Asymmetric Michael reactions catalyzed by a highly efficient and recyclable quaternary ammonium ionic liquid-supported organocatalyst in aqueous media.

A novel ionic liquid-support organocatalyst, which contains the quaternary ammonium ion moiety, was recently developed and successfully applied to the asymmetric Michael reaction in the presence of a newly developed ionic liquid-supported (ILS) benzoic acid as co-catalyst. For the reactions studied, in which various aldehydes and nitroolefins were examined, excellent diastereo- and enantioselectivities were obtained with low catalyst loading. Also, the catalyst could be recycled for ten times without significant loss of enantioselectivity.

Organocatalytic direct asymmetric crossed-aldol reactions of acetaldehyde in aqueous media.

A new type of diarylprolinol-based catalyst, which contains a dioctylamino group in the presence of a newly developed ionic liquid supported (ILS) benzoic acid as cocatalyst, is shown to be an effective catalytic system for the asymmetric direct crossed-aldol reaction of acetaldehyde in aqueous media using brine. For the reactions studied, the catalyst loading could be reduced to 5 mol %; high yields (up to 97%) and high enantioselectivities (up to 92% ee) were also achieved for a wide variety of aromatic aldehyde.

Highly enantioselective and recyclable organocatalytic Michael addition of malonates to α,ß-unsaturated aldehydes in aqueous media.

A new type of pyrrolidine-based organocatalyst, which was developed earlier in our lab, has been found to be very effective for the Michael addition reaction in aqueous solvents involving a wide range of α,ß-unsaturated aldehydes and malonate derivatives. For the reactions studied, good to excellent yields (73%-96%) and high to excellent enantioselectivities (up to 97%) were obtained using this catalyst. In addition, the catalyst could be recycled up to four times with gradual reductions in yields and enantioselectivity observed after the second cycle.

Ionic-liquid-supported (ILS) catalysts for asymmetric organic synthesis.

The asymmetric synthesis of compounds that contain new C-C and C-O bonds remains one of the most important types of synthesis in organic chemistry. Over the years, many different types of catalysts have been designed and used effectively to carry out such transformations. Ionic-liquid-supported (ILS) catalysts represent a new and very effective class of catalysts that are used to facilitate the asymmetric synthesis of such compounds. There are many advantages to using ILS catalysts; they are nontoxic, environmentally benign, and, most important, recyclable. An overview of the design, synthesis, mode of action, and effectiveness of this class of catalysts is reported.

Di(methylimidazole)prolinol silyl ether catalyzed highly Michael addition of aldehydes to nitroolefins in water.

A new pyrrolidine-based organocatalyst for asymmetric reactions has been developed and shown to be a very effective catalyst for the Michael reaction involving various nitroolefins and aldehydes in water. This design is based on the introduction of a hydrophilic group into the pyrrolidine side chain. This catalyst, di(methylimidazole)prolinol silyl ether in combination with sodium bicarbonate as additive effectively catalyzed the Michael addition of aldehydes to nitroolefins in water as solvent in high yields and excellent enantioselectivities.

Ionic liquid-supported (ILS) (S)-pyrrolidine sulfonamide, a recyclable organocatalyst for the highly enantioselective Michael addition to nitroolefins.

A new class of ionic liquid supported (ILS) (S)-pyrrolidine sulfonamide organocatalyst has been developed and shown to be a very effective catalyst for the asymmetric Michael addition reactions of ketones and aldehyde to nitroolefins with high enantio- and diastereoselectivities. This ILS organocatalyst is also easily recycled and could be reused at least five times without significant loss of its ability to affect the outcome of the asymmetric reactions.

Design and synthesis of bistereogenic chiral ionic liquids and their use as solvents for asymmetric Baylis-Hillman reactions.

Three novel chiral ionic liquids (CILs) containing two chiral centers in the side chain bonded to the 2-position of the imidazolium cation and different anions have been synthesized, characterized and used as chiral solvents for asymmetric Baylis-Hillman (BH) reactions; good yields and fair enantioselectivities were obtained.

Design and synthesis of pyridinium chiral ionic liquids tethered to a urea functionality.

Nine chiral room-temperature ionic liquids (RTILs), which contain a chiral moiety and a urea functionality bonded to a pyridinium ring, have been designed and synthesized. The synthesis of these ionic liquids is concise and practical due to the commercial availability of the starting materials. These novel RTILs were readily prepared from 2-(aminomethyl)pyridine and amino acid ester derived isocyanates. We envision that these new chiral RTILs can serve as effective reaction media as well as chiral catalysts for asymmetric reactions, which are presently being investigated in our laboratory.

Design and synthesis of C-2 substituted chiral imidazolium ionic liquids from amino acid derivatives.

[reaction: see text] A series of novel chiral ionic liquids (CILs) has been synthesized and fully characterized. The reaction of 1-methyl-2-imidazolecarboxaldehyde and chiral amino alcohols followed by reduction is key to the design of these new CILs. This is the first time that CILs have been synthesized by introducing chiral scaffolds on the C-2 position of the imidazolium cation of ILs. The simple and straightforward procedure resulted in CILs as colorless oils at room temperature in good yields.

Ionic liquid media resulted in the first asymmetric aminohalogenation reaction of alkenes.

[reaction: see text] The first asymmetric aminohalogenation of functionalized alkenes has been established. The ionic liquid [bmim][BF4] was found to be the only effective media for success as normal organic solvents failed to give any product for this reaction. The reaction is also very convenient to perform by simply mixing the three reactants, cinnamates, N,N-dichloro-p-toluenesulfonamide, and catalyst, together with 4 A molecular sieves at room temperature in [bmim][BF4] in any convenient vial of appropriate size without special protection from inert gases. Good chemical yields (60-72%) and diastereoselectivities (up to 75% de) have been obtained with a good scope of substrates. The resulting individual diastereomers have been cleanly separated via column chromatography. The absolute stereochemistry of the reaction was unambiguously determined by X-ray structural analysis.

New asymmetric halo aldol reaction provides a novel approach to biologically important chiral cyclothers and cycloamines.

[reaction: see text] A new asymmetric halo aldol reaction has been developed by reacting cyclopropyl carbonyl derived enolates with aldehydes. The absolute structure was unambiguously confirmed by X-ray structural analysis. Eight examples were reported with good yields and up to complete control of diastereomeric excesses. These halo aldol products have been readily cyclized in the presence of weak bases to produce chiral 2,3-disubstituted tetrahydrofuran derivatives in good yield without any observed epimerization.

A catalytic reaction of alkynes via multiple-site functionalization.

The first multiple-site activation of alkynes with amine/halogen functionalities has been established. The reaction was performed by treating alkyne with N,N-dichlorobenzenesulfonamide at 80 degrees C in the presence of palladium acetate catalyst. A new mechanism was proposed which involves the novel formation of beta-halovinyl palladium and pi-allylpalladium species. Excellent regio- and stereoselectivities were achieved with the absolute structure determined by X-ray structural analysis.

N,N-dichloro-2-nitrobenzenesulfonamide as the electrophilic nitrogen source for direct diamination of enones.

N,N-dichloro-o-nitrobenzenesulfonamide (2-NsNCl2) was found to be an effective electrophilic nitrogen source for the direct diamination of alpha,beta-unsaturated ketones without the use of any metal catalysts. The reaction is very convenient to carry out without the protection of inert gases. Molecular sieves (4 A) and temperature were found to play key roles in controlling the formations of 3-trichloromethyl and dichloromethyl imidazoline products (16 examples). The 2-Ns-protection group of the resulting diamine products can be easily cleaved under mild Fukuyama's conditions. A new mechanism hypothesis of [2+3] cyclization and N-chlorination has been proposed to explain the product structures, particularly their regio- and stereochemistry.

The effect of the cyclopropyl group on the conformation of chemotactic formyl tripeptides.

Certain formyl peptides are powerful chemoattractants towards neutrophils. In this study, several formyl tripeptides were synthesized and used to investigate the effects of different amino acid residues in position 1 on their ability to stimulate neutrophil chemotaxis. Pig neutrophil chemotaxis towards the formyl tripeptide, HCO-Ac(3)C-Leu-Phe-OMe 1, where Ac(3)C represents 1-amino-1-cyclopropane carboxylic acid, was observed. Pig neutrophil chemotaxis towards a very similar formyl tripeptide, HCO-Aib-Leu-Phe-OMe 2, where Aib represents alpha-amino isobutyric acid, was not observed. Compared to the isopropyl group, it was shown that the cyclopropyl group induces a greater percentage of the E conformation about the formamide functionality in these peptides. For 1 and 2, the E isomer distributions in CDCl3 are 36 and 9%, respectively. Since a major difference between these two peptides is the Z/E isomeric distribution, one implication is that the peptide-receptor site interactions involving the E conformer are more effective than those of the Z conformer. No pig neutrophil chemotaxis towards the formyl tripeptides, HCO-Ala-Leu-Phe-OMe 3 and HCO-Gly-Leu-Phe-OMe 4 was observed. These formyl tripeptides exhibit a low percentage of the E isomer, similar to that of peptide 2.

Asymmetric halo aldol reaction (AHA).

[reaction: see text] The asymmetric halo aldol reaction (AHA) using Evans oxazolidinones as chiral auxiliaries has been established for tandem I-C/C-C bond formations. The new asymmetric reaction provides a practical approach to a variety of halo aldols of a non-Evans type that cannot be easily synthesized by other methods. Excellent diastereoselectivity (>95%) and yields (80-93%) have been obtained for eight examples.