Anion-cation co-operative catalysis by artificial sweetener saccharine-based ionic liquid for sustainable synthesis of 3,4-dihydropyrano[ c ]chromenes, 4,5-dihydropyrano[4,3- b ]pyran and tetrahydrobenzo[ b ]pyrans in aqueous medium.

In this study, a saccharine-based ionic liquid [Bmim]Sac has been found to be a sustainable catalyst for the synthesis of 3,4-dihydropyrano[ c ]chromenes, 4,5-dihydropyrano[4,3- b ]pyran and tetrahydrobenzo[ b ]pyrans scaffolds through Domino Knoevenagel-Michael reaction. The easy recovery of the catalyst and high yield of the products make the protocol attractive, sustainable and economical. A mechanistic hypothesis is discussed using the concept of cooperative catalysis based on the dual (electrophilic/nucleophilic) activation of reactants by [Bmim]Sac. Furthermore, dual hydrogen bonding of saccharinate anions plays an important role in the activation of nucleophiles.