Showing papers in "Tetrahedron-asymmetry in 2007"
TL;DR: An overview of the most important developments and concepts of this flourishing area of catalysis organized by the type of nucleophile involved in the process is reported.
Abstract: The asymmetric organocatalytic conjugate addition of nucleophiles to Michael acceptors is reviewed. Herein an overview of the most important developments and concepts of this flourishing area of catalysis organized by the type of nucleophile involved in the process is reported.
751 citations
TL;DR: In this paper, the authors are grateful to the Spanish Ministerio de Educación y Ciencia, as well as to Generalitat Valenciana and University of Alicante, for their continuous financial support.
Abstract: We are grateful to the Spanish Ministerio de Educacion y
Ciencia, as well as to Generalitat Valenciana and
University of Alicante, for their continuous financial
support.
366 citations
TL;DR: In this article, the organocatalyst acts in this type of process as a clear enzyme mimic, but with an ample substrate scope, allowing the synthesis of complex chiral molecules with several stereogenic elements created in just one process.
Abstract: The achieved level of expertise in organocatalytic processes has allowed synthetic chemists to apply this useful synthetic strategy to enantioselective multicomponent reactions. Although, this new methodology is still in its infancy, the reported results show the possibilities and versatility of this type of reaction, with an extraordinary level of atom efficiency being reached. All examples, from classical Mannich, Biginelli, Michael, and Diels–Alder reactions to new amination–reduction and Tietze reactions, allow the synthesis of complex chiral molecules with several stereogenic elements created in just one process. In fact, the organocatalyst acts in this type of process as a clear enzyme mimic, but with an ample substrate scope.
309 citations
TL;DR: The most recent papers describing the stereoselective synthesis of cyclic quaternary α-amino acids are collected in this paper, where diverse synthetic approaches are classified according to the size of the ring and taking into account the bond that is formed to complete the quaternARY skeleton.
Abstract: The most recent papers describing the stereoselective synthesis of cyclic quaternary α-amino acids are collected in this review The diverse synthetic approaches are classified according to the size of the ring and taking into account the bond that is formed to complete the quaternary skeleton
212 citations
TL;DR: An overview of synthetic approaches to linear and cyclic chiral γ-amino acids and derivatives is presented in this article, where data on the practical applications of these acids are also discussed.
Abstract: γ-Amino acids have attracted considerable attention as biologically active compounds in the central nervous system (CNS) of mammals. Over the last few years, significant interest in the stereoselective synthesis and practical application of linear and cyclic chiral γ-amino acids in the synthesis and design of α,β- and β,γ-hybrid peptides with definite secondary structures and design of nanotubes has been reported, thus demonstrating the theoretical interest and the practical importance of γ-amino acids. An overview of synthetic approaches to linear and cyclic chiral γ-amino acids and derivatives is presented. Data on the practical applications of γ-amino acids are also discussed.
185 citations
TL;DR: The enantiomeric excesses of the isolated alkaloids were determined from their 1H NMR spectra measured in the presence of (+)-(R)-tert-butylphenylphosphinothio(seleno)ic acids as chiral solvating agents as mentioned in this paper.
Abstract: Four alkaloids: (R)-(+)-cryspine A 5, (R)-(+)-octahydroindolo[2,3-a]quinolizidine 8, (R)-(+)-harmicine 19 and (R)-(+)-desbromoarborescidine 22 were prepared via the asymmetric transfer hydrogenation reaction of a prochiral enamine (iminium salt). The enantiomeric excesses of the isolated alkaloids were determined from their 1H NMR spectra measured in the presence of (+)-(R)-tert-butylphenylphosphinothio(seleno)ic acids as chiral solvating agents. The absolute configurations at the newly created stereogenic carbon atoms were confirmed, in all cases, by X-ray crystallography.
92 citations
TL;DR: In this paper, the structures of oxygen heterocylic SAAs have been provided, having 3, 4, 5, 6-membered rings as well as several bicyclic counterparts, and the stereochemical arrangement of the substituents of the sugar ring, its ring-size and the presence of additional functional groups provides a plethora of possible combinations.
Abstract: Sugar amino acids (SAAs) are carbohydrate derivatives bearing both amino and carboxylic acid functionalities. SAAs are very versatile conformationally biased building blocks amenable to serve as glyco- or peptidomimetics. The stereochemical arrangement of the substituents of the sugar ring, its ring-size as well as the presence of additional functional groups provides a plethora of possible combinations. In this overview the structures of oxygen heterocylic SAAs that have been reported thus far are provided, having 3, 4, 5, 6-membered rings as well as several bicyclic counterparts.
92 citations
TL;DR: A systematic procedure based on physical properties to identify more commercially available ionic liquids exhibiting the potential to improve the efficiency of whole cell biocatalyses resulted in the identification of seven other water immiscible ionic fluids.
Abstract: Ionic liquids such as [BMIM][PF 6 ] and [BMIM][NTF] are already known as good alternatives to organic solvents in biphasic biotransformation. Herein, we report about a systematic procedure based on physical properties to identify more commercially available ionic liquids exhibiting the potential to improve the efficiency of whole cell biocatalyses. This approach resulted in the identification of seven other water immiscible ionic liquids. These ionic liquids were rated by their biocompatibility, their substrate- and product-specific distribution coefficients and by for example performed asymmetric reductions of several prochiral ketones. With the use of a recombinant Escherichia coli as biocatalyst, overproducing a Lactobacillus brevis alcohol dehydrogenase and a Mycobacterium vaccae N10 formate dehydrogenase for cofactor regeneration, the great potential of asymmetric whole cell biotransformations in biphasic ionic liquid/water-systems were demonstrated in simple batch processes.
89 citations
TL;DR: In this article, the chiral iminopyridines derived from camphane-derived ketones and picolylamine catalyzed the enantioselective Henry (nitroaldol) reaction between nitromethane and a number of aromatic and aliphatic aldehydes with high yields and good enanti-lectivities.
Abstract: Copper complexes of chiral iminopyridines prepared from camphane-derived ketones and picolylamine catalyzed the enantioselective Henry (nitroaldol) reaction between nitromethane and a number of aromatic and aliphatic aldehydes with high yields and good enantioselectivities. Iminopyridines derived from (1 R )-(+)-camphor and (1 S )-(+)-ketopinic acid gave the best results to afford the opposite enantiomers in each case, despite the fact they have the same stereochemical pattern at the camphane skeleton. The reactions were carried out without air or moisture exclusion.
89 citations
TL;DR: The iridium-catalyzed enantioselective transfer hydrogenation of quinolines with Hantzsch esters was developed with up to 88% ee using [Ir(COD)Cl]2/(S)-SegPhos/I2 as a catalyst as mentioned in this paper.
Abstract: The iridium-catalyzed enantioselective transfer hydrogenation of quinolines with Hantzsch esters was developed with up to 88% ee using [Ir(COD)Cl]2/(S)-SegPhos/I2 as a catalyst.
86 citations
TL;DR: Chiral chromium(III)-salen type complexes derived from 1,2-diaminocyclohexane and 1, 2-diphenylethylenediamine were found to catalyze the enantioselective Henry reaction.
Abstract: Chiral chromium(III)–salen-type complexes derived from 1,2-diaminocyclohexane and 1,2-diphenylethylenediamine were found to catalyze the enantioselective Henry reaction. Various arylaldehydes, trans-cinnamaldehyde, and cyclohexanecarbaldehyde reacted with nitromethane in the presence of (i-Pr)2NEt and salen–CrCl (2 mol %) to give the corresponding adducts in 40–76% ee and in moderate to good yields.
TL;DR: Bi- and monophasic ionic liquid (IL)/buffer systems were successfully employed for the biocatalytic reduction of ketones catalysed by the alcohol dehydrogenase ADH-‘A’ from Rhodococcus ruber via hydrogen transfer.
Abstract: Bi- and monophasic ionic liquid (IL)/buffer systems were successfully employed for the biocatalytic reduction of ketones catalysed by the alcohol dehydrogenase ADH-‘A’ from Rhodococcus ruber via hydrogen transfer. Two different catalyst preparations were employed, namely recombinant ADH-‘A’ ‘immobilised’ in Escherichia coli and partially purified ADH-‘A’. For biphasic systems conversions were acceptable until 20% v v −1 of IL. In contrast, hydroxy-functionalised ‘Tris-like’-ILs were successfully employed in monophasic systems up to 90% v v −1 IL. The use of these solvents allowed highly stereoselective enzymatic carbonyl reductions at substrate concentrations from 1.2 to 1.5 M.
TL;DR: In this paper, the highly diastereoselective conjugate addition of lithium (S)-N-benzyl-N-(α-methyl benzyl)amide to a γ-silyloxy-α,β-unsaturated ester and in situ enolate oxidation with (+)-(camphorsulfonyl)oxaziridine has been used as the key step in the asymmetric synthesis of N,O,O O,Tetra-acetyl d -lyxo-phytosphingosine,
Abstract: The highly diastereoselective conjugate addition of lithium (S)-N-benzyl-N-(α-methylbenzyl)amide to a γ-silyloxy-α,β-unsaturated ester and in situ enolate oxidation with (+)-(camphorsulfonyl)oxaziridine has been used as the key step in the asymmetric synthesis of N,O,O,O-tetra-acetyl d -lyxo-phytosphingosine, jaspine B (pachastrissamine) and its C(2)-epimer.
TL;DR: In this article, the combination of (Sa)-binam- l -Pro (5 ǫ ) and benzoic acid (10 Ã 0 ) was used as catalysts in the direct aldol reaction between different aliphatic ketones and 4-nitrobenzaldehyde under solvent-free reaction conditions.
Abstract: The combination of (Sa)-binam- l -Pro (5 mol %) and benzoic acid (10 mol %) was used as catalysts in the direct aldol reaction between different aliphatic ketones and 4-nitrobenzaldehyde under solvent-free reaction conditions. Three different procedures are assayed: magnetic stirring (method A), magnetic stirring after previous dissolution in THF and evaporation (method B), and ball mill technique (method C), methods A and B being the simplest. These reaction conditions allowed us to reduce the amount of required ketone to 2 equiv to give the aldol product in similar reaction times and regio-, diastero-, and enantioselectivities than in organic or aqueous solvents.
TL;DR: Ionic liquid-supported triazole-pyrrolidine 2, for the direct asymmetric Michael reaction was successfully synthesized in this paper, and the supported catalyst demonstrated good activity and high enantioselectivity in the addition of cyclohexanone to nitroolefins.
Abstract: Ionic-liquid-supported triazole-pyrrolidine 2 , for the direct asymmetric Michael reaction was successfully synthesized. The supported catalyst demonstrated good activity and high enantioselectivity in the addition of cyclohexanone to nitroolefins. Furthermore, the supported catalyst can be readily recovered and reused four times without significant loss of catalytic activity.
TL;DR: The present study demonstrates that both diastereo- and enantioselectivity can be easily modulated by the appropriate combination of an organocatalyst together with an organic base as a co-catalyst.
Abstract: An effective aqua-organocatalytic direct aldol reaction is described. Aromatic amino acids can be a bifunctional catalyst system, which demonstrate excellent reactivity, diastereoselectivity, and enantioselectivity (up to 96% ee) in water without the addition of organic solvents. Furthermore, the present study demonstrates that both diastereo- and enantioselectivity can be easily modulated by the appropriate combination of an organocatalyst together with an organic base as a co-catalyst.
TL;DR: Chiral phosphine-salen type ligand L4 prepared from (R)-2-(diphenylphosphino)-1,1'-binaphthyl-2'-amine was found to be a fairly effective chiral ligand for Cu(I)-promoted enantioselective Henry reactions of arylaldehydes with nitromethane to give the corresponding adducts in moderate to good yields as discussed by the authors.
Abstract: Chiral phosphine-salen type ligand L4 prepared from (R)-2-(diphenylphosphino)-1,1'-binaphthyl-2'-amine was found to be a fairly effective chiral ligand for Cu(I)-promoted enantioselective Henry reactions of arylaldehydes with nitromethane to give the corresponding adducts in moderate enantioselectivities and moderate to good yields. (c) 2007 Elsevier Ltd. All rights reserved.
TL;DR: In this article, a planar chiral [2,2]cyclophane monophosphines are used as catalysts in the reaction of Morita-Baylis-Hillman adducts with phthalimide.
Abstract: Planar chiral [2,2]cyclophane monophosphines are efficient catalyst in the reaction of Morita–Baylis–Hillman adducts with phthalimide. The corresponding allylic substituted products were afforded in high yields and in good to moderate ee.
TL;DR: In this paper, a quinine-mediated ring opening of 3-isobutylglutaric anhydride with cinnamyl alcohol was used to obtain an enantioselective synthesis of (S)-3-aminomethyl-5-methylhexanoic acid (Pregabalin).
Abstract: A highly enantioselective synthesis of (S)-3-aminomethyl-5-methylhexanoic acid 1 (Pregabalin) is reported. The key step of the synthesis is a quinine-mediated ring opening of 3-isobutylglutaric anhydride with cinnamyl alcohol. A Curtius rearrangement and subsequent deprotection provides 1 in high yield and excellent enantiomeric excess.
TL;DR: In this article, a biphasic recognition chiral extraction system was established by adding hydrophobic d ( l )-isobutyl tartrate in 1,2-dichloroethane organic phase and hydrophilic β-cyclodextrin (β-CD) derivative in aqueous phase, which preferentially recognize the α-cyclohexyl-mandelic acid (CHMA) and naproxen (NAP).
Abstract: This paper reports a new chiral separation technology—biphasic recognition chiral extraction for the separation of aromatic acid enantiomers such as α-cyclohexyl-mandelic acid (CHMA) and naproxen (NAP). The biphasic recognition chiral extraction system was established by adding hydrophobic d ( l )-isobutyl tartrate in 1,2-dichloroethane organic phase and hydrophilic β-cyclodextrin (β-CD) derivative in aqueous phase, which preferentially recognize the (R)-enantiomer and (S)-enantiomer, respectively. These studies involve an enantioselective extraction in a biphasic system, where aromatic acid enantiomers form complexes with the β-cyclodextrin derivative in the aqueous phase and d ( l )-isobutyl tartrate in the organic phase, respectively. Factors affecting the extraction mechanism are analyzed, namely the influence of the concentrations of the extractants and aromatic acid enantiomers, the types of the extractants, pH, and temperature. The experimental results show that the biphasic recognition chiral extraction is of much stronger chiral separation ability than the monophasic recognition chiral extraction, which utilizes the cooperations of the forces of the tartrate and the β-CD derivative. Hydroxypropyl-β-cyclodextrin (HP-β-CD), hydroxyethyl-β-cyclodextrin (HE-β-CD), and methyl-β-cyclodextrin (ME-β-CD) have stronger recognition abilities for the (S)-aromatic acid enantiomers than those for (R)-aromatic acid enantiomers, among which HP-β-CD has the strongest ability. d -Isobutyl tartrate preferentially recognizes (R)-CHMA and (S)-NAP, while l -isobutyl tartrate preferentially recognizes (S)-CHMA and (R)-NAP. The maximum enantioselectivities of CHMA and NAP are 2.49 and 1.65, under conditions at which the pH values of the aqueous phases are 2.7 and 2.5, at the ratio of 2:1 of [isobutyl tartrate] to [HP-β-CD].
TL;DR: A set of racemic cyclic and linear ketones, as well as 2-phenylpropionaldehyde, were tested as substrates in the enzymatic Baeyer–Villiger oxidation catalyzed by twoBaeyer-Villiger monooxygenases: phenylacetone monooxyGENase (PAMO) and 4-hydroxyacetophenone mono Oxygenase (HAPMO).
Abstract: A set of racemic cyclic and linear ketones, as well as 2-phenylpropionaldehyde, were tested as substrates in the enzymatic Baeyer–Villiger oxidation catalyzed by two Baeyer–Villiger monooxygenases: phenylacetone monooxygenase (PAMO) and 4-hydroxyacetophenone monooxygenase (HAPMO). Excellent enantioselectivites (E > 200) can be obtained in the kinetic resolution processes depending on the substrate structure and the reaction conditions. The parameters affecting the biocatalytic properties of these enzymes were also studied, in order to establish a deeper understanding of these novel biocatalysts.
TL;DR: In this paper, a practically efficient stereoselective synthesis of pachastrissamine (jaspine B) was described starting from 3,4,6-tri-O-benzyl-d -galactal in eight steps and 11% overall yield.
Abstract: A practically efficient stereoselective synthesis of pachastrissamine (jaspine B) is described starting from 3,4,6-tri-O-benzyl- d -galactal in eight steps and 11% overall yield.
TL;DR: In this paper, two l -proline-based linear polystyrene anchored catalysts 1a and 1b have been synthesized and evaluated in the direct asymmetric aldol reaction of various aromatic aldehydes and ketones.
Abstract: Two l -proline-based linear polystyrene anchored catalysts 1a and 1b have been synthesized efficiently. The catalytic activities and stereoselectivity of these readily tunable and amphiphilic organocatalysts were evaluated in the direct asymmetric aldol reaction of various aromatic aldehydes and ketones. By using 5 mol % of the catalysts, the corresponding products of the aldol reaction were obtained in good yields (up to 94%) and with excellent anti diastereoselectivities (up to 96:4) and enantioselectivities (up to 96% ee) in DMF in the presence of water. The yields of these reactions in a ketone/water mixture were lower than those in wet DMF (up to 76%). However, the stereoselectivity was comparable (up to 93:7 anti / syn ratio and 95% ee, respectively). In addition, catalysts 1a and 1b could be recovered by a simple precipitation and filtration process. They could also be re-used for at least five times without obvious loss of catalytic efficiency.
TL;DR: In this article, the crystal structure of the pure enantiomer has been solved from single-crystal X-ray diffraction, and several consecutive preferential crystallization attempts (AS3PC method) were undertaken between TB = 41°C and TF = 25°C on a 2-L scale.
Abstract: Ethanolamine mandelate (E.M.) crystallizes as a stable conglomerate and has been found to form partial solid solutions. The crystal structure of the pure enantiomer has been solved from single-crystal X-ray diffraction. In order to determine the extreme compositions of the partial solid solutions in equilibrium (87% ee), the isothermal ternary section in the system [(+)-E.M.–(−)-E.M.–(ethanol–water azeotropic mixture)] was established at 25 °C. Several consecutive preferential crystallization attempts (AS3PC method) were undertaken between TB = 41 °C (starting temperature) and TF = 25 °C (final temperature) on a 2-L scale. We initially expected to obtain crude crops whose enantiomeric purities would be close to that defined by the isothermal ternary phase diagram (TF). In fact, the filtered solid phases are of lower enantiomeric excesses: ca. 62% ee. The monitoring of the mother liquor composition over the course of the entrainment shows that the enantiomeric composition of the filtered solid is related to the metastable equilibria involved in the preferential crystallization.
TL;DR: In this article, a meso-sulfonylaziridines with thiols was realized using cinchonine-derived chiral quaternary ammonium salts as the catalyst.
Abstract: Desymmetrization of meso - N -sulfonylaziridines with thiols was realized using cinchonine-derived chiral quaternary ammonium salts as the catalyst. The corresponding chiral thio amines were provided in high yields (80–99%) and in good enantioselectivities (40–73% ee).
TL;DR: Microwave assisted asymmetric Suzuki-Miyaura and Negishi enantioselective cross-coupling reactions were applied to the rapid synthesis of chiral sterically hindered binaphthalene derivatives in reasonable to excellent yields (65-96%) and fair to good enanti-lectivities (43-70% ee) as mentioned in this paper.
Abstract: Microwave assisted asymmetric Suzuki-Miyaura and Negishi enantioselective cross-coupling reactions are reported for the first time, and have been applied to the rapid synthesis of chiral sterically hindered binaphthalene derivatives in reasonable to excellent yields (65–96%) and fair to good enantioselectivities (43–70% ee).
TL;DR: In the presence of (CF3SO2)(2)NH, L-Proline derived triamine 4 catalyzed the reaction of cyclohexanone to a variety of nitroolefins with high yields and excellent diastereoselectivities.
Abstract: L-Proline derived triamine 4 has been developed as a highly efficient and stereoselective organocatalyst for the asymmetric Michael addition of cyclohexanone to nitroolefins. In the presence of (CF3SO2)(2)NH, 4 catalyzed the reaction of cyclohexanone to a variety of nitroolefins with high yields (up to 99%) and excellent diastereoselectivities (up to 99:1 dr) and enantioselectivities (up to 98% ee). (c) 2007 Elsevier Ltd. All rights reserved.
TL;DR: In this article, an asymmetric synthesis of the alkaloid fagomine, which is an inhibitor of mammalian α-glucosidase and β-galactosidases, by means of Sharpless asymmetric dihydroxylation and Pd(II)-catalyzed cyclization, starting from 3-( t -butoxylcarbonylamino)propanol.
Abstract: We report an asymmetric synthesis of the alkaloid fagomine, which is an inhibitor of mammalian α-glucosidase and β-galactosidase, by means of Sharpless asymmetric dihydroxylation and Pd(II)-catalyzed cyclization, starting from 3-( t -butoxylcarbonylamino)propanol.
TL;DR: A siloxy- l -serine organocatalyst has been developed to catalyze direct asymmetric aldol reactions in the presence of water, furnishing the β-hydroxy carbonyl scaffold in high enantio- and diastereoselectivities.
Abstract: A siloxy- l -serine organocatalyst has been developed to catalyze direct asymmetric aldol reactions in the presence of water, furnishing the β-hydroxy carbonyl scaffold in high enantio- and diastereoselectivities. The direct aldol reaction between a selection of aromatic aldehydes and cyclohexanone resulted in good yields and high enantioselectivities.
TL;DR: In the presence of cinchona alkaloid-derived thiourea organocatalyst 1i, ethyl α-cyanoacetate could react with various chalcones to afford Michael adducts with high yields and enantioselectivities.
Abstract: The conjugate addition of ethyl α-cyanoacetate with chalcones has been developed. In the presence of cinchona alkaloid-derived thiourea organocatalyst 1i (10 mol %), ethyl α-cyanoacetate could react with various chalcones to afford Michael adducts with high yields (80–92%) and enantioselectivities (83–95% ee).