New multicomponent domino reaction on water: highly diastereoselective synthesis of spiro[indoline-3,4′-pyrazolo[3,4-b]pyridines] catalyzed by NaCl

A direct and efficient approach for the preparation of medicinally promising pyrazolopyridinyl spirooxindoles has been developed through a sequential one-pot, three-component reaction of easily available isatin, α-cyanoacetic ester or malononitrile, and 5-amino-3-methylpyrazole catalyzed by sodium chloride in water. Desired products were obtained in high to excellent yields using a simple workup procedure. The product synthesized using α-cyanoacetic ester showed high diastereoselectivity in which the stereochemistry of major diastereomer was confirmed by X-ray diffraction analysis. The present green synthesis shows attractive characteristics such as the use of water as the reaction medium, one pot conditions, short reaction period, easy workup/purification, and reduced waste production, without use of any acid or metal promoters.