Organocatalysis in water at room temperature with in-flask catalyst recycling

A new designer surfactant is described containing a covalently bound organocatalyst, proline. This species is water-soluble and, via spontaneous nanomicelle formation, catalyzes aldol reactions on water-soluble or -insoluble substrates in water as the only medium. Recycling the catalyst is trivial, as the amphiphile/catalyst remains in the aqueous phase in the flask.

Investigating ionic effects applied to water based organocatalysed aldol reactions

Saturated aqueous solutions of various common salts were examined for their effect on aqueous aldol reactions catalysted by a highly active C₂-symmetric diprolinamide organocatalyst developed in our laboratory. With respect to the aldol reaction between cyclohexanone and 4-nitrobenzaldehyde, deionised water was always a superior medium to salt solutions though some correlation to increasing anion size and depression in enantiomeric excess could be observed. Additionally, the complete inhibition of catalyst activity observed when employing tap water could be alleviated by the inclusion of ethylenediaminetetraacetate (EDTA) into the aqueous media prior to reaction initiation. Extension of these reaction conditions demonstrated that these ionic effects vary on a case-to-case basis depending on the ketone/aldehyde combination.

Chiral ionic liquids: a compendium of syntheses and applications (2005-2012)

In recent years, the field of chiral ionic liquids (CILs) has undergone exponential growth. As the technology has advanced, new ways of synthesizing stable and structurally diverse ionic liquids have been established. This has led to heretofore unknown applications of CILs as well as in improving efficiency of previously identified applications. In this review article we have compiled a comprehensive database containing structures and physical properties of notable CILs that have been synthesized during the last 6 years. Their applications in the fields of asymmetric organic synthesis, spectroscopy, and chromatography are also illustrated. This is an expansion of our previous review, which covered the literature before 2005.

A highly asymmetric direct aldol reaction catalyzed by chiral proline amide – thiourea bifunctional catalysts

A series of chiral proline amide – thiourea bifunctional catalysts derived from l-proline and chiral diamine were prepared and successfully applied to highly enantioselective direct aldol reactions of cyclohexanone with various aldehydes in excellent yields (85%–97%), diastereoselectivities (anti/syn > 20:1) and enantioselectivities (up to 91% ee).

Enamine catalysis

The reversible reaction of primary or secondary amines with enolizable aldehydes or ketones affords nucleophilic intermediates, enamines. With chiral amines, catalytic enantioselective reactions via enamine intermediates become possible. In this review, structure-activity relationships and the scope as well as current limitations of enamine catalysis are discussed.

Highly diastereo- and enantioselective direct Barbas-List aldol reactions promoted by novel benzamidoethyl and benzamidopropyl prolinamides in water

Four novel benzamido-functionalized prolinamides have been prepared and tested as organocatalysts for enantioselective aldol reaction of aldehydes and cyclic ketones in water. In particular, prolinamide derived from achiral ethylene diamine was the best catalyst leading to anti aldols in excellent diastereomeric (up to 98/2) and enantiomeric (up to 99/1) ratios, thereby showing that lateral amide functionalities might be a key issue for facilitating "in water" chemistry. These catalysts are cheaper and easier to prepare than those previously described.

Highly stereoselective and scalable anti-aldol reactions using N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide: scope and origins of stereoselectivities

A highly enantio- and diastereoselective anti-aldol process (up to >99% ee, >99:1 dr) catalyzed by a proline mimetic-N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide-has been developed. Catalyst loading as low as 2 mol % can be employed. Use of industry-friendly solvents for this transformation as well as neat reaction conditions have been demonstrated. The scope of this transformation on a range of aldehydes and ketones is explored. Density functional theory computations reveal that the origins of enhanced diastereoselectivity are due to the presence of nonclassical hydrogen bonds between the sulfonamide, the electrophile, and the catalyst enamine that favor the major anti-Re aldol TS in the Houk-List model.

Development of an enantioselective route toward the Lycopodium alkaloids: total synthesis of lycopodine

Synthesis of a C(15)-desmethyl tricycle core of lycopodine has been accomplished. Key steps in the synthetic sequence include organocatalytic, intramolecular Michael addition of a keto sulfone and a tandem 1,3-sulfonyl shift/Mannich cyclization to construct the tricyclic core ring system. Synthetic work toward this natural product family led to the development of N-(p-dodecylphenylsulfonyl)-2-pyrrolidinecarboxamide, an organocatalyst which facilitates enantioselective, intramolecular Michael additions. A detailed mechanistic discussion is provided for both the intramolecular Michael addition and the sulfone rearrangement. Finally, the application of these discoveries to the enantioselective total synthesis of alkaloid lycopodine is described.

The direct catalytic asymmetric aldol reaction

Asymmetric aldol reactions are a powerful method for the construction of carbon-carbon bonds in an enantioselective fashion. Historically this reaction has been performed in a stoichiometric fashion to control the various aspects of chemo-, diastereo-, regio- and enantioselectivity, however, a more atom economical approach would unite high selectivity with the use of only a catalytic amount of a chiral promoter. This critical review documents the development of direct catalytic asymmetric aldol methodologies, including organocatalytic and metal-based strategies. New methods have improved the reactivity, selectivity and substrate scope of the direct aldol reaction and enabled the synthesis of complex molecular targets (357 references).