Nano-titania-supported Preyssler-type heteropolyacid: An efficient and reusable catalyst in ultrasound-promoted synthesis of 4H-chromenes and 4H-pyrano[2,3-c]pyrazoles

An efficient and convenient procedure has been described for one-pot multi-component synthesis of tetrahydrobenzo[b]pyrans known as 4H-chromenes and 1,4-dihydropyrano[2,3-c]pyrazole derivatives in the presence of nano-titania-supported Preyssler-type heteropolyacid, n-TiO2/H-14[NaP5W30O110], as a heterogeneous catalyst. The reactions proceeded smoothly under ultrasound irradiation condition to afford the corresponding products in quantitative yields. The catalyst can be easily recovered and reused for several successive fresh runs with no significant loss of catalytic activity.