(Pd/C-mediated)coupling–iodocyclization–coupling strategy in discovery of novel PDE4 inhibitors: a new synthesis of pyrazolopyrimidines

Pyranones fused with a pyrazolopyrimidine moiety were prepared via regioselective construction of pyranone ring using (Pd/C-mediated)coupling–iodocyclization followed by Sonogashira/Heck/Suzuki reactions. The pyrazolopyrimidine based reactant required was obtained via a new H3PO3 mediated condensation reaction. This strategy has led to the discovery of a novel and potentially safe PDE4 inhibitor.