The conjugate addition of cyclic 1,3-dicarbonyl compounds to β,γ-unsaturated α-keto-esters was studied using a series of chiral bifunctional organocatalysts. Takemoto's catalyst was found to be most efficient for this transformation. Excellent yields and good enantioselectivities were achieved for a variety of β,γ-unsaturated α-keto-esters and cyclic 1,3-dicarbonyl compounds. A bifunctional catalytic mechanism is proposed. The method provides a new asymmetric synthetic route for chiral courmarin derivatives.
Chiral bifunctional sulfamides were found to be efficient catalysts for the conjugate addition of ketones to nitroalkenes. Moderate to good enantioselectivities and yields were achieved for the reaction of acetone with a variety of β-aryl-nitroethylenes. Base additives were found to be more efficient than acid additives for the transformation. The reaction of methoxyacetone and cyclopentanone also provided the adducts with moderate enantioselectivities, however in low chemical yields.
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