Cp∗Ir(III) Catalyzed greener synthesis of nitrogenous heterocycles using acceptor less dehydrogenative coupling (ADC) strategy

Abstract

In our preliminary research, we demonstrated excellent catalytic activity of Ir(III) complexes coordinated via a picolinamidato moiety. Utilizing these catalysts, we efficiently synthesized α-alkylated ketones through the hydrogen-borrowing methodology, employing ketones and secondary alcohols in the presence of primary alcohols. Furthermore, we successfully applied an acceptor less dehydrogenative coupling (ADC) strategy using the same series of in-house synthesized Ir(III) catalysts to generate a variety of nitrogen-containing heterocycles, including quinoline, pyrrole, and pyridine derivatives under neat (solvent-free) conditions at 90 °C. Encouraged by these results, we extended the catalytic system to the synthesis of additional nitrogen-rich heterocyclic frameworks such as pyrido[2,3-b]pyrazine, 1,8-naphthyridine, and quinazolin-4(3H)-one derivatives, achieving good to excellent yields. This methodology is particularly attractive due to its environmentally benign nature requiring only a small amount of catalyst (0.3 mol%), base (0.2 mol%) and producing only non-toxic by-products H₂ and H₂O. Overall, this work contributes to the development of sustainable and green synthetic approaches for the construction of valuable nitrogen-containing heterocycles.