Synthesis of Quinoline Derivatives via Cu-Catalyzed Cascade Annulation of Heterocumulenes, Alkynes, and Diaryliodonium Salts

Mechanistic Insights from Density Functional Theory into Rh/Acid-Catalyzed Synthesis of 1,2-Dihydroquinolines via Skeleton-Reorganizing Coupling of Cycloheptatriene and Amines

Density functional theory calculations were conducted to refine our understanding at the molecular level of the synthesis of fused 1,2-dihydroquinolines through Rh- and acid-catalyzed skeleton-reorganizing coupling reactions of cycloheptatriene with amines. The results reveal that the reaction progresses via cascade catalysis, consisting of consecutive steps of Rh-catalyzed intermolecular coupling involving two RhIII-RhI-RhIII transformations with a maximum energy barrier of 27.1 kcal/mol, followed by acid-catalyzed intramolecular skeleton reorganization with a peak energy barrier of 23.3 kcal/mol. The most significant finding of this work is the identification of a new oxidation-reduction mode of the Rh center. This mode is achieved via migration of a proton from the ammonium ion to the metal center and nucleophilic attack-induced intermolecular reductive coupling, distinguishing it from the conventional oxidative addition-reductive elimination process. The acid-catalyzed intramolecular skeleton reorganization necessitates the assistance of a second HOTs molecule, along with its conjugate base, which sequentially facilitates retro-Mannich-type C-C cleavage and the isomerization of the terminal imine to enamine via acid-base catalysis. Our calculations also explain why the azabicyclic tropene byproduct does not compete with the formation of the fused 1,2-dihydroquinoline product. These theoretical insights are expected to provide valuable guidance for further improvements in the efficiency of skeleton-reorganizing coupling reactions between cycloheptatriene and amines.

Diaryliodonium(III) Salts in One-Pot Double Functionalization of C–IIII and ortho C–H Bonds

Since the 1950s, diaryliodonium(III) salts have been demonstrated to participate in various arylation reactions, forming aryl–heteroatom and aryl–carbon bonds. Incorporating the arylation step into sequential transformations would provide access to...

Iodine-imine Synergistic Promoted Povarov-Type Multicomponent Reaction for the Synthesis of 2,2'-Biquinolines and Their Application to a Copper/Ligand Catalytic System

An efficient iodine-imine synergistic promoted Povarov-type multicomponent reaction was reported for the synthesis of a practical 2,2'-biquinoline scaffold. The tandem annulation has reconciled iodination, Kornblum oxidation, and Povarov aromatization, where the methyl group of the methyl azaarenes represents uniquely reactive input in the Povarov reaction. This method has broad substrate scope and mild conditions. Furthermore, these 2,2'-biquinoline derivatives had been directly used as bidentate ligands in metal-catalyzed reactions.

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.

Dimerization–cyclization reactions of isocyanoaryl-tethered alkylidenecyclobutanes via a triplet biradical mediated process

A triplet biradical mediated dimerization–cyclization reaction of isocyanoaryl-tethered alkylidenecyclobutanes to construct macrocyclic skeletons including dihydroquinoline and quinoline units has been reported.

PtCl2-Catalyzed Cycloisomerization of 1,8-Enynes: Synthesis of Tetrahydropyridine Species

The cycloisomerization of 1,8-enynes in the presence of platinum(II) chloride was developed to generate bicyclic nitrogen-containing heterocycle species via 6- endo-dig cyclization and [3,3]-sigmatropic rearrangement in acceptable to good yields. The related control experiments and preliminary mechanistic studies indicate a plausible mechanism involving 1,6- endo-dig aminoplatination of the alkyne and allylic [3,3]-sigmatropic rearrangement with total inversion of the allylic moiety.

DFT calculations on the mechanism of copper-catalysed tandem arylation-cyclisation reactions of alkynes and diaryliodonium salts

We present a computational mechanistic study on the copper(III)-catalysed carboarylation-ring closure reactions leading to the formation of functionalised heterocycles. We have performed DFT calculations along selected routes and compared their free energy profiles. The calculations considered two viable options for the underlying mechanism which differ in the order of the oxazoline ring formation and the aryl transfer steps. In our model transformation, it was found that the reaction generally features the aryl transfer-ring closing sequence and this sequence shows very limited sensitivity to the variation of the substituent of the reactants. On the basis of the mechanism the origin of the stereoselectivity is ascribed to the interaction of the Cu ion with the oxazoline oxygen driving the ring-closure step selectively.

Facile Route to the Synthesis of 1,3-Diazahetero-Cycle-Fused [1,2-a]Quinoline Derivatives via Cascade Reactions

A one-step protocol without transition-metal catalysts with simple post-treatment for the synthesis of 1,3-diazaheterocycle-fused [1,2-a]quinoline derivatives via the cascade reaction of 2-fluorobenzaldehyde (1) and heterocyclic ketene aminals (2) was developed. In the one-step cascade reaction, C=C and C-N bonds were constructed, and the targeted compound can be efficiently obtained by filtering without column chromatography. This protocol describes a valuable route to concisely and feasibly obtain 1,3-diazaheterocycle-fused [1,2-a]quinoline derivatives. The synthetic methodology is particularly attractive because of the following features: low-cost solvent, mild temperature, atom economy, high yield, and potential biological activity of the product.

One-pot regioselective synthesis of 2,4-disubstituted quinolines via copper(ii)-catalyzed cascade annulation

A copper(ii)-catalyzed cascade annulation for the one-pot synthesis of 2,4-disubstituted quinolines has been disclosed.

Base-controlled chemoselectivity reaction of vinylanilines with isothiocyanates for synthesis of quinolino-2-thione and 2-aminoquinoline derivatives

Quinolino-2-thione and 2-aminoquinoline derivatives were obtained by a base-controlled chemo-selective reaction of vinylanilines with alkyl/aryl isothiocyanates.