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

Abstract

Herein, we report a facile synthetic methodology for the preparation of 2,3-dialkylquinolines from anilines and propionaldehydes. This cyclization involved environmentally friendly Nafion® NR50 as an acidic catalyst with microwave irradiation as the heating source. A series of substituted 2-ethyl-3-methylquinolines were prepared from various anilines and propionaldehyde derivatives through this protocol with good to excellent yields. Some new chemical structures were confirmed by X-ray single-crystal diffraction analysis and the related data were provided. The plausible reaction mechanism studies are also discussed.

TMSOTf-mediated Kröhnke pyridine synthesis using HMDS as the nitrogen source under microwave irradiation

“…Based on the above-mentioned results and our previous work, 27 a plausible pathway for the selective synthesis of TAPs and 3-benzyl TAPs is illustrated as shown in Scheme 2 . In cycle A, compound 1a was first activated using TMSOTf to generate intermediate I with the release of the triflate anion.…”

“…In continuation of our efforts in the synthesis of diversified heterocyclic skeletons under microwave (MW) conditions, 27 we recently developed a series of synthetic protocols for the synthesis of substituted nitrogen-containing compounds involving the HMDS/TMSOTf system under MW conditions. 27 a – c On the basis of our previous successful experiments, HMDS serves as a useful N source in this synthetic routes.…”

Environmentally friendly Nafion-catalyzed synthesis of 3-substituted isoquinoline by using hexamethyldisilazane as a nitrogen source under microwave irradiation

“…23 Nafion® NR50 possesses distinctive properties that make it useful as a proton source, enabling its application as a heterogeneous catalyst or an electrode. 24 In our previous research, we successfully utilized Nafion® NR50 as a catalyst to synthesize 2-ethyl-3-methylquinoline from aniline and propionaldehyde 25 and demonstrated its effectiveness in the Friedländer reaction to synthesize quinolinyl ketone (Scheme 2). 26 Considering all of the above, Nafion® NR50 can be employed in various ways for efficient and recyclable synthesis.…”