Palladium mediated regioselective intramolecular Heck reaction: synthesis of 1,3,4-trisubstituted pyrazolo[3,4-b]pyridines, 3H-pyrazolo[3,4-c]isoquinolines and 3H-pyrazolo[4,3-f][1,7]naphthyridines

Abstract

An efficient method was developed for the synthesis of 1,3,4-trisubstituted pyrazolo[3,4-b]pyridines, 3H-pyrazolo[3,4-c]isoquinolines and 3H-pyrazolo[4,3-f][1,7]naphthyridines via intramolecular Heck reactions of imine derivatives of β-halovinyl/aryl aldehydes and 5-aminopyrazoles. This palladium acetate catalyzed reaction afforded good yields of these pyrazolo fused compounds under thermal conditions in the presence of xantphos as the ligand.