An efficient protocol for the synthesis of substituted 5‐amino pyrazole bearing benzo[d]imidazolone Core and their antioxidant activity

Abstract

AbstractAn efficient, facile and regioselective route has been utilized for the synthesis of novel series of 5‐(5‐amino‐1H‐pyrazol‐3‐yl)‐1,3‐dimethyl‐1,3‐dihydro‐2H‐benzo[d]imidazol‐2‐one derivatives (5a‐l). The methyl 3,4‐diaminobenzoate (1) used CDI/DMF system for the cyclization to benzimidazolone followed by N‐methylation and next ACN/n‐BuLi media at −70°C to afford high yielded key intermediate, 3‐(1,3‐dimethyl‐2‐oxo‐2,3‐dihydro‐1H‐benzo[d]imidazol‐5‐yl)‐3‐oxopropanenitrile (4). The final adducts synthesis involved catalytic optimization to generate 5‐amino pyrazole‐based adducts (5a‐l) rather than 3‐amino pyrazole (6a‐l) are discussed. Chromatographic and spectral techniques (1H & 13C NMR, LC–MS, elemental analysis) confirmed the newly synthesized structures and were evaluated for antioxidant activity using DPPH free radical scavenging assay. The entire compounds showed extra (higher) potency against used standard ascorbic acid except 5j (2‐F Ph substituent) while, 5c (−Et substitution) was found to be most potent among others.