Aryl vinyl tellurides

In the case of symmetrical divinyl tellurides, the displacement of both vinyl groups is achieved by employing 2 equiv of n-butyllithium. Aryl vinyl tellurides give a mixture of products, since both Ar-Te and vinyl-Te bonds are transmetallated on reaction with n-BuLi, leading to vinyl- and aryllithiums. The butyl vinyl tellurides give only the desired vinyl-lithiums. The reactions are stereospecific with retention of the C=C bond geometry. °... 

In 1987, Sonoda and co-workers reported that the tellurium-lithium exchange reaction of l-(phenyltelluro)-2-phenylethene with -butyllithium, followed by capture with benzaldehyde, gave the corresponding allylic alcohol with retention of the double-bond configuration.243 It was observed that, depending on the length of time the reaction mixture of the aryl vinyl telluride and -butyllithium was allowed to equilibrate prior to addition of the electrophile, a complex mixtures of products could be formed (Scheme 97).256... 

Acetylenes react with arenetellurolates to form aryl vinyl tellurides. The vinyl groups in vinyl aryl telluriums are converted to vinyl carboxylic acids by carbon monoxide in the presence of stoichiometric amounts of palladium dichloride1 or diacetate2 4. The yield and the product distribution is influenced by the reaction time, the CO pressure, the presence or absence of lithium chloride or triethyl amine, and the concentration of palladium salt. Diphenyl tellurium was converted to benzoic acid1,3. Hexyl phenyl tellurium formed only benzoic acid and no heptanoic acid1. 

The preparation of a variety of vinylic functionalized C-glycosides involves a photochemical reaction between telluroglycosides with aryl alkynes at 120 °C. Glycosyl radicals were initially formed by photohomolysis of the C-Te bond and readily added to the alkyne a vinyl telluride (e.g., 49) was finally obtained by a further attack of RTe- (Scheme 3.32) [82],... 

Several vinylic tellurides are prepared starting from monosubstituted aryl alkynes.41,42,133-136 The yields are usually high and the reports in the literature mention that the stereochemistry of the product is 100% Z. In the same way, only the formation of 1,2-disubstituted vinylic tellurides is reported (Scheme 36). 

Alkynes conjugated to double bonds are hydrotellurated in a similar way to aryl alkynes. The reaction with this class of alkynes is important, since it leads to conjugated double bonds of defined stereochemistry.27,34,41,42,137 In view of the easy access to enynes of defined stereochemistry,138 Z,Z-69 or ,Z-69, vinylic tellurides can be obtained as illustrated in Scheme 37. 

Alkynes conjugated to a triple bond are very reactive systems toward hydrotelluration. The reaction occurs in a shorter reaction time when compared to the reactions commented above. In this case, even disubstituted triple bonds give vinylic tellurides in good yields.41,42,139 140 In the case of non-symmetrical diynes, an order of reactivity is established for the hydrotelluration of triple bonds of the enyne systems (terminal > propargylic > alkyl substituted > aryl substituted).140 This order of reactivity is reflected in the preferential formation of the vinylic tellurides shown in Scheme 39. 

The same author reported the cross-coupling reactions of aryl tellurides with olefins289 and the cross-coupling and homocoupling reactions promoted by palladium involving vinyl tellurides. Different solvents and reaction conditions, including a reoxidant, were used, leading to the products in variable yields. In Scheme 119, some of the obtained results are summarized. 

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-carbonyl vinyl telluride is filtered off and recry stalUzed from EtOH. 

Fiuylzinc halides also undergo coupling with vinyl and aryl tellurides in a variation of the Negishi reaction. In one example, Z-vinylic telluride 35 reacts with 2-furylzinc chloride to furnish 2-vinylfuran 36 in 75% yield [47]. 

Activation of the carbon-tellurium bond is also possible under palladium catalysis, but requires stoichiometric amounts of copper iodide. Vinyl tellurides react with arylzincs in THF at rt in the presence of PdCl2 (20mol%) and Cul (1 equiv.) (Scheme 4.40) [149, 150]. Aryl tellurides react similarly, but require reflux temperature [151]. 

Hydrozirconation of terminal alkynes R-C=CH (R= aryl, alkyl) with 1 affords terminally ( )-Zr-substituted alkenes with high efficiency and excellent stereochemical and regiochemical control (>98%). These alkenylzirconocene complexes are of particular interest for synthetic use [136, 143, 144]. Moreover, beside the electropositive halogen sources [145] and heteroatom electrophiles [3] used in the pioneering studies to directly cleave the Zr-C bond, ( )-vinyl-Zr complexes were recently transformed into a number of other trans-functionalized alkenes such as ( )-vinyl-sul-fides[146], vinylic selenol esters [147], vinyl-sulfones [148], vinyl-iodonium [149], vinyl-(R0)2P(0) [150], and vinilic tellurides [143]. 

Alkyl, aryl, allyl, benzyl, vinyl, ethynyl tellurides, tellurobutadienes, divinyltellurides, tellurobutenines, telluro(thio)- and telluro(seleno)ketene acetals and j3-(phosphorovinyl) tellurides are susceptible to such exchange, giving the corresponding lithium compounds trapped in sequence with selected electrophiles. ... 

Reaction of 116 with monosubstituted aryl alkynes 120 gives the (Z)-vinylic aryltellurium dichlorides 121, which are reduced to the (Z)-vinyl aryl tellurides 122 by reaction with sodium boro hydride.185 Alkynes bearing an OH at C3 react with aryltellurium trichlorides 116 to give cyclic products 124 or 125 depending on the steric demand on C3, in a similar way that was observed in the reaction with tellurium tetrachloride (Section 9.13.4.2.3). 

Recently, the direct transformation of allyl- 206272 and aryl tellurides 209273 into the corresponding organocopper species 207 and 210 by tellurium-copper exchange was described. The resulting allyl 207 or aryl cuprates 210 were captured by coupling with vinyl triflates 208272 or by 1,4-addition to enones 211,273 respectively (Scheme 112). 

The reaction of tellurium with acetylene and iodobenzene in the presence of potassium hydroxide, hexamethylphosphoric triamide, tin(II) chloride, and water under 12 atm acetylene in an autoclave at 100-120° produced diphenyl tellurium, phenyl vinyl tellurium, and divinyl tellurium4. Diphenyl tellurium could be the product of the arylation of the telluride dianion by phenyl iodide. 

It has been reported that sodium-, potassium- calcium- and magnesium-tellurium exchanges are achieved by similar procedures with alkyl, aryl, ethynyl, vinyl, allyl and benzyl tellurides. ... 

A series of primary and secondary alkyl aryl tellurides has been found to undergo rapid (3-10 min) group-transfer cyclization to afford tetrahydrofuran derivatives in good yields (60-74%) under micro vave heating conditions at 250 °C in ethylene glycol or at 180 °C in vater, the only dra vback of the process being the loss in dia-steroselectivity as a consequence of the higher reaction temperature [22]. Li and coworkers have developed a successful method for synthesis of vinyl cycloethers by direct addition of THF and 1,4-dioxane to alkynes reaction occurs at 200 °C in 40-180 min under the action of microwave irradiation (300 W) [23]. 

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