moieties underwent the intramolecular Diels–Alderreaction followed by the extrusion of carbon dioxide to give 3a, 4-dihydrophthalide derivatives. The dihydrophthalides added to the second dienophiles intermolecularly to give 3a,4,5,7a-tetrahydro-5,7a-ethanophthalide derivatives. The stereoselectivity of the 5,7a-ethanophthalides was liable for the two successive reactions.