Environmentally Friendly Nafion-Mediated Friedländer Quinoline Synthesis under Microwave Irradiation: Application to One-Pot Synthesis of Substituted Quinolinyl Chalcones

Abstract

An efficient and eco-friendly synthetic route for Friedländer quinoline synthesis of polysubstituted quinolines is described. This green chemical method starts from various 2-aminobenzophenones and mono- or dicarbonyl synthons and uses reusable Nafion NR50 material as a solid catalyst in ethanol under microwave irradiation. The protocol has a high generality of functional groups and provides the desired quinolines in good to excellent yields. Some structures were confirmed by single-crystal X-ray diffraction analysis.

Environmentally Friendly Nafion-Catalyzed Synthesis of Substituted 2-Ethyl-3-Methylquinolines from Aniline and Propionaldehyde under Microwave Irradiation

“…Among these entries, BF 3 .OEt 2 showed the best performance. According to our previous work [69], we further examined the environmentally friendly solid acid Nafion ® NR50, and the desired product 3a was obtained at 93% yield (entry 15). However, only a 30% yield of 3a was observed when liquid Nafion ® NR117 was used as an acid catalyst (entry 16).…”

“…As illustrated in Scheme 5, changing the substituted group on propionaldehydes 2 did not influence the preparation of corresponding quinolines 6a-6h and gave modest to good yields. Based on our previous experience for the synthesis of quinolines by Friedländer reaction from 2-aminobenzophenone 4a with monocarbonyl synthons [69], it is possible that the electronwithdrawing CF 3 group on 2e change in α-methylene reactivity could also access the Friedländer-type protocol to prepare the desired quinoline 7 by decreasing to one equivalent (Scheme 6). Friedländer quinoline synthesis is the reaction of 2-aminobenzaldehyde with acetylaldehyde to generate quinoline skeleton.…”

“…Friedländer quinoline synthesis is the reaction of 2-aminobenzaldehyde with acetylaldehyde to generate quinoline skeleton. In 2020, we developed a Nafion ® NR50catalyzed Friedländer quinoline synthesis; the related mechanism was also reported [69]. Based on the results of current assays, compounds 1a and 2a are selected as model substrates to speculate the possible mechanism for the desired quinoline 3a synthesis, as shown in Scheme 7.…”

“…In continuation of our investigations toward the synthesis of nitrogen-containing heterocyclic compounds [68][69][70][71], we recently provided a synthetic route for the Friedländer quinoline synthesis from 2-aminobenzophenone and acetylacetone catalyzed by Nafion ® NR50 particles under microwave irradiation ((1) in Scheme 2) [69]. Nafion ® is a commercially available synthetic polymer particle which possesses ionic properties [72].…”

BiCl3-catalyzed green synthesis of 4-hydroxy-2-quinolone analogues under microwave irradiation

“…3,4 Microwave activation, which consists of deep heating of the reaction components, combined with solid catalysis, which has the advantages of reusability, recoverability, and high selectivity, is recognized nowadays as an effective tool in the synthesis of different important heterocyclic systems, such as imidazole, 5 acridinedione, 6 quinazolinone, 7 dihydroquinazolinone, 8 pyridine, 9 dihydropyridine, 10 and quinolone. 11…”