Acetylenchemie. 9. Mitt. Anellierte imidazole aus N‐propinylamid‐vorstufen

Abstract

2‐(N‐Formyl‐N‐prop‐2′‐inyl)‐aminopyridin cyclisiert in siedender Ameisensäure zum 3‐Methylimidazo‐[1,2‐a]pyridin, wobei 3‐Methylen‐2H‐imidazo[1,2‐a]pyridin als Intermediat auftritt. Unter den gleichen Bedingungen bildet sich aus dem 1,3‐Diprop‐2‐inylpyrimido[4,5‐b]chinolin‐2,4‐dion das 1‐Methylimidazo‐[1,2‐a]chinolin‐4‐carbonsäure‐N‐prop‐2′‐inylamid und aus dem 1‐Prop‐2′‐inylbenzo[b][1,8]naphthyridin‐2‐on als neues Ringsystem das 1‐Methyl‐benzo[b]imidazo[1,2,3‐ij][1,8]naphthyridin‐4,7‐dion.

Synthesis of Imidazo[1,2-a]pyridines: “Water-Mediated” Hydroamination and Silver-Catalyzed Aminooxygenation

“…Recently, water has been employed as a solvent-cum-catalyst for the construction of heterocycles. , Aqueous reactions have attracted attention owing to the unique reactivity and selectivity observed that are difficult to achieve in conventional organic solvents . Organic substrates are generally insoluble in water, but reactions have been reported to proceed “on water” to obtain desired products. , In continuation of our studies on the development of green and sustainable methods, − herein we wish to report “water-mediated” synthesis of methylimidazo[1,2- a ]pyridines through intramolecular hydroamination under metal-free conditions.…”

Product Class 5: Azaindolizines with Two Nitrogen Atoms in the Five-Membered Ring

“…12 In the example shown in Scheme 10, ring closure to the tricyclic imidazole-fused product proceeds by a 1,3-dipolar cyclization. [53] The N-tosylimino compound 70, prepared from the parent 2-tosylaminopyridine with iodoacet-amide, undergoes ring closure when reacted with trifluoroacetic anhydride to give the cyclized product 71 in a modest yield. [48] Scheme 10 Synthesis of 3-Ethoxycarbonyl-2-(trifluoromethyl)imidazo[2,1-a]isoquinoline [ Upon reviewing the pertinent literature, some ring closures to the title system can be found that cannot be classified by any of the above methods.…”

A Base Promoted Cyclization of N-Propargylaminopyridines. Synthesis of Imidazo[1,2-a]pyridine Derivatives

“…Analysis of 1 H/ 13 C NMR and mass spectral data fully supported the structure of compound 2 . Very few examples of the related cyclization process of the pyridine derivatives have been reported in the literature, but they employed acid as a solvent or a strong acidic conditions (HCOOH or H 2 SO 4 ) and high temperatures . Since our transformation offers some advantages, we decided to investigate it in more detail.…”