Tailored SnO2@MWCNTs efficient and recyclable nano-catalyst for selective synthesis of 4, 5-dihydropyrrolo [1, 2-a] quinoxalines via Pictet–Spengler reaction

Abstract

Heterocyclic compounds have wide range of applications and Pictet-Spengler reaction is effectual in the synthesis of heterocyclic compounds such as quinoline and isoquinoline. The present work describes an effective Pictet-Spengler-type protocol for the selective synthesis of quinoxaline derivatives from substituted pyrroles and diverse aromatic aldehydes over tailored SnO 2 nanoparticles anchored multi walled carbon nanotubes (SnO 2 @MWCNTs) nano-catalyst under greener reaction condition. An elementary reaction process (chemical synthesis) of oxidation of MWCNTs followed by uniform dispersion of SnO 2 nanoparticles is used to synthesize the SnO 2 @MWCNTs catalyst. The SnO 2 @MWCNTs catalyst was then characterized by using modern spectroscopic and analytical techniques. The activity of catalysts was investigated towards the formation of selective quinoxaline. The reaction progressed with 100% conversion and 93 − 80% yield for the desired product at ambient operating conditions in just 2.30-3.30 h of reaction time. The effect of different parameters such as reaction temperature, time, and loading of SnO 2 on MWCNTs, SnO 2 @MWCNTs catalyst loading were also investigated and discussed in detail. The protocol displayed high tolerance to different functionalities with respect to different substituted aromatic aldehydes to form quinoxaline derivatives in e cient and selective yield. Plausible reaction mechanistic pathway for the selective formation of quinoxaline over SnO 2 @MWCNTs is also proposed. It is believed that, high dispersion of SnO 2 over MWCNTs provided su cient Lewis acidic sites for the reaction to selectively obtain the nal product. Additionally, recyclability of SnO 2 @MWCNTs catalyst was also studied which demonstrated that the catalyst could be e ciently reused for six successive cycles without signi cant loss of activity and selectivity. The present work provides greener approach for synthesis of quinoxaline derivative preparation with high selectivity (free from oxidized quinoxaline as a side-product) and e cient yield.

Accelerated sonosynthesis of chromeno[4,3‐b]quinoline derivatives via marine‐bioinspired tin oxide nanocatalyst

“…[15][16][17][18][19] More specifically, they have been investigated in a variety of organic synthesis reactions due to high catalytic activity, selectivity, and stability. For example, SnO 2 NPs have been served as a heterogeneous catalyst in coumarins, 20 imidazole derivatives, 21 benzimidazoles, 22 2H-indazolo [2,1-b] phthalazine-triones, 23 synthesis of 4, 5-dihydropyrrolo [1, 2-a] quinoxalines 24 reduction, coupling, cycloaddition reactions, among others. Hence, the versatility and effectiveness of SnO 2 nanocatalysts are deemed a promising tool for achieving more sustainable and environmentally friendly chemical processes.…”