European Journal of Organic Chemistry 2018-02-20

ZnCl2 Catalyzed aza‐Diels‐Alder Reaction for Synthesis of 1H‐Pyrazolo[3,4‐b]pyridine‐4,5‐dicarboxylate Derivatives

Fung Fuh Wong; Ching-Chun Tseng; Wan-Ping Yen; Shuo-En Tsai; Yu-Tzu Hu; Hiroyuki Takayama; Yueh-Hsiung Kuo

Index: 10.1002/ejoc.201701761

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Abstract

A new ZnCl2 catalyzed aza‐Diels‐Alder reaction was developed by using pyrazoylimines with acetylenedicarboxylic acid diethyl ester (diethyl but‐2‐ynedioate) to prepare pyrazolo[3,4‐b]pyridine‐4,5‐dicarboxylate. The key strategy of this reaction was the use of ZnCl2 as the catalyst to promote the aza‐Diels‐Alder reaction. Based on the optimized study and economic benefits, the best amount of ZnCl2 was established as 20 mol % of azadiene. On the other hand, N,N‐diisopropylamidinyl N‐pyrazoyl imine was conceived as the best azadiene substrate.