Vinyl tellurides

Negishi coupling of 2-furylzinc chloride with vinyl telluride provided 2-substituted furan with (Z)-double bond in a stereoselective manner, which was used in the total synthesis of l-(Z)-atractylodinol, a biologically active natural product as depicted in the following scheme <06TL8183>... 

In terms of their synthetic use, (E)-vinyl tellurides 56 easily undergo Li/Te exchange upon treatment with wBuLi at — 78 °C (Scheme 4.32). The resulting vinyllithium has con-... 

Dihalocarbenes generated under phase transfer catalysis add to vinylic tellurides to give the corresponding gem-dihaloarylteUuro cyclopropanes. ... 

Alkyl vinyl tellurides can also be prepared by a sequential reaction of divinylic tel-lurides with lithium and alkyl halides in liquid ammonia. ... 

Alkyl- and aryltellurols generated in situ by the well-established reduction of ditellurides with NaBH /EtOH add to terminal acetylenes, giving (Z)-vinylic tellurides. "" ... 

The above-described hydrotelluration have been successfully applied to conjugated enines and dimes, functionalized alkynes and diines. providing a useful method for the synthesis of organoteUuro 1,3-butadienes, organotelluro 1,3-enines and functionalized vinylic tellurides with the Z configuration at the newly formed C=C bond. 

Vinylic tellurides (generalprocedure) Elemental Te (0.6 g, 5.0 mmol) is added to a solution of the vinylic magnesium bromide (5.5 mmol) in THE (10 mL) under reflux and N2 atmosphere, and the reflux maintained for 20 min. The mixture is allowed to reach room temperature and then treated with n-butyl bromide (0.7 g, 5.0 mmol). After stirring for 10 min, the reaction mixture is cooled at 0°C, treated dropwise with saturated aqueous NH4CI, extracted with ether, dried (MgS04) and then evaporated. Kiigelrohr distillation of the residue under vacuum gives the vinyl alkyl tellurides as yellow liquids. 

The divinylic ditellurides, obtained as described, are converted into alkyl vinyl tellurides by reduction with AILiH4 followed by alkylation. ... 

Alkyl vinyl tellurides (general procedure) A solution of the divinylic ditelluride (1.0 mmol) in THF (6 mL) is added dropwise, at room temperature under Nj, to AILiH4 (0.09 g, 2.5 mmol) in THF (3 mL). The dark red colour of the ditelluride disappears. The resulting mixture is treated with butyl bromide (0.3 g, 2.2 mmol) and stirred for 15 min. Then H2O (0.5 mL), 10% aqueous NaOH (0.5 mL) and HjO (0.5 mL) are added in sequence. The product is extracted with ether (3x10 mL). The extract is washed with brine, dried (MgS04) and evaporated, giving the product as a yellow oil. 

Important remarks are that starting from mixtures of ElZ enol derivatives, only the (Z)-vinylic tellurides are obtained, and comparative experiments demonstrate that alkyl tellurolates ( -,. t- and f-BuLi) react faster than the aromatic (PhMgBr, 2-ThLi), and that the reaction time is not influenced by the nature of the leaving group (phosphate, acetate, tosylate and triflate). 

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. 

Diorganyl tellurides add to alkynes via a radical mechanism in the presence of a catalytic amount of a radical initiator such as AIBN or 2,2 -azobis(4-methoxy-2,4-dimethyl-valeronitrile) (In), as well as under irradiation by visible light (tungsten lamp), affording vinylic tellurides in a variable ZIE ratio." ... 

Vinylic tellurides via olefination reactions 3.16.5.1 Homer-Emmons route... 

Preparation of vinyl tellurides. To a mixture of NaH (1 mmol) (80% suspension in oil) and (phenyltelluromethyl)-phosphonate (1 mmol) in THF (5 mL) at reflux under Nj, aldehydes (1 mmol) were added dropwise. Following 3 h at reflux, the solution was cooled to room temperature. Then, saturated aqueous NH4CI was added and the mixture was extracted with diethyl ether. The organic extract was dried (MgS04) and evaporated to give vinyl tellurides, which were purified by column chromatography on silica gel with ethyl acetate/hexane (1 20) or by preparative TLC,... 

Tellurophosphoranes, obtained through a transylidation reaction between tellurenyl halides and phosphoranes, react with aldehydes to give the expected vinylic tellurides as an E Z isomeric mixture (method a). One other methodology involves the treatment of equimolar amounts of phenyl tellurenyl bromide and phosphonium salts with t-BuOK followed by an aldehyde (method b). Under these lithium-salt-free conditions, (Z)-vinylic tellurides are the main products. ... 

The sequential treatment of 1-alkynes with n-BuLi, trialkyl borane and a tellurenyl bromide reaches the (Z)-borosubstituted vinyl telluride which is easily hydrolyzed to the disubstituted vinyl tellurides. The reaction proceeds with high regio- and stereocontrol. ... 

It was observed that the obtained telluroborane fails to react under the Suzuki coupling (Phl/Pd(PPh3)4/Na3P04/DMF) to give trisubstituted vinyl tellurides. 

Vinylic tellurides from vinylboranes. To a solution of cyclohexene (10 mmol) in THF (10 mL) was added a solution of diborane (5 mmol) in THF at 0°C with stirring the precipitate thns formed [(c-Hex)2BH] was stirred at 0°C for 1 h. The reaction mixture was diluted with a solution of a terminal acetylene (5 mmol) added at - 10°C, and the mixture was kept at 0°C for 2 h. After the precipitate had dissolved, the resulting solution was treated with 3 M NaOH (2 mL), diorgano diteUuride (4 mmol) and 3% Pd(PPhj)4, then was reflnxed for 3 h under Nj. After the reaction was complete normal work-up was performed. YmylteUurides were isolated and purified by TLC with petroleum ether (30-60°C) as developer. 

The a-zirconated vinyl tellurides are valuable intermediates for several synthetic manipulations. ... 

Treatment with water gives the corresponding Z tellurides. Reaction with BuSeBr, iodine and A -bromosuccinimide (NBS) gives respectively Te-Se ketene acetals, a-iodo- and a-bromo vinyl tellurides as mixtures of Z and E stereoisomers (in contrast with the total retention of configuration of the above-discussed Zr/Te exchange reactions). The acylation was effected with acylchlorides in the presence of Cul. ... 

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