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

Pyridones, well-known for their ability to photodimerize, have been found t o undergo [4 + 4] photocycloaddition with furan and naphthalene but not wit h benzene. In some cases these reactions can be highly regio- and stereospe cific. Intramolecular reaction with furan produces both cis and trans [4 4] products. The cycloaddition with naphthalene can occur both inter- and i ntramolecularly. The intermolecular reaction yields primarily the cis isome r, whereas the trans isomer is the major product from:the intramolecular re action. A mixture of 4-methoxy-2-pyridone and 2-methoxynaphthalene that cou ld form up to eight regio- and stereoisomers forms largely one [4 + 4] prod uct.