Highly Regioselective, Acid-Catalyzed, Three-Component Cascade Reaction for the Synthesis of 2-aminopyridine-Decorated Imidazo[1,2- a]pyridine

Pd-Catalyzed Aerobic C-H Carbonylative Esterification of Imidazo[1,2-a]pyridines with Alcohols as the Carbonyl Source

A simple and practical method has been developed for the carbonylative esterification of imidazo[1,2-a]pyridines via C(sp2)-H bond functionalization using alkyl alcohols under mild reaction conditions. The carbonyl fragment is sourced from radical-mediated C-C cleavage of the alcohols, providing a green, safe, and economic alternative to traditional carbonyl sources like carbon monoxide. Through this strategy, a number of imidazo[1,2-a]pyridine-3-carboxylates were obtained from simple substrates by a single step.

Synthesis and site selective C-H functionalization of imidazo-[1,2-a]pyridines

Imidazo[1,2-a]pyridine has attracted much interest in drug development because of its potent medicinal properties, therefore the discovery of novel methods for its synthesis and functionalization continues to be an exciting area of research. Although transition metal catalysis has fuelled the most significant developments, extremely beneficial metal-free approaches have also been identified. Even though pertinent reviews focused on imidazo[1,2-a]pyridine synthesis, properties (physicochemical and medicinal), and functionalization at the C3 position have been published, none of these reviews has focused on the outcomes obtained in the field of global ring functionalization. We wish here to describe a brief synthesis and an overview of all the functionalization reactions at each carbon atom, viz, C2, C3, C5, C6, C7 and C8 of this scaffold, divided into sections based on site-selectivity and the type of functionalization methods used.

I2-Mediated [3 + 2] annulation of methyl-azaarenes with alkyl 2-isocyanoacetates or amino acid ester hydrochlorides: selective synthesis of iodine-functionalized and non-iodine-functionalized fused imidazoles

An I2-mediated [3 + 2] annulation of methyl-azaarenes with alkyl 2-isocyanoacetates or amino acid ester hydrochlorides has been demonstrated. This strategy involves the C≡N cleavage of isocyanides and can selectively...

Recent Progress in Metal-Free Direct Synthesis of Imidazo[1,2-a]pyridines

This Mini-Review highlights the most effective protocols for metal-free direct synthesis of imidazo[1,2-a]pyridines, crucial target products and key intermediates, developed in the past decade. The emphases is given on the ecological impact of the methods and on the mechanistic aspects as well. The procedures efficiently applied in the preparation of important drugs and promising drug candidates are also underlined.

Ortho C-H Functionalization of 2-Arylimidazo[1,2-a]pyridines

C-H activation and functionalization is quite promising in recent days as the strategy offers a go-to general method for different bond formations and hence grants synthetic versatility. At the same time, imidazopyridine, a fused bicycle of imidazole moiety with pyridine ring, has a profound impact due to its ubiquitous and prodigious application in medicinal as well as material chemistry. The presence of N-1 atom in 2-arylImidazo[1,2-a]pyridine facilitates the coordination with metal catalysts leading to the formation of ortho-substituted products. This review summarizes all the articles on ortho C-H functionalization of 2-arylImidazo[1,2-a]pyridines published till August 2021.

Iodine Promoted Efficient Synthesis of 2-Arylimidazo[1,2-a]pyridines in Aqueous Media: A Comparative Study between Micellar Catalysis and an "On-Water" Platform

In a new and environmentally sustainable approach, a series of 2-arylimidazo[1,2-a]pyridine derivatives were synthesized in aqueous media in the presence of iodine as a catalyst. The reaction proceeded by condensation of various aryl methyl ketones with 2-aminopyridines to afford 2-arylimidazo[1,2-a]pyridines in good overall yields. Although several of the reactions were efficiently performed "on water", the addition of a surfactant, namely, sodium dodecyl sulphate , was found effective in terms of substrate scope and yield enhancement. Both methods were successfully used for the gram-scale synthesis of a marketed drug, zolimidine. The simple experimental setup, water as "green" media, and inexpensive catalyst are some of the merits of this protocol.

One-pot five-component high diastereoselective synthesis of polysubstituted 2-piperidinones from aromatic aldehydes, nitriles, dialkyl malonates and ammonium acetate

A novel five-component diastereoselective synthesis of polysubstituted 2-piperidinones is reported. The Knoevenagel condensation-Michael addition-Mannich cascade of two equivalents of aromatic aldehydes, nitriles, dialkyl malonates and ammonium acetate or aqueous ammonia in alcohols provides convenient access to alkyl (3SR,4RS,6SR)-5,5-dicyano-2-oxo-4,6-diarylpiperidine-3-carboxylates with three stereocenters in 52-90% or dialkyl (2SR,3RS,4RS,5SR)-2,4-diaryl-3-cyano-6-oxopiperidine-3,5-dicarboxylates with four stereocenters in 38-88%. The formation of products was highly stereoselective, with only one diastereomer formed. Ammonium acetate or aqueous ammonia plays a role both as a catalyst and as a nitrogen source. 2,4,6-triaryl-3,3,5,5-tetracyanopiperidines were obtained as a side products in the reactions with nitro-substituted aldehydes or with ethyl and n-propyl cyanoacetates. A series of 14 2-piperidinones and piperidines was assessed for antimicrobial activity against a panel of five bacteria and two fungi; no significant activity was observed. Two side piperidines with nitro substituents in aromatic ring possess bacteriostatic action against S. aureus ATCC 43300 and A. baumannii ATCC 19606 at 32 ug/mL.