The one-pot domino Knoevenagel-type condensation/Michael reaction of aromatic, heteroaromatic and aliphatic aldehydes with 4-hydroxycoumarin in aqueous media in the presence of ruthenium salt as homogeneous catalyst was investigated. It was found that 5 mol% of RuCl3.nH2O catalyzes biscoumarin synthesis in high yields (70-95%) under optimised, mild, green and environmentally benign reaction conditions in short times (25-35min)
A number of ruthenium complexes were prepared and their catalytic activities in three-component one-pot condensation of aldehydes, malononitrile and 4-hydroxycoumarin or dimedone was considered to afford dihydropyrano[3,2-c]chromenes and tetrahydrobenzo [b]pyran derivatives under optimum reaction conditions. We found that a catalytic amount of RuBr 2 (PPh 3 ) 4 efficiently promotes the reaction in a short time (3-15 min) and with high yield (75-88%).
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