Alkenes oxythallation

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]. 

In some cases, ketones are obtained in high yields by the oxymercuration or oxythallation of alkenes, followed by treatment with PdCb in aqueous THF. 

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). 

When the reaction is applied to alkenes bearing a nucleophile in a suitable position, oxythallation occurs intramolecularly to furnish cyclic products via the corresponding oxythallated adducts (B) (Scheme 9.13). Several useful examples are chosen from many reported reactions (Schemes 9.14 [18], 9.15 [19], 9.16 [20] and 9.17 ]21]). 

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. 

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). ... 

Measurements of 2o /205 j ijj spin-spin couplings for the organothallium compounds formed in oxythallation reactions provides the first direct evidence for trans addition in the oxythallation of acyclic olefins. Products from the reactions of styrene, u-alkylphenols, propylene, and oct-l-ene were studied. The rate constants for the oxythallation of alkenes shows a reasonable correlation with the first ionization energy of the alkenes. Inductive effects were found to be most important in the oxythallation of RCH=CH2 and R R C=CHa alkenes. ... 

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