Enantioselective Michael addition catalyzed by cinchona alkaloids

Abstract

Enantioselective Michael additions of cyclic β-ketoesters to methyl vinyl ketone catalyzed by cinchona alkaloids were studied. The results revealed that the induced enantioselectivity was significantly influenced by both the structure of the catalyst and that of the substrate. Interesting differences in the effect of the structure of the alkaloid on the enantioselectivity of this reaction in the case of three β-ketoesters were discovered. High enantioselectivities were obtained in the reaction of ethyl 2-oxocyclo-pentanecarboxylate and ethyl 2-oxocyclohexanecarboxylate (up to 83 and 80%, respectively) at a low cinchona:reactant ratio of 1:500. As the specific rotations of the product enantiomers were unknown, they were determined by optical rotation and chiral GC measurements and verified by NMR experiments.