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.