Mechanism leading to the observed product of intramolecular aryl Diels–Alder reaction

A mechanistic investigation into the recently reported intramolecular aryl Diels–Alder reaction was carried out using deuterium labeling. These studies led to the conclusion that the initial Diels–Alder adduct is isomerized to a highly conjugated tetra-ene intermediate which undergoes a stereospecific suprafacial 1,5-dienyl hydrogen shift to give the observed product.