Highly stereoselective anti-aldol reactions catalyzed by simple chiral diamines and their unique application in configuration switch of aldol products

Chiral Ionic Liquids Based on l-Cysteine Derivatives for Asymmetric Aldol Reaction

Structure, and consequently properties, of ionic liquids can be easily tailored by changing cation/anion combinations and/or attaching functional groups. By grafting enantiopure moieties to the framework of ionic liquid it is possible to prepare bioinspired chiral molecules that can serve as a reaction medium, additive or even asymmetric catalyst. In this context, new chiral ionic liquids (CILs), based on biomolecules, such as aminoacids (l-Cysteine derivatives), have been synthesised and tested in asymmetric aldol condensation of aldehydes and ketones. The best results were obtained for CILs composed of S-methyl-l-cysteine cation and bis(trifluoromethane)sulfonimide anion, in the reaction of 2- or 4-nitrobenzaldehyde with acetone or cyclohexanone, giving the aldol product in moderate yields 70–76% and high ee values (up to 96%).

Enantioselective formation of quaternary carbon stereocenters in natural product synthesis: a recent update

Covering: 2013-2018 Natural products bearing quaternary carbon stereocenters have attracted tremendous interest from the synthetic community due to their diverse biological activities and fascinating molecular architectures. However, the construction of these molecules in an enantioselective fashion remains a long-standing challenge because of the lack of efficient asymmetric catalytic methods for installing these motifs. The rapid progress in the development of new-generation efficient chiral catalysts has opened the door for several asymmetric reactions, such as Michael addition, dearomative cyclization, polyene cyclization, α-arylation, cycloaddition, allylation, for the construction of quaternary carbon stereocenters in a highly enantioselective fashion. These asymmetric catalytic methods have greatly facilitated the synthesis of complex natural products with improved output and overall efficiency. In this concise review, we highlight the progress in the last six years in complex natural product synthesis, in which at least one quaternary carbon stereocenter has been constructed via asymmetric catalytic technologies, with particular emphasis on the analysis of the stereochemical model of each enantioselective transformation.

Enantiodivergent Aldol Condensation in the Presence of Aziridine/Acid/Water Systems

A series of novel chiral imines was synthesized from corresponding aldehydes and 1-(2-aminoalkyl)aziridines with good chemical yields. Such imines were tested as catalysts in the direct asymmetric aldol reaction between aromatic aldehydes and acetone/cyclohexanone in the presence of catalytic amounts of water and an acidic additive. The corresponding aldol products were formed in excellent yields and with very high enantioselectivities (98% and 99% ee, respectively).

Catalytic enantioselective aldol reactions

Recent developments in catalytic asymmetric aldol reactions have been summarized.

Highly modular dipeptide-like organocatalysts for direct asymmetric aldol reactions in brine

The dipeptide-like organocatalysts have been developed for asymmetric aldol reactions in brine to achieve high yields and enantioselectivities with 1 mol% catalyst-loading.