Indium(III) Triflate-Catalyzed Reactions of Aza-Michael Adducts of Chalcones with Aromatic Amines: Retro-Michael Addition versus Quinoline Formation

Abstract

The indium(III) triflate-catalyzed reaction of aza-Michael adducts of chalcones with aromatic amines has been investigated. The Michael adducts derived from substituted anilines and chalcones underwent retro-Michael addition to give the original starting materials, whereas the adducts derived from 1-naphthylamines and chalcones afforded quinolines. A six-membered cyclic transition state has been proposed to explain the retro-Michael addition, while a Povarov mechanism has been put forward to explain the quinoline formation.

The Povarov Reaction: A Versatile Method to Synthesize Tetrahydroquinolines, Quinolines and Julolidines

“…14,136 Similarly to the synthesis of THQs, these reactions can be catalyzed by Lewis and Brønsted acids such as BF 3 •OEt 2 , 36,40,137-142 BF 3 •O(CH 3 ) 2 , 143,144 FeCl 3 , 145,146 InCl 3 , 147 trifluoromethanesulfonic acid, 148 p-toluenesulfonic acid, 146 CX4SO 3 H, 14,149 TFA, 150,151 camphorsulfonic acid, 152 tris(4-bromophenyl)aminium (TBPA + ), 140,[153][154][155] CBr 4 , 156 iron, 157 copper iodide 158 and iodine. [159][160][161][162][163][164][165][166][167] Furthermore, different triflates have been widely used such as Sc(OTf) 3 , 154,168,169 Yb(OTf) 3 , [170][171][172][173] Cu(OTf) 2 , 174,175 Ce(OTf) 3 , 176,177 Zn(OTf) 2 , 178 AgOTf, 22 In(OTf) 3 179 and Ca(OTf) 2 . 84 Heterogeneous catalysis was also described by using montmorillonite-supported perchloric acid (HClO 4 -Mont).…”

“…Regarding the reaction medium, various polar and nonpolar solvents have been explored, for example, acetonitrile, 2,4,6,[22][23][24][36][37][38] THF, 159,161 DMSO, 160,162,163,166,173 ethanol, 146,[181][182][183] DMF, 158 acetic acid, 157 dichloromethane, 97,138,145,148,150,179,180,184 TFE, 137,152 diethyl ether, 185 dichloroethane, 140,142,151,153,165,186 chloroform 174 and toluene. 147,171,177 Greener alternatives were also reported such as the absence of a solvent 84,149,174,176,178 or the use of a DES (Scheme 13).…”

A novel mass spectrometry-cleavable, phosphate-based enrichable and multi-targeting protein cross-linker

“…Vinyl sulfone-based Michael addition is an attractive methodology for protein modification,30,31 and we have paid much attention to the development of vinyl sulfones for conjugation with peptides and proteins 32–35. Additionally, it is well-known that a high energy will induce retro-Michael addition, which triggers the preferential cleavage of the labile conjugation bond 36,37. In this study, we intend to employ bisvinylsulfones as a novel class of MS-cleavable cross-linkers.…”

Design of Water Stable 1,3‐Dialkyl‐ 2‐Methyl Imidazolium Basic Ionic Liquids as Reusable Homogeneous Catalysts for Aza‐Michael Reaction in Neat Condition

“…A number of Lewis acid‐induced reactions also used with excess amount of reagents, CH 3 CN or 1,2‐dichloroethane as solvent, longer reaction time, polymerization of starting alkene and in certain cases use of excess amount of catalysts such as AlCl 3 , SnCl 4 or TiCl 4 etc . Later on several metal triflates, metal oxides, clay material, and other catalysts were developed in sub‐stoichiometric level. Various sustainable approaches of this addition reaction were also investigated involving heterogeneous acidic or basic catalysts,, use of water and polyethylene glycol as reaction medium, ionic liquid mediated /catalyzed reactions and microwave assisted reaction .…”