Hf(OTf)4 as a Highly Potent Catalyst for the Synthesis of Mannich Bases under Solvent-Free Conditions

摘要

Hf(OTf) was identified as a highly potent catalyst (0.1–0.5 mol%) for three-component Mannich reaction under solvent-free conditions. Hf(OTf) -catalyzed Mannich reaction exhibited excellent regioselectivity and diastereoselectivity when alkyl ketones were employed as substrates. H NMR tracing of the H/D exchange reaction of ketones in MeOH- indicated that Hf(OTf) could significantly promote the keto-enol tautomerization, thereby contributing to the acceleration of reaction rate.