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.