Ionic liquid media resulted in more efficient regio- and stereoselective aminohalogenation of cinnamic esters

The ionic liquid, butylmethylimidazolium tetrafluoroborate ([Bmim][BF4]), was found to be superior to classical organic solvents for the metal catalyzed regio- and stereoselective aminohalogenation of cinnamic esters. The aminohalogenation reaction of cinnamic esters with p-TsNCl₂ proceeded at a faster rate (within 12 h) in the presence of a reduced amount of catalyst (CuOTf, 6.0 mol %). Good yields (76-82%) and excellent regio- and stereoselectivity (one isomer) were achieved for eight examples.     

Chelation-controlled asymmetric aminohalogenation reaction

The chelation-controlled asymmetric aminohalogenation of α,β-unsaturated 3-aryl-N-acyl-N-4-phenyl-2-oxazolidinones have been established by using palladium(II) acetate as the catalyst and as the chelation metal. The reaction is very convenient to perform by simply mixing the three reactants, cinnamates, N,N-dichloro-p-toluenesulfonamide and catalyst together with 4 Å molecular sieves at rt in any convenient vial of appropriate size without special protection from inert gases. Unlike the previous asymmetric aminohalogenation, the ionic liquid, [BMIM][NTf₂], was found to be superior to [BMIM][BF₄] as the reaction media. It was also found that palladium(II) acetate has to be used together with 1 equiv of MeCN to achieve the opposite chelation control. The resulting absolute stereochemistry of the product was unambiguously determined by X-ray structural analysis.     

Ionic liquid-supported proline as catalyst in direct asymmetric aldol reaction

Ionic-liquid-supported proline derivative was synthesized starting from L-proline and was used to catalyze direct asymmetric aldol reaction of acetone with aldehydes. The yield and optical purity of the condensation products, the corresponding β-hydroxy carbonyl compounds were comparable with those obtained under homogeneous conditions. Moreover, the catalyst can be reused for at least four times. Published in Russian in Zhurnal Organicheskoi Khimii, 2008, Vol. 44, No. 12, pp. 1834–1837. The text was submitted by the authors in English.     

Multinuclear Pd/Zn complex-catalyzed asymmetric alkylative ring-opening reaction of oxabicyclic alkenes

A multinuclear palladium catalyst can be used to realize the efficient catalytic asymmetric alkylative ring-opening reaction of oxabicyclic alkenes using dimethylzinc. The use of (R)-BINOL-PHOS bearing bisphosphine and diol moieties is essential for achieving excellent catalytic performance; the corresponding monophosphine and hydroxy-protected derivatives showed lower catalytic activities and/or enantioselectivities. The generation of Pd/Zn-multinuclear complexes is a key feature of the present catalysis.     

Direct catalytic asymmetric cross-aldol reactions in ionic liquid media

Enantioselective proline-catalyzed direct asymmetric cross-aldol reactions with aldehydes were performed in ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate media, which simplified product isolation and catalyst recycling, affording 3-hydroxy aldehydes in high yield with excellent stereoselectivity. In addition, the enhanced reactivity of the asymmetric cross-aldol reactions in ionic liquid allowed the catalyst loading to be lowered significantly.     

Palladium-catalyzed asymmetric carbamoyl-carbonylation of alkenes

An unprecedented palladium-catalyzed asymmetric carbamoyl-carbonylation of tethered alkenes with CO and alcohols has been developed. This reaction provided an efficient route to access oxindoles and γ-lactams bearing β-carbonyl substituted quaternary carbons in good yields with excellent chemo-, regio-and enantioselectivity. Gram-scale synthetic capability and facile transformations of the products to chiral spirooxindole and other functional molecules further illustrated the practicability of this reaction.     

Fully reagent-controlled asymmetric synthesis of (-)-spongidepsin via the Zr-catalyzed asymmetric carboalumination of alkenes (ZACA reaction)

The ZACA reaction has been shown to proceed satisfactorily with internally OH-substituted 1-alkenes, provided that the OH group is unprotected and non-allylic. This reaction was used for reagent-controlled asymmetric construction of 3. Allylic alcohol was converted to 2 in seven steps via iterative ZACA processes and simple chromatography. (-)-Spongidepsin (1) was synthesized by using 2 and 3 through application of the esterification-amidation-ring-closing metathesis protocol previously reported.     

Direct asymmetric aldol reaction in aqueous media using polymer-supported peptide

PEG-PS resin-supported tripeptide/zinc chloride catalyst system has been developed for use in the direct asymmetric aldol reaction of acetone with aldehydes in aqueous media. The peptide catalyst could be separated from the reaction mixture by filtration, and was reusable at least five times without significant change in its activity and selectivity.     

Catalytic asymmetric thiofunctionalization of unactivated alkenes

Catalytic asymmetric sulfenylation of double bonds has been achieved using a BINAM-based phosphoramide catalyst and an electrophilic sulfur source. Simple alkenes as well as styrenes afforded sulfenylated tetrahydrofurans and tetrahydropyrans by closure with pendant hydroxyl or carboxyl groups. Intermolecular thiofunctionalizations were also achieved with simple alcohols or carboxylic acids as the nucleophiles.     

Ionic liquid promoted interrupted Feist-Benary reaction with high diastereoselectivity

A basic ionic liquid, 1-butyl-3-methylimidazolium hydroxide promotes the interrupted Feist-Benary reaction at room temperature under organic solvent-free conditions to produce a variety of substituted hydroxydihydrofurans. The hydroxydihydrofurans are converted to furans (Feist-Benary products) using the ionic liquid, 1-methyl-3-pentylimidazolium bromide at 70-75 °C. The reactions are very clean, high yielding and highly stereoselective.     

Catalytic asymmetric carbohydroxylation of alkenes by a tandem diboration/Suzuki cross-coupling/oxidation reaction

[reaction: see text] Chiral nonsymmetric 1,2-diboron adducts are generated by catalytic enantioselective diboration. Oxidation of these adducts provides 1,2-diols in good yield. Alternatively, 1,2-diboron compounds may be reacted, in situ, with aryl halides wherein the less hindered C-B bond participates in cross-coupling. The remaining C-B bond is then oxidized in the reaction workup thereby allowing for net asymmetric carbohydroxylation of alkenes in a tandem one-pot diboration/Suzuki coupling/oxidation sequence.     

Nickel-catalyzed asymmetric reductive aryl-allylation of unactivated alkenes

Herein we report a nickel-catalyzed asymmetric reductive aryl-allylation of aryl iodide-tethered unactivated alkenes, wherein both acyclic allyl carbonates and cyclic vinyl ethylene carbonates can serve as the coupling partners. Furthermore, the direct use of allylic alcohols as the electrophilic allyl source in this reaction is also viable in the presence of BOC anhydride. Remarkably, this reaction proceeds with high linear/branched-, E/Z- and enantio-selectivity, allowing the synthesis of various chiral indanes and dihydrobenzofurans (50 examples) containing a homoallyl-substituted quaternary stereocenter with high optical purity (90–98% ee). In this reductive reaction, the use of pregenerated organometallics can be circumvented, giving this process good functionality tolerance and high step-economy.

A nickel-catalyzed reductive asymmetric aryl-allylation of tethered unactivated alkenes has been developed, providing diverse benzene-annulated cyclic compounds bearing a quaternary stereocenter with high regio-, E/Z- and enantio-selectivity.     

Ionic liquid mediated recyclable sulphonimide based organocatalysis for aldol reaction

Sulphonimide based organocatalyst was used to catalyze the aldol reaction in ionic liquid media. On the basis of yield and selectivity the ionic liquid mediated system was found superior in comparison with organic solvents. The added advantages of this ionic liquid mediated organocatalysis are easy recovery of product and the recyclability of the organocatalyst.      

Ionic liquid as a green catalytic reaction medium for esterifications

Esterifications of alcohols with carboxylic acids in the room temperature ionic liquid 1-butylpyridinium chloride–aluminium(III) chloride as green reaction medium in catalytic quantities have been investigated. Excellent conversion and selectivities were achieved, and the most of resultant esters could be easily recovered due to immiscibility with the ionic liquid.     

Ionic reaction of halogens with terminal alkenes: the effect of electron-withdrawing fluorine substituents on the bonding of halonium ions

Ionic reactions of terminal alkenes with chlorine (Cl(2)), bromine (Br(2)), and iodine monochloride (ICl) are sensitive to the alkyl substituents, and the positions and number of vinyl fluorine atoms. These perturbations influence the symmetry of the halonium ion intermediates, which can be determined by the distribution of the Markovnikov to anti-Markovnikov products. A vinyl fluorine on the number-2 carbon favors an unsymmetrical intermediate with greater charge on the number-2 carbon unless the alkyl group is electron withdrawing. A vinyl fluorine on the terminal number-1 carbon favors positive charge development on that carbon unless a resonance stabilizing group is on the number-2 carbon. The symmetry of halonium ions with vinyl fluorines on both carbons-1 and -2 depends primarily on the characteristics of the alkyl substituent. Intermediates range from open-ions with the positive charge on carbon-2, to various bridged species, to open-ions on the terminal carbon.     

Carbohydrate-derived iminium salt organocatalysts for the asymmetric epoxidation of alkenes

A new family of carbohydrate-based dihydroisoquinolinium salts has been prepared and tested for potential as asymmetric catalysts for the epoxidation of unfunctionalized alkene substrates, providing up to 57% ee in the product epoxides.