Chiral Amine–Polyoxometalate Hybrids as Recoverable Asymmetric Enamine Catalysts under Neat and Aqueous Conditions

Abstract

AbstractSolid acid–chiral amine hybrids have been synthesized and explored as recyclable and reusable enamine‐type asymmetric catalysts. Simple chiral amine–polyoxometalate (CA–POM) hybrids were identified as the optimal catalysts to promote a range of enamine‐based transformations with high activity and excellent stereoselectivity under either neat or aqueous conditions. A catalyst loading as low as 0.33 mol‐% (1 mol‐% loading of chiral amine) was sufficient to achieve fast reactions and high stereoselectivities. Under both conditions, the CA–POM hybrid catalysts could be easily recycled and reused up to seven times with essentially unchanged stereoselectivity, although diminished activity was observed upon extensive reuse, especially under aqueous conditions.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)