Arylthallium compounds reactions

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]. 

Thallium(III), particularly as the trifluoroacetate salt, is also a reactive electrophilic metallating species, and a variety of synthetic schemes based on arylthallium intermediates have been devised.75 Arylthallium compounds are converted to chlorides or bromides by reaction with the appropriate cupric halide.76 Reaction with potassium iodide gives aryl iodides.77 Fluorides are prepared by successive treatment with potassium fluoride and boron trifluoride.78 Procedures for converting arylthallium compounds to nitriles and phenols have also been described.79... 

The direct carbonylation of arylthallium compounds usually requires high temperatures and pressures, but in the presence of palladium catalysts the reaction proceeds in high yield at room temperature and atmospheric pressure (equation 47). ... 

When the reaction of the arylthallium compound ArTlX2 with the nucleophile Nu" leads to a too stable intermediate AtT1Nu2, competing protonolysis may become predominant. This is circumvented by using copper salts, which favours the removal of a ligand from the thallium metal. According to Uemura et al, this reaction leads to substitution in a concerted process by reductive displacement of... 

The aryl chlorides and aryl bromides are easily prepared by treatment of the arylthallium(III) bis(trifluoroacetates) with the corresponding copper(I) or copper(II) halides. The best yields were obtained with the copper(II) halides in dioxane under reflux. 2 These reactions have been successfully applied by Somei et al to the synthesis of indole derivatives by reaction of the arylthallium compounds with copper(II) salts in DMF. 127,133,134... 

However, aryl cyanides are more directly obtained by reaction of the arylthallium compound with various copper cyanides. Different reaction systems have been reported, such as CuCN or Cu(CN)2 in acetonitrile or pyridine with arylthallium acetate perchlorate monohydrates. Other systems involve the arylthallium bistrifluoroacetate with CuCN in acetonitrileor in DMF. With these systems, a number of aryl cyanides (114), heteroaryl cyanides (115) 25,126 indolyl cyanides (116) and (117)124 148 have been prepared. 

With other halides, the reaction is conveniently performed by treatment of the alkylthdlium compound with the appropriate copper(I) halide. The product yield is increased by the addition of potassium halide.jhe thallium moiety can also be replaced by other groups, similarly to the arylthallium compounds. The cyano group is introduced by reaction with copper(I) cyanide.lSi the thiocyano group by reaction with potassium and/or copper thiocyanate>5i.i52 and the selenocyano group by treatment with potassium selenocyanate. 

Other monovinylthallium(ni) compounds such as (132), the product of oxythallation of acetylenes, react analogously to the arylthallium compounds. Halogenodethallation and pseudohalogeno-dethallation reactions result from the interaction of the oxyalkenylthallium compound with either potassium iodide or with the appropriate copper derivatives. 6... 

For examples of palladium-catalysed reactions involving arylthallium compounds, see ref. 90 and 91. 

The thallium is initially introduced into the position that is most reactive toward electrophiles, but the reaction is reversible, so that heating gives a mixture having a composition governed by the relative thermodynamic stability of the various possible isomers. In some cases, then, thallation followed by isomerization can lead to a product with an orientation different from that obtained by direct electrophilic substitution." The arylthallium compounds can also be converted to phenols via a procedure that involves oxidation and hydrolysis" ... 

Syntheses of dialkylthallium halides with bulky alkyl groups such as trimethyl-silylmethyl and neopentyl have been described, these compounds are dimeric. (Acyloxy)arylthallium compoimds have been prepared from organotin compounds, reactions (40), (41). ... 

The 1,1-dimetallic compounds, R2C(SnMe3)ZnBr, were oxidized by dry air at —10 to 0°C in the presence of Me3SiCl to give aldehydes or ketones, R2C=0. In a related indirect method, arylthallium bis(trifluoroacetates) (prepared by 12-21) can be converted to phenols by treatment with lead tetraacetate followed by triphenylphosphine, and then dilute NaOH. Diarylthallium trifluoroacetates undergo the same reaction. ... 

This phenol synthesis complements the analogous reaction (see below) from arylthallium ditrifluoroacetates (147). Although yields are only moderate, the procedure represents a viable conversion of aryl Grignard reagents to phenols. It is a practical method, however, only when the diarylthallium trifluoroacetate precursor is formed via the Grignard route the alternative synthesis via symmetrization of arylthallium ditrifluoroacetates is obviously circuitous, since the latter compounds may be converted directly to phenols. 

For example, photolysis of a suspension of an arylthallium ditrifluoro-acetate in benzene results in the formation of unsymmetrical biphenyls in high yield (80-90%) and in a high state of purity 152). The results are in full agreement with a free radical pathway which, as suggested above, is initiated by a photochemically induced homolysis of the aryl carbon-thallium bond. Capture of the resulting aryl radical by benzene would lead to the observed unsymmetrical biphenyl, while spontaneous disproportionation of the initially formed Tl(II) species to thallium(I) trifluoroacetate and trifluoroacetoxy radicals, followed by reaction of the latter with aryl radicals, accounts for the very small amounts of aryl trifluoroacetates formed as by-products. This route to unsymmetrical biphenyls thus complements the well-known Wolf and Kharasch procedure involving photolysis of aromatic iodides 171). Since the most versatile route to the latter compounds involves again the intermediacy of arylthallium ditrifluoroacetates (treatment with aqueous potassium iodide) 91), these latter compounds now occupy a central role in controlled biphenyl synthesis. 

Aromatic iodides (3,287). The definitive paper on the synthesis of aromatic iodides by the reaction of arylthallium dilrifluoroacetates with potassium iodide has been published. Four procedures have been developed. I) Thallalion is carried out as usual and then an aqueous solution of potassium iodide is added directly. 2) The intermediate arylthallium ditrifluoroacctatc is isolated and then treated with potassium iodide. 3) For acid-sensitive. substrates solid TTFA in acetonitrile is used for thallalion. 4)These methods are unsuccessful with highly reactive compounds such as naphthalene and diphenyl. In such cases molecular iodine is used as the electrophilic reagent and TTFA is used as oxidant for the hydrogen iodide formed in the reaction. 

The arylthallium(ni) compounds can be easily converted into a variety of substituted aromatic derivatives. This conversion can be performed by three major reaction types, two of them being either typical ligand coupling or ligand exchange reactions involving the presence of a copper species, either as a reagent or as a catalyst. 

Reaction of the arylthallium(IIl) compound with a nucleophile affords a new intermediate arylthallium derivative (89), which then undergoes ligand coupling. ... 

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