4H-1-Benzotellurine

Carboxy-l-organoethen-l-yl tellurium compounds are converted to 4-oxo-4H-1-benzotellurins by treatment with phosphorus pentoxide in methanesulfonic acid1. 

Methoxy-2-phenyl-l-benzotellurinium Perchlorate1 1.81 g (5.0 mmol) of 7-methoxy-2-phenyl-4-oxo-4H-1 -benzotellurin are dissolved in 20 ml] of dry tetrahydrofuran, the solution is cooled to — 78°, and 5.5 ml] of a 20% solution of diisobutyl aluminum hydride in hexane are added dropwise via a syringe. The resultant mixture is then slowly warmed to 20°, 20 m/] of a 1.0 molar sodium hydroxide solution are added, the mixture is stirred at 20° for 1 h, and is then poured into 100 ml] of diethyl ether. The organic phase is washed with brine, dried with anhydrous sodium sulfate, filtered, and concentrated. The residue is dissolved in 25 ml] of acetic acid, 2 ml] of 70% perchloric acid are added, and the solution is allowed to cool. The resultant red precipitate is filtered off, washed with several portions of diethyl ether, and air-dried yield 1.13 g (50%) m.p. 150° (dec). 

When the reaction was carried out with two moles of the Lawesson reagent per mole of the benzotellurin, 2-phenyl-7-methoxy-4-thioxo-4H-l-benzotellurin 1-sulfide was isolated1. 

Methoxy-2-phenyl-4-thioxo-4//-l-benzotellurin 1-sulfide lost the Te-sulfur group in refluxing toluene. At least seven compounds were formed. The major product (20% yield) was 7-methoxy-2-phenyl-4-thioxo-4H-l-benzotellurin. 4,4 -Bis[7-methoxy-2-phenyl-4/7-1 -benzotellurinylidene] refluxed with excess sulfur in xylene produced 7-methoxy-2-phenyl-4-thioxo-4H-l-benzotellurin in 70% yield1. 

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