I2/DMSO-mediated substrate selective oxidation of tetrahydro indole-2,4-dione towards 4-hydroxy isatins and 5,6-dihydro-1H-indole-2,4-dione derivatives
indole-2,4-diones from 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 the presence of DMSO. Mechanistic study suggested that this reaction is substrate selective as corresponding aromatization