Acid-Catalyzed Ring-Opening of 4-Halonortricyclanes. At Last a Solution to the Norbornyl Cation Problem

Abstract

<p>The stereochemistry of acid-catalyzed ring-opening of the cyclopropane ring in nortricyclane, 4-chloronortricyclane and 4-bromonortricyclane in D₂SO₄/acetic acid-d₄ medium has been investigated. Stereochemical analysis was carried out by dmr spectroscopy. The endo:exo deuterium ratios, at C6 of the exo-2-norbornyl trideuteroacetates-d1 are 1.12, 1.35 and 1.61 respectively.</p> <p>These results conclusively establish that the norbornyl cation formed by edge-protonation is an unsymmetrical, classical and rapidly equilibrating species and not a symmetrical non-classical σ-bridged species.</p>