One-pot Synthesis of Tetrahydrobenzo[b]pyrans Catalyzed by PEG-1000 Bridged Primary Amine Functionalized Dicationic Ionic Liquid in Water

A novel poly (ethylene glycol) bridged primary amine functionalized dicationic ionic liquid ([PA-PEG(1000)-DIL][BF4]) was synthesized and characterized by H-1-NMR, C-13-NMR, FT-IR and ESI-MS. The thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis indicated the high thermal stability of [PA-PEG(1000)-DIL][BF4]. It was used as an efficient and recyclable catalyst for the synthesis of substituted tetrahydrobenzo[b]pyrans through a one-pot three-component condensation of aromatic aldehydes, malononitrile and dimedone in 86% approximate to 96% yields within 10 approximate to 30 min in water. This method offers several advantages such as mild reaction conditions, simple operation and environmental friendliness. Furthermore, the catalyst could be easily recovered and reused for at least five runs without obvious loss of catalytic activity.