Biocatalytic one-pot three-component synthesis of 3,3′-disubstituted oxindoles and spirooxindole pyrans using α-amylase from hog pancreas

alpha-Amylase from hog pancreas displayed catalytic promiscuity in three-component reaction for the synthesis of 3,3'-disubstituted oxindoles and spirooxindole pyrans. The reactions between isatins, malononitrile and active methyl or active methylene compounds (acetone, nitromethane, indole, acetylacetone, 4-hydroxylcoumarin and dimedone) offered corresponding products via Knoevenagel/Michael reactions or Knoevenagel/Michael/cyclization reactions in one pot with high to excellent yields of up to 98% under mild reaction conditions. The alpha-amylase showed a broad spectrum of adaptability to various substrates. A possible mechanism of the alpha-amylase catalyzed three-component reaction was proposed.