4-Hydroxycoumarin and its derivatives are known for their anticoagulant, antibacterial, antifungal, antitumor, antibiotic and anti-HIV activities. They are also used as agrochemicals and analytical reagents. In 1999, mesoporous organosilica hybrids were prepared from bridged organosilane precursors ((ŔO)3Si–R–Si(OŔ)3; R: organic bridging group, Ŕ: methyl or ethyl). Such mesoporous hybrids prepared from bridged organosilane precursors have been classified as periodic mesoporous organosilicas (PMOs). PMOs are very attractive as support for heterogeneous catalysts in fine chemicals synthesis among others.
Periodic mesoporous organosilica was shown to be a highly active and efficient recyclable catalyst for the synthesis of 3,3'-arylmethylene-bis-4-hydroxycoumarins from condensation of 4-hydroxycoumarin and different aldehydes using water as a reaction medium.
The significant advantages of this procedure are short reaction times, high to excellent yields, low loading of the catalyst, avoiding the use of toxic transition metals, easy separation and purification of the products and reusability of the catalyst.
