Catalyst-free four-component domino synthetic approach toward versatile multicyclic spirooxindole pyran scaffolds

A new versatile strategy involving a sequential four-component reaction of the nitroketene dithioacetals, alkylamine/benzylamine, isatin and various enolizable active methylene structures (pyrazolone, barbituric acid, 1,3-indandione and 2-hydroxy-1,4-naphthoquinone) as precursors under mild and catalyst-free conditions results in the synthesis of new functionalized spirooxindole pyrans named spiro[indoline-3,4′-pyrano[2,3- c ]pyrazol], spiro[indoline-3,5′-pyrano[2,3- d ]pyrimidine], spiro[indeno[1,2- b ]pyran-4,3′-indoline] and spiro[benzo[ g ]chromene-4,3′-indoline] in moderate to good yields. The use of various active methylene compounds affords a range of skeletally distinct spirooxindole-based heterocycles with potential biological properties. The present strategy has many advantages, such as convenient one-pot operation, simple workup procedures and straightforward isolation without using tedious purification steps such as column chromatography, progress under catalyst-free condition and high molecular diversity. Synthesis of spirooxindole pyrans by a sequential four-component reaction of nitroketene dithioacetals, alkylamine/benzylamine, isatin, and active methylene compounds.