Ammonium niobium oxalate (ANO) as an efficient catalyst in the Paal–Knorr synthesis of N -substituted pyrroles

• Published in: RSC sustainability 2024-02, Vol.2 (2), p.521-527
• Main Authors: Dapper, Luiz H., da Rosa, Kethelyn M., Mena, Viviane T., de Souza, Rodrigo O. M. A., da Silva, Felipe L. N., Anjos, Thiago, Penteado, Filipe, Lenardão, Eder J.
• Format: Article
• Language: English
• ISSN: 2753-8125; 2753-8125
• DOI: 10.1039/D3SU00395G

Ammonium niobium oxalate (ANO) has been proven to be an outstanding cheap, low-toxicity and readily available Lewis acid catalyst for carbonyl activation reactions. Herein, we describe the use of ANO as a catalyst in the Paal–Knorr pyrrole synthesis. The reactions were conducted under mild conditions, not requiring heating or special apparatus, allowing the synthesis of the desired products in up to 99% yield in just 30 min. Additionally, ANO could be reusable up to seven times, without remarkable loss of efficiency. The batch protocol was successfully translated to a continuous-flow environment, with 96% conversion of the starting dione and aniline to the desired pyrrole in 2 min of residence time (a STY of 2.5 g h −1 ). The main protocol's features meet important green chemistry bases, making it a sustainable method to prepare N -substituted pyrrole derivatives.