- Catalytic asymmetric alkylation of aldehydes by diethylzinc in the presence of N-iso-propylephedrine; dependence of enantioselectzvity on Et2Zn:RCHO
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The enantioselective alkylation of a range of aldehydes by diethylzinc in the presence of N-isopropylephedrine has been investigated. Both the yield and the enantioselectivity of the reaction was found to depend on the ratio of Et2Zn to the ald
- Chaloner, Penny A.,Langadianou, Eugenia
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- Stereoselective Synthesis and Modelling-Driven Optimisation of Carane-Based Aminodiols and 1,3-Oxazines as Catalysts for the Enantioselective Addition of Diethylzinc to Benzaldehyde
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The reductive amination of (-)-2-carene-3-aldehyde, prepared in two steps from (-)-perillaldehyde, furnished 2-carene-based allylamines. tert-Butyloxycarbonyl (Boc) or carbobenzyloxy (Cbz) protection of the resulting amines, followed by stereoselective dihydroxylation in highly stereospecific reactions with OsO4 and subsequent deprotection, resulted in N-benzylaminodiols, which were transformed to primary and tertiary aminodiols. The reactions of the N-benzyl- and N-(1-phenylethyl)-substituted derivatives with formaldehyde led to highly regioselective ring closure, resulting in carane-fused 1,3-oxazines. The aminodiols and their 1,3-oxazine derivatives were applied as chiral catalysts in the enantioselective addition of diethylzinc to aldehydes. The best (R) enantioselectivity was observed in the case of the N-((R)-1-phenylethyl)-substituted aminodiol, whereas the opposite chiral direction was preferred when the 1,3-oxazines were applied. Through the use of molecular modelling at an ab initio level, this phenomenon was interpreted in terms of competing reaction pathways. Molecular modelling at the RHF/LANL2DZ level of theory was successfully applied for a mechanism-based interpretation of the stereochemical outcome of the reactions leading to the development of further 1,3-oxazine-based ligands, which display excellent (S) enantioselectivity (95 and 98 % ee) in the examined transformation.
- Szakonyi, Zsolt,Cs?r, árpád,Csámpai, Antal,Fül?p, Ferenc
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- Planar-chiral salen and hemisalen [2.2]paracyclophane ligands for asymmetric diethylzinc addition to aldehydes
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Fourteen multistereogenic symmetric and asymmetric salens based on a [2.2]paracyclophane skeleton have been tested as catalysts for the enantioselective addition of diethylzinc to aldehydes affording the corresponding alcohols in up to 94% enantiomeric excess. Chiral [2.2]paracyclophane hemisalens are applied for the first time as chiral ligands in the Et2Zn addition to benzaldehyde.
- Danilova, Tatyana I.,Rozenberg, Valeria I.,Starikova, Zoya A.,Braese, Stefan
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- Combinatorial chemistry for ligand development in catalysis: Synthesis and catalysis screening of peptidosulfonamide tweezers on the solid phase
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On the basis of a pyrrolidine tweezer 1, a library of peptidosulfonamide tweezers (15a-e, 16a-e was synthesized on the solid phase. This library was screened in a simultaneous substrate screening procedure for the ability to enantioselectively catalyze the Ti(O-i-Pr)4-mediated addition of diethylzinc to aldehydes. One of the best solid-phase tweezer catalyst (i.e., 16d, giving an ee of 32% in solid-phase catalysis) was resynthesized in solution (compounds 20 and 21). The now homogeneous solution-phase catalysis showed even better enantioselectivity (i.e., up to 66%).
- Brouwer, Arwin J.,van Der Linden, Heiko J.,Liskamp, Rob M. J.
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- Novel chiral tridentate Schiff base ligands of the [2.2]paracyclophane series: Synthesis and application
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The first example of the efficient application of chiral tridentate N,O-[2.2]paracyclophane ligands of the imino type for enantioselective diethylzinc addition to aliphatic and aromatic aldehydes is presented. The enantiomeric excess of the resulted secondary alcohols is up to 93% e.e.
- Danilova, Tatyana I.,Rozenberg, Valeria I.,Sergeeva, Elena V.,Starikova, Zoya A.,Braese, Stefan
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- Enantioselective Ethylation of Various Aldehydes Catalyzed by Readily Accessible Chiral Diols
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Four chiral C2-symmetric diols were synthesized in a straightforward three-step reaction and demonstrated excellent enantioselectivities and good overall yields. Their catalytic activities were examined via the addition of diethylzinc to various aldehydes. The enantioselective addition of diethylzinc to 2-methoxybenzaldehyde gave the corresponding chiral secondary alcohol with high yields (up to 95%) and moderate to good enantiomeric excess (up to 88%). All synthesized ligands were evaluated in the addition of diethylzinc to various aldehydes in the presence of an additional metal such as Ti(IV) complexes. Chirality 28:593–598, 2016.
- G?k, Ya?ar,Kili?arslan, Seda,G?k, Halil Zeki,Karayi?it, ?lker ümit
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- N-trityl-aziridinyl(diphenyl)methanol as an effective catalyst in the enantioselective addition of diethylzinc to aldehydes
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High levels of enantioselectivity have been achieved in the diethylzinc addition to both aromatic and aliphatic aldehydes, employing N-trityl- aziridinyl(diphenyl)methanol as the chiral catalyst. The R- and S-antipodes of the catalyst can readily be prepa
- Lawrence, Corrine F.,Nayak, Sandip K.,Thijs, Lambertus,Zwanenburg, Binne
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- Asymmetric trialkylaluminium addition to aldehydes catalyzed by titanium complexes of N-sulfonylated amino alcohols with two stereogenic centers
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The asymmetric methylation, ethylation and allylation of aldehydes using trialkylaluminium reagents catalyzed by titanium(IV) complexes of N-sulfonylated amino alcohols gave excellent enantioselectivities of up to 99% ee.
- You,Hsieh,Gau
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- Polymer-supported N-tritylaziridinyl(diphenyl)methanol as an effective catalyst in the enantioselective addition of diethylzinc to aldehydes
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(matrix presented) Novel polymer-supported N-tritylaziridino alcohol 2 was utilized as chiral ligand in the asymmetric addition of diethylzinc to aldehydes. High enantioselectivities were obtained for both aromatic and aliphatic aldehydes. The catalyst wa
- Ten Holte, Peter,Wijgergangs, Jan-Piet,Thijs, Lambertus,Zwanenburg, Binne
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- Design of a Chiral Ionic Liquid System for the Enantioselective Addition of Diethylzinc to Aldehydes
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An important contribution to the field of asymmetric catalysis is described in this work, as it merges the search for new ligands that can provide high performance in asymmetric catalysis with the extremely important and increasing need for sustainability. New chiral ionic liquids have been synthesised from the amino acid l-cysteine by straightforward routes. With these ligands, we have developed a chiral ionic system that includes chiral ionic liquids and their immobilisation in ionic solvents to provide a chiral supramolecular structure. These new catalytic systems were used in the enantioselective addition of alkylzinc to aldehydes and proved to be very efficient, capable of providing chiral secondary alcohols in excellent enantiomeric excesses and yields. This system also enabled the recycling of the ionic media and the ionic ligand, taking into account green chemistry considerations.
- Ferrari Bach, Mariana,Herzer Griebeler, Cassiana,Gross Jacoby, Caroline,Schneider, Paulo Henrique
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- Kinetic resolution of racemic allylic alcoholsviairidium-catalyzed asymmetric hydrogenation: scope, synthetic applications and insight into the origin of selectivity
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Asymmetric hydrogenation is one of the most commonly used tools in organic synthesis, whereas, kinetic resolutionviaasymmetric hydrogenation is less developed. Herein, we describe the first iridium catalyzed kinetic resolution of a wide range of trisubstituted secondary and tertiary allylic alcohols. Large selectivity factors were observed in most cases (sup to 211), providing the unreacted starting materials in good yield with high levels of enantiopurity (ee up to >99%). The utility of this method is highlighted in the enantioselective formal synthesis of some bioactive natural products including pumiliotoxin A, inthomycin A and B. DFT studies and a selectivity model concerning the origin of selectivity are presented.
- Wu, Haibo,Margarita, Cristiana,Jongcharoenkamol, Jira,Nolan, Mark D.,Singh, Thishana,Andersson, Pher G.
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p. 1937 - 1943
(2021/02/22)
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- Dynamic Kinetic Resolution of Alcohols by Enantioselective Silylation Enabled by Two Orthogonal Transition-Metal Catalysts
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A nonenzymatic dynamic kinetic resolution of acyclic and cyclic benzylic alcohols is reported. The approach merges rapid transition-metal-catalyzed alcohol racemization and enantioselective Cu-H-catalyzed dehydrogenative Si-O coupling of alcohols and hydrosilanes. The catalytic processes are orthogonal, and the racemization catalyst does not promote any background reactions such as the racemization of the silyl ether and its unselective formation. Often-used ruthenium half-sandwich complexes are not suitable but a bifunctional ruthenium pincer complex perfectly fulfills this purpose. By this, enantioselective silylation of racemic alcohol mixtures is achieved in high yields and with good levels of enantioselection.
- Oestreich, Martin,Seliger, Jan
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supporting information
p. 247 - 251
(2020/10/29)
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- Deciphering the mechanism behind efficient enantioselective ethylation with thiazolidine-based amino alcohols
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Taking advantage of the opposite chirality of two privileged starting materials, l-cysteine and d-penicillamine, a wide range of thiazolidine-based amino alcohols was synthesized. l-Cysteine derivatives were more efficient chiral inductors than the d-peni
- Cacho, Vanessa R. G.,Costa, Dora C. S.,Murtinho, Dina,Nunes, Sandra C. C.,Pais, Alberto A. C. C.,Silva Serra, M. Elisa,Tavares, Nélia C. T.
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- Linear β-amino alcohol catalyst anchored on functionalized magnetite nanoparticles for enantioselective addition of dialkylzinc to aromatic aldehydes
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A linear β-amino alcohol ligand, previously found to be a very efficient catalyst for enantioselective addition of dialkylzinc to aromatic aldehydes, has been anchored on differently functionalized superparamagnetic core-shell magnetite-silica nanoparticles (1a and 1b). Its catalytic activity in the addition of dialkylzinc to aldehydes has been evaluated, leading to promising results, especially in the case of 1b for which the recovery by simple magnetic decantation and reuse was successfully verified. This journal is
- Ciprioti, Stefano Vecchio,De Angelis, Martina,Di Pietro, Federica,Iannoni, Marika,Pilloni, Luciano,Primitivo, Ludovica,Ricelli, Alessandra,Righi, Francesco,Righi, Giuliana,Sappino, Carla,Suber, Lorenza
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p. 29688 - 29695
(2020/10/26)
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- Enantioselective addition of diethylzinc to aldehydes catalyzed by 5-cis-substituted proline derivatives
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5-Cis-substituted prolinols, prolinamines, and prolinamine sulfonamides proved to be efficient ligands for the enantioselective addition of diethylzinc to aldehydes, providing up to 99% ee. The sense of asymmetric induction can be controlled by the nature
- Prause, Felix,Wagner, Stefan,Breuning, Matthias
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- CHIRAL METAL COMPLEX COMPOUNDS
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The invention comprises novel chiral metal complex compounds of the formula (I) wherein M, PR2, R3 and R4 are outlined in the description, its stereoisomers, in the form as a neutral complex or a complex cation with a suitable counter ion. The chiral metal complex compounds can be used in asymmetric reactions, particularly in asymmetric reductions of ketones, imines or oximes.
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Page/Page column 18; 19; 21; 23; 24; 25
(2018/11/10)
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- Chiral 2-(2-hydroxyaryl)alcohols (HAROLs) with a 1,4-diol scaffold as a new family of ligands and organocatalysts
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Efficient and modular syntheses of chiral 2-(2-hydroxyaryl)alcohols (HAROLs), novel 1,4-diols carrying one phenolic and one alcohol hydroxyl group, have been developed which led to generation of a small library of structurally diverse HAROLs in enantiomerically pure form. Of the different HAROLs examined, a HAROL based on the indan backbone exhibited the highest activity and enantioselectivity in the 1,2-addition of certain organometallic compounds to aldehydes in the presence of Ti(OiPr)4 (up to 97% y, 88% ee) and performed as a hydrogen-bond donor organocatalyst in the Morita-Baylis-Hillman reaction, promoted by trialkylphosphines.
- Dilek, ?mer,Tezeren, Mustafa A.,Tilki, Tahir,Ertürk, Erkan
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supporting information
p. 268 - 286
(2017/12/06)
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- New chiral amino alcohol ligands for catalytic enantioselective addition of diethylzincs to aldehydes
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A study aimed at the synthesis and structure optimization of new, efficient, optically active β-amino alcohol ligands with a structure suitable for immobilization on magnetite nanoparticles has been carried out. The optimized homogeneous amino alcohol catalysts 13a and 13b, the chirality of which arises from the Sharpless epoxidation of suitable allyl alcohols, were tested by employing the well-established enantioselective amino alcohol-promoted addition of diethylzinc to benzaldehyde, giving the corresponding benzyl alcohol with nearly quantitative yield and ee = 95%. Then, their broad applicability as chiral catalysts was evaluated by carrying out the same reaction on a family of aldehydes, including variously substituted aromatic ones as well as an aliphatic analogue. The results have confirmed the validity of the fine-tuning process performed on ligands 13a and 13b. In fact, both exhibited excellent catalytic activity as demonstrated by the chemical yields and ee obtained from all the tested aldehydes, almost independent of the position and type of substitution in the aromatic ring.
- Sappino, Carla,Mari, Alessandra,Mantineo, Agnese,Moliterno, Mauro,Palagri, Matteo,Tatangelo, Chiara,Suber, Lorenza,Bovicelli, Paolo,Ricelli, Alessandra,Righi, Giuliana
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p. 1860 - 1870
(2018/03/23)
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- Chiral thiazolidines in the enantioselective ethylation of aldehydes: An experimental and computational study
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A library of new chiral thiazolidines was prepared starting from L-cysteine and D-penicillamine in a simple, one-step procedure. 2-Arylthiazolidines were obtained, as diastereoisomeric mixtures, with good yields and in short reaction times, through a new and greener procedure, using microwave irradiation. Their use as chiral ligands in the enantioselective ethylation of aromatic aldehydes was studied and optimized, originating good to excellent conversions and ee up to 94% in 6 h. A series of heteroaromatic and aliphatic substrates were also enantioselectively ethylated with success, with ee up to 77%. The distinct opposite chirality in L-cysteine and D-penicillamine makes the use of these ligands an interesting approach for obtaining both the (S) and (R) enantiomers of the chiral alcohols, compounds with potential applications in the area of fine chemistry. NMR studies were carried out using a diastereoisomeric mixture of thiazolidines, allowing the identification of the most stable structure. Computational studies confirmed this result and also gave important insight into the species involved in the catalytic cycle of the enantioselective alkylation.
- Tavares, Nélia C.T.,Neves, César T.,Milne, Bruce F.,Murtinho, Dina,Pais, Alberto A.C.C.,Serra, M. Elisa Silva
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- Manganese(I)-Catalyzed Enantioselective Hydrogenation of Ketones Using a Defined Chiral PNP Pincer Ligand
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A new chiral manganese PNP pincer complex is described. The asymmetric hydrogenation of several prochiral ketones with molecular hydrogen in the presence of this complex proceeds under mild conditions (30–40 °C, 4 h, 30 bar H2). Besides high catalytic activity for aromatic substrates, aliphatic ketones are hydrogenated with remarkable selectivity (e.r. up to 92:8). DFT calculations support an outer sphere hydrogenation mechanism as well as the experimentally determined stereochemistry.
- Garbe, Marcel,Junge, Kathrin,Walker, Svenja,Wei, Zhihong,Jiao, Haijun,Spannenberg, Anke,Bachmann, Stephan,Scalone, Michelangelo,Beller, Matthias
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supporting information
p. 11237 - 11241
(2017/09/02)
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- Third-Generation Amino Acid Furanoside-Based Ligands from d-Mannose for the Asymmetric Transfer Hydrogenation of Ketones: Catalysts with an Exceptionally Wide Substrate Scope
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A modular ligand library of α-amino acid hydroxyamides and thioamides was prepared from 10 different N-tert-butyloxycarbonyl-protected α-amino acids and three different amino alcohols derived from 2,3-O-isopropylidene-α-d-mannofuranoside. The ligand library was evaluated in the half-sandwich ruthenium- and rhodium-catalyzed asymmetric transfer hydrogenation of a wide array of ketone substrates, including simple as well as sterically demanding aryl alkyl ketones, aryl fluoroalkyl ketones, heteroaromatic alkyl ketones, aliphatic, conjugated and propargylic ketones. Under the optimized reaction conditions, secondary alcohols were obtained in high yields and in enantioselectivities up to >99%. The choice of ligand/catalyst allowed for the generation of both enantiomers of the secondary alcohols, where the ruthenium-hydroxyamide and the rhodium-thioamide catalysts act complementarily towards each other. The catalytic systems were also evaluated in the tandem isomerization/asymmetric transfer hydrogenation of racemic allylic alcohols to yield enantiomerically enriched saturated secondary alcohols in up to 98% ee. Furthermore, the catalytic tandem α-alkylation/asymmetric transfer hydrogenation of acetophenones and 3-acetylpyridine with primary alcohols as alkylating and reducing agents was studied. Secondary alcohols containing an elongated alkyl chain were obtained in up to 92% ee. (Figure presented.).
- Margalef, Jèssica,Slagbrand, Tove,Tinnis, Fredrik,Adolfsson, Hans,Diéguez, Montserrat,Pàmies, Oscar
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p. 4006 - 4018
(2016/12/30)
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- Enantioselective addition of diethylzinc to aldehydes catalyzed by o-xylylene-type chiral 1,4-amino alcohols with an aminal structure
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A series of o-xylylene-type chiral 1,4-amino alcohols with an aminal structure was synthesized starting from (S)-2-(arylaminomethyl)pyrrolidine, o-bromobenzaldehyde, and a diaryl ketone. The enantioselective addition of diethylzinc to aldehydes was examined by using the 1,4-amino alcohols, and the corresponding chiral secondary alcohols were obtained with high enantioselectivities (up to 98% ee).
- Asami, Masatoshi,Hasome, Ayano,Yachi, Naoyuki,Hosoda, Naoya,Yamaguchi, Yoshitaka,Ito, Suguru
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p. 322 - 329
(2016/04/09)
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- Enantioselective addition of organozinc reagents to carbonyl compounds catalyzed by a camphor derived chiral γ-amino thiol ligand
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In this article, the design and synthesis of the chiral camphor derived γ-amino thiol ligand 17 and its application in catalytic enantioselective carbon-carbon forming reactions through the addition of organozinc reagents to carbonyl compounds is described. The catalytic activity and enantioselectivity of ligand 17 is demonstrated in the enantioselective addition of various organozinc reagents to aldehydes and ketoesters, offering the corresponding alcohols in high yields and enantioselectivities. The role of the mercapto group in the highly enantioselective 1,2-addition reaction of organozincs to aldehyde is also discussed.
- Wu, Hsyueh-Liang,Wu, Ping-Yu,Cheng, Ying-Ni,Uang, Biing-Jiun
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p. 2656 - 2665
(2016/05/10)
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- Mechanistic implications of the enantioselective addition of alkylzinc reagents to aldehydes catalyzed by nickel complexes with α-amino amide ligands
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The enantioselective alkylation of aldehydes catalysed by nickel(ii)-complexes derived from α-amino amides was studied by means of density functional theory (DFT) and ONIOM (B3LYP:UFF) calculations. A mechanism was proposed in order to investigate the origin of enantioselectivity. The chirality-determining step for the alkylation was the formation of the intermediate complexes with the involvement of a 5/4/4-fused tricyclic transition state. The predominant products predicted theoretically were of (S)-configuration, in good agreement with experimental observations. The scope of the reaction was examined and high yields and enantioselectivities were observed for the enantioselective addition of Et2Zn and Me2Zn to aromatic and aliphatic aldehydes.
- Escorihuela, Jorge,Burguete, M. Isabel,Ujaque, Gregori,Lledós, Agustí,Luis, Santiago V.
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p. 11125 - 11136
(2016/12/07)
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- Chemo- and Enantioselective Addition and β-Hydrogen Transfer Reduction of Carbonyl Compounds with Diethylzinc Reagent in One Pot Catalyzed by a Single Chiral Organometallic Catalyst
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Using a single chiral phosphoramide-Zn(II) complex as the catalyst, the asymmetric β-H transfer reduction of aromatic α-trifluoromethyl ketones and enantioselective addition of aromatic aldehydes with Et2Zn in one pot were successfully realized, affording the corresponding additive products of secondary alcohols in high yields (up to 99%) with excellent enantioselectivities (up to 98% ee) and the reduction products of α-trifluoromethyl alcohols in good to excellent yields with up to 77% ee.
- Huang, Huayin,Zong, Hua,Bian, Guangling,Song, Ling
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p. 12614 - 12619
(2016/01/09)
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- Enantioselective addition of diethylzinc to aldehydes catalyzed by diastereomeric 1,4-amino alcohols with o-xylylene skeleton
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Two diastereomeric 1,4-amino alcohols with o-xylylene structure (S,R)-2 and (S,S)-3, synthesized from chiral 1,4-diol (S,S)-1, were utilized as chiral ligands for the enantioselective addition of diethylzinc to aldehydes. The stereochemical outcome of the reactions was controlled solely by the absolute configuration of the benzylic carbon bearing amino group, and both enantiomers of 1-substituted propanol were obtained with up to 98% (S) and 96% (R) enantiomeric excesses.
- Asami, Masatoshi,Nagai, Atsushi,Sasahara, Yukihiro,Ichikawa, Ken-Ichi,Ito, Suguru,Hosoda, Naoya
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supporting information
p. 345 - 347
(2015/03/30)
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- Enantioselective addition of diethylzinc to aldehydes catalyzed by (R)-1-phenylethylamine-derived 1,4-amino alcohols
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A series of o-xylylene-type 1,4-amino alcohols, synthesized from (R)-1-phenylethylamine, were used as chiral ligands for the enantioselective addition of diethylzinc to benzaldehyde. (S)-1-Phenyl-1-propanol was obtained with high enantioselectivity in all cases since the stereochemical outcome of the reaction was controlled by the chiral benzylic carbon bearing amino group. Highest catalytic activity was obtained by using (R)-1-{2-[1-(pyrrolidin-1-yl)ethyl]phenyl}cyclohexan-1-ol (1n) derived from (R)-1-(1-phenylethyl)pyrrolidine and cyclohexanone. Various chiral secondary alcohols were obtained by the reaction of diethylzinc and aldehydes in the presence of 1n within 2 h with good to high enantioselectivities.
- Asami, Masatoshi,Miyairi, Naomichi,Sasahara, Yukihiro,Ichikawa, Ken-Ichi,Hosoda, Naoya,Ito, Suguru
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p. 6796 - 6802
(2015/08/24)
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- Synthesis of Ferrocene Oxazoline N,O ligands and Their Application in Asymmetric Ethyl- and Phenylzinc Additions to Aldehydes
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The synthesis of a range of novel gem-disubstituted ferrocene-oxazoline ligands and their application in both the asymmetric ethyl- and phenylzinc additions to aldehydes is reported. These studies reveal that gem-disubstitution of i-Pr-containing ferrocene oxazoline ligands results in increased enantioselectivity compared to their unsubstituted counterparts. Utilizing zinc catalysis, these ligands provided a wide range of secondary alcohols in yields of up to 93% with ee's of up to >99%. An interesting crystal structure of a ferrocene oxide-lithium tetramer showing lithium-nitrogen coordination in the solid state is also presented.
- Nottingham, Chris,Benson, Robert,Müller-Bunz, Helge,Guiry, Patrick J.
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p. 10163 - 10176
(2015/11/03)
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- Dual stereocontrolled alkylation of aldehydes with polystyrene-supported nickel complexes derived from α-amino amides
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Nickel(ii) complexes derived from α-amino amide ligands anchored to gel-type and monolithic polymers act as efficient catalysts for the enantioselective addition of dialkylzinc reagents to aldehydes. Similar to the analogous homogeneous systems, dual stereocontrol in addition products can be achieved by controlling the stoichiometry of the immobilized nickel complex. Aromatic and aliphatic aldehydes were alkylated in good yields with enantioselectivities comparable to those obtained with the homogeneous analogues. These polymer-supported catalysts offer significant advantages as no metal leaching is observed and they can be easily recovered from the reaction mixture by simple filtration and reused for subsequent experiments with consistent catalytic activity.
- Escorihuela, Jorge,Altava, Beln,Burguete, M. Isabel,Luis, Santiago V.
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p. 14653 - 14662
(2015/02/19)
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- Enantioselectivity switch controlled by N,N′-di- or N,N,N′,N′-tetra-substituted chiral thiophosphorodiamide ligands, structural relatives of thioureas, in catalytic additions of diethylzinc to aldehydes
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We have developed a series of new chiral thiophosphorodiamide ligands derived from (1R,2R)-(+)-1,2-diphenylethylenediamine, which are the structural relatives of thioureas. An investigation into their catalytic properties in asymmetric additions of diethylzinc to aldehydes has shown that N,N,N′,N′-tetra-substituted chiral thiophosphorodiamides can give (R)-secondary alcohols with up to 98% yield and 98% ee, while N,N′-di-substituted chiral thiophosphorodiamides give (S)-secondary alcohols with up to 99% yield and 97% ee values. The enantioselectivity switch is highly efficient with a broad substrate scope. We have also proposed hypothetical reaction pathways, which result in an enantioselectivity switch.
- Yue, Huifeng,Huang, Huayin,Bian, Guangling,Zong, Hua,Li, Fangling,Song, Ling
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p. 170 - 180
(2014/02/14)
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- Novel C2-symmetric chiral O,N,N,O-tetradentate 2,2-bipyridyldiolpropane ligands: Synthesis and application in asymmetric diethylzinc addition to aldehydes
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First synthesis of C2-symmetric chiral O,N,N,O-tetradentate 2,2-bipyridyldiolpropane ligands is described. The Mukaiyama-Michael reaction was applied as an important reaction for the synthesis of 2,2-bipyridylpropane 9. Among the ligands synthesized, ligand 11 exhibits excellent chiral induction (up to 97% ee) in diethylzinc addition to various aldehydes. The use of additional Lewis acid such as Ti(OiPr)4 in diethylzinc addition reaction is not required for the present catalytic system.
- Shih, Yi-Shan,Boobalan, Ramalingam,Chen, Chinpiao,Lee, Gene-Hsian
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p. 327 - 333
(2014/04/03)
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- The synthesis of chiral amino diol tridentate ligands and their enantioselective induction during the addition of diethylzinc to aldehydes
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A series of C2-symmetric chiral amino diol tridentate ligands 3a-g were prepared from achiral bulky organolithiums, achiral bulky primary amines, and optically active epichlorohydrin (ECH). The prepared C 2-symmetric chiral amino diol tridentate ligands were capable of inducing enantioselectivity in the model reaction of aromatic and aliphatic aldehydes with diethylzinc with an ee of up to 96%. The enantioselectivity can be modulated by adjusting the steric hindrance of the achiral reagents employed in the synthesis of the chiral ligand. The configuration of the addition product depended on the configuration of the amino diol ligands, which can be simply controlled as desired by using the ECH with the desired configuration during the preparation of the ligand.
- Zhang, An-Lin,Yang, Li-Wen,Yang, Nian-Fa,Liu, Yan-Ling
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p. 289 - 297
(2014/04/03)
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- 2-Pyridylsulfinamides as effective catalysts in the asymmetric alkylation of aldehydes with diethylzinc Dedicated to Dr. N.N. Joshi, National Chemical Laboratory, Pune, India
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Chiral 2-pyridylsulfinamides were shown to be effective catalysts in the alkylation of aryl and alkyl aldehydes with diethylzinc providing the corresponding alcohols in excellent enantioselectivity. Sulfinamide catalysts possessing solitary chirality at the sulfur center produced the product phenethyl alcohol in good enantioselectivity. Diastereomeric sulfinamides possessing chirality at the carbon-bearing nitrogen and at the sulfur of the sulfinamide increased the enantioselectivity of the product alcohols up to >99%. However, there is no effect of the match-mismatch pair of sulfinamide diastereomers on the outcome of the chiral induction of the product phenethyl alcohols. It was conclusively proved that chirality at the sulfur center is mandatory for obtaining good enantioselectivity in the reaction.
- Prasad, Kavirayani R.,Revu, Omkar
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p. 8422 - 8428
(2013/09/02)
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- Synergistic effect of achiral quaternary ammonium salt on asymmetric additions of diethylzinc to aldehydes
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Our investigation has shown that achiral quaternary ammonium salt has a significant synergistic effect on the asymmetric additions of diethylzinc to aldehydes catalyzed by chiral phosphoramide-Zn(II) complex. The addition of 10 mol % NBu4X can dramatically reduce the loading amount of chiral ligand without sacrificing the excellent reactivity and enantioselectivity of the asymmetric reaction.
- Zong, Hua,Huang, Huayin,Bian, Guangling,Song, Ling
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supporting information
p. 2722 - 2725
(2013/06/26)
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- Enantioselective alkylation of aldehydes using dialkylzincs catalyzed by simple chiral diols derived from naturally occurring monosaccharides
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Enantioselective alkylation of aldehydes was achieved in up to 84% ee using dialkylzincs catalyzed by simple diols derived from naturally occurring monosaccharides.
- Michigami, Kyosuke,Hayashi, Masahiko
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supporting information
p. 4221 - 4225
(2013/06/27)
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- C2 symmetrical nickel complexes derived from α-amino amides as efficient catalysts for the enantioselective addition of dialkylzinc reagents to aldehydes
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A series of C2 symmetrical 1:2 Ni:L complexes derived from α-amino amides were studied for the enantioselective addition of dialkylzinc reagents to aldehydes. Different structural elements on the ligands seem to play an important role in determining the observed enantioselectivity. Through optimization of structure and reaction conditions, the best ligand provided secondary alcohols in excellent yields (up to 98%) and enantioselectivity of up to 99% ee for (R)-enantiomer. A transition state model has been proposed to explain the observed enantioselectivities based on computational calculations at the DFT level. Very interestingly, calculations suggest a coordination model of the aldehyde to the metal complex through association of a lone pair of the carbonyl oxygen to the hydrogen atom of an amino group.
- Escorihuela, Jorge,Altava, Belen,Burguete, M. Isabel,Luis, Santiago V.
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p. 551 - 558
(2013/07/27)
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- Synthesis of 1,3-aminonaphthols by diastereoselective Betti-type aminoalkylation of dihydroxy naphthalenes; Diastereoselectivity, absolute configuration, and application
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Dihydroxy naphthalenes have been applied in Betti-type solventless condensation between aldehydes and (S)-phenylethylamine as a chiral auxiliary. A series of chiral 1,3-aminonaphthols has been synthesized and isolated in diastereoisomerically pure form. The absolute configurations of the aminonaphthols synthesized have been determined by means of advanced NMR experiments and confirmed by X-ray crystallography. The new chiral aminonaphthols have been tested as pre-catalysts for the addition of diethyl zinc and alkynyl-Zn-reagents to aldehydes with enantioselectivities of up to 98% ee.
- Marinova, Maya,Kostova, Kalina,Tzvetkova, Pavleta,Tavlinova-Kirilova, Maya,Chimov, Angel,Nikolova, Rosica,Shivachev, Boris,Dimitrov, Vladimir
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p. 1453 - 1466
(2013/12/04)
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- Aryl[2.2]paracyclophane-based chiral regioisomeric analogs of salicyl aldehyde: Novel sources for construction of phenoxy-imine ligands
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The efficient, high-yield approaches to two novel regioisomeric salicyl aldehyde analogs, 4-formyl-13-(2-hydroxyphenyl)-[2.2]paracyclophane and 4-formyl-12-(2-hydroxyphenyl)-[2.2]paracyclophane (iso-FHPhPC and pseudo-FHPhPC, respectively), constructed on the basis of an aryl[2.2]paracyclophane backbone are described. The key stage of the backbone formation is the Suzuki cross-coupling of paracyclophanyl halides with arylboronic acids. Efficient procedures for the resolution of the racemic hydroxy aldehydes into enantiomers via Schiff bases with enantiomers of α-phenylethyl amine were elaborated, and the absolute configurations of enantiomers were established on the basis of X-ray analysis of diastereomeric imines. Starting from these chiral hydroxy aldehydes the first representatives of bi-, tri-, and tetradentate phenoxy-imine ligands belonging to an aryl[2.2]paracyclophane family were obtained. The induction power of the ligands was tested in the Et2Zn asymmetric addition to aldehydes. Copyright
- Zhuravsky, Roman P.,Danilova, Tatiana I.,Antonov, Dmitrii Yu.,Sergeeva, Elena V.,Starikova, Zoya A.,Godovikov, Ivan A.,Il'In, Michail M.,Rozenberg, Valeria I.
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experimental part
p. 156 - 170
(2012/05/20)
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- Synthesis of chiral pyridylphenols for the enantioselective addition of diethylzinc to aldehydes
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Chiral 8-substituted 2-(8,10,10-trimethyl-6-aza-tricyclo[7.1.1.0 2,7]undeca-2(7),3,5-trien-5-yl)-phenols were prepared from a high enantiopurity (>97% ee) of (1R)-(+)-α-pinene, and assessed in the enantioselective addition of diethylzinc to substituted benzaldehydes, giving the (S)-alcohols with enantiomeric excess ranging from 33% to 89%. Interestingly, in all cases, except for those of ortho-chlorobenzaldehyde, ortho- and para-methoxybenzaldehydes, the ee was >71%. The plot of the Hammett substitution constants vs. enantiomeric excess of the diethylzinc addition to either the ortho- or para-substituted benzaldehydes shows a linear correlation.
- Wu, Pei-Shan,Chen, Chinpiao
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experimental part
p. 768 - 781
(2012/08/27)
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- The syntheses of new camphorsulfonylated ligands derived from 2-amino-2'-hydroxy-1,1'-binaphthyl and their enantioselectivities in the addition of dialkylzinc reagents to aldehydes
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A series of new camphorsulfonylated ligands derived from chiral 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN) and (+)-camphorsulfonic acid were synthesized by a short and simple synthetic sequence, and their enantioselective catalytic activities were assessed in the nucleophilic addition reaction of dialkylzinc reagents to aldehydes in the presence of titanium tetraisopropoxide. The most efficient ligand, N-hydroxycamphorsulfonylated (S)-NOBIN, gave (S)-addition products with good yields and up to 87% of ee value. The 1H nuclear magnetic resonance (NMR) and 13C NMR results of the titanium titration experiments on this ligand indicate that the most likely catalytic reactive species involved in this catalytic asymmetric addition is a bimetallic titanium complex. A possible catalytic reaction mechanism is proposed. Copyright
- Bian, Guangling,Huang, Huayin,Zong, Hua,Song, Ling
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p. 825 - 832
(2012/11/07)
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- Enantioselective addition of diethylzinc to aldehydes catalyzed by (S)-1-alkyl-2-(arylamino)methylpyrrolidine
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Several chiral diamines, (S)-1-alkyl-2-(arylamino)methylpyrrolidine, were used as chiral catalysts for the enantioselective addition of diethylzinc to aldehydes. The best results were obtained by employing 0.15 equiv of (S)-2-anilinomethyl-1-benzylpyrrolidine, and chiral secondary alcohols were obtained with high enantiomeric excesses (up to 94% ee).
- Hosoda, Naoya,Ito, Hiroki,Takimoto, Tatsuya,Asami, Masatoshi
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p. 1014 - 1022
(2012/11/07)
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- Enantioselective addition of dialkylzincs to aldehydes catalyzed by (-)-MITH
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An effective catalytic system that imparts high enantioselectivity has been disclosed for the synthesis of optically active alcohols, which may undergo further chemical transformations. The enantioselective alkylation of aldehydes with dialkylzincs to afford the corresponding optically active alcohols with excellent enantioselectvities has been achieved in the presence of 0.1-0.5 mol % of the camphor-derived chiral ligand (-)-2-exo-morpholinoisobornane-10-thiol (MITH) (1) at room temperature or at 0 °C. I zinc so too: The enantioselective alkylation of aldehydes with dialkylzincs yielded the desired alcohol products with up to 99 % ee in the presence of 0.1-0.5 mol % of ligand (-)-2-exo-morpholinoisoborne-10-thiol (1) at room temperature or at 0°C. Copyright
- Cheng, Ying-Ni,Wu, Hsyueh-Liang,Wu, Ping-Yu,Shen, Ying-Ying,Uang, Biing-Jiun
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supporting information
p. 2921 - 2924
(2013/02/22)
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- Cheap and long-life reusable polymer for asymmetric organozinc catalysis based on camphor-derived hydroxyamides
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Polystyrene grafted with a chiral zinc-complexing camphor-derived N,N-disubstituted hydroxyamide is proposed as a new type of functional polymer of high reusability for the development of sustainable organozinc-catalyzed asymmetric reactions. The main goal of this new functional polymer is the ease of the hydroxyamide-moiety preparation (cheap chiral ligand obtained straightforwardly from an enantiopure starting material coming from the chiral pool), as well as its chemical robustness when compared with other related zinc-complexing functional groups. The latter allows the polymer to be active after multiple applications, without significant loss of its catalytic activity. This fact is exemplified by the design and preparation of a polymer functionalized with a bis(hydroxyamide) proved previously as active in the homogeneous enantioselective addition of diethylzinc to aldehydes. The result is a cheap functional polymer with a very high reusability (the enantioselectivity and chemical yield are maintained practically constant after 20 applications). Additionally, a methodology for the multicycle use of these functional polymers is presented. Copyright
- De Las Casas Engel, Tomas,Sanchez-Carnerero, Esther M.,Gallardo-Araya, Claudio M.,Jimenez, Florencio Moreno,Maroto, Beatriz Lora,De La Moya Cerero, Santiago,Sokolovskaya, Ekaterina
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p. 771 - 777,7
(2020/07/30)
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- Stereoselective synthesis of carane-based aminodiols as chiral ligands for the catalytic addition of diethylzinc to aldehydes
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Key intermediate epoxy alcohol 4 was prepared regio- and stereoselectively from (+)-3-carene 1 via carene oxide 2 and (-)-trans-allyl alcohol 3. The lithium perchlorate-catalysed ring opening of 4 with secondary and primary achiral and chiral amines resulted in primary, secondary and tertiary aminodiols. Aminodiols 5-14 were applied as chiral catalysts in the enantioselective addition of diethylzinc to benzaldehyde, resulting in (R)- and (S)-1-phenyl-1-propanol with moderate enantioselectivity. N-Benzyl, N-methyl, and (S)- and (R)-N-methylbenzyl derivatives 7 and 10-13 were transformed into 1,3-oxazines 17-21 via highly regioselective ring closures. When 17-21 were applied as chiral catalysts in the addition of diethylzinc to aromatic and aliphatic aldehydes, high chiral induction in the tricyclic catalysts was observed. The effects of the substituents on the nitrogen of the aminodiols and 1,3-oxazines were studied in detail; the best enantioselectivity was observed in the case of N-methylbenzyl-substituted oxazine 19.
- Szakonyi, Zsolt,Csillag, Kinga,Fueloep, Ferenc
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experimental part
p. 1021 - 1027
(2011/09/20)
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- Switching of enantioselectivity in the catalytic addition of diethylzinc to aldehydes by regioisomeric chiral 1,3-amino sulfonamide ligands
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Twenty chiral 1,3-amino sulfonamides of two classes (2a-i and 3a-k) have been prepared from (-)-cis-2-benzamidocyclohexanecarboxylic acid (1) and studied as ligands for catalytic enantioselective addition of Et2Zn to a variety of aromatic and aliphatic aldehydes. The ligands 2 and 3 are regioisomers in which the position of the amine and sulfonamide groups is exchanged. Each class of ligands with the same chirality was shown to afford sec-alcohols with the opposite stereochemistry. Structural surveys revealed that the combination of tertiary amino and p-toluenesufonylamido groups works most effectively for the reaction. Through optimization of the structural and reaction conditions, the best ligands quantitatively provided both enantiomeric secondary alcohols in good to excellent enantioselectivity of up to 94% and 98% ee for (S)- and (R)-enantiomers, respectively.
- Hirose, Takuji,Sugawara, Kazuyuki,Kodama, Koichi
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experimental part
p. 5413 - 5428
(2011/08/05)
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- α-Pinene-type chiral Schiff bases as tridentate ligands in asymmetric addition reactions
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A group of tridentate Schiff bases derived from (+)-α-pinene were synthesized. The steric effects in the transition state, the importance of π-π stacking interactions as well as the electronic effects of aryl aldehydes according to Hammett constant values in the enantioselective addition of Et2Zn to aldehydes with the use of Schiff bases as chiral ligands are described. Also, a variety of aldehydes were cyanated using a catalyst prepared in situ from titanium tetraisopropoxide and chiral Schiff bases. The influence of a conjugated double-bond in the cyanation substrates on enantioselectivity was observed. The chemical structures of the chiral Schiff base-titanium alkoxide complexes are discussed based on their 1H and 13C NMR spectra. 3D models of the Zn2-complex catalyst and Ti-complex catalyst containing α-pinane-type Schiff bases based on X-ray diffraction experiments are postulated. The models presented were consistent with the reported chirality of the addition product and observed ee.
- Jaworska, Magdalena,Blocka, Ewelina,Kozakiewicz, Anna,Welniak, Miroslaw
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experimental part
p. 648 - 657
(2011/07/08)
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- Bidentate Schiff bases derived from (S)-α-methylbenzylamine as chiral ligands in the electronically controlled asymmetric addition of diethylzinc to aldehydes
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A group of bidentate Schiff bases derived from enantiomerically pure (S)-α-methylbenzylamine was synthesized. Crystal structure was determined for three compounds. Schiff bases were used as chiral ligands in the asymmetric addition of Et2Zn to aldehydes. The obtained enantioselectivity was e.e.=8-94% depending on the substrate and the best was observed for (S,E)-2-(1-(1-phenylethylimino)-ethyl)phenol. The enantioselectivity increase was connected with the substituent-induced electronic effects in the substrate molecules. Molecular modeling resulted in the models of the 3D structures of Zn-Zn complex catalysts containing investigated Schiff bases, which were consistent with the reported chirality of the addition product and explained observed e.e. The presented transition state models allow explaining the change of the absolute configuration of diethylzinc addition product in the case of using ortho-substituted aldehydes. ARKAT-USA, Inc.
- Jaworska, Magdalena,Welniak, Miroslaw,Zieciak, Justyna,Kozakiewicz, Anna,Wojtczakb, Andrzej
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experimental part
p. 189 - 204
(2011/08/21)
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- Synthesis of novel 1,4-bissulfonamide ligands for enantioselective addition of diethylzinc to aldehydes
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Several novel chiral sulfonamide ligands based on (1R,2S,4R,5S)-1,4- diamino-2,5-dimethylcyclohexane skeleton have been synthesized and their application in the enantioselective addition of diethylzinc to aldehydes was investigated in the presence of Ti(O
- Yang, Minghua,Sun, Jiangtao,Zhu, Chengjian
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experimental part
p. 1697 - 1702
(2012/01/13)
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- Application of novel enantiopure hydroxymethyl-substituted pyridine derivatives in asymmetric catalysis
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The synthetic modification of enantiopure hydroxymethyl-substituted pyridine derivatives leading to novel chiral ligands is described. A set of these pyridine derivatives was examined as ligands in asymmetric transformations such as enantioselective alkylations or alkynylations of aldehydes, the asymmetric copper-catalyzed Henry reaction and the asymmetric allylation of benzaldehyde with allyl(trichloro)silane. This first screening revealed that several of the pyridine derivatives prepared are effective ligands affording high yields and good enantioselectivities. The asymmetric alkylation of aldehydes with diethylzinc provided yields of up to 93% with an enantiomeric excess of up to 88%. The asymmetric Henry reaction was also efficiently catalyzed by one of the prepared ligands affording (S)-2-nitro-1-phenylethanol in 68% yield and with 70% ee. Copyright
- Eidamshaus, Christian,Reissig, Hans-Ulrich
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experimental part
p. 1644 - 1652
(2012/02/01)
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- A systematic study of chiral homoprolinols and their derivatives in the catalysis of enantioselective addition of diethylzinc to aldehydes
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Homoprolinol analogs, a class of optically active γ-amino alcohols, were examined systematically in the enantioselective addition reactions of diethylzinc to aldehydes. By comparison of the results catalyzed by these γ-amino alcohols with those by the β-amino alcohols based on pyrrolidine architecture reported in the literature references, we have observed that the γ-amino alcohols are superior to the corresponding β-amino alcohols when the nitrogen and the oxygen are unsubstituted. Among the homoprolinols we tested, 2b gave the best results (45-88% yields, 44-81% ee) in the addition reactions. To the best of our knowledge, 2b has been noticed as one of the most efficient γ-amino alcohol catalysts based on pyrrolidine framework.
- Liu, Chang-Lu,Wei, Chang-Yong,Wang, Shi-Wen,Peng, Yun-Gui
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experimental part
p. 921 - 928
(2012/06/17)
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- Synthesis, resolution, and applications of 3-amino-2,2-dimethyl-1,3- diphenylpropan-1-ol, a conformationally restricted 1,3-aminoalcohol
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Efficient synthetic routes to both syn and anti diastereomers of a conformationally restricted 1,3-aminoalcohol were devised. Resolution of the aminoalcohols was accomplished through diastereomeric salt with R-(-)-O-acetyl mandelic acid. These aminoalcoho
- Patil,Gonnade,Joshi
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scheme or table
p. 5036 - 5041
(2010/08/20)
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- Structural and electronic effects of oxazolidine ligands derived from (1R,2S)-ephedrine in the asymmetric addition of diethylzinc to aldehydes
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The purpose of this research was to determine the activity of chiral oxazolidine ligands prepared from (1R,2S)-ephedrine for the enantioselective addition of diethylzinc to aldehydes. The configuration on the newly formed C2 stereogenic center was determined as (2S) by X-ray structural analysis. Oxazolidine ligands reveal medium enantioselectivity with the ee exceeding 57%, and the yields obtained being 68-99%. The results indicate that the absolute configuration of the addition product depends not only on the N3-methyl as an important stereocontrol element but also on both the electronic and steric effects of the substrates and oxazolidine ligands.
- Blocka, Ewelina,Jaworska, Magdalena,Kozakiewicz, Anna,Welniak, Miroslaw,Wojtczak, Andrzej
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experimental part
p. 571 - 577
(2010/08/06)
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- (1R,5R)-1-(1-dimethylaminoethyl)-2-isopropylidene-5-methylcyclohexanol as a chiral ligand in the enantioselective addition of diethylzinc to aldehydes
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An efficient chiral ligand, (1R,5R)-1-(1-dimethylaminoethyl)-2- isopropylidene-5-methylcyclohexanol, has been developed for the enantioselective addition of diethylzinc to some prochiral aldehydes to afford S-alcohols. The overall conversion rate was 80-98% with excellent enantiomeric excess (79-98%). Georg Thieme Verlag Stuttgart ? New York.
- Yadav, Ashok K.,Kumar, Manoj,Yadav, Tripti,Jain, Renuka
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scheme or table
p. 712 - 714
(2010/06/13)
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- Structurally constrained C1-1,1′-bisisoquinoline-based chiral ligands: geometrical implications on enantioinduction in the addition of diethylzinc to aldehydes
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New highly constrained chiral C1-1,1′-bisisoquinoline ligands have been synthesized. X-ray crystallographic analysis of these ligands showed peculiar structural differences between the parent 1′,2′,3′,4′-tetrahydro-1,1′-bisisoquinolin e and its alkyl, acyl and sulfonyl derivatives. The consequences of their geometrical conformations on enantioinduction were examined by employing the enantioselective addition of diethylzinc to aldehydes. Such conformations greatly affected the catalytic efficiency of these ligands.
- Qi, Gao,Judeh, Zaher M.A.
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experimental part
p. 429 - 436
(2010/07/02)
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- Enantioselective addition of diethylzinc to aldehydes catalyzed by d-glucosamine derivatives: Highly pronounced effect of trifluoromethylsulfonamide
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We present the synthesis of β-hydroxy sulfonamides derived from d-glucosamine and their application as ligands in titanium tetraisopropoxide promoted enantioselective addition of diethylzinc to benzaldehyde and selected aromatic and aliphatic aldehydes. The N-trifluoromethylosulfonamido-d-glucosamine derivative is one of the most active ligands known and only 1 mol% of the ligand is sufficient for efficient catalysis of diethylzinc addition. The reaction is highly enantioselective for some aromatic aldehydes and enantiomeric excess up to 99% was obtained.
- Bauer, Tomasz,Smoliński, S?awomir
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experimental part
p. 247 - 251
(2010/11/18)
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- The synthesis of new oxazoline-containing bifunctional catalysts and their application in the addition of diethylzinc to aldehydes
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The straightforward preparation of new modular oxazoline-containing bifunctional catalysts is reported employing a microwave-assisted Buchwald-Hartwig aryl amination as the key step. Covalent attachment of 2-(o-aminophenyl)oxazolines and pyridine derivati
- Coeffard, Vincent,Mueller-Bunz, Helge,Guiry, Patrick J.
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experimental part
p. 1723 - 1734
(2009/06/27)
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- Synthesis of new Schiff base-camphorsulfonyl amide ligands and in situ screening in the asymmetric additions of organozinc reagents to aldehydes
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We have designed and synthesized a new library of highly modular Schiff base-camphorsulfonyl amide ligands from readily available starting materials. These ligands have been used in the asymmetric addition of diethyl zinc to aldehydes in good yields (up to 91%) and high enantioselectivities (up to 93%). Moreover, when the ligands were used in the asymmetric addition of phenylacetylene to aldehydes, good yields and moderate to high ee values (up to 90%) were obtained. The introduction of the camphorsulfonyl moiety into the ligands is highly critical for the selectivities of the reactions.
- Sun, Jiangtao,Pan, Xu,Dai, Zhenya,Zhu, Chengjian
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experimental part
p. 2451 - 2457
(2009/04/11)
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