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With aryllead tricarboxylates

The reaction of arenes with aryllead tricarboxylates performed in trifluoroacetic acid, affording biarenes, takes place via a cationic 7t-complex.162 Since azulenes form 7r-donor/acceptor complexes with various 7r-acids, the arylation of 4,6,8-trimethylazulene 108 was attempted with />-methoxyphenyllead triacetate 1 (Equation (135)).163 Only one isomer of 1-arylazulene 109 was formed although in a modest 27% isolated yield. Based on recovered unreacted azulene, the effective yield was 43%. A dimer 110, 3,3 -dianisyl-l,l -biazulene (4% yield), was suggested to result from the one-electron oxidation of the intermediate 4-methoxyphenyl cation in the 7t-complex. [Pg.421]

In parallel to their work on the arylation reactions with aryllead tricarboxylates, Pinhey et al have examined, although in much less detail, the reactivity of vinyllead tricarboxylates as vinylation reagents for soft nucleophiles. 9,11... [Pg.232]

Aromatic compounds can also be arylated by aryllead tricarboxylates. Best yields ( 70-85%) are obtained when the substrate contains alkyl groups an electrophilic mechanism is likely. Phenols are phenylated ortho to the OH group (and enols are a phenylated) by triphenylbismuth dichloride or by certain other Bi(V) reagents. O-Phenylation is a possible side reaction. As with the aryllead tricarboxylate reactions, a free-radical mechanism is unlikely. ... [Pg.932]

C-Arylation. These aryllead tricarboxylates are useful for arylation of ji-illkrloncs and /l-keto esters. Yields are high with substrates containing only one acidic hydrogen. [Pg.358]

T -Keto esters and aryllead tricarboxylates react in chloroform in the presence of pyridine to give a-arylated products (Scheme 13.3) [32]. A variety of substrates can be used in this arylation reaction an exception is keto esters with two a-hydrogen atoms. [Pg.724]

Aryllead tricarboxylates have been shown to react in trifluoroacetic acid with a range of aromatic compounds to give biaryls [31c]. With aromatic compounds that are more electron-rich than toluene the yields are generally good and the method is a useful synthesis of unsymmetrical biaryls (Scheme 13.18). It has been reported that a cationic intermediate generated from aryllead tricarboxylates was probably involved. [Pg.729]

Lead tetraacetate reacts with arenes to lead either to aromatic nucleus substitution or to substitution on the benzylic position of the side chain. Substitution on the nucleus involves electrophilic attack of (AcO)3Pb " to give aryllead tricarboxylates. Subsequently, these aryl species react with acid to afford eventually the corresponding aryl esters. ... [Pg.214]

Direct electrophilic plumbation of aromatic compounds can be used to prepare a small range of aryllead tricarboxylates.limited to substrates which are more electron rich than halobenzenes. Plumbation of halobenzenes can be conveniently performed by treatment with lead tetraacetate in the presence of trichloroacetic or trifluoroacetic acid. For the plumbation of compounds of intermediate reactivity between the halobenzenes and 1,3-dimethoxybenzene, the use of haloacetic acid (mono-, di- or trichloroacetic acid) is required to optimize the yield of aryllead triacetates. For 1,3-dimethoxybenzene and the more electron-rich aromatics, the reaction can be suitably performed in acetic acid. [Pg.214]

In a series of outstanding papers, Pinhey et al have shown that aryllead tricarboxylates react with soft nucleophiles to afford C-arylation products. These aryllead derivatives behave as aryl cation equivalents in reactions which involve a ligand coupling mechanism (see section 7.5).9 2 ju most cases, the reactions proceed in chloroform at 40-60 C in the presence of pyridine as a base with a ratio of substrate to organolead derivative to pyridine of 1 1 3. The substrates which easily undergo C-arylation include phenols, p-dicarbonyl compounds and their vinylogues, a-cyanoesters, a-hetero-substituted ketones, enamines and nitroalkanes. A very limited number of non-carbon nucleophiles has also been reported to react. [Pg.216]

The mechanistic studies on the reactions of organolead tricarboxylates have been performed only with aryllead compounds. Due to the similarity in the reactivity between aryl, vinyl and alkynyl compounds, it is likely that a similar ligand coupling mechanism is operating in the three systems. In the case of the vinyl reagents, the intervention of an alkylidenecarbene has been excluded. [Pg.236]

Phenols are reacted with aryllead(IV) tricarboxylates in the presence of pyridine to give, predominantly the ortho-, but also considerable amount of para-arylated products [66]. In this fashion, 4-methoxyphenyllead(IV) triacetate (484), upon reaction with 2,6-dimethylphenol (487), gave orf/io-arylated product 488 in 75-90% yield where no ara-arylation occured. Fully substituted phenol 458 bearing very bulky ort/zo-substituents furnished the /zara-arylated compound 489, as sole product in 30% yield, in both cases with the loss of aromaticity of phenolic ring [66], Scheme 34. Anilines can be arylated with aryllead(IV) tricarboxylates at nitrogen in the presence of copper(II) acetate under very mild conditions. However, the C-arylation has been effected upon previous treatment of unprotected aniline with ferf-butylmagnesium... [Pg.269]

Although H NMR spectra of aryllead triacetates can be recorded in CDCI3 solution in the presence of tetra-methylsilane, cleavage of the methyl-silicon bond takes place when tetramethylsilane is treated with an aryllead(rv) tricarboxylate in trifluoroacetic acid.164 When the aryl moiety is substituted with an electron-withdrawing group, quantitative conversion of TMS was observed to give aryl(methyl)lead dicarboxylates 111, (Equation (136)) that were even isolated in two instances, although in modest to moderate yields 55% yield for the 4-fluorophenyl compound and 23% yield for the 4-trifluoroacetamidophenyl compound. [Pg.421]

Aryllead, vinyllead, and alk-l-ynyllead tricarboxylates behave as aryl, vinyl and alkynyl cation equivalents to react with a variety of nucleophiles, especially soft carbon nucleophiles such as T -dicarbonyl compounds, phenols, and nitroalkanes. In these reactions, unique regioselectivity is obtained in which there is a preference for the generation of quaternary carbon centers. This aspect of reactivity has been put to use in a number of natural product syntheses and can result in the formation of highly hindered structures. [Pg.724]

Aryllead(IV) tricarboxylates, ArPb(OOCR)3 [64], undergo the arylation of electron-rich arenes under very mild reaction conditions, usually at room temperature within a few hours, to produce the respective biaryls in moderate to high yields. The reaction involves the electrophilic aromatic substitution, and with mono-substituted benzenes, all three isomeric biaryls are obtained, with ortho-isomer as the major product [65-69], Scheme 30. [Pg.267]

The electrophilicity of lead in the aryllead(IV) tricarboxylates can be increased by replacing an acetate group with more electron-withdrawing substituents, e.g. trifluoroacetate. This can be accomplished by performing the reaction with ArPb(OAc)3 in more acidic acetic acid derivatives chloroacetic, dichloroacetic, trichloroacetic or trifluoroacetic acid. In this manner, phenyllead(IV) triacetate (482) reacts with anisole to give the isomeric methoxybiphenyls 91, 483, 78 in 32% yield [65], Scheme 31. [Pg.268]

The aryllead(IV) tricarboxylates can be prepared, among several possible routes, the most conveniently by the reaction of aryltri-n-butylstannanes [66], or arylboronic acids [67] with lead(IV) acetate in the presence of mercury(II) trifluoroacetate as the catalyst, or, in the case of electron-rich arenes such as polyalkoxybenzenes, by direct plumbylation with Pb(OAc)4 or its derivatives. Scheme 32. [Pg.268]

Beside haloacetic acids, this reaction can be strongly accelerated by aluminum chloride, trifluoroacetate, Al(OCOCF2CF3)3, or Al(OCOCF2CF2CF3)3 (8 eq. to ArPb(OAc)3). These fluorinated carboxylic salts were readily prepared by careful addition of the given acid to resublimed aluminum chloride [65]. These catalysts allow to perform the arylation with less reactive arenes such as toluene and benzene. The main side-reaction which occurs during the aryllead(IV) tricarboxylates involving reactions in trifluoroacetic acid is the protodeplumbylation. This reaction produces the parent arene by protonation of aryllead(IV) compound, and may become the major process [65,66]. [Pg.268]


See other pages where With aryllead tricarboxylates is mentioned: [Pg.870]    [Pg.664]    [Pg.907]    [Pg.234]    [Pg.217]    [Pg.509]    [Pg.870]    [Pg.664]    [Pg.907]    [Pg.234]    [Pg.217]    [Pg.509]    [Pg.169]    [Pg.719]    [Pg.382]    [Pg.391]    [Pg.215]    [Pg.270]    [Pg.270]    [Pg.312]    [Pg.270]    [Pg.270]    [Pg.312]    [Pg.163]    [Pg.15]    [Pg.722]    [Pg.287]    [Pg.287]   
See also in sourсe #XX -- [ Pg.932 ]




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Arenes with aryllead tricarboxylate

Aryllead tricarboxylates

Tricarboxylates

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