Enantioselective Conjugate Addition of R₂Zn to α,β-Unsaturated Aldehydes and Ketones

Significance

Bräse reports the first examples of copper-free asymmetric conjugate addition of a dialkylzinc to α,β-unsaturated aldehydes. By using a chiral Schiff base catalyst, the reaction gave the 1,4-product in excellent enantioselectivities and moderate to excellent chemoselectivity over a 1,2-addition. Addition of dialkylzinc to α,β-unsaturated ketones gave exclusively the conjugate addition product in good to excellent enantioselectivities. The chiral aldehyde product is an important intermediate for further functionalization such as in asymmetric aldol or 1,2-addition of another organozinc reagent to build biologically interesting structures.