Diastereoselective Addition of PhSCF 2 SiMe 3 to Chiral N - tert -Butanesulfinyl Ketimines Derived from Isatins: Synthesis of Enantioenriched gem -Difluoromethylenated Spiro-pyrrolidinyl and Spiro-piperidinyl Oxindoles.

A convenient and efficient synthetic strategy to prepare enantioenriched gem -difluoromethylenated spiro-pyrrolidinyl and spiro-piperidinyl oxindoles is described. Fluoride-mediated diastereoselective nucleophilic addition of PhSCF 2 SiMe 3 to chiral N - tert -butanesulfinyl ketimines derived from isatins was a key step and provided diastereomeric adducts, which were readily separable. Removal of the chiral sulfinyl group followed by structural manipulation afforded chiral gem -difluoromethylenated spiro-pyrrolidinyl and spiro-piperidinyl oxindoles.