Titania‐silica nanoparticles ensemblies assisted heterogeneous catalytic strategy for the synthesis of pharmacologically significant 2,3‐diaryl‐3,4‐dihydroimidazo[4,5‐b]indole scaffolds

Abstract

Present paper elicits the multicomponent reaction (MCR) strategy assisted by titania nanoparticles hosted on silica (TiO2.SiO2 NPs) as heterogeneous catalyst to synthesize a series of pharmacologically significant 2,3‐diaryl‐3,4‐dihydroimidazo[4,5‐b]indole derivatives. To the best of our information, the use of isatin as one of the precursors was hitherto unreported. The decrease in reaction time, low catalyst loading, high product yield (up to 92%), and excellent reusability of the catalyst (up to 7 cycles) put this protocol under the umbrella of green chemistry tenets. Characterization of catalysts was achieved through a number of techniques viz., energy‐dispersive X‐ray (EDX) spectroscopy, field emission scanning electron microscopy (FESEM), powder X‐ray diffraction (XRD), fourier transform infrared (FTIR) spectra of adsorbed pyridine, temperature‐programmed desorption of ammonia, and porosity measurements by nitrogen adsorption (Brunauer–Emmett–Teller [BET] method). Also, the structures of synthesized compounds were corroborated on the basis of FTIR, nuclear magnetic resonance (NMR), mass, and elemental analyses data.

Hydromagnesite sheets impregnated with cobalt–ferrite magnetic nanoparticles as heterogeneous catalytic system for the synthesis of imidazo[1,2-a]pyridine scaffolds

“…† where, D is the average crystallite size, K is the particle shape factor whose value is 0.9, l is the X-ray wavelength of Cu-Ka radiation (1.54056 A), b is the full width at half maximum (FWHM) of a selected peak and q is the Bragg's angle. 24,26 Accordingly, the average crystallite size for CoFe 2 O 4 -HMS, CoFe 2 O 4 MNPs, and HMS attained from the above-mentioned equation were found to be 12.30, 16.97, and 14.78 nm, respectively, which is in accordance with the results obtained by eldemission scanning electron microscopy (FE-SEM) (Fig. 3) and nitrogen adsorption isotherm (Fig.…”

“…24,25 Therefore, to circumvent all these bottlenecks, herein, we report a green and efficient protocol for the synthesis of amalgamated imidazo-pyridine derivatives in high to excellent yields considering recyclable PEG 400 as the reaction medium under aerobic conditions. Furthermore, despite the multifarious properties associated with heterogeneous nanocomposite catalysts and pharmacologically signicant imidazo-fused pyridine scaffolds, and in continuation to our work towards nanocatalysis-oriented synthesis, 25,26 we demonstrate the unprecedented ultrasonicassisted environmentally friendly synthesis of highly functionalized imidazo [1,2-a]pyridines in the presence of hydromagnesite sheets impregnated with cobalt-ferrite magnetic nanoparticles (CoFe 2 O 4 -HMS) as a recyclable magnetic nanocatalyst composite under mild and green reaction conditions via A 3 -coupling followed by 5-exo-dig cyclization. To the best of our knowledge, this is the rst report to date on the use of hydromagnesite sheets impregnated with cobalt-ferrite magnetic nanoparticles (CoFe 2 O 4 -HMS) as a heterogeneous nanocatalyst for the synthesis of imidazo[1,2-a]pyridines scaffolds.…”

Multiwalled carbon nanotubes crowned with nickel‐ferrite magnetic nanoparticles assisted heterogeneous catalytic strategy for the synthesis of benzo[d]imidazo[2,1‐b]thiazole scaffolds

“…where, D is the average crystallite size, K is the particle shape factor whose value is 0.9, λ is the X-ray wavelength of Cu-Kα radiations (1.54056 A ), θ is the Bragg's angle and β is the full width at half maximum (FWHM) of a diffracted peak. [26] Subsequently, the average crystallite size of the Multiwall carbon nanotubes decorated with nickel-ferrite magnetic nanoparticles (NiFe 2 O 4 -CNTs) was acquired from the above stated equation and found to be 3.49 nm, that is intrinsically in accordance with the results attained by field emission scanning electron microscopy ( Figure 4) and nitrogen adsorption-desorption isotherm (Figure 9).…”

“…The average crystallite size has been determined to utilize the Debye‐Scherrer equation, [ 39 ] where, D is the average crystallite size, K is the particle shape factor whose value is 0.9, λ is the X‐ray wavelength of Cu‐Kα radiations (1.54056 A°), θ is the Bragg's angle and β is the full width at half maximum (FWHM) of a diffracted peak. [ 26 ]…”

“…[24] Also, despite the diversified advantages associated with carbon nanotubes, its use as a catalyst is hitherto unrivaled, although this can leads to the expedient synthesis of imidazo fused benzothiazole scaffolds. On keeping these observations in mind and continuation of our interest toward nanocatalysis, [25][26][27][28][29] we propose an alternative eco-friendly synthetic methodology for the synthesis of highly functionalized benzo[d]imidazo [1,2-b]thiazoles using multiwall carbon nanotubes mediated with nickelferrite magnetic nanoparticles (NiFe 2 O 4 -CNTs), as an efficacious, economical and noncorrosive heterogeneous catalyst, under aerobic conditions via. A 3 coupling followed by 5-exo-dig cyclization.…”