One Pot Synthesis of 4H-Pyran Derivatives by Use of Efficient and Recyclable Catalyst

Background: Pyrans are one of the most significant skeletons of oxygen-containing heterocyclic molecules, which exhibit a broad spectrum of medicinal applications. Green one-pot methodologies for synthesizing these heterocyclic molecules have received significant attention. The paper focusses on a simple approach to synthesize 4H-pyran derivatives by one pot multi-component reaction of aromatic aldehyde, β-ketoester or β-diketone with the use of Nd2O3 as recyclable and efficient catalyst. Methods: The reagents ethyl acetoacetate (2mmol) and 4-chlorobenzaldehyde (1mmol) and varying amount of L-proline or Nd2O3 catalyst were stirred or refluxed in PEG-400, water or H2O/EtOH (1:1) solvent to yield 4H pyran. The reaction time and yield of the product was monitored. 20 mmol of Nd2O3 catalyst was sufficient to catalyze the reaction in good yield. The optimized conditions of the reaction were effectively implemented to synthesise various 4H pyran derivatives. The synthesized compounds were characterized and confirmed by different spectroscopic techniques like 1H NMR and FTIR. The values reported are well in agreement with the expected values. Results: The results yielded lesser reaction time of around 30 to 54 mins with a yield of around 82 to 94 %. The reaction required only 20mmol catalyst in (1:1, v/v, ml) of H2O/C2H5OH mixed solvents. It demonstrates the low cost, simple work up process using H2O/ C2H5OH as greener solvents. Conclusions: Neodymium (III) oxide (Nd2O3) is a powdered rare earth metal oxide used as a novel catalyst which can be recovered through simple filtration, rinsed with hot ethanol, and dried at 1500C for further use. The recovered catalyst can be reused successfully at least three times with minimal loss in activity.