“…In this context, numerous metal salts and complexes, such as Bi(OTf) 3 , 7 Zn(OTf) 2 , 8 Zr(salphen)Cl 2 , 9 FeCl 3 , 2 and (NH 4 ) 2 [Ce(NO 3 ) 6 ], 10 have produced the desired indolinones in good to excellent yields. A range of other acid catalysts such as p-toluenesulfonic acid, 11 sulfamic acid, 12 and Wells− Dawson-type tungstophosphoric heteropolyacid 13 have also been utilized to carry out the synthesis. However, most of the above methods are associated with one or more drawbacks, such as the use of exhaustible metal reserves, harsh and corrosive acids, tedious workup procedures, and unrecyclable catalysts.…”