Thallium, Triethyl

N-Alkylations, especially of oxo-di- and tetra-hydro derivatives, e.g. (28)->(29), have been carried out readily using a variety of reagents such as (usual) alkyl halide/alkali, alkyl sulfate/alkali, alkyl halide, tosylate or sulfate/NaH, trialkyloxonium fluoroborate and other Meerwein-type reagents, alcohols/DCCI, diazoalkanes, alkyl carbonates, oxalates or malon-ates, oxosulfonium ylides, DMF dimethyl acetal, and triethyl orthoformate/AcjO. Also used have been alkyl halide/lithium diisopropylamide and in one case benzyl chloride on the thallium derivative. In neutral conditions 8-alkylation is observed and preparation of some 8-nucleosides has also been reported (78JOC828, 77JOC997, 72JOC3975, 72JOC3980). 

A simple, high-yield procedure for the conversion of ArTlXj into ArjTlX compounds has recently been described 90). This symmetrization reaction, the mechanism of which is not known, can be effected by treatment of the ArTlX2 compound either with triethyl phosphite or with hot aqueous acetone. As a wide variety of ArTlXj compounds can now be easily prepared by electrophilic thallation of aromatic substrates with thallium(III) trifluoroacetate (q. v.), symmetrization represents the method of choice for the preparation of the majority of ArjTlX compounds. Only about twenty mixed compounds, RR TIX, have been prepared so far, and the only general synthetic procedure available consists of a disproportionation reaction between an RTIX2 species and another organometallic reagent [e.g., Eqs. (5)-(7)]. 

Whereas the solvent influence on the and chemical shifts of the apolar tetramethylsilane is comparatively small (Ad ca. 0.5... 1.5 ppm), much greater effects are observed in the case of dipolar molecules such as 4-fluoro-nitrosobenzene and triethyl-phosphane oxide (Ad ca. 3. .. 25 ppm) as well as for the thallium(I) ion (Ad > 2000 ppm ). 

Lead triethyl chloride, thallous chloride, methyl chloride Lead diethyl dichloride, thallous chloride, ethyl chloride. Thallium diphenyl chloride, mercuric chloride. Benzylmercm-io oldoride, thallous chloride. 

Several other metal salts have been proposed to react with acid halides to give acid anhydrides in good yield. Thus, thallium carboxylates in etheral suspension may be treated with acid halides to lead to acid anhydrides in high yield. The method has the advantage that thallium chloride can be separated by filtration and the product is isolated after evaporation of the solvent. Another synthetic possibility exists in the desulfurization of thioesters with mercury(II) carboxylates. Mercuiy(II) carboxylates can also be reacted with triethyl phosphite or tri-n-butylphosphine to provide acid anhydrides in yields of 60-80%. Another possibility is offered by the reaction of 1 mol of iV,Af-dicyclohexylthiourea and 2 mol of silver or mercury(II) carboxylates. Mixed carboxylatocarbamato anhydrides follow from the room temperature reaction of iV, -dialkylcarbamato metal derivatives with acid chlorides. Either Na, Cu", Ti" or V" are employed. ... 

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