its coupling with allylic... 

Apphcations of ultrasound to electrochemistry have also seen substantial recent progress. Beneficial effects of ultrasound on electroplating and on organic synthetic apphcations of organic electrochemistry (71) have been known for quite some time. More recent studies have focused on the underlying physical theory of enhanced mass transport near electrode surfaces (72,73). Another important appHcation for sonoelectrochemistry has been developed by J. Reisse and co-workers for the electroreductive synthesis of submicrometer powders of transition metals (74). 

Electroreductive coupling of ben2otrifluorides with sacrificial aluminum or magnesium anodes in the presence of acetone, carbon dioxide, or /V, /V-dimethylformamide provides a novel route to ArCF2-derivatives (310). 

Naphthaleneamine. 1-Naphthylamine or a-naphth5iamine/7i5 -i2- can be made from 1-nitronaphthalene by reduction with iron—dilute HCl, or by catalytic hydrogenation it is purified by distillation and the content of 2-naphthylamine can be reduced as low as 8—10 ppm. Electroreduction of 1-nitronaphthalene to 1-naphthylamine using titania—titanium composite electrode has been described (43). Photoinduced reduction of 1-nitronaphthalene on semiconductor (eg, anatase) particles produces 1-naphthylamine in 77% yield (44). 1-Naphthylamine/7J4-J2-. can also be prepared by treating 1-naphthol with NH in the presence of a catalyst at elevated temperature. The sanitary working conditions are improved by gas-phase reaction at... 

A.sahi Chemical EHD Processes. In the late 1960s, Asahi Chemical Industries in Japan developed an alternative electrolyte system for the electroreductive coupling of acrylonitrile. The catholyte in the Asahi divided cell process consisted of an emulsion of acrylonitrile and electrolysis products in a 10% aqueous solution of tetraethyl ammonium sulfate. The concentration of acrylonitrile in the aqueous phase for the original Monsanto process was 15—20 wt %, but the Asahi process uses only about 2 wt %. Asahi claims simpler separation and purification of the adiponitrile from the catholyte. A cation-exchange membrane is employed with dilute sulfuric acid in the anode compartment. The cathode is lead containing 6% antimony, and the anode is the same alloy but also contains 0.7% silver (45). The current efficiency is of 88—89%, with an adiponitrile selectivity of 91%. This process, started by Asahi in 1971, at Nobeoka City, Japan, is also operated by the RhcJ)ne Poulenc subsidiary, Rhodia, in Bra2il under Hcense from Asahi. 

In order to prepare thin fdms of (SN) on plastic or metal surfaces, several processing techniques have been investigated, e.g., the electroreduction of [SsNs]" salts. Powdered (SN) is prepared by the reaction of (NSC1)3 with trimethylsilyl azide in acetonitrile/ The sublimation of (SN) at 135°C and at pressure of 3 x 10 Torr. produces a gas-phase species, probably the cyclic [SsNs] radical, that reforms the polymer as epitaxial fibres upon condensation/... 

The electroreductive cyclization of the furanone 118 (R = -(CH2)4CH=CH— COOMe Scheme 36) using a mercury pool cathode, a platinum anode, a saturated calomel reference electrode, and a degassed solution of dry CH3CN containing -Bu4NBr as the electrolyte, gave the spirocyclic lactones 119 and 120 in a ratio 1.0 1.1 (Scheme 37)(91T383). 

Electroreductions of 2//-thiopyrans 13a and 13b each afforded an equimolar mixture of isomeric dihydrothiopyrans 14a and 14b (Scheme 4) (97MI2). Although the products were not separated, no 13a 13b or 14a 14b interconversion was... 

In this work the possibility of the existence of 1,2-dihydro isomer with the core structure 42 was not considered. Recently, however, it was shown that 1,2-dihydropyridazines could be prepared by careful electroreduction of the corresponding pyridazines, and that their stability depends significantly on the ring substitutions. Thus, dimethyl l,2-dihydropyridazine-3,6-dicarboxylate 43a (R = H) is reasonably stable and rearranges into the 1,4-dihydro tautomer 43b only at a more negative potential, while the tautomerization in its tetrasubstituted analog 43a (R = COOMe) occurs more readily (Scheme 14) [00TL647]. 

Electrophotography, 6,122 Electroplating addition reagents, 6, 5 coordination compounds, 6,4 Electroreduction plutonium(IV)... 

Metal-free poly-4-vinyl-4 -methyl-2,2 -bipyridine films on electrodes have been prepared by the electroreductive polymerization of a Rh complex and subsequent leaching of the metal by a strong complexand. The films can incorporate a variety of transition metals... 

Among the peculiar features of 2-bromoamides there are the following i) possibility of substitution at the tertiary C-Br (RCO2H, RR NH, or a saccharide, as the nucleophiles) ii) chiral stability and stereochemical control at the secondary C-Br atom (RR NH, ROH or a saccharide as the nucleophiles) iii) the presence of bromine allows cyclic voltammetry and electroreduction at controlled potential both of starting compounds and relevant intermediates iv) the Ca polarity can be reversed upon electroreduction, and the resulting Ca enolate forms a C-C bond (CO2 as the electrophile). 

The electrochemical results suggested to explore the possibility of creating a C-C bond between the electrogenerated a-carbanion fi and carbon nucleophiles. Results of practical importance have hitherto been obtained upon electroreduction of 2-bromoisobutyramides in acetonitrile at Hg or Pt cathodes, in the presence of carbon dioxide and an alkylating agent. The enolate-amide fi undergoes quantitative carboxy-alkylation, to yield ester amides of 2,2-dimethylmalonic acid (ref. 16). 

Electrochemical methods allowed to shed light on the different reaction mechanisms, both in homogeneous and heterogeneous (Ag20 promoted) systems. Furthermore, electroreduction reverses the C-Br bond polarity, allowing the formation of a C-C bond with an electrophile (f.ex. CO2). 

In a similar type of process, imines have been dimerized to give 1,2-diamines, by a number of procedures, including treatment with TiCLj—In/aqueous EtOH, Zn/aqueous NaOH, Cp2VCl2/Zn/PhMe2SiCl, with Sml2, and I for silylated imines) NbCl4(thf)2. When electroreduction was used, it was even... 

In another example of a radical process at the pyrrole C-2 position, it has been reported that reductive radical cycloaddition of l-(2-iodoethyl)pyrrole and activated olefins, or l-(oj-iodo-alkyl)pyrroles 34 lead to cycloalkano[a]pyrroles 35 via electroreduction of the iodides using a nickel(II) complex as an electron transfer catalyst <96CPB2020>. Thus, it appears the radical chemistry of pyrroles portends to be a fertile area of research in the immediate or near future. 

Ni(cyclam)](C104)2-catalyzed electroreduction of olefmic bromide 106 produced piperidone 107 in moderate yield <96JOC(61)677>. 

Electroreduction of the cationic Rh(IlI) complex [Rh(Por)(MeNFl2)2l in CH2CI2 followed by reaction with alkyl halides has been utilized to form a-alkyl products. The reaction scheme proposed for this reaction was one-electron reduction of Rh(lll) to form Rh(Por)-. This can either dimerize or attack the carbon atom of the alkyl halide RCH2X, the latter step involving elimination of either X- or 2t7.2.ix reactions of Co(ll) and Fe(II) porphyrins M(Por) with... 

In this section primarily reductions of aldehydes, ketones, and esters with sodium, lithium, and potassium in the presence of TCS 14 are discussed closely related reductions with metals such as Zn, Mg, Mn, Sm, Ti, etc., in the presence of TCS 14 are described in Section 13.2. Treatment of ethyl isobutyrate with sodium in the presence of TCS 14 in toluene affords the O-silylated Riihlmann-acyloin-condensation product 1915, which can be readily desilylated to the free acyloin 1916 [119]. Further reactions of methyl or ethyl 1,2- or 1,4-dicarboxylates are discussed elsewhere [120-122]. The same reaction with trimethylsilyl isobutyrate affords the C,0-silylated alcohol 1917, in 72% yield, which is desilylated to 1918 [123] (Scheme 12.34). Likewise, reduction of the diesters 1919 affords the cyclized O-silylated acyloin products 1920 in high yields, which give on saponification the acyloins 1921 [119]. Whereas electroreduction on a Mg-electrode in the presence of MesSiCl 14 converts esters such as ethyl cyclohexane-carboxylate via 1922 and subsequent saponification into acyloins such as 1923 [124], electroreduction of esters such as ethyl cyclohexylcarboxylate using a Mg-electrode without Me3SiCl 14 yields 1,2-ketones such as 1924 [125] (Scheme 12.34). 

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