Alkyne [2 + 2 + 2] Cyclotrimerization Catalyzed by a Low-Valent Titanium Reagent Derived from CpTiX₃ (X = Cl, O‑i‑Pr), Me₃SiCl, and Mg or Zn

Inter-, partially intra-, and intramolecular [2 + 2 + 2] cycloadditions of alkynes were catalyzed by a low-valent titanium species generated in situ from the reduction of CpTi­(O-i-Pr)₃, CpTiCl₃, or Cp*TiCl₃ with Mg or Zn powder in the presence of Me₃SiCl. The role of Me₃SiCl as an additive in the reaction mechanism is discussed.