We report an efficient synthetic route for the synthesis of tetrahydro indole 2,4-dionesfrom readily available β-enaminones and glyoxal and subsequent I2/DMSO-mediated oxidation/aromatization of tetrahydro indole 2,4-dione to produce 4-hydroxyisatin derivatives. The key aspect of this protocol includes the dual catalytic activity of molecular iodine in presence of DMSO. Mechanistic study suggested this reaction is substrate selective as corresponding aromatization and sp3 C-H oxidation stops in presence of 6,6-disubstituted tetrahydro indole 2,4-dione. Additionally, a thorough investigation into the synthesis of tetrahydro indole 2,4-dione followsacid-catalyzedcyclization/dehydration/enol-keto tautomerism from β-enaminones and glyoxal.

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