Base catalysis as an alternative explanation for an apparent deuterium solvent isotope effect in the photochemical reactions of α,β-unsaturated esters

Abstract

An apparent deuterium solvent isotope effect upon the photochemical reactions of the α,β-unsaturated esters ethyl 3,4,4-tri-methyl-2-pentenoate, 1, and ethyl 3,4-dimethyl-2-pentenoate, 4, is re-examined; it is concluded that the changes in reaction rate can be attributed to interception of the reaction intermediates (photochemically produced dienols) by basic impurities present in the solvent used. This conclusion is used to explain the apparently anomalous photochemistry of esters 1 and 5 in non-deuterated solvents. The results described also exemplify the use of a base to enhance the efficiency and to alter the direction of deconjugation in the photochemical conversion of α,β-unsaturated esters to their β,γ-unsaturated isomers.