Highly Active Water-Soluble and Recyclable Organocatalyst for the Asymmetric 1,4-Conjugate Addition of Nitroalkanes to α,β-Unsaturated Aldehydes

A novel strategy for the catalytic asymmetric conjugate addition of nitroalkanes to alpha,beta-unsaturated aldehydes in aqueous media has been developed by using diarylprolinol silyl ether in combination with benzoic acid as a water-soluble organocatalyst providing the desired adducts in good to excellent enantioselectivities (up to 95% ee). This catalyst can be recycled at least five times with only a slight reduction in activity and selectivity. In addition, the synthetic procedure presented is simple, practical and environmentally benign.