N-Donor ligand activation of titanocene for the Biginelli reaction via the imine mechanism

Abstract

The remarkable activation of stable titanocene dichloride (Cp₂TiCl₂) was achieved using N-donor ligand urea in an alcoholic solvent, leading to the formation of a Ti(IV) species [(MeO)₂Ti(NHCONH₂)]⁺, the existence of which was verified by ESI-MS, ESI-MS/MS, and NMR. Catalyzed by the newly formed Ti(IV) species, a myriad of 3,4-dihydropyrimidin-2-(1H)-ones were produced via a three-component Biginelli reaction. Further mechanistic investigation indicated that the Biginelli reaction had taken place via the imine route.