Ring opening of dihydro-2-pyridones and intramolecular Diels–Alder reactions

A new ring-opening reaction of 5,6-dihydro-2-pyridones was discovered. Compounds 1 and 7 were converted to the dienoic amides 2 and 8 by reaction with sodium hydride at room temperature. N-Allylation of compounds 2 and 8 followed by IMDA reaction provided the cis-fused hexahydro-1-indolones 5 and 10, respectively. Treatment of compounds 5 and 10 with DBU in refluxing ethyl acetate gave the conjugated products 6 and 11, which were further transformed to the amides 12–15. The phenylthio group of compound 11 was substituted by a methyl group to give product 16.