Thallation alkenes

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]. 

Thallated aziridines can be opened with TPAA in high yield, giving trans-ando esters (Scheme 61). A similar sequence with cyclohexene yields rrSteroid alkenes yield azido alcdiols with chromyl azide."... 

The direct introduction of the two-carbon unit of the heterocyclic ring, ortho to an existing carboxylic acid (ester) can be achieved in two ways ort/io-bromobenzoates can be coupled with 7r-(2-methoxyallyl)nickel bromide for the introduction of acetonyl, or thallation of benzoic acids, ortho to the carboxyl, can be followed by palladium-catalysed coupling with alkenes. Benzoates carrying an ortho acetylenic substituent can be ring closed using mercuric acetate, as shown below." ... 

Larock reported direct thallation as one alternative, demonstrating successful intermolecular trapping with alkenes, alkenyl halides, allenes, and vinylcyclopro-panes (Scheme 2.32) [76]. 

Electrophilic mercuration and thallation of aromatic compounds, alkenes and alkynes are considered in Chapter 3. 

Benzoic acid and substituted benzoic acids are readily thallated by thallium(III) trifluoroacetate. Subsequent reaction with palladium chloride and simple alkenes, allylic or vinyl halides, or vinyl esters result in the formation of isocoumarins eg ... 

Thallium compounds, especially in the form of thallium(i) and thallium(iii) salts, are ahle to mediate a great numbers of reactions, including oxidative rearrangements of ketones and alkenes, cyclisation reactions, a-oxidation of ketones, aromatic thallations, oxidative couplings, oxidations of phenols and nitrogen compounds and disulfide bond formation, thus, constituting a useful tool in synthetic organic chemistry. However, their application as catalysts has been less explored and there are only a few successful examples reported in the literature. 

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