Spirooxindoles have become a privileged
skeleton given their broad
and promising activities in various therapeutic areas. The strategies
and catalyst systems described here highlight recent advances in the
enantioselective synthesis of spirooxindoles via organocascade strategies.
Various organocatalysts with distinct activation modes have found
application in constructing these sophisticated compounds. This review
focuses on the enantioselective synthesis of spirooxindoles via organocascade
strategies and is organized on the basis of three primary starting
materials and then further subdivided according to the types of organocatalyst.
These methods are of importance for the synthesis of complex natural
products and the design of new pharmaceutical compounds. We believe
that compounds based on spirooxindole skeletons have the potential
to provide novel therapeutic agents and useful biological tools.
The first phosphoric acid-catalyzed asymmetric direct arylative reactions of 2-naphthols with quinone derivatives have been developed, providing efficient access to a class of axially chiral biaryldiols in good yields with excellent enantioselectivities under mild reaction conditions. This approach is a highly convergent and functional group tolerant route to the rapid construction of axially chiral compounds from simple, readily available starting materials. The excellent stereocontrol of the process stems from efficient transfer of stereochemical information from the chiral phosphoric acid into the axis chirality of the biaryldiol products. Preliminary results demonstrate that the biaryldiols can act as efficient chiral ligands in asymmetric transformations.
A general and efficient method for accessing enantiomerically pure arylpyrroles by utilizing the catalytic asymmetric Paal-Knorr reaction has been developed for the first time. A wide range of axially chiral arylpyrroles were obtained in high yields with good to excellent enantioselectivities. The key to success is the use of the combined-acid catalytic system involving a Lewis acid and a chiral phosphoric acid for achieving effective enantiocontrol. Noteworthy is that an unexpected solvent-dependent inversion of the enantioselectivity was observed in the above-mentioned asymmetric reaction.
An efficient enantioselective classic three-component Passerini reaction with a broad substrate scope in the presence of a chiral phosphoric acid catalyst has been developed. This represents the general example for classic three-component Passerini reaction with good to excellent enantioselectivies involving aromatic aldehydes and the bulky pivalaldehyde under mild reaction conditions. The feature of this method is highlighted by using a chiral phosphoric acid to activate carboxylic acid, aldehyde, and isocyanide for the facile construction of widely useful complex compounds.
Axially chiral compounds play an important role in areas such as asymmetric catalysis. The tyrosine click-like reaction is an efficient approach for synthesis of urazoles with potential applications in pharmaceutical and asymmetric catalysis. Here we discover a class of urazole with axial chirality by restricted rotation around an N–Ar bond. By using bifunctional organocatalyst, we successfully develop an organocatalytic asymmetric tyrosine click-like reaction in high yields with excellent enantioselectivity under mild reaction conditions. The excellent remote enantiocontrol of the strategy originates from the efficient discrimination of the two reactive sites in the triazoledione and transferring the stereochemical information of the catalyst into the axial chirality of urazoles at the remote position far from the reactive site.
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