A carbon quantum dot-encapsulated micellar reactor for the synthesis of chromene derivatives in water

An efficient protocol for the synthesis of 4H-chromene derivatives via a one-pot multicomponent reaction was developed using a self-assembled catalyst system. The self-assembling nature of the fabricated catalyst is unique, consisting of carbon-quantum dots (CQDs) and ionic liquids (ILs). At the critical micelle concentration (CMC), the ILs organize themselves as micelles and the CQDs are trapped inside, forming a CQD-colloidal reaction system (CRS). The reactions of naphthols with aromatic aldehydes and malononitrile in the CQD-CRS system gave excellent yields of 4H-chromene derivatives at room temperature in 15 min upon sonication. The present method provides a high EcoScale score and a low E-factor, validating the greenness of the procedure. The self-aggregating nature of the catalyst is highly advantageous as it can be recycled and reused provided the CMC is maintained. To the best of our knowledge, this is the first example of a self-assembled CQD-based catalyst in aqueous media. CQD-CRS can be considered a designer's catalyst, as by changing the ILs/CQDs components, multiple variants could be produced under different solvent conditions.