2H-1,3-Ditellurole

H-1,3-Ditelluroles treated in acetonitrile with triphenylcarbenium tetrafluoroborate were converted to 1,3-ditellurolium cations at — 30°. These cations rearranged to 1,2-ditcllurolium cations at + 30°2 (p. 796). 

The CIS- or /ra j-isomers of 2-benzylidene-4-phenyl-2H-l, 3-ditellur ole were transformed to a 1 1 mixture of the cis- and trani-compounds upon treatment with a trace of acidh The cis- and ira -2-benzylidene-4-phenylditelluroles reacted with isopentyl nitrite to produce trans-2-[nitroso(phenyl)methylene]-4-phenyl-2H-1,3-ditellurole and with benzenediazoni-mm tetrafluoroborate in dimethylformamide to give cis-2-[benzeneazo(phenyl)methylene]-4-phenyl-2H-1,3-ditellur ole. ... 

H-l,3-ditellurole. Under an atmosphere of argon, 0.23 g (2.4 mmol) of trimethylsily-lacetylene are dissolved in 5 mL dry tetrahydrofuran. The solution is cooled to -70°C. n-Butyl lithium (1.0 mL, 2.4 M, 24 mmol) is dropped into the stirred solution. Then 0.20 g (2.0 mmol) of tellurium powder is added. The mixture is warmed to 20°C and kept at this temperature for 2 h. To this mixture, cooled again to -70°C, is added a solution of 0.35 g (2.0 mmol) of chloroiodomethane in 1 mL of tetrahydrofuran. The mixture is stirred for 15 min and then quenched with 50 mL water. The product is extracted with three 15 mL portions of dichloromethane. The combined extracts are washed with brine, dried with anhydrous sodium sulphate and filtered. The filtrate is concentrated to give trimethylsilylethynyl chloromethyl tellurium as a pale-yellow oil. Tellurium powder (0.125 g, 1.0 mmol) is added to 2 mL of a 1 M solution (2.0 mmol) of lithium triethylborohydride in ethanol. The mixture is stirred at 20°C for 2 h under an atmosphere of argon. Then 2 mL of 1 M sodinm ethoxide in ethanol are added followed by 0.27 g (1.0 mmol) of trimethylsilylethynyl chloromethyl tellurium dissolved in 2 mL dimethylformamide. The mixture is stirred for 15 h at 20°C, then diluted with 25 mL water and extracted with three 15 mL portions of dichloromethane. The combined extracts are dried with anhydrons sodinm snlphate, fdtered and the filtrate concentrated. The residue is chromatographed on silica gel with hexane/dichloromethane (1 1) as mobile phase. The fractions containing the prodnct are concentrated and recrystallized from methanol 65% yield, m.p. 85°C. 

However, a reinvestigation of this reaction resulted in the isolation of orange plates with a melting point of 216° (from acetone). This substance did not have the absorption maximum at 400 nm characteristic for the Te—Techromophore. NMR-spectral data indicated that this substance was a 1 1 mixture of cis- and trans-2-benzylidene-5-phenyl-2H-l,3-ditellurole and not a 1,2-ditellurole. 

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