A highly efficient large-scale asymmetric Michael addition of isobutyraldehyde to maleimides promoted by a novel multifunctional thiourea

A novel class of chiral multifunctional thioureas bearing a chiral lipophilic beyerane scaffold and a primary amino group were designed and prepared. The thioureas were proven to be effective for catalyzing the asymmetric Michael addition between isobutyraldehyde and maleimides with only 0.5 mol % catalyst loading, and exhibited double asymmetric induction. Both of the catalysts afforded the corresponding adduct with high to excellent yields (up to 98%) and excellent enantioselectivities (up to 99%). Furthermore, this catalytic system can be used efficiently in large-scale reactions with the yields and enantioselectivities being maintained at the same level.