Chiral amine organocatalysts for the syn-aldol reaction involving substituted benzaldehydes and hydroxyacetone

Catalytic Efficiency of Primary α-Amino Amides as Multifunctional Organocatalysts in Recent Asymmetric Organic Transformations

Chiral primary α-amino amides, consisting of an adjacent enamine bonding site (Bronsted base site), a hydrogen bonding site (Bronsted acid site), and flexible bulky substituent groups to modify the steric factor, are proving to be extremely valuable bifunctional organocatalysts for a wide range of asymmetric organic transformations. Primary α-amino amides are less expensive alternatives to other primary amino organocatalysts, such as chiral diamines and cinchona-alkaloid-derived primary amines, as they are easy to synthesize, air-stable, and allow for the incorporation of a variety of functional groups. In recent years, we have demonstrated the catalytic use of simple primary α-amino amides and their derivatives as organocatalysts for the aldol reaction, Strecker reaction, Michael tandem reaction, allylation of aldehydes, reduction of N-Aryl mines, opening of epoxides, hydrosilylation, asymmetric hydrogen transfer, and N-specific nitrosobenzene reaction with aldehydes.

Amino Acylguanidines as Bioinspired Catalysts for the Asymmetric Aldol Reaction

The binding and stabilizing effect of arginine residues in certain aldolases served as inspiring source for the development of a family of amino acylguanidine organocatalysts. Screening and optimization led to identify the threonine derivative as the most suitable catalyst for the asymmetric aldol addition of hydroxyacetone, affording the syn diastereomer in high ee. In contrast, the proline derivative yielded the anti diasteromer. MMFF models suggest the presence of an extensive hydrogen bonding network between the acylguanidinium group and the reaction intermediates.

Catalytic enantioselective aldol reactions

Recent developments in catalytic asymmetric aldol reactions have been summarized.

Amine-catalyzed direct aldol reactions of hydroxy- and dihydroxyacetone: biomimetic synthesis of carbohydrates

This article presents comprehensive studies on the application of primary, secondary, and tertiary amines as efficient organocatalysts for the de novo synthesis of ketoses and deoxyketoses. Mimicking the actions of aldolase enzymes, the synthesis of selected carbohydrates was accomplished in aqueous media by using proline- and serine-based organocatalysts. The presented methodology also provides direct access to unnatural L-carbohydrates from the (S)-glyceraldehyde precursor. Determination of the absolute configuration of all obtained sugars was feasible using a methodology consisting of concerted ECD and VCD spectroscopy.