Nickel-accelerated addition of dialkylzinc reagents to aldehydes. Application to enantioselective synthesis

The reaction of several dialkylzinc reagents with aromatic aldehydes 1 in the presence of a catalytic amount of nickel(II) acetylacetonate (5 mol%) at 0 degrees C gave the expected addition products 2 in 1 h in very good yields. Aliphatic aldehydes 1 required stirring at room temperature for 24 h to afford the addition products in good yields. In comparison with non-catalyzed reactions this process represents a great improvement in reaction rate and selectivity for the formation of addition products. The enantioselective addition of diethylzinc to benzaldehyde 1a in the presence of the nickel catalyst and chiral aziridino alcohols 3 results in an interesting switch of the sense of the asymmetric induction in comparison with the nickel-free process.