Synthesis of Imidazo[5, 1‐a]isoquinoline and Its 3‐Substituted Analogues Including the Fluorescent 3‐(1‐Isoquinolinyl)imidazo[5, 1‐a]isoquinoline

Abstract

Compounds having imidazo[5, 1‐a]isoquinoline nucleus have been synthesised. Selenium dioxide oxidation of a mixture of various aldehydes and 1‐isoquinolinemethylamine yielded the respective 3‐substituted imidazo[5, 1‐a]isoquinolines in good yields. When 1‐isoquinolinemethylamine was employed without any aldehyde, 3‐(1‐isoquinolinyl)imidazo[5, 1‐a]isoquinoline (IQ‐1) was isolated. This IQ‐1 is fluorescent and all the compounds were thoroughly characterized. Molecular structures of IQ‐1 and 3‐(2‐hydroxyphenyl)imidazo[5, 1‐a]isoquinoline (IQ‐4) have been confirmed by single crystal X‐ray diffraction technique.

A new synthetic route for synthesis of 3‐substituted imidazo[1,5‐a]pyridines

“…Thus, stirring the 1:1 mixture of 2-picolylamine and various aldehydes in presence of selenium dioxide in ethanol at room temperature afforded the respective imidazo[1,5-a]pyridines (Scheme 1). As observed with the case of 1-isoquinolinemethylamine [32], 3-(pyridin-2-yl)imidazo[1,5-a]pyridine (5-10%) was also formed as a minor product along with the expected product. Aldehydes such as aromatic, heterocyclic, aliphatic as well as phenyl ring with -OMe group at ortho, meta, and para positions yielded the respective products.…”

“…In the course of our studies on the formation of imidazo[5,1‐ a ]isoquinoline, we developed a synthesis of 3‐substituted imidazo[5,1‐ a ]isoquinolines via the oxidative cyclization of 1‐aminomethylisoquinoline using selenium dioxide as an oxidant [32]. This reaction gives a series of imidazo[5,1‐ a ]isoquinolines in good to excellent yields.…”

Luminescent Imidazo[1,5‐a]pyridine Scaffold: Synthetic Heterocyclization Strategies‐Overview and Promising Applications

“…[12][13][14][15] To obtain these structural modifications it is of paramount importance to know the available different synthetic approaches to introduce functional groups, spacers or additional conjugated systems (such as imidazo-quinoline). [16][17][18][19][20][21] The distinctive emission of the impy moiety typically lies in the 450-530 nm range, with a large Stokes shift (up to 150 nm) and good quantum yield (ranging from 10% to 50%). Due to their structural flexibility and tuneable optical behaviours, impy luminescent products represent excellent candidates to be widely employed for different applications such as downshifting [22][23][24] and optoelectronic devices.…”

“…In general, impy skeleton could be designed to obtain luminescent ligands from transition metal complexes, to connect other fluorophores (as BODIPY or rhodamine), [8–11] or to act as a fluorogenic centre itself [12–15] . To obtain these structural modifications it is of paramount importance to know the available different synthetic approaches to introduce functional groups, spacers or additional conjugated systems (such as imidazo‐quinoline) [16–21] …”

Synthesis of imidazo[1,5-a]pyridines via cyclocondensation of 2-(aminomethyl)pyridines with electrophilically activated nitroalkanes

“…Most synthetic approaches rely on various cyclocondensations of nucleophilic (2-aminomethyl)pyridine precursors, introducing a new five-membered ring. Typically, carboxylic acids [16][17][18][19][20], acyl anhydrides [21][22][23], acyl chlorides [24][25][26][27], esters [28], thioamides [29][30][31], dithionates [32,33], or thiocarbamates [34] are employed as electrophilic components, but oxidative cyclocondensations with aldehydes have also been showcased [35][36][37]. However, given the importance of these targets, new preparative methods are still in high demand.…”