Development of bifunctional salen catalysts: rapid, chemoselective alkylations of alpha-ketoesters.

Lewis acid-Lewis base salen complexes have been identified as highly efficient catalysts for the addition of dialkylzincs to alpha-ketoesters. In contrast to aldehydes or ketones, the reaction between diethylzinc and alpha-ketoesters is significant in the absence of catalyst. In the presence of catalyst, the reaction rate is increased over 100-fold relative to the background. Furthermore, the reduction product, which is a major coproduct with other catalysts, is not observed with these bifunctional salens. As a result, high yields of the addition products can be obtained (57-99%). Both the Lewis acid and Lewis base portions of the catalyst are critical to the reactivity and selectivity. The two separate portions of the catalyst have been shown to function in a cooperative manner.