Microwave promoted and improved thermal synthesis of spiro[indole-pyranobenzopyrans] and spiro[indole-pyranoimidazoles]

Spiro [indole-pyranoimidazoles] (5) and spiro[indole-pyranobenzopyrans] (6) are readily synthesized in one step in 86-92 and 91-97% yields by the Michael condensation of 3-dicyanomethylene-2H-indol-2-ones (2) with I -phenyl-2-thiohydantoin (3) and 4-hydroxy-2H-1-benzopyran-2-one (4), respectively, without using any catalyst under different reaction conditions (conventional heating and microwave irradiation using (A) polar solvents (b) neutral alumina/silica gel as inorganic solid support in solvent free conditions). 2 was synthesized in situ by the Knoevenagel condensation of indole-2,3-dione (1) and malononitrile in the absence of any catalyst. 100% conversion was observed in most cases on TLC which also showed the formation of a single product. The comparison between the various methods is established.