Arylthallium ditrifluoroacetates

It has been reported previously (147), and will be discussed in detail later, that arylthallium ditrifluoroacetates may be converted in good yield to phenols by treatment with lead tetraacetate in trifluoroacetic acid solution followed by addition of 1 mole of triphenylphosphine. The immediate product of the above reaction, an aryl trifluoroacetate, is hydrolyzed... 

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. 

It has been reported that photolysis of arylthallium ditrifluoroacetates in benzene suspension results in replacement of the thallium substituent by a phenyl group (i.e., phenylation) to give unsymmetrical biphenyls in excellent yield (152) this reaction is summarized in Section III,C. An analogous reaction occurs upon photolysis of diarylthallium trifluoroacetates in benzene suspension unsymmetrical biphenyls are formed in comparable yield (40-95%). The mechanism of this conversion is undoubtedly similar to that... 

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. 

A further demonstration of the efficacy of photolysis of ArTlXj compounds is the recently described synthesis of aromatic nitriles by photolysis of solutions of arylthallium ditrifluoroacetates in aqueous potassium cyanide... 

Thiophenols may also be synthesized via the photochemical decomposition route 156). Thus, treatment of arylthallium ditrifluoroacetates with an aqueous solution of potassium Ar,AT-dimethyldithiocarbamate led in quantitative yields to the formation of the corresponding aryl AT,A -dimethyl-dithiocarbamates. Subsequent photolysis in aqueous acetone then led to disulfides which were reduced to the thiophenols. A small amount of aryldithiocarbamate formed as a by-product in the photolysis was converted to the same thiophenol by hydrolysis. The overall reaction sequence is illustrated in Eq. (18). 

Thallation-carbonylation.2 Catalytic amounts of PdCl2 permit carbonylation of arylthallium ditrifluoroacetates (3, 287) at room temperature and atmospheric pressure. This sequence permits synthesis of esters, lactones, anhydrides, and various heterocycles. 

Aryl diazonium tetrafluoroborates, 298 Aryllithiums, 76 Aryl methyl ethers, 50 1-Axylnaphthalide ligans, 49-50 N-Arylsulfonyl-2-phenylaziridines, 169 1-Aryltetralones, 370 Arylthallium ditrifluoroacetates, 300 Avenaciolide, 305, 306 Azacyclanones, 398 Azetidines, 169 Azetidinone, 192 Azides, 48... 

Aromatic iodides (3,287). The definitive paper on the synthesis of aromatic iodides by the reaction of arylthallium ditrifluoroacetates with potassium iodide has been published.1 Four procedures have been developed. 1) Thallation is carried out as usual and then an aqueous solution of potassium iodide is added directly. 2) The intermediate arylthallium ditrifluoroacetate is isolated and then treated with potassium iodide. 3) For acid-sensitive substrates solid TTFA in acetonitrile is used for thallation. 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. 

Treatment of the arylthallium ditrifluoroacetates with an excess of aqueous potassium cyanide leads to the formation of complex ions [ArTl(CN)3] K+. On photolysis in the presence of excess potassium cyanide these are converted into the nitriles by a radical reaction. Yields are 35-80%. 

Unsymmetrical biphenyls,4 Arylthallium ditrifluoroacetates are phenylated in high yield when irradiated5 in benzene. The reaction is useful because the replacement of thallium by the phenyl group occurs cleanly. The method is particularly... 

Aryldiazonium tetrahaloborates, 16 Aryl methyl ethers, 115 Arylthallium ditrifluoroacetates, 287-288 Aryl trifluoroacetates, 287 Asparagine, 102 Aspidosperma alkaloids, 196 (+)-Aspidospermidine, 196 Asymmetric synthesis, 199—200 Aurantiocladin, 7 Autoxidation, 245... 

Synthesis of aromatic iodides. Treatment of an arylthallium ditrifluoroacetate with aqueous potassium iodide at room temperature results in rapid precipitation of thallium iodide and formation of the corresponding aromatic iodide in high yield 2... 

Synthesis of phenols and aromatic nitriles.3 In a new phenol synthesis, an aromatic hydrocarbon is first thallated with the reagent in trifluoroacetic acid to give an arylthallium ditrifluoroacetate (which can be isolated) and then oxidized with lead tetraacetate in the presence of 1 equivalent of triphenylphosphine. The resulting aryl trifluoroacetate is then hydrolyzed with dilute base. The triphenyl-... 

---