Asymmetric organocatalytic conjugate addition of dialkyl phosphites to N-unprotected isatylidene malononitriles: access to 3-phospho-2-oxindoles with chiral quaternary stereocenters

摘要

The enantioselective Michael addition of dialkyl phosphites to N-unprotected isatylidene malononitriles has been established for the first time by using a simple bifunctional tertiary amine-thiourea catalyst. The corresponding adducts, 3-phospho-2-oxindoles, containing a chiral quaternary carbon center at the 3-position of the oxindole, were obtained in good to excellent yields (up to 98%) with moderate to excellent enantioselectivities (up to 95% ee). In addition, optically active 3,3'-disubstituted oxindoles bearing carboxylate and phosphonate groups were facilely obtained by the oxidative degradation of the Michael adducts.