Nickel-mediated synthesis of dialkynyl and trialkynyl ethenes - Demetallation reactions

Article abstract of DOI:10.1016/S0020-1693(97)05485-6

Metalorganic syntheses of the title compounds starting from 1-alkynes and Ni(cod)(PMe₃)₂ or Ni(PMe₃)₄ consist of less than six steps and afford better than 50% overall yields of isolated compounds. Elimination of the metal by reductive C,C coupling in diorganonickel complexes under 1 bar CO and workup in aqueous hydrochloric acid are the key steps in the preparation of (RC≡C)R′C=C(R)(C≡CR) (R=SiMe₃, CMe₃; R′=H, CH₃, C₆H₅, C≡CH, C≡CCH₃, C≡CCMe₃, C≡CSiMe₃, C≡CSiPh₃, C≡CC₆H₅, C≡CC₆H₄F, C≡CC₆H₁₁, C≡CCH₂SiMe₃). Starting from 3-bromopropyne the initial C,C-coupling reaction is followed by an oxidative addition of the CH₂Br function to zerovalent nickel and a second C,C coupling, which generates the tetradecadienetetrayne skeleton of (RC≡C)(R)C=(RC≡C)C-C≡C-CH₂-CH ₂-C≡C-(RC≡C)C=C(C≡CR)-(R)(R=SiMe₃).