Green synthesis of pyrazolo[3,4-b]quinolinones was designed using bioproduct pyridine-2-carboxylic acid (P2CA) as a green and efficient catalyst. The multi-component reaction of aldehydes, 1,3-cyclodiones and 5-amino-1-phenyl-pyrazoles regioselectively produced pyrazolo[3,4-b]quinolinones in excellent yield (84–98%). Recyclization of the catalyst was also investigated. The electronic effect of the various substituents in aromatic rings indicated that the reaction proceeded through the carbocation intermediate. This newly designed protocol very quickly constructed products conventionally under milder conditions.

中文翻译：

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吡啶-2-羧酸作为快速多组分合成吡唑并[3,4-b]喹啉酮的有效催化剂

以生物产物吡啶-2-羧酸（P2CA）为绿色高效催化剂，设计了吡唑并[3,4- b ]喹啉酮的绿色合成。醛、1,3-环二酮和 5-氨基-1-苯基-吡唑的多组分反应区域选择性地产生了吡唑并[3,4- b ]喹啉酮，产率很高（84-98%）。还研究了催化剂的再循环。芳环中各种取代基的电子效应表明反应是通过碳正离子中间体进行的。这种新设计的协议非常快速地在较温和的条件下常规构建产品。