Metal-assisted reactions. Part 17. Ring-opening and dimerization of cyclic ethers by titanium halides

Abstract

Reaction of TiCl₄ or TiBr₄ with a variety of cyclic ethers gives, predominantly, products resulting from simple ring-opening or from ring-opening with simultaneous condensation to dimeric species. The variations in yields of these two kinds of products might be correlated qualitatively with an initial formation of the complex TiX₄·2E (X = Cl or Br; E = cyclic ether) in which the ethers were held in a cis or trans relationship. Although such a correlation might suggest that TiCl₄ but not TiBr₄ exerts a template effect on the condensation, stereochemical considerations of the reaction products indicate otherwise. TiCl₃ and VCl₃ do not give similar results and TiF₄ gives no reaction.