On water synthesis of pyran–chromenes via a multicomponent reactions catalyzed by fluorescent t-ZrO2 nanoparticles†
Here, we have demonstrated fluorescent tetragonal ZrO2 nanoparticle (t-ZrO2 NP) catalyzed green one-pot multicomponent protocol for the synthesis of diverse pyran-fused chromene analogues such as 2-aminochromene, dihydropyrano[3,2-c]chromene, and chromeno[4,3-b]chromene derivatives in water. The rate of the reactions and yields of the products increased significantly in water. In addition, t-ZrO2 NPs showed a higher reactivity than monoclinic ZrO2 NPs. The t-ZrO2 NPs were recycled and the gradual decrease in yield of the product using recycled catalyst could possibly be due to the decrease in Zr-content associated with a decrease in the oxygen vacancies which was evident from fluorescence and atomic absorption studies. However, the tetragonal phase of the catalyst remained intact even at the 10th cycle.