Dynamic Kinetic Asymmetric Transformations of β-Stereogenic α-Ketoesters by Direct Aldolization

Dynamic Kinetic Asymmetric Transformation of Racemic Diastereomers: Diastereo- and Enantioconvergent Michael-Henry Reactions to Afford Spirooxindoles Bearing Furan-Fused Rings

Dynamic kinetic asymmetric transformation (DYKAT) reactions of racemic diastereomer mixtures that afford the products as essentially single diastereomers with high enantioselectivities are described. We demonstrated the DYKAT in the diastereo- and enantioselective synthesis of spirooxindoles bearing furan-fused rings. The starting materials of the DYKAT, dihydrobenzofuranone derivatives, were synthesized in racemic diastereomer mixtures, and these were transformed to the spirooxindole derivatives in high yields with high diastereo- and enantioselectivities through Michael-Henry cascade reactions with nitrostyrenes under organocatalytic conditions. In the reactions, regardless the stereochemistry of the starting materials, all the four isomers were transformed to single diastereomers with high enantioselectivities, and four new chiral centers were created.

Catalytic Enantioselective Formal (4+2) Cycloaddition by Aldol-Aldol Annulation of Pyruvate Derivatives with Cyclohexane-1,3-Diones to Afford Functionalized Decalins

The decalin structure is found in bioactive molecules. We have developed catalytic enantioselective formal (4+2) cycloaddition reactions via aldol-aldol cascade reactions between pyruvate-derived diketoester derivatives and cyclohexane-1,3-dione derivatives that afford highly functionalized decalin derivatives. The reactions were performed using a quinidine-derived catalyst under mild conditions. Decalin derivatives bearing up to six chiral carbon centers including tetrasubstituted carbon centers were synthesized with high diastereo- and enantioselectivities. Five to six stereogenic centers were generated from achiral molecules with the formation of two C-C bonds in a single transformation resulting in the formation of the decalin system.

Direct Zinc(II)-Catalyzed Enantioconvergent Additions of Terminal Alkynes to α-Keto Esters

The addition of terminal alkynes to racemic β-stereogenic α-keto esters was achieved in high levels of stereoselectivity, affording versatile tertiary propargylic alcohols containing two stereocenters. This environmentally benign enantioconvergent reaction proceeds with perfect atom economy, requires no solvent, and is catalyzed by a non-toxic zinc salt. The alkyne moiety can be leveraged in downstream transformations including hydrogenation to the corresponding saturated tertiary alcohol, which represents the product of a formal enantioconvergent aliphatic nucleophile addition.