Reaction with arylthallium compounds

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... 

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. 

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... 

Reaction of the arylthallium(III) compound with an electrophile affords an intermediate cationic arylthallium derivative (90), which then undergoes elimination of the thallium moiety. Examples of this type of reactivity are the reactions of arylthallium(III) compounds with bromine affording aryl bromide, with iodine affording aryl iodide, 1 8-110 or with nitrosyl chloride giving nitroso-benzene. l ... 

The reaction of arylthallium(III) compounds (83) with potassium bromide gave the dibromoaryl thallium derivatives (100), which decomposed rapidly either on storage or on gentle heating into aryl... 

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... 

The reaction of arylthallium(III) compounds with potassium cyanide affords stable arylthallium(IV) cyanide complexes, l l which can only decompose upon photolytic activation, indicative of a radical mechanism. 1 5 Decomposition of these complexes by heating does not afford the aryl cyanide in efficient yields. Pyrolysis afforded only trace amounts of the cyanide, l Heating a water solution of... 

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. 

Similarly to the reaction of arylthallium(III) compounds, the reaction of potassium iodide with (121), the product of oxythallation of alkenes, afforded the derived oxy-iodination product (123) in good yields through the alkylthallium diiodide intermediate (122). ... 

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... 

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" ... 

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. ... 

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. 

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

The formation of iodobenzene by treatment of phenylthallium(III) compounds with potassium iodide was reported, without experimental details, by Challenger et al in the 1930 s. 2,113 jhe potential and synthetic interest of this iododethallation reaction was extensively studied by McKillop and Taylor in the early 1970 s.8 7-89 Although arylthallium(III) compounds prepared by reaction of the arenes with thallium tris(trifluoroacetate) (84) can be isolated, they can also be directly converted into aryl iodides by addition of aqueous potassium iodide to the thallation reaction mixture. An intermediate arylthallium(III) diiodide (91) was suggested to be formed and to decompose intramolecularly to lead to the aryl iodide. ... 

Treatment of arylthallium(III) compounds with metal nitrites in trifluoroacetic acid affords the corresponding nitrosoarenes, which are oxidised to the nitroarenes. The reaction was suggested to occur by electrophilic attack of NO+ on the carbon-thallium bond. l ... 

Arylthallium bis(trifluoroacetate)s are converted by successive treatment with KF and BF3 into aryl fluorides.Thallium(iii) nitrate (TTN) readily oxidizes dialkyl sulphides and selenides to the corresponding sulphoxides or selenoxides, and 2-(alkylthio)-l-arylethanones (37) into compounds (38) in methanolic solution.In a modification of the TTN oxidative conversion of aryl alkyl ketones into arylacetic acids, enol ethers derived from the ketones are used instead of the ketones themselves. This reduces the formation of side products. Cyclic aralkyl ketones (39) may be ring-expanded and alkylated to give compounds (40) via treatment of their Wittig-derived alkenes with TTN/ an extrapolation of the basic reaction discovered previously. 

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). ... 

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