Photoreactivity of 2-pyridones with furan, benzene, and naphthalene. Inter- and intramolecular photocycloadditions

Pyridones, well-known for their ability to photodimerize, have been found to undergo 4 + 4] photocycloaddition with furan and naphthalene but not with benzene. In some cases these reactions can be highly regio- and stereospecific. Intramolecular reaction with furan produces both cis and trans 4 + 4] products. The cycloaddition with naphthalene can occur both inter- and intramolecularly. The intermolecular reaction yields primarily the cis isomer, whereas the trans isomer is the major product from the intramolecular reaction. A mixture of 4-methoxy-2-pyridone and 2-methoxynaphthalene that could form up to eight regio- and stereoisomers forms largely one 4 + 4] product.