Study of Very Reactive Tautomeric Phenol Dienones as Dienes in Diels−Alder Reactions

Masked ortho-benzoquinones are very reactive as diene partners in Diels-Alder reactions. Careful exploration of the orbital factors that govern their surprising behavior shows that their LUMO is almost as electron demanding as that of o-benzoquinone itself. Methyl substituents at either end of their diene system influence the activation energy through modification of the reaction pathway being more or less asynchronous.