The first organocatalytic asymmetric synthesis of dihydrofuran-spirooxindoles having a linkage at the 2-position of the dihydrofuran motif has been developed from dioxindoles and benzylidene malononitriles.
The first highly diastereo-and enantioselective synthesis of bridged O,O-acetals embedded with spirooxindoles has been developed. Dioxindoles and 2-hydroxy cinnamaldehydes were employed as the reaction partners in this method. The desired products were obtained via diaryl prolinol TBS ether catalyzed Michael reaction followed by acetal formation with TFA.
An efficient organocatalytic asymmetric synthesis of 2,3,4-trisubstituted tetrahydrofurans and tetrahydropyrans has been developed using tandem iminiumÀ enamine catalysis. The process comprises of a double Michael addition reaction between γ/δ-hydroxy-α,β-unsaturated carbonyls and enals. The products of this reaction are obtained in high enantio-and diasteroselectivities and some further synthetic transformations have been performed.
The first organocatalytic enantioselective synthesis of bridged O,O‐ketals embedded with spirooxindoles has been developed. Dioxindoles and ortho‐hydroxy‐benzylidene acetones were engaged as the reaction partners in this method. The desired products were obtained via epi‐cinchonine primary amine catalyzed Michael reaction followed by ketal formation with TFA.
The first organocatalytic asymmetric synthesis of spiro-dihydropyrano cyclohexanones has been developed via the cascade reaction between cyanoketones and cyclic 2,4-dienones.
The first highly enantioselective organocatalytic reaction employing 2-hydroxyacetophenones is disclosed, namely Michael-hemiacetalization reaction of 2-hydroxyacetophenones with enals. The combination of a primary amine and a secondary amine catalyst was found to be the best choice for this methodology. The products of this reaction were obtained in high enantio- and diastereoselectivities and were converted to a variety of biologically important γ-butyrolactones.
An organocatalytic enantioselective synthesis of dihydrofuran-spirooxindoles has been developed. Dioxindoles and trans-α-cyano-α,β-unsaturated ketones were engaged as the reaction partners in this method. The desired products were obtained via bifunctional squaramide catalyzed Michael reaction followed by Pinner reaction and isomerization.
This review article summarizes the recent developments of organocatalytic asymmetric ene reactions. Ene reaction is one of the most useful methods for the formation of C−C bonds in organic synthesis. After the development in 1943 by Kurt Alder, this reaction was thoroughly studied, and various catalytic asymmetric reports were published. This is an updated review on the organocatalytic asymmetric ene reactions.
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