La(OTf)3-catalyzed, three-component synthesis of spiro[Indolo-3,10′-indeno[1,2-b]quinolin]-2,4,11′-triones in PEG-400 under conventional heating and ultrasonic irradiation

An efficient La(OTf)3-catalyzed three-component reaction has been developed for the synthesis of highly substituted spiro[indolo-3,10′-indeno[1,2-b]quinolin]-2,4,11′-triones in polyethylene glycol (PEG-400) under conventional heating and ultrasonic irradiation. The most exciting feature of this methodology is its mechanism involving the unusual ring opening of an isatin moiety followed by recyclization. All the reactions resulted in good yield of products. The important features of this reaction are use of green solvent, good yields, less reaction times, and recyclability of the catalyst.