Alkynes oxythallation

Another synthetic route to monoorganothallium compounds is the reaction of aryl or vinyl derivatives of mercury(II) or tin(IV) with TIX3 (X = halide, carboxy-late). Monoalkylthallium derivatives are intermediates m the oxidation of alkenes and alkynes by thallium(III) salts (oxythallation) (see Section 7). 

Although the examples are less compared than for alkenes, cyclopropanes and allenes are also oxidized by Tl(lll) salts via oxythallation (Schemes 9.18 [22], 9.19 [23], and 9.20 [24]). Alkynes react with TTN to give a variety of oxidation products such as diketones and carboxylic acids via oxythallation, the products depending on the substitution pattern on the alkynes (Schemes 9.21-9.23 [25]). 

Alkyl and vinylthallium(in) compounds are mostly obtained by oxythallation of alkenes or alkynes. They can also be formed by transmetallation between, for example, an organomercury compound and thallium(ni) salts. Various types of reactivity have been observed for these compounds. The evolution of the carbon-thallium bond into functionalised products usually takes place homolytically or heterolytically. The ligand coupling process has also been evoked to rationalize a small number of transformations. 

The reaction of terminal acetylenes with thallium(iii) acetate in chloroform gives a new type of oxythallation adduct (132). This was claimed to be one of the intermediates in the thallium(in) salt-catalysed conversion of acetylenes to ketones. Reduction of the adduct with borohydride gave the vinyl acetate (133) (Scheme 74). Aliphatic and aromatic alkynes, when treated with tetrachloroauric acid in methanol give ketones in better yield than obtained in the mercury(n) catalysed reaction. ... 

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