Organocatalytic Enantioselective γ-Position-Selective Mannich Reactions of β-Ketocarbonyl Derivatives

Catalytic asymmetric Mannich reactions of β-ketocarbonyl derivatives (such as β-ketoesters and (2-oxopropyl)phosphonate), resulting in the formation of a C–C bond at the γ-position of the β-ketocarbonyl derivatives with high enantioselectivities, are reported. The bond formation at the α-position of the β-ketoester was reversible, and the γ-position-reacted product δ-amino β-ketoester derivative was kinetically formed and was stable. The dynamic kinetic process was key for the direct access to the γ-position-reacted products from β-ketocarbonyls under catalytic conditions.

MnO2 as a terminal oxidant in Wacker oxidation of homoallyl alcohols and terminal olefins

Efficient and mild reaction conditions for Wacker-type oxidation of terminal olefins of less explored homoallyl alcohols to β-hydroxy-methyl ketones have been developed by using a Pd(ii) catalyst and MnO2 as a co-oxidant. The method involves mild reaction conditions and shows good functional group compatibility along with high regio- and chemoselectivity. While our earlier system of PdCl2/CrO3/HCl produced α,β-unsaturated ketones from homoallyl alcohols, the present method provided orthogonally the β-hydroxy-methyl ketones. No overoxidation or elimination of benzylic and/or β-hydroxy groups was observed. The method could be extended to the oxidation of simple terminal olefins as well, to methyl ketones, displaying its versatility. An application to the regioselective synthesis of gingerol is demonstrated.

Direct Catalytic Asymmetric Synthesis of Oxindole-Derived δ-Hydroxy-β-ketoesters by Aldol Reactions

Direct asymmetric synthesis of δ-hydroxy-β-ketoesters was accomplished via regio- and enantioselective aldol reactions of β-ketoesters with isatins catalyzed by cinchona alkaloid thiourea derivatives. The C-C bond formation of the reactions occurred only at the γ-position of the β-ketoesters. Reaction progress monitoring and product stability analyses under the conditions that included the catalyst indicated that the γ-position reaction products were formed kinetically. Various δ-hydroxy-β-ketoesters bearing 3-alkyl-3-hydroxyoxindole cores relevant to the development of bioactive molecules were synthesized.