P-Methoxyphenyltellurium trichloride

Reduction of aryltellurium trichlorides with sodium ascorbate (typical procedure). p-Methoxyphenyltellurium trichloride (0.30 g, 0.88 mmol) was added to a stirred solution of sodium ascorbate (0.53 g, 2.7 mmol) in water/methanoEacetone (1 mL + 5 mL + 5 mL). After 5 h, water (50 mL) and CH2CI2 (50 mL) were added and the two phases separated. The organic phase was dried (CaCl2) and the solvent evaporated in vacuo. Flash chromatography (Si02 CH2CI2) yielded 0.20 g (97%) of bis(p-methoxyphenyl) ditelluride. 

Tellurocyclization (typical procedure) A mixture of j3-keto ester (2 mmol) and p-methoxyphenyltellurium trichloride (2.2 mmol) in 30 mL of recently distilled chloroform was heated under reflux. The solvent was evaporated and the residue filtered through silica gel using chloroform as eluent. 

Detellurative carbonylation of aryltellurium trichloride NiiCO) method (typical procedure). Ni(CO)4 (2.6 mL, 20 mmol) is added to p-methoxyphenyltellurium trichloride (2.0 g,... 

Bromodetelluration of aryltellurium trichlorides (typical procedure) A mixture of p-methoxyphenyltellurium trichloride (0.68 g, 2 mmol) and bromine (0.64 g, 4 mmol) in MeCN (20 mL) is stirred at 35 5°C for 20 h. After work-up as described above, GLC analysis using ethyl cinnamate as the internal standard shows the presence of o,p-dibromo-p-methoxybenzene (69.5%) and a trace of p-methoxybromobenzene. 

Method A solution of p-methoxyphenyltellurium trichloride (0.34 g, 1.0 mmol) in benzene (200 mL) is irradiated with a high-pressure mercury lamp in the presence of atmospheric oxygen for 1 h (formation of a black precipitate). The mixture is filtered and the filtrate is washed with brine and then dried (MgS04). GLC analysis shows the presence of p-chloromethoxybenzene [0.14 g (70%)] (and minor amounts of o,p-dichloro-methoxy-benzene and p-methoxybiphenyl) using p-chlorotoluene, 2,4-dichlorotoluene and p-methylbiphenyl as the internal standard, respectively. 

TeCl4 has been found to display reactivity toward alkynes similar to that of p-methoxyphenyltellurium trichloride, whereas it reacts with aromatic and 3-hydro-xyalkynes by different mechanisms as shown by the characteristic stereochemistries of the products. The complete anti-stereospedfidty of the additions of TeCU to all propargyl alcohols studied is consistent with a cyclic chelated telluronium ion intermediate 87 in this reaction (Figure 3.8). Using ESI-MS and ESI-MS(/MS),... 

---