From organyl tellurolates and electrophilic acetylenes

Organyl tellurolate anions effect 1,4-additions to acetylenes bearing electron-withdrawing groups such as acetylenic ketones, aldehydes, esters, diacetylenic ketones, as well as acetylenic phosphonates and sulphones giving 2-substituted vinyl tellurides with Z configuration. 

Addition of aryl tellurolates to acetylenic ketones (general procedure) NaBH4 (0.55 g, 15 mmol) is added in small portions, under N2, to a solution of the diaryl ditelluride (5 mmol) in EtOH (20 mL) at room temperature. A solution of the acetylenic ketone (10 mmol) in EtOH (10 mL) is then added to the reaction mixture, with stirring. The resulting precipitate of the 2-carbonylvinyl telluride is filtered off and recrystallized from EtOH. 

The obtained telluroacroleins have been submitted to a Wittig methylenation giving the expected tellurodienes.  

By treating alkynes with diaryl ditellurides and sodium arylsulphonates in AcOH/H O, an flnh-tellurosulphonation takes place. Some of the obtained tellurosulphones have been converted into the corresponding dibromides. In the case of R=Mc3Si a desilylate product is formed.  

Anti-tellurosulphonation of 1-alkynes.A solution of alkyne (1.1 mmol), sodium arylsul-phinate (5 mmol) and diorgano ditelluride (0.5 mmol) in 5 mL of 80% aqueous acetic acid was heated at 80°C for 24 h (R=Ph, 5.2 h). The reaction mixture was diluted with 20 mL of AcOEt, washed with saturated aqueous sodium bicarbonate, dried over Na2S04 and concentrated in vacuum. Crude products, were concentrated under vacuum, and the residues were purified by preparative TLC on silica gel (AcOEt/hexanes, 1 10), treated with 1 equiv of Br2 in AcOEt and concentrated under vacuum. The residues were purified by recrystallization with CH3OH/HCCI3. 

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