Review on 4-Hydroxycoumarin Chemistry: Synthesis, Acylation and Photochemical Properties

Abstract

Hydroxycoumarins are important compounds exhibiting several physical, chemical and biological properties. These compounds represent a part of secondary metabolites that are natural compounds and are studied for their importance in organic synthesis. Among the most well-known hydroxycoumarins are 7-hydroxycoumarin and 4-hydroxycoumarin. The objective of this review is to raise awareness of the reactivity of 4-hydroxycoumarin and its applications. In this study, we review the methods of synthesis and acylation of this compound as well as studies on the photochemical properties of its derivatives. Several methods for the synthesis of 4-hydroxycoumarin have been described in the literature, most of which use simple phenol and 1-(2-hydroxyphenyl)ethanone or 2’-hydroxyacetophenone as starting compounds. Other synthesis pathways exist, but they are based on intermediate synthesis compounds. About 4-hydroxycoumarin acylation, the literature reports two main types of acylation such as C-acylation and O-acylation. Several authors have synthesized and studied C-acylation in liquid medium and the solvent free. As for O-acylation, its compounds are more recent and less studied. Some studies have also been conducted on the photochemical properties of 4-hydroxycoumarin and its derivatives. Some compounds have proven to be excellent UV absorbers, others have fluorescent properties. With regard to the photo-acid properties generally sought in the hydroxycoumarins group, studies have shown that 4-hydroxycoumarin, unlike 7-hydroxycoumarin, cannot be considered as an active photo-acid.