A concise and efficient protocol for the regioselective synthesis of dual 1,4-dihydropyridines with several substituted patterns has been developed from a cascade cyclization of enaminones and aldehydes in different media (EtOH/CH3CN). The one-pot cascade reaction involves at least five reactive sites and generates multiple C–C and C–N bonds. The established protocol explores the chemistry of enaminones
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