ZnCl₂‐Catalyzed Aza‐Diels–Alder Reaction for the Synthesis of 1<i>H</i>‐Pyrazolo[3,4‐<i>b</i>]pyridine‐4,5‐dicarboxylate Derivatives

Abstract

A new ZnCl 2 ‐catalyzed aza‐Diels–Alder reaction was developed for the preparation of pyrazolo[3,4‐ b ]pyridine‐4,5‐dicarboxylates through the reaction of pyrazoylimines with acetylenedicarboxylic acid diethyl ester (diethyl but‐2‐ynedioate). Based on optimization studies and economic factors, the best amount of ZnCl 2 was established to be 20 mol‐% relative to the azadiene. On the other hand, N , N ‐diisopropylamidinyl N ‐pyrazoyl imine was found to be the best azadiene substrate.