Piperidinium borate as efficient and recyclable catalyst for one-pot, three-component, environmentally friendly synthesis of pyran-annulated heterocycles and 2-amino‑3‑cyano‑4H‑pyrans

Abstract

Piperidinium borate was a safe catalyst for synthesizing pyran-annulated heterocycles and 2-amino‑3‑cyano‑4H‑pyrans. The synthesis of functionalized pyran by reaction of aldehydes, malononitrile, and 5-methyl-2,4-dihydro-3H-pyrazol-3-one/ barbituric acid/ mono or 1,3-dicarbonyl compounds via one-pot three-component Knoevenagel and Michael-type addition reaction. This condensation reaction proceeds in a mixture of ethanol and water as a green reaction medium at 80 °C to give the desired densely functionalized pyrazoles/pyrimidinone/2-amino‑3‑cyano‑4H‑pyrans in good to excellent yields. The environmentally friendliness of the process was evaluated using atom economy (AE), E-factor, and reaction mass efficiency, indicating a good level of sustainability. These multicomponent reactions offer several interesting advantages, including time-saving, readily available starting materials, moderate reaction conditions, waste minimization, high atom efficiency, avoidance of hazardous organic solvents or catalysts, and ease of workup.