Highly efficient catalyst-free domino conjugate addition, decarboxylation and esterification/amidation of coumarin carboxylic acid/esters with pyrazolones: a green chemistry approach

Tandem conjugate addition, decarboxylation and esterification/amidation of coumarin 3-carboxylic acid derivatives with pyrazolones have been developed. The reactions were performed with coumarin 3-carboxylic acid/esters and pyrazolone in alcohol as a solvent to afford the corresponding pyrazolyl 2-hydroxy phenylpropionate derivatives. Amines and green solvents were employed for amidation in the addition reaction. The methodology has advantages such as excellent yields, a broad substrate scope, catalyst-free, easy purification by simple filtration without any workup, mild conditions and does not require any organic solvents, ligands, base or any additives. This is a green and general synthetic protocol, which could be applicable for the synthesis of substituted pyrazolyl phenyl propionate/amide derivatives. This approach demonstrates the importance of the coumarin 3-carboxylic acid/ester core structure for Michael addition.