Direct construction of 3',4'-dihydrospiro[pyrrol-3,2'-oxindoles] through a cascade Michael/cyclization reaction of 3-aminoindolin-2-ones with enones/enals

A simple and efficient cascade Michael/cyclization reaction of 3-aminoindolin-2-ones with enones/enals was identified for the synthesis of potentially biologically active 3',4'-dihydrospiro[pyrrol-3,2'-oxindoles], using DBU as an efficient catalyst and ethylene glycol as an environmentally benign solvent. More diverse 3',4'-dihydrospiro[pyrrol-3,2'-oxindoles] analog libraries were prepared in good yields (up to 97%). The structure of 3',4'-dihydrospiro[pyrrol-3,2'-oxindoles] was confirmed by mass spectrometry analysis, NMR analysis and single crystal X-ray diffraction. The main advantages of this method include the availability of startingmaterials, simple experimental operation, short reaction time, as well as high yields observed.