Paterno-Buechi Reaction of Unsymmetrically Substituted Furans: Temperature Effect on the Regio and Stereoselectivity

Abstract

The temperature effect on the regio- and stereo selectivity in the [2+2] phetocycloaddition of carbonyl compounds (benzaldehyde, benzophenone) with unsymmetrically substituted fruns (2-methylfrun, 3-methylfrun) has been investigated to clarify the reaction mechanism. The regioselectivity (double-bond selection) for the reaction with benzaldehyde is not largely dependent on the temperature. The Eyring plot is found to be linear. In contrast, the regioselectivity for the reaction with benzophenone is found to be largely dependent on the temperature. The Eyring plot is not linear. The unusual non-linearity of the Eyring plot is accessed by the difference of the conformational distribution of the intermediary triplet 1,4-diradicals.