A Metal/Solvent/Additive Free Compliant Route to Ullmann-Type C-N Coupling using Ionic Liquid Entangled Porphyrin Heterogeneous Photocatalyst

摘要

N-Substituted pyrrole derivatives have been attracted as a prime source of biologically active compounds as therapeutic agents including antimicrobial, analgesic, and familiar antiproliferative agents in cancer treatment. Several metal-free reports have been documented for photocatalytic C-C/C-N bond formation to facilitate the synthesis of intermediates in pharmaceutical industries. In this protocol, we develop the scope of such methods, creating a green approach to achieve Ullmann-type C-N coupling. Particularly, we reveal a metal/solvent/additive-free route, for the synthesis of N-substituted pyrroles using novel Bronsted acid-functionalized porphyrin grafted on 1,2,4-triazole-based ionic liquid (BAFPcTzIL) comprising donor-acceptor moiety. This new stable photocatalyst was confirmed by FT-IR, (HNMR)-H-1, UV-Vis spectra to know Hammett acidity and energy bandgap by DR spectra. The optimized protocol was used significantly for reactions of morpholine, indole, pyrazole, imidazole, and benzimidazole with various inactivated aryl halides with good to excellent yields, under irradiations of 5 W LED in a homemade photocatalytic reactor. Moreover, the BAFPcTzIL could be readily separated by simple filtration and reused for 6 consecutive runs with admirable yield. The leaching test confirmed that porphyrin behaved like a perfect heterogeneous photocatalyst for C-N bond formation and might be attracted toward the synthesis of intermediates/scaffolds in the pharma and fine chemical industry.