Environmentally benign synthesis of 2,4-diarylquinolines under metal- & solvent-free conditions

FeCl3-catalyzed regioselective ring-opening of aryl oxirane with 4-hydroxycoumarin for the synthesis of furo[3,2-c]coumarins

“…Subsequently, intermediate A reacts with 4-hydroxy-6-methylcoumarin ( 1a ) to provide intermediate B by regioselective epoxide ring-opening at the less hindered site of styrene oxide ( 2a ). 13–15 Then, the chloride anion (Cl − ), obtained from [FeCl 4 ] − , assists in breaking of the Fe–O bond to provide the intermediate C . Next, Cl − removes the hydrogen atom from intermediate C , which generates the negatively charged oxygen atom, which facilitates the cyclization of intermediate C by eliminating one molecule of water to provide the cyclized intermediate D .…”

Recent advancement in the synthesis of quinoline derivatives via multicomponent reactions

“…73 Next, we developed a new eco-friendly method for producing 2,3-diarylquinolines 91 in a one-step process that combines arylamines 1, benzaldehyde 5 and styrene oxide 23. 74 The reaction takes place at 120 °C in the presence of 20 mol% p-TSA, eliminating the need for additional metal catalysts, additives, or oxidizing agents. Detailed investigations into the mechanism of the reaction established the vital function of p-TSA and demonstrated Organic & Biomolecular Chemistry Review that air serves as the exclusive oxidizing agent.…”

“…Then, the synthesis of 2,4-diarylquinolines 90 was reported via a three-component reaction of arylamine 1 , aryl aldehyde 5 and aryl acetylene 12 under solvent-free conditions at a temperature of 110 °C, employing 30 mol% p -toluenesulfonic acid as catalyst. 73 Next, we developed a new eco-friendly method for producing 2,3-diarylquinolines 91 in a one-step process that combines arylamines 1 , benzaldehyde 5 and styrene oxide 23 . 74 The reaction takes place at 120 °C in the presence of 20 mol% p -TSA, eliminating the need for additional metal catalysts, additives, or oxidizing agents.…”

FeCl3-Catalyzed Decyanative [4 + 2] Annulation of α-Aminonitriles with Alkynes: Access to 2,4-Diaryl Quinolines in Batch and Continuous-Flow Processes

“…4c The reported studies of this tandem protocol emphasize copper-5 and iron-based catalysts 6 followed by the emergence of various conditions such as montmorillonite 7a and other metal catalysts 7b,c and with some studies on Brønsted acids. 8 As a continuation of efforts in developing new methodologies for 2,4-disubstituted quinolines, recently several innovative protocols have emerged 9 based on A 3 coupling, oxidative coupling, 10 and other starting materials to use their synthetic utility over organic transformations. Zhang et al (2020) disclosed the synthesis of 2,4-disubstituted quinolines (2-alkyl or 2-carboxylate) using stoichiometric loading of I 2 and Mn(OAc) 3 from 2-vinyl styrenes with β-ketoesters via a C− C cleavage reaction (Scheme 1b).…”