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Diastereoselectivity
Kinds of Diastereoselectivity Selected AbstractsAsymmetric Cyclopropanation of Optically Active (1-Diethoxyphosphoryl)vinyl p -Tolyl Sulfoxide with Sulfur Ylides: A Rationale for DiastereoselectivityEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2005Wanda H. Midura Abstract The title sulfoxide (S)-(+)- 1a was found to react with sulfur ylides affording the corresponding cyclopropanes in high yields. With fully deuterated dimethyl(oxo)sulfonium methylide, (CD3)2S(O)CD2, the cyclopropanation reaction occurred in a highly diastereoselective manner producing the cyclopropane 4a - d2 as a major diastereomer in which the newly formed quaternary ,-carbon atom is chiral due to isotopic substitution (CH2 vs. CD2). The diastereomer 4b - d2, having the opposite configuration at the ,-carbon atom, was obtained starting form the 2,2-dideuterio substituted vinyl sulfoxide, (S)-(+)- 1a - d2, and the nondeuterated ylide. The diastereomeric ratio in both reactions was found to be ca. 10:1. The reaction of (S)-(+)- 1a with diphenylsulfonium isopropylide yielded the cyclopropane (+)- 7 as a single diastereomer. X-ray structural studies of the crystalline 1-phosphorylvinyl sulfoxide 9 as well as density functional calculations (B3LYP/6-31G*) on (1-phosphoryl)vinyl sulfoxides revealed the origin of the experimentally observed diastereoselectivities and allowed us to propose a transition state model for the cyclopropanation reaction of chiral 1-phosphorylvinyl sulfoxides. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Remarkable Electronic Effect on the Diastereoselectivity of the Heck Reaction of Methyl Cinnamate with Arenediazonium Salts: Formal Total Synthesis of (±)-Indatraline and (±)-SertralineADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 9 2009Julio Cezar Pastre Abstract An efficient and stereoselective protocol for the preparation of ,,,-disubstituted acrylates in good to high yields by means of a Heck,Matsuda arylation was accomplished. The method employs a base- and ligand-free Heck arylation reaction of methyl cinnamate using both electron-deficient and electron-rich arenediazonium salts as electrophiles. The Heck reaction displays a remarkable electronic dependence regarding the diastereoselectivity of the arylation process, which correlates with the electronic nature of the arenediazonium salts employed. A rationale for the observed diastereoselectivity is presented. The overall methodology provides a convenient route to 3-arylindanones and 4-aryltetralones allowing the concise formal total syntheses of the therapeutically important psychoactive compounds (±)-indatraline and (±)-sertraline. [source] Alteration of the Diastereoselectivity of 3-Methylaspartate Ammonia Lyase by Using Structure-Based MutagenesisCHEMBIOCHEM, Issue 13 2009Hans Raj Abstract 3-Methylaspartate ammonia-lyase (MAL) catalyzes the reversible amination of mesaconate to give both (2S,3S)-3-methylaspartic acid and (2S,3R)-3-methylaspartic acid as products. The deamination mechanism of MAL is likely to involve general base catalysis, in which a catalytic base abstracts the C3 proton of the respective stereoisomer to generate an enolate anion intermediate that is stabilized by coordination to the essential active-site MgII ion. The crystal structure of MAL in complex with (2S,3S)-3-methylaspartic acid suggests that Lys331 is the only candidate in the vicinity that can function as a general base catalyst. The structure of the complex further suggests that two other residues, His194 and Gln329, are responsible for binding the C4 carboxylate group of (2S,3S)-3-methylaspartic acid, and hence are likely candidates to assist the MgII ion in stabilizing the enolate anion intermediate. In this study, the importance of Lys331, His194, and Gln329 for the activity and stereoselectivity of MAL was investigated by site-directed mutagenesis. His194 and Gln329 were replaced with either an alanine or arginine, whereas Lys331 was mutated to a glycine, alanine, glutamine, arginine, or histidine. The properties of the mutant proteins were investigated by circular dichroism (CD) spectroscopy, kinetic analysis, and 1H NMR spectroscopy. The CD spectra of all mutants were comparable to that of wild-type MAL, and this indicates that these mutations did not result in any major conformational changes. Kinetic studies demonstrated that the mutations have a profound effect on the values of kcat and kcat/KM; this implicates Lys331, His194 and Gln329 as mechanistically important. The 1H NMR spectra of the amination and deamination reactions catalyzed by the mutant enzymes K331A, H194A, and Q329A showed that these mutants have strongly enhanced diastereoselectivities. In the amination direction, they catalyze the conversion of mesaconate to yield only (2S,3S)-3-methylaspartic acid, with no detectable formation of (2S,3R)-3-methylaspartic acid. The results are discussed in terms of a mechanism in which Lys331, His194, and Gln329 are involved in positioning the substrate and in formation and stabilization of the enolate anion intermediate. [source] ChemInform Abstract: Silane-Controlled Diastereoselectivity in the Tris(pentafluorophenyl)borane-Catalyzed Reduction of ,-Diketones to Silyl-Protected 1,2-Diols.CHEMINFORM, Issue 24 2010Miranda K. Skjel Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Highly Efficient One-Pot, Three-Component Mannich Reaction Catalyzed by Boric Acid and Glycerol in Water with Major "syn" Diastereoselectivity.CHEMINFORM, Issue 43 2009Chhanda Mukhopadhyay Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Effect of Additives on Chemoselectivity and Diastereoselectivity in the Catalytic Epoxidation of Chiral Allylic Alcohols with Hydrogen Peroxide and Binuclear Manganese Complexes.CHEMINFORM, Issue 24 2009Hamdullah Kilic Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Directed Diastereoselectivity in the Asymmetric Claisen/Metathesis Reaction Sequence.CHEMINFORM, Issue 41 2008Nicolas P. Probst Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Chiral N-Allylpyrroles as Versatile Substrates under Rhodium-Catalyzed Hydroformylation: Good Regio- and Diastereoselectivity at Room Temperature and High Pressure.CHEMINFORM, Issue 9 2008Roberta Settambolo Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Control of Diastereoselectivity in Tandem Asymmetric Reactions Generating Nonadjacent Stereocenters with Bifunctional Catalysis by Cinchona Alkaloids.CHEMINFORM, Issue 23 2007Baomin Wang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Stereochemistry of the Tetrabutylammonium Cyanide Catalyzed Cyanosylilation of Cyclic ,,,-Epoxyketones , Dependence of the Diastereoselectivity on the Ring Size.CHEMINFORM, Issue 50 2006Ana Aljarilla Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Diastereoselectivity in [2, + 2,] Photocycloaddition of Cholesteryl Cinnamate to Methyl 9-Phenanthrenecarboxylate: Control of the Stereoselectivity in Liquid Crystalline Phase.CHEMINFORM, Issue 52 2004Hajime Maeda Abstract For Abstract see ChemInform Abstract in Full Text. [source] Diastereoselectivity of Ru-Catalyzed [5 + 2] Cycloadditions.CHEMINFORM, Issue 9 2004Barry M. Trost Abstract For Abstract see ChemInform Abstract in Full Text. [source] Simple Diastereoselectivity on Addition of ,-Haloalkyl Grignard Reagents to Benzaldehyde.CHEMINFORM, Issue 38 2003Volker Schulze Abstract For Abstract see ChemInform Abstract in Full Text. [source] Complete ,-Facial Diastereoselectivity in Diels,Alder Reactions of Dissymmetric 2,4-Cyclohexadienones.CHEMINFORM, Issue 48 2002Hui-Fang Hou Abstract For Abstract see ChemInform Abstract in Full Text. [source] Diastereoselectivity of Tandem Michael Addition,Alkylation Reactions: A Convenient Method for One-Pot Synthesis of ,-Branched 2,3-Diphenylglutaric Acid Derivatives.CHEMINFORM, Issue 35 2002L. Viteva Abstract For Abstract see ChemInform Abstract in Full Text. [source] ChemInform Abstract: Study of the Diastereoselectivity of Cobalt-Mediated [2 + 2 + 2] Cycloadditions of Substituted Linear Enediyne Esters.CHEMINFORM, Issue 18 2002Franck Slowinski Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] ChemInform Abstract: Enhanced Diastereoselectivity in Asymmetric Crotylation Reactions Using Propargylic Dicobalt Hexacarbonyl Complexes.CHEMINFORM, Issue 48 2001Meng Sui Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Origin of Diastereoselectivity in the Organolanthanide-Mediated Intramolecular Hydroamination/Cyclisation of Aminodienes: A Computational Exploration of Constrained Geometry CGC,Ln Catalysts,CHEMISTRY - A EUROPEAN JOURNAL, Issue 32 2007Sven Tobisch Dr. Abstract The regulation of ring-substituent diastereoselectivity in the intramolecular hydroamination/cyclisation (IHC) of ,-substituted aminodienes by constrained geometry CGC,lanthanide catalysts (CGC=[Me2Si(,5 -Me4C5)(tBuN)]2,) has been elucidated by means of a reliable DFT method. The first survey of relevant elementary steps for the 1-methyl-(4E,6)-heptadienylamine substrate (1) and the [{Me2Si(,5 -Me4C5)(tBuN)}Sm{N(TMS)2}] starting material (2) identified the following general mechanistic aspects of Ln-catalysed aminodiene IHC. The substrate-adduct 3 -S of the active CGC,Ln,amidodiene compound represents the catalyst's resting state, but the substrate-free form 3, with a chelating amidodiene functionality is the direct precursor for cyclisation. This step proceeds with almost complete regioselectivity through exocyclic ring closure by means of a frontal trajectory, giving rise to the CGC,Ln,azacycle intermediate 4. Subsequent protonolysis of 4 is turnover limiting, whilst the ring-substituent diastereoselectivity is dictated by exocyclic ring closure. Unfavourable close interatomic contacts between the substrate's ,-substituent and the catalyst backbone have been shown to largely govern the trans/cis selectivity. Substituents of sufficient bulk in the ,-position of the substrate have been identified as being vital for stereochemical induction. The present study has indicated that the diastereoselectivity of ring closure can be considerably modulated. The variation of the lanthanide's ionic radius and introduction of extra steric pressure at the substrate's ,-position and/or the CGC N centre have been identified as effective handles for tuning the selectivity. The quantification of these factors reported herein represents the first step toward the rational design of improved CGC,Ln catalyst architectures and will thus aid this process. [source] Computational Investigations on the General Reaction Profile and Diastereoselectivity in Sulfur Ylide Promoted AziridinationCHEMISTRY - A EUROPEAN JOURNAL, Issue 17 2007Deepa Janardanan Abstract Mechanism and diastereoselectivity of sulfur ylide promoted aziridination reactions were studied by density functional theory with inclusion of solvent effects through the continuum solvation model. The general reaction pathway was modeled for the addition of substituted sulfur ylides (Me2S+CH,R) to an aldimine ((E)-methyl ethylidenecarbamate, MeHCNCO2Me). The nature of the substituents on the ylidic carbon atom substantially affects the reaction profile. The stabilized (R=COMe) and semistabilized (R=Ph) ylides follow a cisoid addition mode leading to trans aziridines via anti betaine intermediates. The simplest model ylide (unstabilized, R=H) underwent cisoid addition in a similar fashion. In the case of stabilized ylides product diastereoselectivity is controlled by the barriers of the elimination step leading to the 2,3- trans aziridine, whereas it is decided in the addition step in the case of semistabilized ylides. The importance of steric and electronic factors in diastereoselective addition (2 and 5) and elimination (5) transition states was established. Comparison of results obtained with the gas-phase optimized geometries and with the fully optimized solvent-phase geometries reveals that the inclusion of solvent effects does not bring about any dramatic changes in the reaction profiles for all three kinds of ylides. In particular, diastereoselectivity for both kinds of ylides was found to be nearly the same in both these approaches. [source] Synthesis of Binaphthyl Sulfonimides and Their Application in the Enantioselective Michael Addition of Ketones to NitroalkenesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 27 2010Shurong Ban Abstract Novel types of L -proline-based binaphthyl sulfonimides and sulfonamides were found to be efficient organocatalysts for the asymmetric Michael addition of ketones to nitroalkenes to provide optically active ,-nitroketone derivatives of synthetic and biological importance. After the fine optimization of solvents, temperature, and additive, good to excellent enantioselectivities and diastereoselectivities (71,96,%,ee, up to >99:1,dr) can be achieved. [source] 2,5-Disubstituted Pyrrolidines as Chiral Auxiliaries in Radical Reactions: A Theoretical ApproachEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2010Miglena K. Georgieva Abstract The radical addition to amides derived from chiral 2,5-disubstituted pyrrolidines has been theoretically studied by the use of density functional methods and the results compared with known experimental data. The results agree quite well with those obtained experimentally and allow the full rationalization of the factors influencing the diastereoselectivity. Steric effects are the main factors determining the selectivity, but electronic interactions can also be very important when the attacking alkene is ,,,-conjugated, as in acrylic esters or acrylamides. Additions at the ,- and ,-positions of the amide chain in the auxiliary are subject to different rules, with the former usually yielding high diastereoselectivities both experimentally and theoretically, whereas the latter is theoretically predicted to occur with low selectivity. We fully rationalize these two opposite behaviours and suggest several ways to circumvent this limitation, thus strongly increasing the interest of this type of structure as chiral auxiliaries in radical reactions. [source] Indium-Promoted Acyloxyallylation Reaction of Azetidine-2,3-diones in Aqueous Media: A New Route to Densely Functionalized 3-Substituted 3-Hydroxy-,-lactams,EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 26 2008Benito Alcaide Abstract Densely functionalized 3-substituted 3-hydroxy-,-lactams have been obtained by acyloxyallylation reaction of azetidine-2,3-diones with 3-bromopropenyl acetate or benzoate in aqueous media promoted by indium under Barbier conditions. Two new stereocenters were formed; the stereochemistry at the new C-3 quaternary center was fully controlled by placing a bulky chiral substituent at C-4. However, poor diastereoselectivities were observed in the new allylicstereocenter formed (up to 58,% de).(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Polymer-Immobilized Pyrrolidine-Based Chiral Ionic Liquids as Recyclable Organocatalysts for Asymmetric Michael Additions to Nitrostyrenes under Solvent-Free Reaction ConditionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 7 2008Pinhua Li Abstract A polymer immobilized pyrrolidine-based chiral ionic liquid 5a was synthesized and was found to be a highly efficient catalyst for the Michael additions of ketones and aldehydes to nitrostyrenes, which afforded the corresponding adducts in good yields (up to 97,%), excellent enantioselectivities (up to >99,% ee) and high diastereoselectivities (up to >99:1 dr) under solvent-free reaction conditions. In addition, the catalyst 5a could be reused at least eight times without a significant loss of its catalytic activity and stereoselectivity.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Unusual Magnesium Chloride Catalyzed Non-Evans anti -Aldol Reactions of an Enolizable L -Threose DerivativeEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 34 2007James McNulty Abstract The magnesium chloride catalyzed anti -aldol reaction of phenyl acetate derived oxazolidinones proceeds readily with enolizable L -threose derivative 8 to provide anti -aldol adducts in high yields and with very high diastereoselectivities. The reaction is also efficient with aromatic aldehydes and provides slightly lower diastereoselectivities. This extension allows access to stereochemically defined fragments applicable to the synthesis of alkaloid and phenylpropanoid derivatives.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Highly Enantio- and Diastereoselective One-Pot Reactions in Aqueous Media: Combined Asymmetric Rh-Catalyzed Conjugate Addition/Metal-Mediated AllylationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2006Sara Källström Abstract 1,3-Disubstituted, enantiopure cyclohexanols have been prepared in very high diastereoselectivities and good yields by a concise one-pot method combining the enantioselective rhodium-catalyzed conjugate addition of arylboronic acids with indium-mediated allylation into a highly efficient one-pot reaction in aqueous media. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Asymmetric Mannich-Type Reaction of a Chiral N -(tert -Butylsulfinyl) Ketimine with Imines: Application to the Synthesis of Chiral 1,3-DiaminesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 13 2006Cui-Hua Zhao Abstract Deprotonation of the chiral N -(tert -butylsulfinyl) ketimine 1 followed by trapping with imines 2 afforded the ,-aminoimines 3 as the Mannich-type products in high diastereoselectivities (99:1 dr). As versatile synthons chiral ,-amino imines 3 could be transformed into enantiomeric ,-amino ketone and chiral syn - or anti -1,3-diamines with high diastereomeric excess by hydrolysis or reduction, respectively. Moreover, the nucleophilic addition of organometallicreagents to chiral ,-amino imines 3 could provide 1,1,3-trisubstituted 1,3-diamines with high diastereoselectivities. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Diastereoselective Reactions of the Tiglic Acid Functionality Mediated by Oxazolidine Chiral Auxiliaries: A Mechanistic Comparison of DMD andm -CPBA Epoxidations versus Singlet Oxygen and PTAD Ene ReactionsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2005Aurelia Pastor Abstract 2,2-Dimethyloxazolidines have been utilized as chiral auxiliaries for the diastereoselective functionalization of the optically active tiglic acid derivatives (S)- 1 by means of epoxidation with DMD or m -CPBA and ene reactions with 1O2 or PTAD. In the DMD and m -CPBA epoxidations, high diastereoselectivities but opposite senses of diastereomer selection were observed. In contrast, the stereochemistry of the 1O2 and PTAD ene reactions depended on the size of the attacking enophile: whereas essentially perfect diastereoselectivity was obtained with PTAD, much lower stereoselection was observed with 1O2. The stereochemical results for the DMD and m -CPBA epoxidations and the PTAD ene reaction are explained in terms of the energy differences for the corresponding diastereomeric transition states, dictated by steric and electronic effects. The PTAD ene reaction for these tiglic acids (S)- 1 provides, after removal of the chiral auxiliaries, an attractive synthetic route for optically active ,-amino acid derivatives.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] A Lewis Acid Promoted Asymmetric Umpolung Reaction with ChiralN -Sulfinyl Imines as the ElectrophilesEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2005Xin Xu Abstract An new asymmetric umpolung reaction has been developed by reacting N -sulfinyl imines with 2-lithio-2-phenyl-1,3-dithiane. The reaction was conducted at between ,20 and,25 °C in THF in the presence of Et2AlCl as the Lewis acid promoter. Excellent diastereoselectivities (up to >95,% de) and chemical yields (64,95,%) have been achieved for nine substrates with all individual isomers separated and characterized. The absolute structure of the chiral products has been unambiguously determined by synthetic conversions to a known sample. 2-Lithio-2-phenyl-1,3-dithiane was found to be much less reactive than its 2-methyl counterpart, which was reported very recently. All individual isomers have been readily separated by column chromatography. The absolute structure of the chiral products has been unambiguously determined by conversion into a known compound. This method provides an easy access to enantiomerically pure ,-amino ketones. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Asymmetric Cyclopropanation of Optically Active (1-Diethoxyphosphoryl)vinyl p -Tolyl Sulfoxide with Sulfur Ylides: A Rationale for DiastereoselectivityEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 4 2005Wanda H. Midura Abstract The title sulfoxide (S)-(+)- 1a was found to react with sulfur ylides affording the corresponding cyclopropanes in high yields. With fully deuterated dimethyl(oxo)sulfonium methylide, (CD3)2S(O)CD2, the cyclopropanation reaction occurred in a highly diastereoselective manner producing the cyclopropane 4a - d2 as a major diastereomer in which the newly formed quaternary ,-carbon atom is chiral due to isotopic substitution (CH2 vs. CD2). The diastereomer 4b - d2, having the opposite configuration at the ,-carbon atom, was obtained starting form the 2,2-dideuterio substituted vinyl sulfoxide, (S)-(+)- 1a - d2, and the nondeuterated ylide. The diastereomeric ratio in both reactions was found to be ca. 10:1. The reaction of (S)-(+)- 1a with diphenylsulfonium isopropylide yielded the cyclopropane (+)- 7 as a single diastereomer. X-ray structural studies of the crystalline 1-phosphorylvinyl sulfoxide 9 as well as density functional calculations (B3LYP/6-31G*) on (1-phosphoryl)vinyl sulfoxides revealed the origin of the experimentally observed diastereoselectivities and allowed us to propose a transition state model for the cyclopropanation reaction of chiral 1-phosphorylvinyl sulfoxides. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Stereoselective Aldol Reactions Catalyzed by Acyclic Amino Acids in Aqueous MicellesHELVETICA CHIMICA ACTA, Issue 1 2007Dong-Sheng Deng Abstract The catalytic properties of all proteinogenic, acyclic amino acids for direct aldol reaction in H2O, assisted by various surfactants, were investigated. The basic and neutral amino acids were shown to be efficient catalysts, giving rise to good-to-excellent yields of adducts (up to 95%), with moderate-to-good diastereoselectivities (up to 86%), L -arginine being the most-effective catalyst. The syn/anti diastereoisomer ratio could be readily tuned by proper choice of the amino acid used. Also, the range of substrates that underwent the reaction was extended to less-reactive aldehydes carrying electron-donating Br substituents. [source] | |||||||||||||||||||||||||