An eco-friendly innovative halide and metal-free basic ionic liquid catalyzed synthesis of tetrahydrobenzo [b] pyran derivatives in aqueous media: A sustainable protocol

A novel imidazolium-based highly efficient, recoverable, and reusable basic ionic liquid [PEMIM][OH] was synthesized using a very simple approach. This ionic liquid was employed as a catalyst for the multicomponent synthesis of tetrahydrobenzo[b]pyran derivatives by the condensation of dimedone, malononitrile and various substituted aldehydes as key starting materials in aqueous media. Novelty, the efficacy of the catalyst, high yields of desired products, greener approach, high atom economy and use of aqueous media make this protocol worthwhile. The inventive idea of employing halide and a metal-free ionic liquid catalyst establishes this as a sustainable process. The cost-effective isolation of pure, high yielded desired product by sidestepping the column and recrystallization technique was also demonstrated in this protocol. A plausible mechanism for the formation of tetrahydrobenzo [b] pyran is proposed. The novel catalyst and synthesized compounds were characterized by using various analytical techniques such as FTIR, 1H NMR, 13C NMR, DEPT-135, LC-Mass, Elemental, HSQC, HPLC, TG-DSC, TG-DTG and single crystal XRD analysis.