Comprehensive Review on the Synthesis of [1,2,3]Triazolo[1,5-a]Quinolines

This report outlines the evolution and recent progress about the different protocols to synthesize the N-heterocycles fused hybrids, specifically [1,2,3]triazolo[1,5-a]quinoline. This review encompasses a broad range of approaches, describing several reactions for obtaining this since, such as dehydrogenative cyclization, oxidative N-N coupling, Dieckmann condensation, intramolecular Heck, (3+2)-cycloaddition, Ullman-type coupling and direct intramolecular arylation reactions. We divided this review in three section based in the starting materials to synthesize the target [1,2,3]triazolo[1,5-a]quinolines. Starting materials containing quinoline or triazole units previously formed, as well as starting materials which both quinoline and triazole units are formed in situ. Different methods of obtaining are described, such as metal-free or catalyzed conditions, azide-free, using conventional heating or alternative energy sources, such as electrochemical and photochemical methods. Mechanistic insights underlying the reported reactions were also described in this comprehensive review.

Electrosynthesis of 1,2,3-Benzotriazines through an Iodide-Catalyzed Skeletal Editing of 3-Aminoindazoles

This report describes an environmentally benign synthesis of 1,2,3-benzotriazines through an iodide-catalyzed electro-oxidative N-centered [1,2]-rearrangement of 3-aminoindazoles. The developed method demonstrates the activation of heteroatoms via electrochemically generated reactive iodide species without using any metal catalysts and peroxides. The protocol features practical and mild reaction conditions and displays a wide substrate scope. Various mechanistic experiments and cyclic voltammetric studies have been instrumental in elucidating the reaction mechanism, operating via a skeletal rearrangement of 3-aminoindazoles.

Advances in organocatalyzed synthesis of organic compounds

The recent advancements in utilizing organocatalysts for the synthesis of organic compounds have been described in this review by focusing on their simplicity, effectiveness, reproducibility, and high selectivity which lead to excellent product yields. The organocatalytic methods for various derivatives, such as indoles, pyrazolones, anthrone-functionalized benzylic amines, maleimide, polyester, phthalimides, dihydropyrimidin, heteroaryls, N-aryl benzimidazoles, stilbenoids, quinazolines, quinolines, and oxazolidinones have been specifically focused. The review provides more understanding by delving into potential reaction mechanisms. We anticipate that this collection of data and findings on successful synthesis of diverse compound derivatives will serve as valuable resources and stimulating current and future research efforts in organocatalysis and industrial chemistry.

Continuous Flow Synthesis of Benzotriazin-4(3H)-ones via Visible Light Mediated Nitrogen-Centered Norrish Reaction

We report a new protocol for the synthesis of substituted benzotriazin-4(3H)-ones which are underrepresented heterocyclic scaffolds with important pharmacological properties. Our method exploits acyclic aryl triazine precursors that undergo a photocyclization reaction upon exposure to violet light (420 nm). Continuous flow reactor technology is exploited to afford excellent yields in only 10 min residence time with no additives or photocatalysts needed. The underlying reaction mechanism appears to be based on an unprecedented variation of the classical Norrish type II reaction with concomitant fragmentation and formation of N-N bonds. Scalability, process robustness, and green credentials of this intriguing transformation are highlighted.

Silver-Catalyzed Skeletal Editing of Benzothiazol-2(3H)-ones and 2-Halogen-Substituted Benzothiazoles as a Rapid Single-Step Approach to Benzo[1,2,3]thiadiazoles

A facile silver(I)-catalyzed reaction of benzothiazol-2(3H)-ones with NaNO2, or using AgNO2 directly, enables a single-step transformation to the corresponding benzo[1,2,3]thiadiazoles in moderate to excellent yields, with wide functional group compatibility. It can also be performed in a one-pot manner from readily available 2-halobenzothiazoles. This intriguing transformation involving an atom replacement in the S,N-heteroarene ring thus provides rapid access to isobenzothiadiazoles (while avoiding the usage of unstable precursors) and also expands the toolbox of modern skeletal editing reactions.

Copper(I)-Catalyzed Nitrosylation/Annulation Cascade of Enaminones with tert-Butyl Nitrite: Access to 1H-1,2,3-Triazole 2-Oxides

The direct synthesis of triazole 2-oxides has posed a challenge in the field of N-heterocyclic chemistry. A novel copper(I)-catalyzed nitrosylation/annulation cascade of enaminones provides a straightforward route to 1H-1,2,3-triazole 2-oxides by forming new C-N, N=N, and N-N bonds using noncorrosive tert-butyl nitrite (TBN) as both the N and NO sources. The synthetic protocol features easily accessible starting materials, wide substrate scopes, and good tolerance toward various functional groups while avoiding use of explosive azides.

Catalytic Aerobic N-Nitrosation by Secondary Nitroalkanes in Water: A Tandem Diazotization of Aryl Amines and Azo Coupling

Secondary nitroalkanes underwent oxygen-mediated nitro-nitrite isomerization, serving as versatile N-nitrosating agents under aerobic conditions. To capitalize on the newly discovered aerobic nitro-nitrite isomerization phenomenon, a phase-transfer catalysis system employing KSeCN and TBAI was developed, in which the tandem diazotization and azo coupling with nitroalkanes as well as N-nitrosation of amines were accomplished. The current tandem diazotization and azo coupling strategy provides a facile synthesis of areneazo-2-(2-nitro)propane derivatives, a safe synthetic alternative to aryl diazonium salts.

One-Pot Tandem Nickel-Catalyzed α-Vinyl Aldol Reaction and Cycloaddition Approach to [1,2,3]Triazolo[1,5-a]quinolines

A one-pot tandem approach to [1,2,3]triazolo[1,5-a]quinolines was developed from (E)-β-chlorovinyl ketones and 2-azidoaryl carbonyls using a sequence of α-vinyl aldol and azide-alkyne cycloaddition reactions. In particular, the intramolecular azide-alkyne cycloaddition of allenol intermediates was readily promoted by a synergistic action of NEt₃ and nickel catalysts. Given that the [1,2,3]triazolo[1,5-a]quinolines are useful synthetic precursors to α-diazoimines through ring-chain isomerization process, the subsequent denitrogenative transformations should provide ready access to valuable heterocyclic compounds.

Domino Aza-Annulations of Enynyl-/(Alkynyl)aryl-acetonitriles to Access Nitrogen-Enriched Heterocycles

Unprecedented domino aza-annulations of (E)-2-en-4-ynyl-acetonitriles (generated from the Morita-Baylis-Hillman acetates of propiolaldehydes for the first time) with sodium azide under metal- and oxidant-free conditions for the assembly of triazolo-pyridines are accomplished. The developed strategy offers broad substrate scope, extending to (2-alkynyl)aryl and indolyl-acetonitriles to provide the corresponding triazolo-fused isoquinolines and β-carbolines, respectively, in good yields. Additionally, the synthetic utility of the products is demonstrated via denitrogenative coupling of fused triazoles with different nucleophiles.

A Predictive Chemistry DFT Study of the N2O Functionalization for the Preparation of Triazolopyridine and Triazoloquinoline Scaffolds

The whole reaction mechanism of the functionalization of N2O for the synthesis of triazolopyridine and triazoloquinoline scaffolds has been unveiled by means of DFT calculations. The rate determining step of...

Nitrous oxide as a diazo transfer reagent: the synthesis of triazolopyridines

Nitrous oxide is a potential diazo transfer reagent, but its applications in organic chemistry are scarce. Here, we show that triazolopyridines and triazoloquinolines are formed in the reactions of metallated 2-alkylpyridines or 2-alkylquinolines with N₂O. The reactions can be performed under mild conditions and give synthetically interesting triazoles in moderate to good yields.

One-pot synthesis of N-substituted benzannulated triazoles via stable arene diazonium salts

A mild and effective one-pot synthesis of 1,2,3-benzotriazin-4(3H)-ones and benzothiatriazine-1,1(2H)-dioxide analogues has been developed. The method involves the diazotisation and subsequent cyclisation of 2-aminobenzamides and 2-aminobenzenesulfonamides via stable diazonium salts, prepared using a polymer-supported nitrite reagent and p-tosic acid. The transformation was compatible with a wide range of aryl functional groups and amide/sulfonamide-substituents and was used for the synthesis of pharmaceutically important targets. The synthetic utility of the one-pot diazotisaton-cyclisation process was further demonstrated with the preparation of an α-amino acid containing 1,2,3-benzotriazin-4(3H)-one.

Indium-mediated annulation of 2-azidoaryl aldehydes with propargyl bromides to [1,2,3]triazolo[1,5-a]quinolines

An efficient indium-mediated cascade annulation reaction of 2-azidoaryl aldehydes with propargyl bromides is reported. The aromatic 5/6/6-fused heterocycles, [1,2,3]triazolo[1,5-a]quinoline derivatives, could be constructed in one pot in moderate yields with a broad substrate scope. Mechanistic studies indicated that the reaction proceeded through allenol formation, azide-allene [3 + 2] cycloaddition, and dehydration. The synthetic potential of the products including the denitrogenative functionalization and the Pd-catalyzed coupling reactions has also been explored.

A three-component approach to isoxazolines and isoxazoles under metal-free conditions

A 1,3-dipolar cycloaddition of 2-methylquinoline, tert-butyl nitrite (TBN) and alkynes or alkenes for the synthesis of biheteroaryls containing both isoxazoline/isoxazole and quinoline motifs has been developed. In this protocol, TBN serves as a convenient N-O source to convert 2-methylquinoline into intermediate nitrile oxides in situ.