Lanthanide amide-catalyzed one-pot reaction of isatins, dialkyl phosphite, and activated alkenes was developed and a series of spiro[cyclopropan-1,3'-oxindoles] were obtained in moderate to excellent yields. The reaction is stereoselective and the two substituents at the 2 and 3-positions of the cyclopropane in the major product are in the trans configuration. A four-step mechanism involving the Pudovik reaction, Brook rearrangement, Michael addition, and intramolecular nucleophilic substitution is proposed, and an umpolung strategy was used in the process.