Ionic and Covalent Copper(II)-Based Catalysts for Michael Additions. The Mechanism

Cu(SbF6)2-AdamBox and copper(II) bis-(5-tert-butylsalicylaldehydate) catalyze the Michael addition in neutral media. Mechanistic studies, based on UV−vis, IR, and electrospray ionization mass spectrometry (ESI-MS), suggest that copper enolates of the β-dicarbonyl formed in situ are the active nucleophilic species.