Recent synthetic methodologies for imidazo[1,5-a]pyridines and related heterocycles

Imidazo[1,5-a]pyridine is a significant structural component of a large number of agrochemicals and pharmaceuticals. The synthesis of imidazo[1,5-a]pyridine has been a subject of intense research for numerous decades. A large number of transformations are now available to conveniently access imidazo[1,5-a]pyridine from readily available starting materials. This review details the recent development in imidazo[1,5-a]pyridine construction involving cyclocondensation, cycloaddition, oxidative cyclization, and transannulation reactions.

Copper-catalyzed aerobic oxidative domino cyclization of methyl azaarenes with 6-amino-pyrimidine-2,4-diones and pyrazol-5-amines: access to dipyrimidine/dipyrazolo-fused pyridines

An aerobic copper-catalyzed oxidative domino cyclization of methyl azaarenes with 6-amino-pyrimidine-2,4-diones and pyrazol-5-amines for the synthesis of dipyrimidine/dipyrazolo-fused pyridines was reported.

Reactions involving aryl methyl ketone and molecular iodine: a powerful tool in the one-pot synthesis of heterocycles

The preparation of heterocyclic compounds has attracted great attention in organic chemistry because of their extensive application in the field of bioactive molecules, materials science, and natural products.

Electrochemical oxidative synthesis of 2-benzoylquinazolin-4(3H)-one via C(sp3)–H amination under metal-free conditions

An electrochemically induced C(sp3)–H amination of 2-aminobenzamides with ketones using TBAI as a catalyst was developed, and provided 2-benzoylquinazolin-4(3H)-ones under metal-free conditions.

Iodine-Promoted Multicomponent Synthesis of 2,4-Diamino-1,3,5-triazines

A novel and efficient multicomponent cyclization of methyl ketones, cyanamides, and arylamines for the synthesizing 2,4-diamino-1,3,5-triazines via consecutive formation of four C-N bonds is reported. This multicomponent reaction is characterized by the employment of two molecules of cyanamide for double C(sp³)-H amination of methyl ketones, avoiding complicated prepreparation of substrates and expanding the substrate scope. Furthermore, this multicomponent cyclization strategy provides a new approach for generating diverse 2,4-diamino-1,3,5-triazines with a broad substrate scope under mild conditions.

Sulfoxide Reduction/C(sp3)-S Metathesis Cascade in Ionic Liquid

A sulfoxide reduction/C-S bond metathesis cascade between sulfoxides and alkyl bromides has been developed to access high-value sulfides without the use of any catalysts or bases. In this cascade, classical Kornblum oxidation is employed to reduce sulfoxides with alkyl bromides in ionic liquid. This protocol features high functional tolerance, mild conditions, promising scalability, and sustainable solvents.

I2/TBHP-Mediated tandem cyclization and oxidation reaction: Facile access to 2-substituted thiazoles and benzothiazoles

The efficient synthesis of 2-substituted thiazoles and benzothiazoles has been accomplished employing readily available cysteine esters and 2-aminobenzenethiols as N and S sources.

An iodine/DMSO-catalyzed sequential one-pot approach to 2,4,5-trisubstituted-1H-imidazoles from α-methylene ketones

A sequential one-pot approach to 2,4,5-trisubstituted imidazoles has been developed from α-methylene ketones and aldehydes. This methodology employs air-moisture stable reaction conditions and an inexpensive iodine/DMSO system affording a diverse range of known and novel (substrate scope) 2,4,5-trisubstituted imidazoles in moderate to excellent yields. The iodine/DMSO system was extended to the domino convergent synthesis of two functionalized intermediates, benzil and benzaldehyde, to produce the final product.

I2-Catalyzed Oxidative Cross-Coupling Reaction of Methyl Ketones and 2-(2-Aminophenyl) Benzimidazole: Facile Access to Benzimidazo[1,2-c]quinazoline

A general and efficient iodine-catalyzed metal-free oxidative cross-coupling reaction of methyl ketones with 2-(1H-benzo[d]imidazol-2-yl)aniline has been established. This is a new synthetic strategy for the synthesis of benzimidazo[1,2-c]quinazoline derivatives involving C(sp³)-H oxidation, condensation, and cyclization processes.

I2-Promoted formal [3+2] cycloaddition of α-methylenyl isocyanides with methyl ketones: a route to 2,5-disubstituted oxazoles

An I₂-promoted formal [3+2] cycloaddition for access to oxazoles has been demonstrated. This is the first example of a Lewis acid-promoted formal [3+2] cycloaddition of isocyanides with methyl ketones involving the C[triple bond, length as m-dash]N cleavage of isocyanides. The salient feature of this approach is unconventional 2,5-disubstituted oxazole formation from isocyanides and ketones rather than 4,5-substituted oxazoline.

Selective access to dipyrazolo-fused pyridines via formal [3 + 2 + 1] heteroannulation of methyl ketones with pyrazol-5-amines

A fascinating new form of the Hantzsch reaction with methyl ketones and pyrazol-5-amines for the selective synthesis of dipyrazolo-fused pyridines has been discovered.

Iodine/DMSO oxidations: a contemporary paradigm in C–N bond chemistry

A new era in the organic synthetic world is demanding greener protocols for the execution of reactions.