Aim and Objective: Results of pharmacological studies have revealed that chromenes
(2H-1-benzopyran derivatives) and xanthenes (dibenzopyrans) constitute major classes of
heterocyclic compounds, due to their useful biological activities. Moreover, during the last decade,
the use of metal oxide nanoparticles (NPs) as heterogeneous catalysts has been extensively studied
due to their high physical and chemical abilities. The aim of the ongoing research was to prove the
catalytic efficiency of the synthesized TiO2 NPs supported by carbon nanotubes (TiO2-CNTs) for the
preparation of these heterocyclic scaffolds.
Materials and Methods: The present work is focused on a green and efficient synthesis of
benzopyrano[b]benzopyran-6-ones and xanthenols via a pseudo three-component reaction of
salicylaldehydes with active methylene compounds including 4-hydroxycoumarin (4-hydroxy-2H-1-
benzopyran-2-one) or 3,4-methylenedioxyphenol, in a molar ratio of 1:2. The reaction was carried
out in the presence of the synthesized TiO2-CNTs as a catalyst in aqueous media at room
temperature. The synthesized catalyst was fully characterized by the scanning electron microscopy
(SEM), the transmission electron microscopy (TEM), the powder X-ray diffraction (XRD), and the
energy dispersive X-ray detector (EDX) techniques. All the synthesized compounds were
characterized by IR, 1H and 13C NMR spectroscopy, as well as elemental analyses.
Results: Sixteen target compounds containing benzopyrano[b]benzopyran-6-ones and
xanthenols were successfully synthesized in high yields (92-98%) within short reaction times (1.5-3
Conclusion: In this research, TiO2-CNTs were used as an efficient recyclable catalyst for the
synthesis of benzopyrano[b]benzopyran-6-ones and xanthenols by the pseudo three-component
reaction of salicylaldehydes with active methylene compounds including 4-hydroxycoumarin (4-
hydroxy-2H-1-benzopyran-2-one) or 3,4-methylenedioxyphenol. The introduced method is mild,
environmentally benign and effective to give the products in high yields and in short reaction times.