A new MCM-41 supported HPF6 catalyst for the library synthesis of highly substituted 1,4-dihydropyridines and oxidation to pyridines: report of one-dimensional packing towards LMSOMs and studies on their photophysical properties†
Abstract
A new heterogeneous MCM-41 silica supported HPF6 catalyst has been synthesized and characterized using an array of sophisticated analytical techniques like BET, XRD, HRTEM, EDX, 29Si MAS NMR, TGA, FTIR, and pH measurement. The broad applicability of silica-HPF6 was probed through a library synthesis of highly substituted 1,4-dihydropyridines (1,4-DHPs). The 1,4-DHPs are further oxidized to pyridines with aqueous H2O2 as stoichiometric oxidant which is considered as an abundant and green oxidant. The pyridines spontaneously generate low molecular mass self-aggregated organic materials (LMSOMs). Their one-dimensional packing and interesting photophysical properties are reported. Synthesis using water as a solvent is of paramount importance for its sustainable green impact. Further, carbon dioxide and water were the only by-products, which added to its attractiveness. This silica-HPF6 catalyst retained its activity even after being exposed to ambient atmosphere for 10 days.