Intramolecular photocyclization of ortho-hydroxycinnamates: from synthesis of coumarins to photodegradable polymers

Abstract

Coumarins are of great interest mainly due to their numerous biological applications. Trans-o-hydroxycinnamic acid, its esters and amides are suitable starting materials for the synthesis of coumarins, which requires prior E-Z isomerization of the double bond followed by a cyclization step. Such isomerization can be carried out, among other methods, through a photochemical process in the presence of a sensitizer, either initiated by UV light or mediated by visible light using organic or transition metal photocatalysts or in the absence of a photocatalyst taking advantage of a UV-Vis bathochromic displacement of o-hydroxycinnamates under basic conditions.