Aromatic compounds mercuration

Similarly to mercuration reactions, Pd(OAc)2 undergoes facile palladation of aromatic compounds. On the other hand, no reaction of aromatic compounds takes place with PdClj. PdCl2 reacts only in the presence of bases. The aro-... 

The transmetallation of various organometallic compounds (Hg, Tl, Sn, B, Si, etc.) with Pd(II) generates the reactive cr-aryl, alkenyl, and alkyl Pd compounds. These carbopalladation products can be used without isolation for further reactions. Pd(II) and Hg(II) salts have similar reactivity toward alkenes and aromatic compounds, but Hg(II) salts form stable mercuration products with alkenes and aromatic rings. The mercuration products are isolated and handled easily. On the other hand, the corresponding palladation products are too reactive to be isolated. The stable mercuration products can be used for various reactions based on facile transmetallation with Pd(II) salts to generate the very reactive palladation products 399 and 400 in rim[364,365]. 

Thallation of aromatic compounds with thallium tris(trifluoroacetate) proceeds more easily than mercuration. Transmetallation of organothallium compounds with Pd(II) is used for synthetic purposes. The reaction of alkenes with arylthallium compounds in the presence of Pd(Il) salt gives styrene derivatives (433). The reaction can be made catalytic by use of CuCl7[393,394], The aryla-tion of methyl vinyl ketone was carried out with the arylthallium compound 434[395]. The /9-alkoxythallium compound 435, obtained by oxythallation of styrene, is converted into acetophenone by the treatment with PdCh[396]. 

Whereas most reactions in the isoxazole series are undoubtedly those of electrophilic substitution, mercuration of isoxazoles, as well as some cases of mercuration of aromatic compounds, could be considered as homolytic reactions. However, the ready mercuration of... 

Mercuration of aromatic compounds can be accomplished with mercuric salts, most often Hg(OAc)2 ° to give ArHgOAc. This is ordinary electrophilic aromatic substitution and takes place by the arenium ion mechanism (p. 675). ° Aromatic compounds can also be converted to arylthallium bis(trifluoroacetates), ArTl(OOCCF3)2, by treatment with thallium(III) trifluoroacetate in trifluoroace-tic acid. ° These arylthallium compounds can be converted to phenols, aryl iodides or fluorides (12-28), aryl cyanides (12-31), aryl nitro compounds, or aryl esters (12-30). The mechanism of thallation appears to be complex, with electrophilic and electron-transfer mechanisms both taking place. 

Aromatic compounds react with mercuric salts to give arylmercury compounds.69 Mercuric acetate or mercuric trifluoroacetate are the usual reagents.70 The reaction shows substituent effects that are characteristic of electrophilic aromatic substitution.71 Mercuration is one of the few electrophilic aromatic substitutions in which proton loss from the a complex is rate determining. Mercuration of benzene shows an isotope effect kB/kD = 6,72 which indicates that the [Pg.1026]

Organomercuric compounds require nucleophilic assistance by soft iodide anions (cf. Section 9.6.3.2.2) for participation in cross-coupling reactions.158 The reaction is useful for aryl-aryl cross-coupling in those cases in which the organomercury species are obtained by direct mercuration of aromatic compounds (38).159... 

Aromatic compounds react with mercuric salts to give arylmercury compounds.63 The reaction shows substituent effects that are characteristic of electrophilic aromatic... 

The use of mercury has the merit of easy preparation of the aryl mercury compounds directly from the aromatic compound and an inorganic mercury salt, sometimes in complete regioselective manner. Preparation of the other metallated species generally involves more synthetic steps. An example of a radiofluorode-mercuration reaction (Scheme 29) is the synthesis of 6-p F]fluorometaraminol... 

Another electrophilic substitution reaction which has been examined for both a free ligand and its metal complexes is mercuration. The rate of mercuration of aromatic compounds can generally be given by a second order expression of the type ... 

Hundreds of reports have been published on electrophilic mercuration of a variety of aromatic compounds and uses of the resulting organomercurials in synthesis [5, 7-11]. Although in this chapter, we will not discuss synthetic applica-... 

Investigation of the use of acetyl hypofluorite in acetic acid for the regiocontrolled monofluorination of aromatic compounds starting from the corresponding mercurated derivatives has been carried out by Visser and coworkers29 (equation 19). On the basis of the observed fluorinated (7), acetoxylated (8) and methylated (9) products, a one-electron-transfer mechanism leading to an intermediate radical cation was proposed which might... 

The mercuration of aromatic compounds is of sufficiently general applicability to be classed with such processes as bromination, nitration, and sulfonation, and is particularly easily carried out in the case of phenols and amines. 

The carboxylates of indium and thallium are obtained by dissolving the oxides in acid. Acetate and trifluoroacetate salts are used extensively as reagents in organic synthesis. Certain other thallium compounds have been used also. The trifluoroacetate, T1(02CCF3)3, will directly thallate aromatic compounds to give arylthal-lium species, for example, C6H5T1(02CCF3)2 (cf. aromatic mercuration, Section 15-15) and oxidize arenes to biaryls. 

Iv) Aromatic Mercuration . Aromatic compounds are metallated by electrophilic Hg salts ... 

Aromatic Compounds.—Regioselective mercuration at position 2 was reported for oestradiyl 3-methyl ether 17-acetate with Hg(OAc)2-CH3CN and allowed the preparation of the 2-chloro-, -bromo-, and -iodo-derivatives.54 The major product (41 %) of the reaction between oestrone and Ph5Bi was reported to be the 2,4-... 

Thallium carboxylates, particularly the acetate and trifluoroacetate, which can be obtained by dissolution of the oxide in the acid, are extensively used in organic chemistry.14 Both Tl metal and Tl1 salts such as the acetylaceton-ate also have specific uses. One example is the use of thallium(m) acetate in controlled bromination of organic substances such as anisole. The trifluoroacetate will directly thallate (cf. aromatic mercuration, Section 18-9) aromatic compounds to give aryl thallium ditrifluoroacetates, e.g., C6H5Tl(OOCCF3)2. It also acts as an oxidant, inter alia converting para-substituted phenols into p-quinones. 

The simplest reaction is the mercuration reaction of aromatic compounds, which is commonly achieved by the action of mercuric acetate in methanol, e.g.,... 

There are two main processes for direct preparation of arylmercuric salts, namely, mercuration of aromatic compounds and the so-called Nesmeyanov reaction. 

Arylmercuric salts can be obtained with extraordinary ease by mercuration of aromatic compounds with mercury salts, the reaction involving direct replacement of hydrogen by mercury ... 

This shows that aromatic compounds are not all mercurated at the same speed in fact, amines, phenols, and aromatic ethers react especially readily, aromatic hydrocarbons such as benzene more slowly, and halo- and nitro-benzenes particularly slowly. 

Iodine can be introduced into aromatic compounds by the action of the free halogen, if the reaction is carried out under conditions which bring about the removal of the hydriodic acid formed as the result of the substitution. For example, iodo-benzene is formed when benzene is heated with iodine and nitric acid, mercuric oxide, iodic acid, or other substances which react with hydriodic acid. Reactions of this kind are used in a limited number of cases only as a means of preparing iodo derivatives. Free iodine also converts aniline, C6H5.NH2, into substitution-products. In this case the hydriodic acid formed is removed, as the result of the formation of a salt of aniline, C6H5NH2.HI. 

---