Palladium-catalyzed direct ortho-alkoxylation of 1-aryl-1H-indazoles via C–H bond activation

Title : Palladium-catalyzed direct ortho-alkoxylation of 1-aryl-1H-indazoles via C–H bond activation

Abstract:

A palladium-catalyzed, PIDA-promoted cross-dehydrogenative coupling (CDC) strategy has been developed for the direct and regioselective ortho-alkoxylation of 1-aryl-1H-indazoles through C-H bond functionalization. To the best of our knowledge, this study represents the first direct alkoxylation of 1-aryl-1H-indazole frameworks via C-H activation, providing a concise approach to structurally diversified indazole derivatives. The developed protocol utilizes readily available primary and secondary aliphatic alcohols, encompassing both cyclic and acyclic substrates, which function as alkoxylating partners as well as reaction media. Under operationally simple reaction conditions, a broad range of electron-donating and electron-withdrawing substituted 1-aryl-1H-indazoles underwent selective ortho-C–H alkoxylation to furnish the corresponding products in yields of up to 80%. The reaction exhibited broad substrate compatibility and tolerated a variety of substituents on the aromatic framework, demonstrating the synthetic flexibility of the method.

Importantly, the methodology also enabled access to C-2′-alkoxylated derivatives, further highlighting its potential for regioselective structural diversification of the 1-aryl-1H-indazole scaffold. The control experiments were performed to gain insight into the reaction pathway, and the observed results support the involvement of a radical-mediated process in the transformation. The synthetic utility of the developed protocol was further demonstrated through gram-scale experimentation, establishing that the reaction could be performed beyond the small-scale conditions without significant loss of efficiency. In addition, a one-pot methoxy-to-alcohol conversion was successfully achieved, providing a useful functional handle for subsequent synthetic transformations and further elaboration of the resulting indazole products.

Beyond the synthetic scope, selected synthesized compounds were evaluated for their anticancer activity against various cancer cell lines. Several derivatives exhibited promising inhibitory effects, with favorable IC₅₀ values, suggesting that the structurally diversified 1-aryl-1H-indazole derivatives generated through this methodology may possess potential as biologically relevant scaffolds. Overall, this study establishes a practical and efficient C-H functionalization strategy for the direct alkoxylation of previously unexplored 1-aryl-1H-indazole frameworks. The combination of regioselective C-H functionalization, broad alcohol scope, operational simplicity, scalability, and demonstrated biological activity provides a useful platform for the synthesis and preliminary biological exploration of functionalized indazole derivatives.
 

Biography:

I am a PhD researcher scholar in the Department of Medicinal Chemistry at the National Institute of Pharmaceutical Education and Research (NIPER), Raebareli, Lucknow, India, working under the supervision of Dr. Sandeep Chaudhary since August 2022. My research focuses on the development of novel synthetic methodologies through C-H bond activation of bioactive heterocycles, including 1-aryl-1H-indazole and pyrazolo[1,5-a]pyrimidine scaffolds, with potential applications in anticancer drug discovery. In parallel, I employ scaffold-hopping strategies for the design and synthesis of novel small molecules with potential anticancer activity. My research interests encompass organic synthesis, C-H bond functionalization, medicinal chemistry, scaffold hopping, and the discovery of biologically relevant small molecules.