Use of sodium salt of cyclic β-formylester for synthesis of dihydro-2H-furo[2,3-d]pyrazolo[3,4-b]pyridines and pyrazolo[3,4-b]pyrrolo[2,3-d]pyridines

The chemoselective reaction of the sodium salt of alpha-formyl-gamma-butyrolactone and 5-aminopyrazole furnished dihydrofuro[2,3-d]pyrazolo[3,4-b]pyridine at two different reaction conditions, i.e., with NH4OAc or in refluxing AcOH. The same reactants when refluxed in MeOH and AcOH produced a pyrazolylamino dihydrofuranone derivative. A mixture of 2-chloroethyl-4-chloropyrazolopyridines and dihydrofuro[2,3-d]pyrazolo[3,4-b]pyridine derivatives was obtained on refluxing the intermediate dihydrofuranone in POCl3. A one-step synthesis of tricyclic pyrazolopyrrolopyridines and thienopyrazolopyridines resulted from SNAr reaction of 2-chloroethyl-4-chloropyrazolopyridines with primary aromatic amines and with thiourea.