Organothallium reagents

The nonoxidative applications of thallium in organic synthesis are relatively few. Organothallium reagents act as mild nucleophiles. Thus, acid chlorides can be alkylated by R3TI, as can a-haloethers. Nucleophilicity is greater for R4TD. Alkyltrimethylthallate(III) is prepared from MesTl and RLi, and may be used to alkylate a,/ -unsaturated ketones. ... 

Activated tertiary and secondary alkyl halides can react with triorga-nothallium compounds with the formation of a new carbon-carbon bond. For example, reaction of trityl chloride with trimethylthallium smoothly occurred in five minutes at 20 °C to give 1,1,1-triphenylethane in 78% yield (Scheme 20.6). Several different alkyl chlorides and bromides reacted in the same way. Reaction with mixed dimethyl-allq nyl organothallium reagents also occurs chemoselectively, with the transfer of the alkynyl group. 

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. 

Thallium(I) halides can be converted into organothallium compounds by treatment with a highly reactive reagent. Thus, MesTl is formed from Til and methyllithium in the presence of methyl iodide, and this reaction is believed to go via initial formation of MeTl followed by oxidative addition of Mel, and reaction with LiMe . 

In a similar vein, organothallium bromides can be prepared by the action of an alkylmagnesium halide reagent on either TlBrs or TlBr. ... 

Organometallic compounds such as organolithium compounds, Grignard reagents, organotin compounds and organothallium compounds react with platinum halides to afford organoplatinum compounds [11,13,19-27]. For example, reactions are shown in eqs. (21.6)-(21.13). The order of the stability of the many compounds obtained by these reaction methods are as follows ... 

I. Morishkima, T. Inubushi, S. Uemura, and H. Miyoshi. Nitroxide as a nuclear spin decoupling reagent. Application to C n.m.r. studies of organothallium compounds. J. Amer. Chem. Soc., 1978,100, 354. 

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