Synthesis of New (3´-Indolyl)pyrazolo[3,4-b]Pyridine via Vinylogous Anomeric Based Oxidation under Mild and Green Conditions

In recent years, phosphorus acid tag is a valuable synthon due to its application at the preparationof catalysts, inhibitors, metal adsorbent and extractants [1]. Molecules with indole nucleushave attracted great interest due to the very important biological and pharmacologicalactivities,such as antibacterial, antifungal, antiviral, anticonvulsant, cardiovascular, optimal inhibitory,antihypertensive, anticholinergic and antiproliferative activities [2-3]. Pyridine moietyis one of the most important scaffolds which has found in the many pharmaceuticals andnatural products due to their biological and medicinal properties such as inhibiting HIV protease,antidepressant, anti-inflammatory, inhibiting acetylcholinesterase, treating hypotension orhypertension [4]. Herein, we wish to develop vinylogous anomeric based oxidation mechanismat the preparation of (3´-indolyl)pyrazolo[3,4-b]pyridines from aryl aldehydes, 3-(1Hindol-3-yl)-3-oxopropanenitrile and 3-methyl-1-phenyl-1H-pyrazol-5-amine in the presenceof a catalytic amount of melamine hexakis(methylene)hexakis(phosphonic acid) [MHMHPA]under mild and green conditions (Fig. 1). (***) Fig. 1 Catalytic synthesis of (3´-indolyl)pyrazolo[3,4-b]pyridines in the presence of MHMHPA