Hf(OTf) 4 -Catalyzed Three-Component Synthesis of N -Carbamate-Protected β-Amino Ketones.

Hafnium(IV) triflate (Hf(OTf) ₄ ) has been identified as a potent catalyst for the direct three-component synthesis of β-carbamate ketones. This new method, featuring a low catalyst loading, fast reaction rate, and solvent-free conditions, provided facile access to a diversity of carbamate-protected Mannich bases. A mechanistic investigation indicated that the three-component reaction proceeds via sequential aldol condensation and aza-Michael addition, but not the Mannich-type pathway.