3-Bromobenzotellurophene

Bromobenzotellurophene ° A mixture of 2.0 g (19.6 mmol) of phenylacetylene, 1.0 g (6.3 mmol) of tellurium dioxide, 2.0 g (23 mmol) of lithium bromide aud 50 uiL of acetic acid is heated uuder reflux for 20 h, cooled to 20°C, aud poured iuto 150 uiL of diethyl ether. Aqueous sodium hydrogeu carbouate solutiou (5%) is added uutil all the acid has beeu ueutralized. The orgauic phase is separated, dried with auhydrous calcium chloride, fdtered aud evaporated. The browu, oily residue is dissolved iu a mixture of 30 mL of carbou tetrachloride aud 10 mL of petroleum ether (b.p. 30 0°C). Chloriue is carefully bubbled through this solutiou uutil precipitatiou of the product ceases. The yellow precipitate is filtered and recrystallized from acetonitrile. Yield 2.2 g (92%) m.p. 263-265°C. 

The obtained 3-bromobenzotellurophene dichloride is suspended in diethyl ether and an excess of 5% aqueous sodium disulphite solution is added. The mixture is shaken thoroughly until all of the organic material has dissolved. The organic layer is separated, dried with anhydrous calcium chloride, filtered, and the filtrate is evaporated. The oily residue is pure 3-bromobenzotellurophene. Yield 100%. 

Bromobenzotellurophene is cleaved by n-BuLi forming butyl-2-ethynylphenyl telluride. ... 

Semicarbazones of other ketones did not react similarly to produce benzotellurophenes. Selenium dioxide is known to convert certain semicarbazones to acetylenes1. Tellurium dioxide is expected to effect a similar conversion. However the 3-bromobenzotellurophene would be the expected product from the reaction of phenylacetylene and a tellurium(IV) bromide acetate. 

Bromobenzotellurophene did not react with phenyl lithium. Butyl lithium in diethyl ether/hexane cleaved the tellurophene ring, even at — 50°, yielding butyl 2-ethynylphenyl tellurium2. 

Chlorobenzotellurophene, when refluxed in trifluoroacetic acid for a few hours, produced 3-oxo-2,3-dihydrobenzotellurophene in 84% yield. 3-Bromobenzotellurophene gave only a 7% yield. 3-Chloro-2-methylbenzotellurophene did not react2. 

Attempts to prepare a Grignard reagent from 3-bromobenzotellurophene were unsuccessful2. 

Butyl lithium in hexane cleaved 3-bromobenzotellurophene, even at — 50°, forming butyl 2-ethynylphenyl tellurium3. 

Butyl 2-Ethynylphenyl Tellurium3 A solution of 0.5 g (1.6 mmol) of 3-bromobenzotellurophene in 30 ml of diethyl ether is cooled to — 50°, 1.95 mmol of butyl lithium in hexane are added, and, after 30 min, the mixture is hydrolyzed with wet diethyl ether and then with water. The organic phase is separated, dried with anhydrous calcium chloride, filtered, and evaporated. The oily residue is chromatographed on silica gel with petroleum ether as the mobile phase to give an oil (Rf = 0.5) yield 0.33 g (71%). 

When tellurium dioxide, lithium bromide, and the semicarbazone of methyl phenyl ketone reacted in acetic acid, 6-bromobenzotellurophene was isolated in 9% yield1. 

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See also in sourсe #XX -- [ , ]

See also in sourсe #XX -- [ , ]

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