A mild method for the synthesis of bis-pyrazolo[3,4-b:4′,3′-e]pyridine derivatives

Abstract A mild and efficient method for the synthesis of bispyrazolo[3,4- b :4′,3′- e ]pyridines from 5-aminopyrazoles and aromatic aldehydes using an inexpensive FeCl 3 catalyst is reported. The reaction temperature was reduced from 220–250 °C to 130 °C compared to conventional methods. A large proportion of the products precipitated directly from the mixture at room temperature. Aliphatic and α,β-unsaturated aldehydes selectively resulted in formation of the corresponding 1 H -pyrazolo[3,4- b ]pyridine derivatives. A possible domino reaction mechanism was also proposed. Several aryl alkynyl groups were introduced to these tricyclic molecules via the Sonogashira coupling reaction.