Aryllead triacetate

Over the past 40 years aryllead triacetates have been applied as both N- and C-arylating reagents and cross-coupling partners in organic synthesis. The synthesis and application of aryllead triacetate reagents is a key aspect of this section of this PhD project and an overview of this key class of arylaling reagents will now be discussed. 

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The procedure described here serves to illustrate a new, general method for effecting the < -arylation of g-dicarbonyl compounds by means of an aryllead triacetate under very mild conditions. Although the first synthesis of an aryllead triacetate was reported relatively recently, a wide range of these compounds can now be readily prepared. The most direct route to these compounds is plumbation of an aromatic compound with lead tetraacetate, and in the procedure reported here p-methoxyphenyllead triacetate has been prepared in this way. It may also be obtained by reaction of the diarylmercury with lead tetraacetate, a longer, but more general method of synthesis of aryllead triacetates. 

Aryllead triacetates are also good reagents for aryladon of stabilized carbanions, including le anion of nltro ilkanes fEq 5 70 As a related reaction, ct-vinyladon"° or ct-acetyladon" f nitre compounds is possible using vinyllead triacetates or ilky nyllead tr... 

Aryl iodides and fluorides can be prepared from arylthallium bis(trifluor-oacetates) (see 12-21), indirectly achieving the conversions ArH —> Arl and ArH ArF. The bis(trifluoroacetates) react with KI to give Arl in high yields. Aryllead triacetates, ArPb(OAc)3, can be converted to aryl fluorides by treatment with BFs-etherate. ... 

The use of an optically active R BCl2 (where R is a substituent boaring a chiral center) gave secondary amines of essentially 100% optical purity. Aryllead triacetates, ArPb(OAc)3, give secondary amines, ArNHAr, when treated with primary aromatic amines, Ar NH2, and Cu(OAc)2- ... 

Aryllead triacetates are also good reagents for arylation of stabilized carbanions, including... 

The electrochemical reduction of aryllead triacetates was smdied by Chobert and Devaud82, as a re-examination of some previous work83 to detect the role of intermediates such as [ArPb(OAc)2]V The reductions were carried out by polarography in acetic acid or acidic alcohol solutions and show three diffusion controlled waves. The first step involves a single electron transfer to produce a radical anion which dimerizes, arylates the electrode or hydrolyzes to phenol ... 

Alkyl-tin bonds can be cleaved with lead tetraacetate, the reactivity falling in the order Ar m Me > Et > Bu >> Pr1 (Equation (130)) and the reaction of ArSnBu3 provides a convenient route to the aryllead triacetates, ArPb(OAc)3.344... 

The reactions of the 5-oxazolanes 14 with aryllead triacetates are examples of the typical arylation of heterocycles by which products 15 are formed. After hydrolysis and decarboxylation, heterocyclic compounds 15 are converted to the arylglycines 16 in yields of 81-93% (Equation (5)).33... 

Only a few more recent examples of the numerous studies on N-arylations with aryllead triacetates will be discussed here. For earlier publications in this field, the interested reader is referred to the pioneering arylations of aliphatic and aromatic amines by Barton s group, 8 as well as the comprehensive review article by Elliott and... 

Imines, sulfonamides, and hydantoins undergo copper-catalyzed arylation by aryllead triacetates in the same manner. In many cases, prior conversion of the N-H bonds into the corresponding sodium salts is recommended.43 44... 

Stille-type reactions can be performed under analogous conditions. For example, reactions of aryllead triacetates with arylboronic acids give rise to the respective biaryls in yields of around 75%.46... 

Reactions of aryllead triacetates with olefins (Heck-type reactions) proceed similarly but do not require Cul as co-catalyst. From the numerous reported reactions, that of phenyllead triacetate with 2,3-dihydrofuran is mentioned as a typical example. This affords the C-C coupling product 27 in 68% yield, together with 10% of the homocoupling product (Equation (ll)).47... 

Donnelly, D.M.X., Fitzpatrick, B.M., and Finet, J-P., Aryllead triacetates as synthons for the synthesis of biflavonoids. Part 1. Synthesis and reactivity of a flavonyllead triacetate, J. Chem. 

Aryllead triacetates a-arylate ketones highly selectively, working well for tertiary a-carbons, or secondary ones activated by a phenyl group,146 thus favouring arylation of positions that are typically already crowded, making the reaction very useful synthetically. 

Arylation of nitroalkanes. An aryllead triacetate arylates nitroalkanes and the nitronate salts at the a-position in DMSO in 60-75% yield.5... 

Arylalkanoic acids, 109 Arylanthranilamides, 367 4-Arylbutanoic acids, 321 Aryl diazoalkanes. 565 Aryldiazonium chlorides. 495 Aryllead triacetates, 31-32... 

Aryllead triacetates, ArPb(OCOCH3)3. These reagents can be obtained by reaction of an aryl compound with lead tetraacetate in dichloroacetic acid or trichloroacetic acid (the reaction is slow in acetic acid).1 Another general route is reaction of a iliaiyltnercury with lead tetraacetate.2,3... 

Amine arylation.1 This reaction can be effected at 25° with aryllead triacetates in the presence of Cu(OAc)2. Yields are high in reactions of anilines substituted by electron-releasing groups. Only primary linear aliphatic amines are arylated, albeit in poor yield. 

N-Arylation of various azoles (or their anions) was readily accomplished with p-tolyllead triacetate in the presence of copper(II)acetate [95JOC5678] however, die applicability of this procedure to other aryllead triacetates was not discussed. Solvent-dependent palladium-mediated allylations [95JHC1325] and Mitsunobu-based asymmetric alkylations [95JOC2008] of imidazoles and benzimidazoles have also been reported. 

Mixed arylation of bifunctional substrates, such as those containing two /3-ketoester groups in their structure can be made. This possibility was used to synthesize unsymmetrically substituted compounds containing two different aryl groups (Scheme 2). One-pot treatment of the dibenzyl 3,7-dioxobicyclo [3.3.0]-octane-2,6-dicarboxylate 6 with a mixture of two aryllead triacetates 7 and 8 afforded a mixture of the unsymmetrical diaryl derivative 10 with the two symmetrical diaryl compounds 9 and 11. When the arylation was performed with 1.1 equiv. of each aryllead reagents 7 and 8, a mixture of 9-11 in a ratio 0.46 1 0.72 was obtained. This ratio became 0.43 1 0.49, when 0.86 equiv. of 7 and 1.33 equiv. of 8 were used. This compound 10, isolated in a 33% yield, was eventually elaborated to complete a total synthesis of ( ) methyl piperitol.25... 

Hydroxycoumarins are cyclic, completely enolized /3-ketoesters. In their reactions with aryllead triacetates, they behave more like phenols than like /3-ketoesters bearing two a-hydrogens. Indeed monoarylation took place... 

The nature of the acyl ligand of the aryllead triacetate has no influence on the diastereomeric ratio (Equation (19)). It is interesting to note that, when the sodium salt of the /3-ketoesters was treated with p-MeOC6H4Pb(OCOR)3 at 25 °G, the arylated product was obtained in 60% yield with a 9 1 diastereomeric ratio.49... 

The reaction of 4-(methoxycarbonyl)chroman-3-one with aryllead triacetates afforded the expected 4-aryl derivatives 28 in moderate to good yields (see Section 9.09.2.1, Equation (6)). However, with longer reaction times the products of bis-arylation 29 were obtained in moderate yields (Equation (35)). Unsymmetrically disubstituted chro-man-3-ones were obtained by treatment of the pure product of monoarylation, the 4-monosubstituted compound, with a second aryllead triacetate (Equation (36)). 

In their early studies, Pinhey et al. showed that, when the reaction of a phenol with an aryllead triacetate is performed in the presence of pyridine, only the C-arylated dienones 35 and 36 are formed in a nearly quantitative yield (90% ortho para ratio of 4 1) (Equation (38)). Under their classical conditions (phenol organolead triacetate base in a ratio 1 1 3), the reaction of methylated phenols only proceeded in high yield when both ortho-positions are substituted. There is a preference for attack ipso to a methoxyl group compared to a methyl group.45 453... 

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