Showing papers in "Advanced Synthesis & Catalysis in 2008"
TL;DR: In this paper, a review summarizes the development of diverse homogeneous catalytic methods for the synthesis of indoles from alkynes and different N nucleophiles such as arylhydrazines, aniline derivatives, ary l isonitriles and nitroarenes.
Abstract: In the past decade alkynes have become attractive starting materials for the synthesis of a variety of indole derivatives. This review summarizes the development of diverse homogeneous catalytic methods for the synthesis of indoles from alkynes and different N nucleophiles such as arylhydrazines, aniline derivatives, aryl isonitriles and nitroarenes.
322 citations
TL;DR: In this paper, the recent advances in catalytic asymmetric hydrophosphonylation of aldehydes and imines are discussed and several proposed mechanisms for the different possibilities of asymmetric induction and the application of this catalytic methodology to the enantioselective synthesis of α-amino and α-hydroxy phosphonates.
Abstract: In this review, recent advances in catalytic asymmetric hydrophosphonylation of aldehydes and imines are discussed. We also summarize several proposed mechanisms for the different possibilities of asymmetric induction and the application of this catalytic methodology to the enantioselective synthesis of α-amino and α-hydroxy phosphonates. A variety of metal-based chiral catalysts as well as several organic catalysts have been exploited as suitable systems for the preparation of enantiomerically pure phosphonates. The recent evolution and future trends of those and other catalytic systems are described.
218 citations
TL;DR: Various w-transaminases were tested for the synthesis of enantiomerically pure amines from the corresponding ketones employing d -o rl-alanine as amino donor and lactate dehydrogenase to remove the side-product pyruvate to shift the unfav- ourable reaction equilibrium to the product side.
Abstract: Various w-transaminases were tested for the synthesis of enantiomerically pure amines from the corresponding ketones employing d -o rl-alanine as amino donor and lactate dehydrogenase to remove the side-product pyruvate to shift the unfav- ourable reaction equilibrium to the product side. Both enantiomers, (R)- and (S)-amines, could be pre- pared with up to 99% ee and > 99% conversions within 24 h at 50 mM substrate concentration. The activity and stereoselectivity of the amination reac- tion depended on the w-transaminase and substrate employed; furthermore the co-solvent significantly influenced both the stereoselectivity and activity of the transaminases. Best results were obtained by em- ploying ATA-117 to obtain the (R)-enantiomer and ATA-113 or ATA-103 to access the (S)-enantiomer with 15% v v 1 DMSO.
196 citations
TL;DR: In this article, the mean size of the Pd particles over the SiO 2 -Al 2 O 3 support was found to depend on the Si/Al ratio, and a decrease in the Si /Al ratio resulted in an increase in the mean number of Pd nanoparticles.
Abstract: Silica-alumina (SiO 2 -Al 2 O 3 )-supported palladium catalysts prepared by adsorption of the tetrachloropalladate anion (PdCl 4 2- ) followed by calcination and reduction with either hexanol or hydrogen were studied for the aerobic oxidation of alcohols. The mean size of the Pd particles over the SiO 2 -Al 2 O 3 support was found to depend on the Si/Al ratio, and a decrease in the Si/Al ratio resulted in a decrease in the mean size of the Pd nanoparticles. By changing the Si/Al ratio, we obtained supported Pd nanoparticles with mean sizes ranging from 2.2 to 10 nm. The interaction between the Pd precursor and the support was proposed to play a key role in tuning the mean size of the Pd nanoparticles. The Pd/SiO 2 -Al 2 O 3 catalyst with an appropriate mean size of Pd particles could catalyze the aerobic oxidation of various alcohols to the corresponding carbonyl compounds, and this catalyst was particularly efficient for the solvent-free conversion of benzyl alcohol. The intrinsic turnover frequency per surface Pd atom depended significantly on the mean size of Pd particles and showed a maximum at a medium mean size (3.6-4.3 nm), revealing that the aerobic oxidation of benzyl alcohol catalyzed by the supported Pd nanoparticles was structure-sensitive.
177 citations
TL;DR: An efficient multi-gram scale synthesis protocol of a variety of P,N ligands is described in this article, where the synthesis is achieved in a two-step reaction, first the amine is deprotonated and subsequently the chlorophosphine is added to yield the corresponding P-N ligand.
Abstract: An efficient multi-gram scale synthesis protocol of a variety of P,N ligands is described. The synthesis is achieved in a two-step reaction. First, the amine is deprotonated and subsequently the chlorophosphine is added to yield the corresponding P,N ligand. Deprotonation of the amine is normally achieved with n-BuLi at low temperature, but for the preparation of ligands with a 2,2′-dipyridylamino backbone and phosphines with a high steric demand KH has to be employed in combination with reaction temperatures of 110 °C for the salt metathesis step. The reaction of two equivalents of a selected P,N ligand with one equivalent of the iridium complex [IrCl(cod)]2 (cod=1,5-cyclooctadiene) affords P,N ligand-coordinated iridium complexes in quantitative yield. X-Ray single crystal structure analysis of one of these complexes reveals a monomeric five-coordinated structure in the solid state. The iridium complexes were used to form catalysts for the N-alkylation of aromatic amines with alcohols. The catalyst system was optimized by studying 8 different P,N ligands, 9 different solvents and 14 different bases. Systematic variation of the substrate to base and the amine to alcohol ratios as well as the catalyst loading led to optimized catalytic reaction conditions. The substrate scope of the developed catalytic protocol was shown by synthesizing 20 different amines of which 12 could be obtained in isolated yields higher than 90%. A new efficient catalyst system for the selective monoalkylation of primary aromatic and heteroaromatic amines with primary aromatic, heteroaromatic as well as aliphatic alcohols has been established. The reaction proceeds with rather moderate catalyst loadings.
174 citations
TL;DR: Three cloned enoate reductases from the "old yellow enzyme" family of flavoproteins were investigated in the asymmetric bioreduction of activated alkenes, showing a remarkably broad substrate spectrum by reducing α,β-unsaturated aldehydes, ketones, maleimides and nitroalkenes.
Abstract: Three cloned enoate reductases from the "old yellow enzyme" family of flavoproteins were investigated in the asymmetric bioreduction of activated alkenes. 12-Oxophytodienoate reductase isoenzymes OPR1 and OPR3 from Lycopersicon esculentum (tomato), and YqjM from Bacillus subtilis displayed a remarkably broad substrate spectrum by reducing α,β-unsaturated aldehydes, ketones, maleimides and nitroalkenes. The reaction proceeded with absolute chemoselectivity - only the conjugated C=C bond was reduced, while isolated olefins and carbonyl groups remained intact - with excellent stereoselectivities (ees up to >99%). Upon reduction of a nitroalkene, the stereochemical outcome could be determined via choice of the appropriate enzyme (OPR1 versus OPR3 or YqjM), which furnished the corresponding enantiomeric nitroalkanes in excellent ee. Molecular modelling suggests that this "enzyme-based stereocontrol" is caused by subtle differences within the active site geometries.
170 citations
TL;DR: The new Bronsted acid-catalyzed hydride-proton-hydride transfer cascade can be applied to prepare new molecular scaffolds with up to three new stereocenters in an efficient one-pot reaction sequence.
Abstract: A new asymmetric Bronsted acid-catalyzed cascade reaction involving a 1,4-addition, enantioselective protonation and 1,2-addition has been developed. This organocatalytic cascade not only provides for the first time 3- and 2,3-substituted tetrahydroquinolines and octahydroacridines in good yields with high dia- and enantioselectivities under mild reaction conditions but additionally represents the first example of a chiral Bronsted acid-catalyzed protonation reaction in an organocatalytic domino reaction. Furthermore, the new Bronsted acid-catalyzed hydride-proton-hydride transfer cascade can be applied to prepare new molecular scaffolds with up to three new stereocenters in an efficient one-pot reaction sequence.
166 citations
TL;DR: In this article, palladium-catalyzed direct arylations of 1,2,3-triazoles with aryl chlorides were accomplished through conventional heating at reaction temperatures of 105-120 °C.
Abstract: Generally applicable, palladium-catalyzed direct arylations of 1,2,3-triazoles with aryl chlorides were accomplished through conventional heating at reaction temperatures of 105-120 °C. Thereby, intra-and intermolecular C-H bond functionalizations were achieved with a variety of differently substituted chlorides as electrophiles, bearing numerous valuable functional groups.
155 citations
TL;DR: In this article, the coupling of primary and secondary unactivated alkyl bromides with Grignard reagents was performed in good yields under mild conditions by using a new catalytic system: consisting of cobalt chloride and tetramethylethylenediamine (Cocl 2.2LiI, 4TMEDA).
Abstract: The coupling of primary and secondary unactivated alkyl bromides with alkyl-Grignard reagents was performed in good yields under mild conditions by using a new catalytic system: consisting of cobalt chloride and tetramethylethylenediamine (Cocl 2 .2LiI, 4TMEDA). The reaction is very chemoselective since ketone, ester and nitrile functions are tolerated.
154 citations
TL;DR: Palladium on metal oxides and on activated carbon with particular properties (high palladium dispersion, low degree of reduction, water content) are shown to be highly active (tunrover number, TON =20,000; turnover frequency, TOF= 16,600).
Abstract: Palladium on metal oxides and on activated carbon with particular properties (high palladium dispersion, low degree of reduction, water content) are shown to be highly active (tunrover number, TON =20,000; turnover frequency, TOF= 16,600), selective and robust catalysts for Suzuki cross-couplings of aryl bromides and activated aryl chlorides. Catalysts and reaction protocol offer combined advantages of high catalytic efficiency under ambient conditions (air and moisture), easy separation and reuse and quantitative recovery of palladium. The palladium concentration in solution during the reaction correlates clearly with the progress of the reaction and indicates that dissolved molecular palladium is in fact the catalytically active species. Dissolved palladium is redeposited onto the support at the end of the reaction. Additional minimization of the palladium content in solution (down to 0.1 ppm) could be achieved by simple procedures which meet the requirements of pharmaceutical industry.
141 citations
TL;DR: In this article, the half-sandwich scorpionate complexes were synthesized, characterized and shown to act as selective catalysts for the peroxidative oxidation (with hydrogen peroxide) of cyclohexane to cycloenhexanol and cycloehexanone, under mild conditions (at room temperature and using an aqueous solution of H 2 O 2 ).
Abstract: The new half-sandwich scorpionate complexes [hydridotris(1-pyrazolyl)methane]vanadium trichloride, ([VCl 3 {HC(pz) 3 }] 1 (pz=pyrazolyl), [tris(1-pyrazolyl)methanesulfonate]vanadium trichloride, [VCl 3 {SO 3 C(pz) 3 }] 2, [hydrido(1-pyrazolyl)-methane]iron dichloride, [FeCl 2 {HC(pz) 3 }] 3, lithium [tris( 1 -pyrazolyl)methanesulfonate] dichloroferrate, Li[FeCl 2 {SO 3 C(pz) 3 }]4, and [tris(1-pyrazolyl)methanesulfonate]copper chloride, [CuCl{SO 3 C(pz) 3 }] 5 were synthesized, characterized and shown to act, as well as the related (tripyrazolylmethane)copper dichloride, [CuCl 2 {HC(pz) 3 }] 6, as selective catalysts (or catalyst precursors) for the peroxidative oxidation (with hydrogen peroxide) of cyclohexane to cyclohexanol and cyclohexanone, under mild conditions (at room temperature and using an aqueous solution of H 2 O 2 ). The iron complexes are the most active ones (reaching TON values up to ca. 690), the effects of a variety of factors are reported and the reaction is shown to proceed via both C- and O-centred radical mechanisms, conceivably involving a metal-based oxidant.
TL;DR: In this paper, the authors used catalytic primary amine salt A, derived from 9-amino-(9-deoxy)-epi-hydroquinine and D-N-Boc-phenylglycine, in which both the cation and the anion are chiral, that exhibits high reactivity and selectivity for iminium ion catalysis with enones.
Abstract: The highly enantioselective organocatalytic sulfa-Michael addition to α,β-unsaturated ketones has been accomplished using benzyl and tert-butyl mercaptans as the sulfur-centered nucleophiles. Optically active products are obtained in high yields and good to excellent stereocontrol (up to 96 % ee) from a large variety of enones. Central to these studies has been the use of the catalytic primary amine salt A, derived from 9-amino-(9-deoxy)-epi-hydroquinine and D-N-Boc-phenylglycine, in which both the cation and the anion are chiral, that exhibits high reactivity and selectivity for iminium ion catalysis with enones.
DSM1
TL;DR: The monodentate BINOL-derived phosphoramidite PipPhos is used as ligand for the iridium-catalyzed asymmetric hydrogenation of 2- and 2,6-substituted quinolines as mentioned in this paper.
Abstract: The monodentate BINOL-derived phosphoramidite PipPhos is used as ligand for the iridium-catalyzed asymmetric hydrogenation of 2- and 2,6-substituted quinolines If tri-ortho-tolylphosphine and/or chloride salts are used as additives enantioselectivities are strongly enhanced up to 89% NMR indicates that no mixed complexes are formed upon addition of tri-ortho-tolylphosphine
TL;DR: In this article, water-soluble 1,2,3-triazolyl dendrimers were synthesized by click chemistry and used to stabilize palladium nanoparticles (PdNPs).
Abstract: Water-soluble 1,2,3-triazolyl dendrimers were synthesized by “click chemistry” and used to stabilize palladium nanoparticles (PdNPs). These new “click” dendrimer-stabilized nanoparticles (DSN) are highly stable to air and moisture and are catalytically active for olefin hydrogenation and Suzuki coupling reaction, in aqueous media, under ambient conditions using a low amount of palladium (0.01 mol% Pd). Kinetic studies show high catalytic efficiency and high stability for the new “click” DSN in both reactions. The complexation of potassium tetrachloropalladate (K2PdCl4) to the triazole ligands present in the dendritic structures was monitored by UV/vis and, after reduction, the nanoparticles were characterized by transmission electron microscopy (TEM).
TL;DR: In this paper, a simple and efficient synthesis of oxazolidinones was developed through a copper-catalyzed coupling of aldehydes, amines, and terminal alkynes under atmospheric pressure of carbon dioxide.
Abstract: A simple and efficient synthesis of oxazolidinones was developed through a copper-catalyzed coupling of aldehydes, amines, and terminal alkynes under atmospheric pressure of carbon dioxide.
TL;DR: Screening was carried out to identify strains useful for the preparation of (R)-1-cyclopropylethylamine and (R-sec-butylamine by resolution of the racemic amines with an (S)-specific transaminase, and several Bacillus megaterium strains from the authors' culture collection as well as several soil isolates were found to have the desired activity.
Abstract: Screening was carried out to identify strains useful for the preparation of (R)-1-cyclopropylethylamine and (R)-sec-butylamine by resolution of the racemic amines with an (S)-specific transaminase. Several Bacillus megaterium strains from our culture collection as well as several soil isolates were found to have the desired activity for the resolution of the racemic amines to give the (R)-enantiomers. Using an extract of the best strain, Bacillus megaterium SC6394, the reaction was shown to be a transamination requiring pyruvate as amino acceptor and pyridoxal phosphate as a cofactor. Initial batches of both amines were produced using whole cells of Bacillus megaterium SC6394. The transaminase was purified to homogeneity to obtain N-terminal as well as internal amino acid sequences. The sequences were used to design polymerase chain reaction (PCR) primers to enable cloning and expression of the transaminase in E. coli SC16578. In contrast to the original B. megaterium process, pH control and aeration were not required for the resolution of sec-butylamine and an excess of pyruvate was not consumed by the recombinant cells. The resolution of sec-butylamine (0.68 M) using whole cells of E. coli SC16578 was scaled up to give (R)-sec-butylamine⋅1/2 H2SO4 in 46.6% isolated yield with 99.2% ee. An alternative isolation procedure was also used to isolate (R)-sec-butylamine as the free base.
TL;DR: Pseudomonas cepacia lipase supported in the 1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid is an alternative “green” method for the production of biodiesel from the alcoholysis of soybean oil as mentioned in this paper.
Abstract: Pseudomonas cepacia lipase supported in the 1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid is an alternative “green” method for the production of biodiesel from the alcoholysis of soybean oil. The transesterification reaction catalyzed by this ionic liquid-supported enzyme can be performed at room temperature, in the presence of water and without the use of organic solvents. It is also compatible with various alcohols (including isoamyl alcohol). The biodiesel is separated by simple decantation and the recovered ionic liquid/enzyme catalytic system can be re-used at least four times without loss of catalytic activity and selectivity.
TL;DR: In this paper, a rapid and efficient cross-coupling reaction of sodium tetraphenylborate with aryl bromides was carried out in water at 120°C in the presence of a polymer-supported palladium catalyst and potassium carbonate under focused microwave irradiation.
Abstract: A rapid and efficient cross-coupling reaction of sodium tetraphenylborate with aryl bromides was carried out in water at 120 °C in the presence of a polymer-supported palladium catalyst and potassium carbonate under focused microwave irradiation. All four phenyl groups of sodium tetraphenylborate participated in the reaction and produced polyfunctional biaryls in excellent yields. The polymeric catalyst can be easily separated from the reaction mixture and reused more than 10 times without showing any decrease in activity.
TL;DR: In this paper, Raney nickel and cobalt were used as heterogeneous catalysts for chiral amines, as an alternative to metals like palladium or ruthenium, and a two-pot process was proposed in which the liquid was alternatingly shuttled between two vessels containing the solid racemization catalyst and the biocatalyst.
Abstract: Raney metals were studied as heterogeneous catalysts for racemization and dynamic kinetic resolution (DKR) of chiral amines, as an alternative to metals like palladium or ruthenium. Both Raney nickel and cobalt were able to selectively racemize various chiral amines with high selectivity. In the racemization of benzylic primary amines, the minor formation of side products, e.g., secondary amines, can be suppressed by varying the hydrogen pressure. In the racemization of aliphatic amines over Raney catalysts, the selectivity is very high, with the enantiomeric amine as the sole product. DKR of racemic aliphatic amines can be performed with immobilized Candida antarctica lipase B and Raney nickel in one pot; for 2-hexylamine, a yield of 95 % of the acetylated amide was achieved, with 97 % ee. Attention is devoted to the compatibility of the enzyme and the metal catalyst during the DKR. For benzylic primary amines, a two-pot process is proposed in which the liquid is alternatingly shuttled between two vessels containing the solid racemization catalyst and the biocatalyst. After 4 such cycles, the amide of (R)-1-phenylethylamine was obtained with 94 % yield and more than 90 % ee.
TL;DR: A series of naphthalene-bridged P,N-type sulfoximine ligands and their iridium complexes have been synthesized in this article and applied in the enantioselective hydrogenation of quinoline derivatives.
Abstract: A series of naphthalene-bridged P,N-type sulfoximine ligands and their iridium complexes have been synthesized. They were applied in the enantioselective hydrogenation of quinoline derivatives, and enantioselectivities up to 92% ee have been achieved in the hydrogenation of 2-methylquinoline.
TL;DR: In this article, a highly enantioselective Friedel-Crafts aminoalkylation of indoles with imines generated in situ from trifluoroacetaldehyde methyl hemiacetal and aniline was presented.
Abstract: In combination with the advantages of organocatalysis, we have developed a highly enantioselective Friedel-Crafts aminoalkylation of indoles with imines generated in situ from trifluoroacetaldehyde methyl hemiacetal and aniline Novel chiral trifluoromethyl-containing compounds were obtained in high yields with excellent enantioselectivities This methodology was further extended to difluoroacetaldehyde methyl hemiacetal to demonstrate the broad scope of substrates
TL;DR: Control experi- ments demonstrated that the Suzuki reaction cata- lyzed by the in situ generated palladium nanoparti- cles can be carried out much quicker than that using the preprepared particles under the same conditions.
Abstract: An aerobic, ligand-free Suzuki coupling re- action catalyzed by in situ generated palladium nano- particles in polyethylene glycol with an average mo- lecular weight of 400 Da (PEG-400) at room temper- ature has been developed. This catalytic system is a very simple and highly active protocol for the Suzuki coupling of aryl chlorides with arylboronic acids, which proceed smoothly in excellent yields in short times using low catalyst loadings. Control experi- ments demonstrated that the Suzuki reaction cata- lyzed by the in situ generated palladium nanoparti- cles can be carried out much quicker than that using the preprepared particles under the same conditions. The formation of palladium nanoparticles in PEG- 400 was promoted by arylboronic acids.
TL;DR: In this paper, 4-substituted acyloxyproline derivatives with different hydrophobic properties of the acyl group were easily synthesized and used as catalysts in the direct asymmetric aldol reaction between cyclic ketones (cyclohexanone and cyclopentanone) and several substituted benzaldehydes.
Abstract: New 4-substituted acyloxyproline derivatives with different hydrophobic properties of the acyl group were easily synthesized and used as catalysts in the direct asymmetric aldol reaction between cyclic ketones (cyclohexanone and cyclopentanone) and several substituted benzaldehydes. Reactions were carried out using water, this being the best reaction medium examined. Screening of these catalysts showed that compounds bearing the most hydrophobic acyl chains [4-phenylbutanoate and 4-(pyren-1-yl)butanoate] provided better results. The latter catalysts were successfully used in only 2 mol% at room temperature without additives to give aldol products in excellent stereoselectivities. These results demonstrate that derivatization of the proline moiety with the proper simple hydrophobic substituent in the 4-position can furnish highly active and stereoselective catalysts without the need of additional chiral backbones in the molecule. Finally, an explanation of the observed stereoselectivities in the presence of water is provided.
TL;DR: In this article, a new hybrid silica with urea-based bipyridyl bridging units has been synthesized by a sol-gel process, which is an efficient heterogeneous catalyst for the Ullmann coupling of aryl halides with phenols.
Abstract: A new hybrid silica with urea-based bipyridyl bridging units has been synthesized by a sol-gel process. The copper-complexed hybrid silica is an efficient heterogeneous catalyst for the Ullmann coupling of aryl halides with phenols. It is easily withdrawn and recovered from the reaction media by filtration. It is also a versatile catalyst for subsequent reactions with several substrates yielding products with the same efficiency even after ten re-uses and with minimal leaching. This is the first example of the use of a copper-complexed bridged silsesquioxane for the preparation of a recoverable catalyst in modern Ullmann chemistry. This may represent a promising route to the reduction of waste while maintaining economic viability.
TL;DR: In this paper, an inexpensive and experimentally simple, iron-catalyzed N-arylation reaction of NH-sulfoximines with aryl iodides is reported.
Abstract: An inexpensive and experimentally simple, iron-catalyzed N-arylation reaction of NH-sulfoximines with aryl iodides is reported. This complementary method to the known palladium- and copper-catalyzed ones features the use of a combination of environmentally friendly FeCl3 and N,N′-dimethylethylenediamine (DMEDA) as catalytic system and allows the efficient preparation of various N-arylsulfoximines in high yields.
TL;DR: A small quantity of iron(II) triflate (25 to 5 mol%) catalyzes the aziridination reactions of enol silyl ethers with tosylimino(iodo)benzene (PhINTs) in acetonitrile to give α-N-tosylamido ketones by subsequent aziridine ring opening Olefins are converted into aziridsines by 5 mol% of this catalyst system Both reactions afford the corresponding products in moderate to good yields as mentioned in this paper.
Abstract: A small quantity of iron(II) triflate (25 to 5 mol%) catalyzes the aziridination reactions of enol silyl ethers with tosylimino(iodo)benzene (PhINTs) in acetonitrile to give α-N-tosylamido ketones by subsequent aziridine ring opening Olefins are converted into aziridines by 5 mol% of this catalyst system Both reactions afford the corresponding products in moderate to good yields In the presence of chiral ligands asymmetric aziridinations have been achieved
TL;DR: A metal-free very highly efficient and concise oxidative-coupling reaction promoted by 2,3-dichloro-5,6-dicyanoquinone (DDQ) between diarylallylic sp3 CH and active methylenic sp3CH bonds is reported.
Abstract: A metal-free very highly efficient and concise oxidative-coupling reaction promoted by 2,3-dichloro-5,6-dicyanoquinone (DDQ) between diarylallylic sp3 CH and active methylenic sp3 CH bonds is reported. The corresponding products are obtained in good to excellent yields.
TL;DR: In this article, the use of glycerol as solvent was shown to accelerate the reaction rate of an organic reaction even starting from more hydrophobic substrates than those usually used on water.
Abstract: Whereas the beneficial effect of water on reaction rate is decreased with an increase of the reactant's hydrophobicity, we report here that the use of glycerol as solvent was able to considerably accelerate the reaction rate of an organic reaction even starting from more hydrophobic substrates than those usually used on water. Moreover, the possibility of directly using crude glycerol generated by the biodiesel industry economically and environmentally improves the interest of using glycerol as solvent.
TL;DR: In this paper, a variety of indoles with ethyl 3,3,3-trifluoropyruvate catalyzed by novel chiral m-phenylene- bis(imidazoline)-copper(II) complexes or the bis-(imidrazoline)-achiral acid combination afforded products with high enantioselectivity.
Abstract: Enantioselective Friedel-Crafts alkylations of a variety of indoles with ethyl 3,3,3-trifluoropyruvate catalyzed by novel chiral m-phenylene- bis(imidazoline)-copper(II) complexes or the bis-(imidazoline)-achiral acid combination afforded products with high enantioselectivity. Both enantiomers of indole derivatives can be prepared with high enantioselectivities by tuning the N-substituents of the imidazoline.
TL;DR: In this paper, a Friedel-Crafts reaction of 4,7-dihydroindoles with β,γ-unsaturated α-keto esters by a chiral N-triflyl phosphoramide was realized.
Abstract: A highly efficient Friedel-Crafts reaction of 4,7-dihydroindoles with β,γ-unsaturated α-keto esters by a chiral N-triflyl phosphoramide was realized, affording the 2-substituted 4,7-dihydroindoles with up to 98% ee for a wide range of substrates. The Friedel-Crafts alkylation together with a subsequent oxidation of the product with p-benzoquinone led to a 2-alkylated indole derivative in 98% ee.