Regio- and stereo-selectivity in [_π2 +_π2] photocycloaddition reactions between cyclopent-2-enone and electron-rich alkenes

Abstract

The [π2 +π2] photocycloaddition reactions between cyclopent-2-enone and various electron-rich alkenes proceed in both good quantum yields and useful chemical yields. The stereochemistry of the cycloadducts (1)–(5) has been determined by chemical ionization mass spectrometry and chemical transformations. The regioselectivity increases with increasing nucleophilicity of the alkene, and the stereoselectivity depends on the steric properties of the alkene substituents. The reaction between cyclopent-2-enone and 1-ethoxy-1-ethylthioethylene occurs in a fully regio- and stereo-specific way.