Properties of 2,3-dihydro-imidazolo[1,2-a]pyridines. (Review)

Abstract

From our previous review [1], in which we discussed the synthcsis, structure, tautomerism, and nomenclature of 2,3-dihydroimidazo[l,2-a]pyridines, it tbllows that compounds of type A-C have wide-ranging practical applications.Data on the chemical properties of 2-oxoimidazopyridincs B, which have amphoteric characteristics and tbrm watcr-solublc salts with mineral acids and alkalies, wcrc studied in detail and analyzed in [2]. They wetc used to obtain many dycs [3][4][5], which were also synthesized [6] from 3-oxoimidazo[l,2-a]pyridines C. Their solutions can fluoresce [7, 8] and sometimcs cxhibit chemiluminescence [9]. However, there is considerably less information on the 3-oxo derivatives, and this is explained by their relative instability -many of them are sensitive to nuclcophilcs [6,[10][11][12][13][14][15][16][17] and to light [13, 18], are readily oxidized by atmospheric oxygen [13, 18], and decompose when heated [19] and sometimes even at room temperaturc [20]. More stable are the mesoionic l-substituted 3-oxoilnidazo[ 1,2-a]pyridines, which dissolve in watcr [8, 13, 19] and can lbrm hydrates [ 13, 21 ].

Synthesis of Imidazopyridines from the Morita–Baylis–Hillman Acetates of Nitroalkenes and Convenient Access to Alpidem and Zolpidem

“…2005, 48, chemists to pursue the synthesis of numerous imidazopyridine derivatives 6 and study their properties. 7 Synthetic approaches include reaction of aminopyridines with R-functionalized and R,β-unsaturated carbonyl compounds, 1,3-dicarbonyl compounds, vicinal diols as well as with simple aldehydes and ketones, often in a multicomponent reaction. 8À10 Reactions involving Sandmeyer conditions, rearrangement, cycloaddition, Michael addition and other miscellaneous ones were also employed for the synthesis of imidazopyridines.…”

Arylglyoxals in Synthesis of Heterocyclic Compounds

“…Substituted fused heterocycles can be found in many types of synthetic and naturally occurring medicinal substances such as coelenterazine, an imidazolopyrazinone derivative . It was found that imidazo[1,2- a ]pyrazinones exhibit a significant solvatochromism and bio- and chemiluminescence. , Imidazo[1,5- a ]pyridines possess various applications such as dyes, optical data carriers, pesticides, fungicides, hypoglycemic agents, and compounds exhibiting antitumor, anti-inflammatory, antipyretic, and analgesic activity . Oxidative condensation–cyclization of aldehydes with 2-aminomethylpyridines − or Pictet–Spengler strategy − are among the most important routes to synthesize of these types of fused heterocycles …”

Imidazopyridinium and Pyridopyrimidium Bromides: Synthesis and Hydrolysis

“…130 °C) under a nitrogen atmosphere for 18 h did produce a quaternary ammonium heterocycle, but not 4 . Rather, this N , N -dialkylation produced imidazopyridinium bromide 7a − c ( m = 1) as the sole product. Intrigued by this transformation and the fact that imidazopyridium salts are reported to have hypoglycemic, type I allergy, and neuromuscular blocking properties, we decided to further investigate the synthesis and hydrolysis reactions of these imidazopyridium salts.…”