Synthesis of Urushiol Derivatives by the Fries Rearrangement

Abstract

The photo- and thermal-induced Fries rearrangement reactions of some unsaturated aliphatic esters of benzene-1,2-diol (catechol) have been studied. Photorearrangement and thermal rearrangement favoured products correspond to ortho and para migration respectively, but the thermal rearrangement may be accompanied by indanones, chromanones and other products which were formed through subsequent side reactions of the double bond. Photoinduced Fries rearrangement of 2-hydroxy-phenyl oleate followed by reduction of the carbonyl group gave monosubstituted catechol derivatives with an unsaturated C₁₈ side chain in either the 3- or the 4-position. These alkenylcatechol derivatives are related in structure to chemical components isolated from oriental lacquer trees, such as urushiol from Rhus verniciflua or thitsiol from Melanorrhoea usitata.