Surface-driven imidazolium-coated periodic mesoporous organosilicas for selective synthesis of electron-deficient 2-arylbenzo[d]oxazoles

Selective synthesis driven by appropriate support properties of heterogeneous catalysts is promising, but longterm process to explore. In this work, we prepared and confirmed series of hydrophobic ethyl bridges modulated periodic mesoporous organosilica fixed with 1-methyl-3-(3-(trimethoxysilyl)propyl)-1H-imidazole-3-iumiodide (MBIm-PMO-x). The contents of hydrophobic ethyl bridges (x) were 0, 5, 15, 25, 35 mol%. These materials were applied for synthesizing heterocyclic compound 2-arylbenzoxazoles with arylaldehydes and 2-aminophenol. Among them, MBIm-PMO-15, hydrophobic ethyl bridge was 15 mol%, dramatically enhanced the yields of synthesizing electron-deficient 2-arylbenzoxazoles. For substrates with different electronic properties, we found MBIm-PMO-15 exhibited the reversed catalytic activity in relation to corresponding homogeneous MBIm. Further research, FT-IR adsorption and UV-vis detection tests demonstrated this kind heterogeneous catalyst surface prefers adsorbing electron-deficient intermediates Schiff base to electron-rich ones. It is the specific adsorption motivate MBIm-PMO-15 highly selectivity towards electron-deficient 2-arylbenzoxazoles. In a broader vision, surface driven selective adsorption of heterogeneous catalyst for substrate could act as an alternative strategy to get special target products.