Water-SDS-[BMIm]Br composite system for one-pot multicomponent synthesis of pyrano[2,3- c ]pyrazole derivatives and their structural assessment by NMR, X-ray, and DFT studies.

Here, we report a simple, efficient, and green protocol for the one-pot synthesis of pyrano[2,3- c ]pyrazole derivatives via a sequential three-component strategy using aromatic aldehydes, malononitrile and pyrazolin-5-one in a water-SDS-ionic liquid system. This is a base and volatile organic solvent-free approach that could be applicable to a wide substrate scope. The key advantages of the method over other established protocols are very high yield, eco-friendly conditions, chromatography-free purification and recyclability of the reaction medium. Our study revealed that the N -substituent present in pyrazolinone controls the selectivity of the process. N -unsubstituted pyrazolinone favours the formation of 2,4-dihydro pyrano[2,3- c ]pyrazoles whereas under identical conditions N -phenyl substituent pyrazolinone favours the formation 1,4-dihydro pyrano[2,3- c ]pyrazoles. Structures of the synthesized products were established by NMR and X-ray diffraction techniques. Energy optimized structures and energy gaps between the HOMO-LUMO of some selected compounds were estimated using density functional theory to explain the extra stability of the 2,4-dihydro pyrano[2,3- c ]pyrazoles over 1,4-dihydro pyrano[2,3- c ]pyrazoles.