Organothallium couplings

The aryl-thallium bond is thus apparently capable of displacement either by electrophilic or by suitable nucleophilic reagents. Coupled with its propensity for homolytic cleavage (spontaneous in the case of ArTlIj compounds, and otherwise photochemically induced), ArTlXj compounds should be capable of reacting with a wide variety of reagents under a wide variety of conditions. Since the position of initial aromatic thallation can be controlled to a remarkable degree, the above reactions may be only representative of a remarkably versatile route to aromatic substitution reactions in which organothallium compounds play a unique and indispensable role. 

In this chapter, we will focus on the chemistry of organoantimony, organoselenium, organotellurium and organothallium compounds, for which some typical ligand coupling reactions, although in a relatively limited number, have been reported over the years. 

The ligand coupling and ligand transfer mechanisms explain a number of transformations of organothallium compounds. The best studied reaction is the carbon-iodine conversion for the synthesis of aryl iodides, but other efficient conversions have been also described. 

There is also a lot of structural information for other thallium(III) compounds (e.g., organothallium compounds), which has been obtained from the spin-spin coupling pattern of their NMR spectra. However, no interatomic distances have been obtained in this way. 

Indole-5-boronic add has also been used successfully in Suzuki coupling <92H(34)1395). Organothallium derivatives have also been used in Suzuki coupling reactions. The 4-substituted thallation intermediate from indole-3-carboxaldehyde can be coupled with both aryl and vinyl-boronic acids (Equation (122)) <86CPB397i>. 

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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