Efficient Chiral Organocatalyst Research Articles

DFT stimulation and experimental insights of chiral Cu(II)-salen scaffold within the pocket of MWW-zeolite and its catalytic study.

A Cu(II)-salen complex encapsulated in MWW-framework as an efficient chiral organocatalyst was developed for the synthesis of 3,4-dihydropyrimidin-2-(1H)-one (DHPMs) derivatives via an asymmetric pathway. In order to confirm its structural properties, single-crystal X-ray diffraction, powder XRD, BET, XPS, FE-SEM, EDX, UV-Vis, and FTIR spectra were used. Using computer-assisted DFT calculations, the Cu(II)-salen complex has been fine-tuned to fit into the pocket of the porous MWW support while keeping its chirality. This organocatalyst was shown to be a potent catalyst for the formation of the desired DHPMs product under short reaction times. Furthermore, this green protocol allows rapid and simple isolation of active MWW-trapped Cu(II)-salen scaffolds and its reusability in at least five consecutive runs without losing much of its activity.

Chiral Imidazolium Prolinate Salts as Efficient Synzymatic Organocatalysts for the Asymmetric Aldol Reaction.

Chiral imidazolium l-prolinate salts, providing a complex network of supramolecular interaction in a chiral environment, have been studied as synzymatic catalytic systems. They are demonstrated to be green and efficient chiral organocatalysts for direct asymmetric aldol reactions at room temperature. The corresponding aldol products were obtained with moderate to good enantioselectivities. The influence of the presence of chirality in both the imidazolium cation and the prolinate anion on the transfer of chirality from the organocatalyst to the aldol product has been studied. Moreover, interesting match/mismatch situations have been observed regarding configuration of chirality of the two components through the analysis of results for organocatalysts derived from both enantiomers of prolinate (R/S) and the trans/cis isomers for the chiral fragment of the cation. This is associated with differences in the corresponding reaction rates but also to the different tendencies for the formation of aggregates, as evidenced by nonlinear effects studies (NLE). Excellent activities, selectivities, and enantioselectivities could be achieved by an appropriate selection of the structural elements at the cation and anion.

The organocatalytic highly enantioselective Knoevenagel condensation: applications in the synthesis of various chiral amide derivatives

In this work, efficient organocatalysts were designed, synthesized and successfully applied to the Knoevenagel condensation. In this reaction, different α-branched aldehydes were treated with various malonate compounds to give the desired products up to 97% yield and excellent e.r up to 99.68:0.32 under the mild reaction conditions. Moreover, the Knoevenagel product was converted into different chiral amide derivatives in higher enantioselectivity. We have designed and synthesized efficient chiral organocatalysts and successfully applied to the Knoevenagel condensation reaction. In this reaction, the different α-branched aldehydes were treated with various malonate derivatives to give enantiomerically enriched Knoevenagel products with higher chemical yield (up to 97%) and excellent e.r up to 99.68 0.32 via dynamic kinetic resolution. Further the Knoevenagel adduct was converted into enantiomerically enriched valuable γ-alkyl-substituted amides without loss in enantiomeric ratio.

Pyrrolidine-carbamate based new and efficient chiral organocatalyst for asymmetric Michael addition of ketones to nitroolefins

The novel ((S)-pyrrolidin-2-yl)methyl phenylcarbamate was synthesized and used as an efficient organocatalyst for the asymmetric Michael addition of cyclic/acyclic ketones to nitroolefins. Interestingly, the resulting Michael adducts were obtained in good to high yields (up to 96%) with excellent stereoselectivity (ee up to >99%, dr up to >99:1) without using any additive.

ChemInform Abstract: Design and Synthesis of a s‐Triazene Based Asymmetric Organocatalyst and Its Application in Enantioselective Alkylation.

A very efficient chiral organocatalyst was prepared from the readily available cyanuric chloride. The asymmetric catalyst exhibited a highly enantioselective catalytic performance for the alkylation of a glycinate Schiff base, which provides a useful procedure for the enantioselective synthesis of structurally diverse natural and unnatural α-alkyl-α-amino acids.

Design and synthesis of a s-triazene based asymmetric organocatalyst and its application in enantioselective alkylation

A very efficient chiral organocatalyst was prepared from the readily available cyanuric chloride.

Binaphthol-derived phosphoric acids as efficient chiral organocatalysts for the enantiomer-selective polymerization of rac-lactide

A high enantiomer-selectivity for the polymerization of rac-lactide was achieved using chiral binaphthol-derived monophosphoric acids as organocatalysts. During the polymerization, d-lactide (DLA) preferentially polymerized via kinetic resolution with the maximum selectivity factor (kD/kL) of 28.3. The selective polymerization of DLA was derived from a dual activation, i.e., monomer activation and chain-end activation.

Synthesis of Chiral Organocatalysts derived from Aziridines: Application in Asymmetric Aldol Reaction

We report the synthesis of a new series of highly efficient chiral organocatalysts derived via the regio- and stereoselective ring opening of chiral aziridines with azide anions. The catalysts have proved to be very efficient for a direct asymmetric aldol reaction, both with cyclic as well as acyclic ketones in brine with 2 mol % of catalyst loading, and afforded the products in excellent yields (up to 99%) and enantioselectivities (up to >99%). The chiral aldol adduct obtained has further been converted to a chiral azetidine ring via a convenient pathway.

(2S,5S)‐Pyrrolidine‐2,5‐dicarboxylic Acid, an Efficient Chiral Organocatalyst for Direct Aldol Reactions.

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Asymmetric allylation of N-benzoylhydrazones promoted by novel C2-symmetric bis-sulfoxide organocatalysts

Novel C 2-symmetric bis-sulfoxide/ N-oxide ( R, R)- 5 was prepared in good yield according to the Andersen protocol with ( S)-menthyl p-tolyl sulfinate (2 equiv) and the dilithium derivate of 2,6-dimethylpyridine N-oxide. Reduction of ( R, R)- 5 to pyridine/bis-sulfoxide ( R, R)- 6 was accomplished by means of Katritzky’s procedure (Fe 0/AcOH). Both bis-sulfoxides ( R, R)- 5 and ( R, R)- 6 are efficient chiral organocatalysts in the asymmetric allylation of N-benzoyl hydrazones derived from both aldehydes and ketones.

(2 S,5 S)-Pyrrolidine-2,5-dicarboxylic acid, an efficient chiral organocatalyst for direct aldol reactions

Enantioselective aldol reaction of ketones with aldehydes catalyzed by (2 S,5 S)-pyrrolidine-2,5-dicarboxylic acid in the presence of an equal molar amount of Et 3N was described. By using the new chiral organocatalyst, the direct aldol condensation products were obtained in reasonable yields and up to 90% ee.