Thallium reagents ketones

Symmetrical and unsymmetrical benzoins have been rapidly oxidized to benzils in high yields using solid reagent systems, copper(II) sulfate-alumina [105] or Oxone-wet alumina [105, 106] under the influence of microwaves (Scheme 6.32). Conventionally, the oxidative transformation of a-hydroxy ketones to 1,2-diketones is accomplished by reagents such as nitric acid, Fehling s solution, thallium(III) nitrate (TTN), ytterbium(III) nitrate, ammonium chlorochromate-alumina and dayfen. In addition to the extended reaction time, most of these processes suffer from drawbacks such as the use of corrosive acids and toxic metals that generate undesirable waste products. 

The availability of strongly chelating extractant reagents for a number of metals has lead to the development of procedures in which the metal is extracted from minimally treated blood or urine and then quantified by atomic absorption analysis. The metals for which such extractions can be used include cobalt, lead, and thallium extracted into organic solvent as the dithiocarbamate chelate, and nickel extracted into methylisobutyl ketone as a chelate formed with ammonium pyrro-lidinedithiocarbamate. 

Flavanones - Isoflavones. Although Koser s reagent (1) is known to effect a-tosyloxylation of ketones,1 the reaction with flavanones (2) results in an oxidative 1,2-aryl shift to provide isoflavones (3) in 74-80% yield.2 This conversion has been effected previously with thallium salts. 

The oxidative reanangement of cyclic alkenes and ketones often leads to ring expansion or ring contraction reactions. The reagents generally used for this purpose are hypervalent main group oxidants such as thallium(III), lead(lV), iodine(III) and selenium(IV), aldiough palladium(II) has been used as well. 

Lunarine (26), one of the typical neolignans, is biosynthesized by the ortho-para radical coupling between two molecules of p-hydroxycinnamic acid. In this connection, oxidative coupling reactions of 4-substituted phenols have been extensively stndied using thallium trifluoroacetate (TTFA), potassium ferricyanide (K3[Fe(CN)g]) and other reagents. p-Cresol (27) was also electrolyzed at a controlled potential (+0.25 V vi. SCE) in a basic medium to afford Pummerer s ketone 28 in 74% yield. The snggested mechanism is given in Scheme 4. 

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. ... 

E. C. Taylor, A. McKillop, and coworkers. Thallium in organic synthesis 49. Oxidative rearrangement of chalcone dimethylketals to methyl-2,3-diaryl-3-methoxypropanoates with thallium(m) trinitrate in trimethylorthoformate. J. Org. Chem., 1977, 42, 4167 50. A convenient synthesis of thallium(i) cyanide, a useful reagent in organic synthesis (for conversion of aroyl chlorides to aromatic a-ketonitriles). J. Org. Chem., 1978, 43, 2280 51. Oxidation of enolizable ketones to a-nitratoketones by thallium(in) nitrate in acetonitrile. 

---