Aqueous synthesis of 2-aryl-3-nitro-2H[sbnd]chromenes via l-prolinamide mediated tandem oxa-Michael Henry reactions

Abstract

An efficient and aqueous protocol has been developed for the synthesis of 2-aryl-3-nitro-2H-chromene derivatives. This protocol involves the l-prolinamide mediated tandem oxa-Michael Henry reaction between a variety of β-nitrostyrenes and salicylaldehyde. Among the screened solvents, the catalytic efficiency of prolinamides was found to be high in chloroform, but the best results were obtained in water to provide the 2-phenyl-3-nitro-2H-chromene in excellent yields. Substrate scope was also investigated using various substituted β-Nitrostyrenes. All reactions worked well to provide the corresponding products in very high yields. Theoretical calculations were performed to find out the reaction pathways and nature of transition state at 3–21G* basis set and TS1 corresponding to the product (S)-3a, was found favorable by 1.13 kcal/mol over TS2 corresponding to the product (R)-3a.