Lewis acid promoted diastereoselective addition of TMSCN and TMSCF3 to isatin-derived N-sulfinyl ketimines: synthesis of optically active tetrasubstituted 3-aminooxindoles.

A practical and efficient method for preparation of highly enantiomerically enriched 3-cyano-3-aminooxindoles and 3-trifluoromethyl-3-aminooxindoles with up to 99% optical purity by a Lewis acid promoted diastereoselective Strecker reaction and trifluoromethylation of isatin-derived N-tert-butanesulfinyl ketimines has been developed. This protocol allows direct use of N-free isatin substrates under mild conditions.