Synthesis and application of melamine-based nano catalyst with phosphonic acid tags in the synthesis of (3′-indolyl)pyrazolo[3,4-b] pyridines via vinylogous anomeric based oxidation

A novel nanostructured melamine-based organo solid acid with phosphorus acid tags was designed, synthesized and fully characterized. The catalytic activity of the resulted melamine hexakis(methylene)hexakis(phosphonic acid) (MHMHPA) as a heterogeneous catalyst was also investigated via an one-pot reaction between cyanoacetylindole, 3-methyl-1-phenyl-1H-pyrazol-5-amine, and an aromatic aldehyde. (3'-Indolyl)pyrazolo[3,4-b] pyridines were produced in good yields under refluxing ethanol. The solid catalyst can be recovered easily and reused without a significant loss of its catalytic activity.