Synthesis of Quinolines and Isoquinolines via Site-Selective, Domino Benzannulation of 2- and 3-Chloropyridyl Ynones with Nitromethane

Benzannulation of Functionally Enhanced Indole-3-carbaldehydes with Ynones and Alkynoates: A Domino Approach to Bioactive Carbazoles─Synthesis of Clauolenzole A, Calothrixin A & B, Methyl Carbazole-3-carboxylate, and Quinocarbazole

A flexible, regioselective, benzannulation strategy toward multifunctional carbazoles from 2-(2-oxo-2-arylethyl)indole-3-carbaldehydes, employing either ynones or alkynoates as reaction partners, has been envisaged and implemented. This enabling access to variegated carbazoles in one-flask operation leads to strategic substituent diversification via reaction partner variation. The efficacy and applications of this methodology are demonstrated through 23 examples and concise syntheses of bioactive clauolenzole A, calothrixin A & B, methyl carbazole-3-carboxylate, and pharmacophoric quinocarbazole.

Direct Two Carbon Ring Expansion of 1-Indanones with Ynones: An Eco-Friendly, One-Flask Approach to Functionally Enriched 5H-Benzo[7]annulenes

Direct 2C-ring expansion of 1-indanones with ynones to 5H-benzo[7]annulenes has been observed, and its generality has been gauged (19 examples). Overall, this simple and convenient cascade process to 5H-benzo[7]annulenes involves engagement of 1-indanone with two ynone moieties with formation of three new C-C σ-bonds, cleavage of C-C σ-bond, and concurrent functionality amplification. The resulting seven-membered ring, laced with an opportunistic disposition of four proximal functional groups, offers avenues for their further productive interplay. Our new approach embraces many green and eco-friendly features.

Diversified Stitching of Ynones with Oxindole-3-oxy acrylates: One-Flask Spiro-annulation Protocol toward Assorted 3H/5H-Spiro[furan-2,3'-indolin]-2'-ones

Spiroannulation of oxindole-3-oxy acrylates with ynones involving two overlapping, base differentiated cascades has been observed. Initial exposure of ynones and oxindole 3-oxy acrylates to K2CO3 triggered a tandem Michael-Michael cascade to deliver a pair of spiroannulated diastereomers. Further exposure to LiHMDS led to deep restructuring through a second multistep cascade involving stereoselective recreation of the C3 quaternary center to furnish 3H-spiro[furan-2,3'-indolin]-2'-ones with functional amplification and scrambling. This new scaffold can be directly accessed in a one-flask operation from ynones and oxindole-3-oxy acrylates.

Synthesis and Applications of Asymmetric Catalysis Using Chiral Ligands Containing Quinoline Motifs

In the past decade, asymmetric synthesis of chiral ligands containing quinoline motifs, a family of natural products displaying a broad range of structural diversity and their metal complexes have become the most significant methodology for the generation of enantiomerically pure compounds of biological and pharmaceutical interest. This review provides comprehensive insight on the plethora of nitrogen-based chiral ligands containing quinoline motifs and organocatalysts used in asymmetric synthesis. However, it is circumscribed to the synthesis of quinoline-based chiral ligands and metal complexes, and their applications in asymmetric synthesis as a homogeneous and heterogeneous catalyst.

Stitching Ynones with Nitromethanes: Domino Synthesis of Functionally Enriched Benzofurans and Benzothiophenes

A convenient one-pot benzannulation of regioisomeric 2- or 3-substituted furan and thiophene ynones with a range of nitromethanes has been discovered to directly access densely and diversely functionalized benzofurans and benzothiophenes. In this protocol, the nitro group in nitromethanes functions as recursive carbanion activator to setup tandem Michael addition-6π-electrocyclization, and its eventual sacrificial elimination facilitates aromatization and overall benzannulation. This benzannulation was also explored with furan/thiophene based o-halo ynones wherein a Michael addition-S_NAr process operates and nitromethanes leave their imprint to deliver nitro substituted benzo-furans and -thiophenes.

Synthetic and medicinal perspective of quinolines as antiviral agents

In current scenario, various heterocycles have come up exhibiting crucial role in various medicinal agents which are valuable for mankind. Out of diverse range of heterocycle, quinoline scaffold have been proved to play an important role in broad range of biological activities. Several drug molecules bearing a quinoline molecule with useful anticancer, antibacterial activities etc have been marketed such as chloroquine, saquinavir etc. Owing to their broad spectrum biological role, various synthetic strategies such as Skraup reaction, Combes reaction etc. has been developed by the researchers all over the world. But still the synthetic methods are associated with various limitations as formation of side products, use of expensive metal catalysts. Thus, several efforts to develop an efficient and cost effective synthetic protocol are still carried out till date. Moreover, quinoline scaffold displays remarkable antiviral activity. Therefore, in this review we have made an attempt to describe recent synthetic protocols developed by various research groups along with giving a complete explanation about the role of quinoline derivatives as antiviral agent. Quinoline derivatives were found potent against various strains of viruses like zika virus, enterovirus, herpes virus, human immunodeficiency virus, ebola virus, hepatitis C virus, SARS virus and MERS virus etc.

Orthogonal Strapping of o-Haloaryl Ynones with Pyrazolones: A One-Pot, Domino Process toward Spiropyrazolones

A new class of spiroannulated pyrazolone scaffolds have been assembled from diverse o-haloaryl ynones and β-bromoalkenyl ynones via base mediated, one-pot, metal free, orthogonal strapping (tethering) mediated by the recursive anion(s) derived from pyrazolones. These convenient, preparatively useful transformations proceed through either a tandem Michael addition-intramolecular S_NAr reaction or a tandem Michael addition-intramolecular Ad_NE process to furnish a range of pharmacophoric, diverse, spiroannulated pyrazolones from readily accessible precursors.

Access to 2-Alkyl/Aryl-4-(1H)-Quinolones via Orthogonal "NH3" Insertion into o-Haloaryl Ynones: Total Synthesis of Bioactive Pseudanes, Graveoline, Graveolinine, and Waltherione F

An efficient one-pot synthesis of 4-(1H)-quinolones through an orthogonal engagement of diverse o-haloaryl ynones with ammonia in the presence of Cu(I), involving tandem Michael addition and ArCsp₂-N coupling, is presented. The substrate scope of this convenient protocol, wherein ammonium carbonate acts as both an in situ ammonia source and a base toward diverse 2-substituted 4-(1H)-quinolones, has been mapped and its efficacy validated through concise total synthesis of bioactive natural products pseudanes (IV, VII, VIII, and XII), graveoline, graveolinine, and waltherione F.

Recent advances and prospects in the metal-free synthesis of quinolines

Metal-free synthesis of quinolines has recently gained attention, and this review focuses on the recent advances in the metal-free synthesis of quinolines.