Cobalt(II) chloride hexahydrate (CoCl2·6H2O) has been found to be an efficient catalyst for the one-pot synthesis of biscoumarin derivatives through a combination of aromatic aldehydes and 4-hydroxycoumarin in aqueous media at 70°C. Several types of aromatic aldehyde, containing electron-withdrawing groups as well as electron-donating groups, were used in the reaction and in all cases the desired products were synthesized successfully. The present approach offers remarkable advantages such as short reaction times, excellent yields, straightforward procedure, easy purification, environment friendliness, and low catalyst loading. 1. Introduction Coumarin derivatives, especially biscoumarins, are important compounds in organic synthesis due to their wide spectrum of pharmacological properties such as antifungal, anti-HIV, anticancer, anticoagulant, antithrombotic, antimicrobial, and antioxidant [1–5]. These compounds are also utilized as urease inhibitors [6]. A number of methods have been reported for the synthesis of these compounds in the presence of various catalysts like molecular iodine [7], sodium dodecyl sulfate (SDS) [8], tetrabutylammonium bromide (TBAB) [9], ([][HSO4]) [10], tetrabutylammonium hexatungstate ([W6O19]) [11], sulfated titania (TiO2/) [12], ruthenium(III) chloride hydrate (·) [13], n-dodecylbenzene sulfonic acid (DBSA) [14], and silica chloride nanoparticles (nano SiO2Cl) [15]. However, these methods suffer from one or more disadvantages such as low yields of products, long reaction times, use of expensive catalyst, toxic solvents, or harsh reaction conditions. Therefore, introducing a clean procedure by the use of green and environmentally friendly catalyst with high catalytic activity, moderate temperature, and short reaction time accompanied with excellent yield for the production of biscoumarin derivatives is needed. We hoped to develop a more general protocol for the efficient synthesis of biscoumarin derivatives via ·, which have recently attracted much attention as catalyst to organic synthesis due to their low toxicity and easy availability [16–18]. 2. Results and Discussion We herein present efficient and eco-friendly procedure for the synthesis of biscoumarin derivatives (3 a–m) by three-component condensation of 4-hydroxycoumarin (1) and aromatic aldehyde (2) catalyzed by · in water-ethanol solvent system 70°C (Scheme 1). Scheme 1: Synthesis of biscoumarins. For this study, a reaction between 4-hydroxycoumarin (2？mmol) and 3-nitrobenzaldehyde (1？mmol) was examined as the model reaction. Initial studies showed that better
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