Mechanistic Investigations of the Acid‐Catalyzed Cyclization of a Vinyl <i>ortho</i>‐Quinone Methide

Abstract

Acid-catalyzed and thermal cyclization of an isolable vinyl ortho-quinone methide has been kinetically and computationally investigated. We propose that both reactions proceed through rate-limiting exo-alkylidene bond isomerization followed by faster oxa-6π electrocyclization. The vinyl ortho-quinone methide was found to be surprisingly basic, allowing for quantitative protonation with relatively weak acids. In addition, we have identified a new mode of Diels–Alder dimerization of vinyl ortho-quinone methides.