Unusual Diastereoselectivity in Intramolecular Diels−Alder Reactions of Substituted 3,5-Hexadienyl Acrylates. Preference for a Boatlike Structure of the Six-Atom Tether Due to Ester Overlap

Thermolysis of the 3,5-hexadienyl acrylates (a) proceeds via the transition state E in which the connecting chain adopts a boatlike conformation due to a preference for maintaining ester overlap to afford the products b with good diastereoselectivity.