Cinchonine-driven multi-component domino Knoevenagel–Michael strategy: metal-free synthesis of quinoline-based 4H-pyran and tetrahydro-4H-chromene derivatives

Cinchonine-catalyzed simple, expeditious, and efficient protocol for the synthesis of quinoline-based 4H-pyran and tetrahydro-4H-chromenes has been demonstrated via one-pot domino Knoevenagel–Michael cyclocondensation reaction of aromatic aldehyde, active methylene compound and activated C–H acids like alkylacetoacetates/dimedone in ethanol under reflux. This protocol enables a rapid construction of diverse range of 4H-pyran and tetrahydro-4H-chromene derivatives from readily available starting materials. Short reaction time, mild reaction conditions, broad substrate scope, high yields, metal-free approach, and purification without column chromatography are notable features of this methodology.