Enaminone, Enaminoesters, and Related Compounds in the Metal‐Free Synthesis of Pyridines and Fused Pyridines

Abstract

This minireview presents the synthesis and applications of enaminones, enaminoesters, and related compounds. A metal‐free synthesis of pyridines and fused pyridines, pyridyl‐substituted amino acids, hydroxy acids, and polyols which is enabled by ring switching methodology is described, as well as a simple metal‐free synthesis of aryl‐substituted pyridines, and polysubstituted pyridines from polysubstituted butadiene.

Synthesis of 6,7-Dihydro-1H,5H-pyrazolo[1,2-a]pyrazoles by Azomethine Imine-Alkyne Cycloadditions Using Immobilized Cu(II)-Catalysts

“…According to the proposed mechanism, the use of hydrolytically more stable enamine C-N bond should reduce detachment of Cu(II)-enaminone complex from the solid support and, thus, improve reusability of the catalyst. To confirm this hypothesis, we prepared silica gel-bound enaminone 14 using 4-aminobenzoic acid ( 12 ) as a bifunctional linker, which was bound to 3-aminopropyl silica gel ( 3 ) via a robust amide bond and to the enaminone 2f through a stronger N -arylenamine C-N bond ( Scheme 6 ) [ 28 , 29 , 30 , 31 , 32 , 33 , 63 , 64 ]. Acid-catalyzed transamination of 2f with 4-aminobenzoic acid ( 12 ) gave the carboxy-functionalized enaminone 13 , which was amidated with 3 using 1,1′-carbonyldiimidazole (CDI) as activating reagent.…”

“…Acid-catalyzed reactions with N -, C -, and O -nucleophiles take place under mild conditions by substitution of the dimethylamino group to give β-functionalized propenoates. With ambident nucleophiles, enaminones undergo cyclization into different heterocyclic systems [ 28 , 29 , 30 , 31 , 32 , 33 ]. Enaminones are also used as alkenes in cycloaddition reactions [ 34 , 35 , 36 , 37 , 38 ] and as bidentate N, O ligands [ 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 ] and tetradentate acacen-type ligands [ 27 , 50 , 51 , 52 , 53 , 54 ] to coordinate metal ions.…”

“…In contrast to the rather extensive use of immobilized copper complexes in azide-alkyne cycloadditions (CuAAC) [ 62 ], their applications in CuAIAC reactions are almost unknown [ 26 ]. 3-Aminopropyl silica gel-immobilized Cu(II)-enaminone complexes would be easy to prepare via a transamination reaction [ 28 , 29 , 30 , 31 , 32 , 33 , 63 , 64 ], could serve as heterogeneous Cu(II) catalysts for the synthesis of pyrazolo[1,2- a ]pyrazoles, and would complement well the known examples of heterogeneous Cu(0)- [ 41 ], Cu(I)- [ 65 , 66 , 67 , 68 , 69 ], and Cu(II)-catalysts [ 26 ] in the CuAIAC reaction. Herein, we report the results of this study confirming the suitability of these new enaminone-based heterogeneous copper catalysts in regioselective [3 + 2] cycloadditions of 1-benzylidene-5,5-dimethyl-3-oxopyrazolidin-1-ium-2-ides to methyl propiolate leading to methyl 1-aryl-7,7-dimethyl-5-oxo-6,7-dihydro-1 H ,5 H -pyrazolo[1,2- a ]pyrazole-2-carboxylates.…”

Pleiotropic Properties of Amphiphilic Dihydropyridines, Dihydropyridones, and Aminovinylcarbonyl Compounds

“…[ 41 ]. Therefore, up to now, most of the research in the field of enamines have been devoted to the elaboration of new strategies and synthetic methods, but lack biological studies [ 42 ]. 2-Amino-3-alkoxycarbonylalkylammonium halides with long alkyl chains have appeared as a new class of enaminoesters and were elaborated as a transfection agent for RNS transfection [ 27 ].…”

Synthesis, In Vitro Cytotoxicity and Bleomycin‐Dependent DNA Damage Evaluation of Some Heterocyclic‐Fused Pyrimidinone Derivatives

“…Enaminones are readily available precursors and their usefulness in the construction of bioactive heterocycles has recently received significant attention . On the other hand, pyrimidinone derivatives have appeared as potent drugs in the field of chemotherapy.…”