The oxidation of 3a,8a-dihydroxy-2-(alkyl/benzylthio)indeno[1,2-d]imidazol-8(3H)-ones to give the corresponding
3-(alkyl/benzylthio)-9b-hydroxy-1H-imidazo[5,1-a]isoindole-1,5(9bH)-dione derivatives in
good to excellent yields at room temperature using two oxidants, periodic acid in aqueous ethanol and
lead(IV) acetate in acetic acid, has been reported.