Synthesis of 5-amino-1H-pyrazolo[4,3-b]pyridine derivatives and annulation of imidazole and pyrimidine rings thereto

1-Alkyl-N-Boc-5-formylpyrazol-4-amines react with malononitrile and cyanoacetamide to form 5-amino-1H-pyrazolo[4,3-b]pyridine nitriles and amides, respectively. Cyclocondensation of the obtained derivatives with chloroacetaldehyde, bromotrifluoroacetone, or ethyl bromopyruvate leads to the formation of imidazo[1,2-a]pyrazolo[3,4-e]pyridines or to pyrazolo[3′,4′,5,6]pyrido[2,3-d]pyrimidine derivatives in cyclocondensation with orthoesters, ethyl oxalyl chloride, or carbonyldiimidazole.