Reversal of enantioselectivity in cobalt(<sc>ii</sc>)-catalyzed asymmetric Michael-alkylation reactions: synthesis of spiro-cyclopropane-oxindoles

Herein, an asymmetric Michael-alkylation reaction with a reversal of enantioselectivity catalyzed by chiral cobalt complexes is reported. Using 2.5 mol% of Co(acac)(2)-imidazolidine-pyrroloimidazolone pyridine as catalyst, a Michael-alkylation reaction between 3-chloro-oxindoles and beta,gamma-unsaturated-alpha-ketoesters was achieved, yielding chiral spiro-cyclopropane-oxindoles with a complete and controlled switch in stereoselectivity (up to 99% and -98% ee). The hydrogen bonding between the N-H group in the ligand and the oxyanion of the enolate derived from 3-chloro-oxindole is proposed to direct the reversal of enantioselectivity.