β-Cyclodextrin Effects on the Photo-Fries Rearrangement of Aromatic Alkyl Esters

Article abstract of DOI:10.1021/jo00070a034

The photolysis of phenyl propionate (1a) and phenyl valerate (1b) in water and in solutions containing β-cyclodextrin (CD) leads to the corresponding p-hydroxyphenyl alkyl ketone 2, o-hydroxyphenyl alkyl ketone 3, and phenol 4.When the reactions are carried out in the presence of oxygen there is a decrease in the total amount of rearrangement products, but the inhibition is less marked in the presence of CD.The <3>/<2> ratio for 1b increases when CD concentration changes from 0 to 10 mM.These changes are due to the increase in the quantum yield for the formation of 3 and a decrease in the quantum yield for 2 in the solutions containing CD.The <3>/<2> ratio for 1a decreases in the presence of CD although both quantum yields increase with CD concentrations.Under the conditions used in this study, the substrate reacted in the bulk solution and in the cavity of CD.The quantum yields for the formation of 3 and 4, Φ_CD³ and Φ_CD⁴, are higher for the included substrate than the corresponding values for the free substrate while Φ_CD² is higher than Φ_w² for 1a but lower for 1b.This effect is attributed to the different orientation of the substrates in the cavity of CD.Besides, Φ_CD⁴ also increases due to the availability of hydrogens bonded to secondary carbons in the cavity of the cyclodextrin.