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TaCl5-catalyzed homo-coupling of disubstituted acetylenes under the action of EtAlCl2 and Mg
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1  Institute of Petrochemistry and Catalysis of Russian Academy of Sciences
Academic Editor: Julio A. Seijas (registering DOI)

The reaction of homo-coupling of alkynes using zirconium- and titanium-containing reagents is an important basis for the efficient synthesis of polymer, oligomers and macrocycles. It is generally accepted that the homo-coupling takes place through the intermediate formation of “Cp2Zr” or “Cp2Ti” species that can be generated by the interaction of Cp2ZrCl2 or Cp2TiCl2 with alkali and alkaline earth metals, as well as with alkyl derivatives of metals. The most widely used reagents include Negishi reagent (“Cp2ZrBu2”), Takahashi reagent (“Cp2ZrEt2”), and Rosenthal reagent (Cp2Zr(py)TMSC≡CTMS). The well-known system of reagents Ti(OPr)4 - i-PrMgBr should also be mentioned. Recently, we have shown the promise of using a reagent based on tantalum (TaCl5 – Mg) for the reduction of propargylamines. Continuing these studies, in order to develop new catalytic systems for the homo-coupling of acetylenic compounds, in this work we studied the TaCl5-catalyzed reaction of dialkyl-substituted acetylenes with EtAlCl2 and Mg.
We have established for the first time that the reaction of dialkyl-substituted acetylenes with EtAlCl2 and magnesium in the presence of catalytic amounts of tantalum (V) chloride in a toluene solution after hydrolysis and deuterolysis gives tetraalkyl-substituted (E,E)-buta-1,3-dienes in high yield. A selective method for the preparation of tetraalkyl-substituted (Z,Z)-1,4-dichlorobuta-1,3-dienes based on the reaction of aluminacyclopentadienes formed in situ with methanesulfonyl chloride has been developed. A plausible scheme for the catalytic conversion has been proposed.

Keywords: acetylenes; homo-coupling; tantalum catalysis; organoaluminums;