An Effective One-Pot Access to 2-Amino-4H-benzo[b]pyrans and 1,4-Dihydropyridines via [gamma]-Cyclodextrin-Catalyzed Multi-Component Tandem Reactions in Deep Eutectic Solvent

A simple, highly efficient and green route for the synthesis of 2-amino-4H-benzo[b]pyrans and 1,4-dihydropyridines has been developed by using [gamma]-cyclodextrin ([gamma]-CD) as catalyst in deep eutectic solvent (DES) of urea-choline chloride (urea-ChCl), for the first time, accomplished via a one-pot, three-component strategy. All the reactions were successfully carried out under mild conditions and gave good to excellent yields (86-98%) in 8-28 min in the presence of 5 mol% of the [gamma]-CD catalyst. The short reaction time, green reaction medium, moderate reaction conditions, simple work-up procedure and use of easily available reagents are the attractive features of this novel synthetic method. More importantly, the urea-ChCl-[gamma]-CD catalytic system was regenerated and reused up to 6 times with a slight drop in the product yields.