TMSOTf-Catalyzed [4 + 2] Annulation of Ynamides and β-(2-Aminophenyl)-α,β-ynones for the Synthesis 2-Aminoquinolines

A metal-free TMSOTf-catalyzed [4 + 2] annulation of ynamides with β-(2-aminophenyl)-α,β-ynones enables the regiospecific and facile assembly of 2-aminoquinoline frameworks. The catalyst TMSOTf presented a remarkable advancement compared to previously reported transition-metal catalysts. A wide range of 3-aryl/alkyl-substituted 2-aminoquinolines were generated in moderate to excellent yields due to the mild conditions.

Green Synthesis of Electrophilic Alkenes Using a Magnesium Catalyst under Aqueous Conditions and Mechanistic Insights by Density Functional Theory

A green approach for the synthesis of electrophilic alkenes has been developed via Knoevenagel condensation between active methylene compounds and carbonyl compounds using Mg powder under aqueous conditions. In this strategy, Mg(OH)2 acts as a catalyst, which was generated in situ by the reaction between metallic Mg (20 mol %) and water. Mg was found to be an efficient, nontoxic, and inexpensive metal catalyst system for producing a range of electrophilic alkenes in excellent yields (≤98%). A gram-scale synthesis of electrophilic alkenes has been developed, and Mg metal was recovered and recycled up to three times without an appreciable loss of catalytic activity. A catalytic cycle was proposed, and the reaction mechanism was investigated using density functional theory. The key steps are enolization of ethyl cyanoacetate, C-C bond formation, and then regeneration of the catalyst via metathesis with H2O. The overall reaction occurs easily with a maximum ΔG°⧧ value of 7.9 kcal/mol for the rate-determining C-C bond formation step. Our protocol has several advantages and can be further extended to one-pot sequential Knoevenagel condensation and Michael addition, and one-pot sequential Knoevenagel condensation and chemoselective reduction can be used for the synthesis of valuable precursors of pharmaceutical products under green and aqueous conditions.

Leveraging Zn(II) Catalyst: Synthesis of Amidoquinolines via (3 + 3) Heteroannulation of Aromatic Amines and Ynamides

Herein, we present a Zn(II)-catalyzed (3 + 3) heteroannulation reaction between aromatic amines and 1,3-diynamides for the synthesis of amidoquinolines. A large number of aromatic amines are well tolerated, furnishing quinoline derivatives in up to excellent yield. Notably, various reactive functional groups have survived under the optimal reaction conditions, highlighting the mildness of the developed protocol. In addition, amines derived from bioactive molecules show modest reactivity.

Cobalt-catalyzed tandem one-pot synthesis of polysubstituted imidazo[1,5-a]pyridines and imidazo[1,5-a]isoquinolines

An efficient cobalt-catalyzed tandem one-pot method has been developed for the synthesis of polysubstituted imidazo[1,5-a]-N-heteroaromatics. The method involves Knoevenagel condensation followed by cobalt-catalyzed direct alkenylation to give the desired polysubstituted imidazo[1,5-a]pyridines and imidazo[1,5-a]isoquinolines in a one-pot manner. This method exhibits a broad substrate scope, provides moderate to good (39-74%) yields and is amenable to scale-up to the gram scale.

Recent Advances in the Tandem Copper-Catalyzed Ullmann-Goldberg N-Arylation–Cyclization Strategies

N‒Aryl bond formation under copper catalysis has been playing a pivotal role and has been extensively used as a key step in the total syntheses of several therapeutic molecules. The...

Solvent-Dependent Cyclization of 2-Alkynylanilines and ClCF2COONa for the Divergent Assembly of N-(Quinolin-2-yl)amides and Quinolin-2(1H)-ones

Herein, we present an expedient Cu-catalyzed [5 + 1] cyclization of 2-alkynylanilines and ClCF₂COONa to divergent construction of N-(quinolin-2-yl)amides and quinolin-2(1H)-ones by regulating the reaction solvents. Notably, nitrile acts as a solvent and performs the Ritter reactions. ClCF₂COONa is used as a C1 synthon in this transformation, which also represents the first example for utilization of ClCF₂COONa as an efficient desiliconization reagent. The current protocol involves in situ generation of isocyanide, copper-activated alkyne, Ritter reaction and protonation.

Recent Developments of Quinoline Derivatives and their Potential Biological Activities

Heterocyclic compounds containing the quinoline ring play a significant role in organic synthesis and therapeutic chemistry. Polyfunctionalized quinolines have attracted the attention of many research groups, especially those who work on drug discovery and development. These derivatives have been widely explored by the research biochemists and are reported to possess wide biological activities. This review focuses on the recent progress in the synthesis of heterocyclic compounds based-quinoline and their potential biological activities.

Recent Progress in the Synthesis of Quinolines

BACKGROUND

Quinoline-containing compounds present in both natural and synthetic products are an important class of heterocyclic compounds. Many of the substituted quinolines have been used in various areas including medicine as drugs. Compounds with quinoline skeleton possess a wide range of bioactivities such as antimalarial, anti-bacterial, anthelmintic, anticonvulsant, antiviral, anti-inflammatory, and analgesic activity. Due to such a wide range of applicability, the synthesis of quinoline derivatives has attracted a lot of attention of chemists to develop effective methods. Many known methods have been expanded and improved. Furthermore, various new methods for quinoline synthesis have been established. This review will focus on considerable studies on the synthesis of quinolines date which back to 2014.

OBJECTIVE

In this review, we discussed recent achievements on the synthesis of quinoline compounds. Some classical methods have been modified and improved, while other new methods have been developed. A vast variety of catalysts were used for these transformations. In some studies, quinoline synthesis reaction mechanisms were also displayed.

CONCLUSION

Many methods for the synthesis of substituted quinoline rings have been developed recently. Over the past five years, the majority of those reported have been based on cycloisomerization and cyclization processes. Undoubtedly, more imaginative approaches to quinoline synthesis will appear in the literature in the near future. The application of known methods to natural product synthesis is probably the next challenge in the field.

Step-economical synthesis of 3-amido-2-quinolones by dendritic copper powder-mediated one-pot reaction

The one-pot protocol by the dendritic copper powder-mediated Knoevenagel condensation/annelation is delineated here for the synthesis of 3-amido-2-quinolones. It is practical with moisture tolerance and easy setup, and is compatible with many functional groups under mild conditions. This method was applied for the preparation of the key intermediates of biologically relevant 3-amido-2-quinolones.

Palladium-Catalyzed Cyclization of N-Acyl- o-alkynylanilines with Isocyanides Involving a 1,3-Acyl Migration: Rapid Access to Functionalized 2-Aminoquinolines

A simple and expedient approach for the synthesis of functionalized 2-aminoquinolines via palladium-catalyzed annulation of N-acyl- o-alkynylanilines with isocyanides has been developed with high atom economy, in which an unconventional 6- endo-dig cyclization process is observed. Further investigations of the mechanism demonstrated that an intramolecular acyl migration of the N-protecting groups was involved in this transformation.

Tandem cyclization of o-alkynylanilines with isocyanides triggered by intramolecular nucleopalladation: access to heterocyclic fused 2-aminoquinolines

Herein, a novel strategy for the synthesis of various heterocyclic fused 2-aminoquinolines via palladium-catalyzed tandem cyclization of o-alkynylanilines with isocyanides has been developed. This process includes trans-oxy/aminopalladation, isocyanide insertion, elimination and 1,3-hydrogen migration. Besides high atom and step economy, this method shows good functional group compatibility with excellent chemo- and regioselectivities under mild reaction conditions.

Copper-catalyzed cascade reaction: synthesis of pyrimido[4,5-b]quinolinones from 2-chloroquinoline-3-carbonitriles with (aryl)methanamines

Cu-catalyzed cascade reaction of 2-chloroquinoline-3-carbonitriles with benzyl amines using sodium hydroxide in aerobic atmosphere has been developed for the synthesis of pyrimido[4,5-b]quinoline-4-ones.

Design, synthesis and crystallographic study of novel indole-based cyano derivatives as key building blocks for heteropolycyclic compounds of major complexity

A four-stage reaction sequence has been designed and developed for the synthesis of highly functionalized enolate esters as key building blocks for the synthesis of novel heteropolycyclic compounds of potential pharmaceutical value. The sequence starts with simple commercially available indoles and proceeds via 3-(indol-3-yl)-3-oxopropanenitriles, which react with 2-bromobenzaldehyde to form the corresponding chalcones; these are readily reduced to dihydrochalcones, which are in turn acylated to form the enolate esters. The compounds in this sequence have been characterized by IR and ¹H and ¹³C NMR spectroscopy, by mass spectrometry and by elemental analysis. The molecular and supramolecular structures are reported for representative examples, namely (E)-3-(2-bromophenyl)-2-(1-methyl-1H-indole-3-carbonyl)acrylonitrile, C₁₉H₁₃BrN₂O, (Ib), (2RS)-2-(2-bromobenzyl)-3-(1-methyl-1H-indol-3-yl)-3-oxopropanenitrile, C₁₉H₁₅BrN₂O, (IIb), and (2RS)-3-(1-benzyl-1H-indol-3-yl)-2-(2-bromobenzyl)-3-oxopropanenitrile, C₂₅H₁₉BrN₂O, (IIc), the latter two of which crystallize with Z' = 2, and (E)-1-(1-acetyl-1H-indol-3-yl)-3-(2-bromophenyl)-2-cyanoprop-1-en-1-yl acetate, C₂₂H₁₇BrN₂O, (III), and (E)-1-(1-benzyl-1H-indol-3-yl)-3-(2-bromophenyl)-2-cyanoprop-1-en-1-yl benzoate, C₃₂H₂₃BrN₂O, (IV). The structure of the related chalcone (E)-2-benzoyl-3-(2-bromophenyl)prop-2-enenitrile, (V), has been redetermined at 100 K, where it is monoclinic, as opposed to the triclinic form reported at ambient temperature.

A copper catalyzed multicomponent cascade redox reaction for the synthesis of quinazolinones

A copper catalyzed multicomponent cascade redox reaction for the synthesis of various quinazolinones starting from easily available 2-bromobenzamides, benzylic alcohols and sodium azide as a nitrogen source has been developed.