Preparation of 1,5-Dihydro­pyrazolo­[3′,4′:5,6]­pyrano­[3,4‑b]­pyridines via a Microwave-Assisted, Palladium-Catalyzed Regioselective C–H Heteroarylation of Electron-Rich Pyrazoles

Here we report the first synthesis of a family of novel heterocyclic compounds based on a 5-dihydropyrazolo[3',4':5,6]pyrano[3,4-b]pyridine core. In the course of our drug discovery programs, we had need to access the previously unknown 5-dihydropyrazolo[3',4':5,6]pyrano[3,4-b]pyridine core. Initial attempts required long reaction times, which led to degradation and side products. Reaction optimization identified a Pd-catalyzed, microwave-assisted C-H heteroarylation protocol for the rapid, general, and high yielding synthesis of this tricyclic core (as well as related analogs) suitable to drive optimization efforts.