Immobilized TiO 2 nanoparticles on carbon nanotubes: an efficient heterogeneous catalyst for the synthesis of chromeno[ b ]pyridine derivatives under ultrasonic irradiation.

A new protocol for the synthesis of chromeno[ b ]pyridine derivatives is described via a three-component reaction of 4-aminocoumarin, aromatic aldehydes and malononitrile catalyzed by TiO 2 nanoparticles immobilized on carbon nanotubes (TiO 2 -CNTs) as an efficient heterogeneous catalyst under ultrasonic irradiation in water. The sustainable and economic benefits of the protocol are the high yields of products, short reaction time, simple work-up procedure, and use of a non-toxic and reusable catalyst.