Tellurides, alkenyl

Cross-over experiments suggest that the homocoupling reaction occurs between an alkenyl telluride and an alkenyl Pd species, which is formed via the migration of an alkenyl moiety from Te to Pd. 

Tetrakis(triphenylphosphine)palladiuin(0)-copper(l) iodide. 18,349-350 20,369 Coupling reactions. a-Fluorovinylstannanes are a source of a-fluorostyrenes by virtue of their capacity of partaking in the Stille coupling. A synthesis of (Z)-alkenes is based on the Pd(0)-catalyzed exchange of alkenyl tellurides or selenides with zinc followed by the Negishi coupling. ... 

Enyne and arylalkene synthesis from alkenyl tellurides can proceed with transmetallation to give Zn species. Alternatively, the partial reduction of 1,3-diynes via hydrotelluration, Te/Li exchange, and protonation also provides ( 7-enynes. ... 

An alternative preparation of stereodeflned cw-a,/3-substituted alkenylzinc reagents involves transmetallation of the corresponding trialkenylboranes or alkenyl tellurides with diethylzincJ f The alkenylzincs thus obtained undergo Negishi coupling with aryl iodides in good yields (Scheme 31). 

Catalytic carbopalladation is a ubiquitous process and alkynes are viable substrates. Alkenyl tellurides couple efficiently with alkynes with retention of the double bond geometry. Relatively large amounts of palladium catalyst are required.Oxidative dimerization of monoterpenes has been assumed to involve alkenylpalladium(ii) intermediates. Alkenylpalladium(ii) and di(alkenyl)palladium(iv) complexes have been put forward as intermediates in a similar reaction of halogenoterpenes. The subject has been reviewed concerning the formation of heterocycles by intramolecular cyclization of intermediate alkenylpalladium intermediates. ... 

Generation of a selenoaldehyde, a selenoketone, and telluroaldehydes by [3,3] sig-matropic rearrangement of allyl alkenyl selenides and tellurides [139]... 

Dialkynyl tellurides are obtained in moderate yield by the one-pot reaction of TeCl4 with LiN(SiMe3)2, followed by the addition of a terminal acetylene. Alkenyl tellurium(II) derivatives may also be prepared by the addition of arenetellurenamides or Te[N(SiMe3)2]2 to the C = C bond of dimethylacet-ylene dicarboxylate.180... 

Alkenyl-substituted -dicarbonyl compounds, upon the same conditions, give rise to 2,5-disubstituted tetrahydrofurans bearing exocyclic double bonds. The products, upon treatment with NaBH, are reduced to the corresponding tellurides which in turn are converted into tellurium-free methyl derivatives by treatment with TBTH. ... 

It was later observed" that the above Te-Zn exchange reaction is not a general method to prepare alkenyl Zn reagents, but is restricted to vinylic tellurides bearing Ph, ester, or MejSi groups at the a-position, able to stabilize the formed vinyl zinc. 

Isotellurazoles 4 were obtained in low yields (3-11%) by the one-pot reaction of alkynyl ketones with hydroxylamino-O-sulfonic acid and K2Te in aqueous solution containing sodium acetate (83S824 87H1587). A plausible mechanism of the reaction includes formation of the oxime derivative and subsequent nucleophilic addition of telluride anion to the triple bond followed by cyclization to 4. The reaction is accompanied by the formation of telluro bis(alkenyl ketones) 5 in yields approximately equal to those of 4. When alkynyl aldehydes are used instead of ketones, the single reaction products are the tellurobis(alkenyl nitriles) 6 (83S824). 

Selenals, selones, and tellurals generated in situ via [3,3] sigmatropic rearrangements of allyl alkenyl selenides and tellurides 167 can be trapped by 2,3-dimethyl-l,3-butadiene affording the expected cycloadducts (Equation 68) <1995CL135>. Higher yields were noted in less-hindered cases where the selenium and tellurium aldehyde... 

J13.2 Alkenyl Sulfides, Sulfones, Selenides and Tellurides... 

Organocopper reagents. Dialkenyl tellurides are readily transformed into copper reagents for conjugate addition, on reaction with CuCN-RLi. When the tellurides contain both alkyl and alkenyl groups they are also transformed into alkenylcuprates. 

Enynes (Z)-Alkenyl butyl tellurides couple with 1-alkynes at room temperature in the presence of PdCl2-CuI. 

Halogen-lithium exchange. Special uses of this method include functionalization of bromoallylamine, preparation of a-silylaldehydes, synthesis of alkenyl tri-flones, trifluoromethyl ketones, alkylidenecyclopentanes" and diaryl tellurides. ... 

E)-Alkenyl chalcogenides. The aUcenylzirconocene chlorides are converted into selenides and tellurides" by reaction with organochalcogen halides. 

Yamago, Yoshida and co-workers reported that tellurol esters bearing alkyl, aryl, alkenyl carbon residues react with 2,6-xylyl isonitrile at 100 °C for 6 h to give the a-acyl-substituted imidoyl tellurides 102 in good to high yields (Eq. 69) [ 127]. 

Reductive cleavage of sulphides, selenides, and tellurides on Raney nickeP and cleavage by lithium in THE, leading to secondary or tertiary alkyl-lithium compounds, are useful synthetic operations novel variations are involved in the cleavage of dialkenyl sulphides with EtjSiH (giving low yields of silyl sulphides) and of alkenyl, aryl, and allyl sulphides and selenides with PPhj and... 

---