Al@Cu@TiO 2 Nanocomposite: A Novel Recyclable Heterogeneous Catalyst for the Preparation of Chromenes

A convenient and efficient one-pot procedure for the synthesis of pyrano[3,2- c ]chromenes has been developed via three-component condensation of 4-hydroxycoumarin, aromatic aldehydes, and malononitrile in the presence of a catalytic amount of nano-titanium oxide doped with aluminum and copper salts (Al@Cu@TiO 2 ) as a novel nanocatalyst. The catalyst was prepared via the reaction of titanium(IV) isopropoxide, Al(NO 3 ) 3 , and Cu(NO 3 ) 2 in aqueous methanol. The proposed protocol offers various advantages such as shorter reaction times, use of a heterogeneous catalyst, and high yield of products in combination with simple experimental and workup procedures. The catalyst can be recovered and reused for at least five runs without any significant impact on the yields.