Asymmetric Intramolecular Ene Reaction Catalyzed by a Chiral Titanium Reagent and Synthesis of (—)‐ε‐Cadinene

A highly diastereo‐ and enantio‐selective intramolecular ene reaction was developed by employing a chiral titanium reagent generated in situ from TiCl₂(OPrⁱ)₂ and a tartrate‐derived chiral 1,4‐diol. This reaction afforded masked cyclohexanone and cyclopentanone derivatives with high optical purities which were synthetically useful chiral building blocks. From the intramolecular ene product (—)‐ε‐cadinene was synthesized by the use of the newly developed intramolecular Michael reaction.