One‐Pot Knoevenagel–Michael–Cyclization Cascade Reaction for the Synthesis of Functionalized Novel 4H‐pyrans by Using ZnCl2 as a Catalyst

Abstract

An expedient and cost‐effective protocol has been developed for the synthesis of novel 2‐methyl‐6‐(methylamino)‐5‐nitro‐4‐(4‐aryl)‐4H‐pyran‐3‐carboxylate derivatives. This domino, one‐pot, three‐component reaction was carried out between β‐ketoesters, aromatic aldehydes, and (E)‐N‐methyl‐1‐(methylthio)‐2‐nitroethenamine (NMSM) in the presence of 30 mol% anhydrous ZnCl2 under the neat condition at 120°C. The synthesized 4H‐pyran derivatives were characterized by spectroscopic techniques such as IR, 1H NMR, 13C NMR, CHNS, and HRMS. The molecular structure of compound methyl‐2‐methyl‐6‐(methylamino)‐5‐nitro‐4‐(4‐nitrophenyl)‐4H‐pyran‐3‐carboxylate 4a was confirmed by the single crystal X‐ray analysis. This solvent‐free protocol has several advantages such as shorter reaction time, an inexpensive catalyst, good yields, simple workup, and column‐free purification.