- Deactivation mechanisms of iodo-iridium catalysts in chiral amine racemization
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The homogenous, [IrCp?I2]2, SCRAM catalyst (1) is active in the racemization of chiral amines. NMR, kinetic and structural mechanistic studies have determined the cause of catalyst deactivation to occur when ammonia or methylamine are liberated by hydrolysis or aminolysis of the intermediate imine, which tightly coordinate to the iridium centre to block turnover. Control of moisture and substrate concentration can suppress deactivation, whilst partial reactivation of spent catalyst was identified using hydroiodic acid.
- Kwan, Maria H.T.,Pokar, Nisha P.B.,Good, Catherine,Jones, Martin F.,Munday, Rachel,Screen, Thomas,Blacker, A. John
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supporting information
(2020/12/29)
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- Screening and characterization of a diverse panel of metagenomic imine reductases for biocatalytic reductive amination
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Finding faster and simpler ways to screen protein sequence space to enable the identification of new biocatalysts for asymmetric synthesis remains both a challenge and a rate-limiting step in enzyme discovery. Biocatalytic strategies for the synthesis of chiral amines are increasingly attractive and include enzymatic asymmetric reductive amination, which offers an efficient route to many of these high-value compounds. Here we report the discovery of over 300 new imine reductases and the production of a large (384 enzymes) and sequence-diverse panel of imine reductases available for screening. We also report the development of a facile high-throughput screen to interrogate their activity. Through this approach we identified imine reductase biocatalysts capable of accepting structurally demanding ketones and amines, which include the preparative synthesis of N-substituted β-amino ester derivatives via a dynamic kinetic resolution process, with excellent yields and stereochemical purities. [Figure not available: see fulltext.]
- Marshall, James R.,Yao, Peiyuan,Montgomery, Sarah L.,Finnigan, James D.,Thorpe, Thomas W.,Palmer, Ryan B.,Mangas-Sanchez, Juan,Duncan, Richard A. M.,Heath, Rachel S.,Graham, Kirsty M.,Cook, Darren J.,Charnock, Simon J.,Turner, Nicholas J.
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p. 140 - 148
(2021/01/04)
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- Synthesis of limonene β-amino alcohol from (R)-(+)-α-methylbenzylamine and (+)-limonene 1,2-epoxide
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Two new compounds of β-amino alcohol are obtained using (R) - (+) - α-methylbenzylamine as starting material which is converted into two amines. Each of these compounds reacted in excess with a 1: 1 mixture of cis and trans-limonene oxide in the presence of water as a catalyst. The products obtained show that β-amino alcohol derived from trans-limonene oxide is obtained and unreacted cis-limonene oxide from the reaction mixture as well as the amine is attained. Whereas the addition of the synthesized carbamate of the same primary amine over the 1: 1 mixture of cis and trans -limonene oxide in the presence of water results in the hydrolysis product and the recovery of unreacted trans-limonene oxide.
- Ait Said, Lyazid,El Bachiri, Abdelhadi,El Haimer, Chaimaa,El Hammoumi, Mohamed Merouane,Khoukhi, Mostafa
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- Tackling N-Alkyl Imines with 3d Metal Catalysis: Highly Enantioselective Iron-Catalyzed Synthesis of α-Chiral Amines
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A readily activated iron alkyl precatalyst effectively catalyzes the highly enantioselective hydroboration of N-alkyl imines. Employing a chiral bis(oxazolinylmethylidene)isoindoline pincer ligand, the asymmetric reduction of various acyclic N-alkyl imines provided the corresponding α-chiral amines in excellent yields and with up to >99 % ee. The applicability of this base metal catalytic system was further demonstrated with the synthesis of the pharmaceuticals Fendiline and Tecalcet.
- Blasius, Clemens K.,Gade, Lutz H.,Heinrich, Niklas F.,Vasilenko, Vladislav
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p. 15974 - 15977
(2020/07/04)
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- Asymmetric Synthesis of Primary and Secondary β-Fluoro-arylamines using Reductive Aminases from Fungi
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The synthesis of chiral amines is of central importance to pharmaceutical chemistry, and the inclusion of fluorine atoms in drug molecules can both increase potency and slow metabolism. Optically enriched β-fluoroamines can be obtained by the kinetic resolution of racemic amines using amine transaminases (ATAs), but yields are limited to 50 %, and also secondary amines are not accessible. In order to overcome these limitations, we have applied NADPH-dependent reductive aminase enzymes (RedAms) from fungal species to the reductive amination of α-fluoroacetophenones with ammonia, methylamine and allylamine as donors, to yield β-fluoro primary or secondary amines with >90 % conversion and between 85 and 99 % ee. In addition, the effect of the progressive introduction of fluorine atoms to the α-position of the acetophenone substrate reveals the effect of mono-, di- and tri-fluorination on the proportion of amine and alcohol in product mixtures, shedding light on the promiscuous ability of imine reductase (IRED)-type dehydrogenases to reduce fluorinated acetophenones to alcohols.
- González-Martínez, Daniel,Cuetos, Aníbal,Sharma, Mahima,García-Ramos, Marina,Lavandera, Iván,Gotor-Fernández, Vicente,Grogan, Gideon
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p. 2421 - 2425
(2020/03/25)
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- CHIRALITY SENSING WITH MOLECULAR CLICK CHEMISTRY PROBES
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The present invention relates to an analytical method that includes providing a sample potentially containing a chiral analyte that can exist in stereoisomeric forms, and providing a probe selected from the group consisting of coumarin-derived Michael acceptors, dinitrofluoroarenes and analogs thereof, arylsulfonyl chlorides and analogs thereof, arylchlorophosphines and analogs thereof, aryl halophosphites, and halodiazaphosphites. The sample is contacted with the probe under conditions to permit covalent binding of the probe to the analyte, if present in the sample; and, based on any binding that occurs, the absolute configuration of the analyte in the sample, and/or the concentration of the analyte in the sample, and/or the enantiomeric composition of the analyte in the sample is/are determined. The probe may be a coumarin-derived Michael acceptor, a di nitrofluoroarene or analog thereof, an arylsulfonyl chloride or analog thereof, an arylchlorophosphine or analog thereof, an aryl halophosphite, or a halodiazaphosphite.
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- Secondary amines as coupling partners in direct catalytic asymmetric reductive amination
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The secondary amine participating asymmetric reductive amination remains an unsolved problem in organic synthesis. Here we show for the first time that secondary amines are capable of effectively serving as N-sources in direct asymmetric reductive amination to afford corresponding tertiary chiral amines with the help of a selected additive set under mild conditions (0-25 °C). The applied chiral phosphoramidite ligands are readily prepared from BINOL and easily modified. Compared with common tertiary chiral amine synthetic methods, this procedure is much more concise and scalable, as exemplified by the facile synthesis of rivastigmine and N-methyl-1-phenylethanamine.
- Wu, Zitong,Du, Shaozhi,Gao, Guorui,Yang, Wenkun,Yang, Xiongyu,Huang, Haizhou,Chang, Mingxin
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p. 4509 - 4514
(2019/04/29)
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- A general and atom-efficient continuous-flow approach to prepare amines, amides and imines via reactive N-chloramines
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Chloramines are an important class of reagents, providing a convenient source of chlorine or electrophilic nitrogen. However, the instability of these compounds is a problem which makes their isolation and handling difficult. To overcome these hazards, a continuous-flow approach is reported which generates and immediately reacts N-chloramines directly, avoiding purification and isolation steps. 2-Chloramines were produced from the reaction of styrenes with N-alkyl-N-sulfonyl-N-chloramines, whilst N-alkyl or N,N’-dialkyl-N-chloramines reacted with anisaldehyde in the presence of t-BuO2H oxidant to afford amides. Primary and secondary imines were produced under continuous conditions from the reaction of N-chloramines with base, with one example subsequently reduced under asymmetric conditions to produce a chiral amine in 94% ee.
- Jolley, Katherine E.,Chapman, Michael R.,John Blacker
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p. 2220 - 2228
(2018/09/04)
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- Stereogenic Lock in 1-Naphthylethanamine Complexes for Catalyst and Auxiliary Design: Structural and Reactivity Analysis for Cycloiridated Pseudotetrahedral Complexes
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A series of optically active pseudo-tetrahedral five-membered cyclometalated 1-naphthylethanamine iridium(III) complexes were prepared and characterized to analyze the efficacy of the stereogenic conformational lock in both solid and solution phases. The synthesis of the iridacycles was diastereoselective, and the compounds were found to be conformationally rigid. In comparison to its phenyl derivative, the structural lock prevented oxidation of the amine moiety within the five-membered organometallic ring during its synthesis. With up to three stereogenic centers in one of the naphthalene complexes, the stereochemistry of the metallacycle remained stable to both thermal and chemical changes. In terms of catalytic performance, the complexes displayed excellent activity for the asymmetric hydrogen transfer reaction, albeit with modest enantioselectivities.
- Chen, Houguang Jeremy,Hong Xiang Teo, Ronald,Li, Yongxin,Pullarkat, Sumod A.,Leung, Pak-Hing
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supporting information
p. 99 - 106
(2018/01/17)
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- Direct Asymmetric Hydrogenation of N-Methyl and N-Alkyl Imines with an Ir(III)H Catalyst
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A novel cationic [IrH(THF)(P,N)(imine)] [BArF] catalyst containing a P-stereogenic MaxPHOX ligand is described for the direct asymmetric hydrogenation of N-methyl and N-alkyl imines. This is the first catalytic system to attain high enantioselectivity (up to 94% ee) in this type of transformation. The labile tetrahydrofuran ligand allows for effective activation and reactivity, even at low temperatures. Density functional theory calculations allowed the rationalization of the stereochemical course of the reaction.
- Salomó, Ernest,Gallen, Albert,Sciortino, Giuseppe,Ujaque, Gregori,Grabulosa, Arnald,Lledós, Agustí,Riera, Antoni,Verdaguer, Xavier
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supporting information
p. 16967 - 16970
(2018/12/14)
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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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- Imine Reductase-Catalyzed Intermolecular Reductive Amination of Aldehydes and Ketones
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Imine reductases (IREDs) have emerged as promising biocatalysts for the synthesis of chiral amines. In this study, the asymmetric imine reductase-catalyzed intermolecular reductive amination with NADPH as the hydrogen source was investigated. A highly chemo- and stereoselective imine reductase was applied for the reductive amination by using a panel of carbonyls with different amine nucleophiles. Primary and secondary amine products were generated in moderate to high yields with high enantiomeric excess values. The formation of the imine intermediate was studied between carbonyl substrates and methylamine in aqueous solution in the pH range of 4.0 to 9.0 by 1H NMR spectroscopy. We further measured the kinetics of the reductive amination of benzaldehyde with methylamine. This imine reductase-catalyzed approach constitutes a powerful and direct method for the synthesis of valuable amines under mild reaction conditions. IRED all about it: The intermolecular asymmetric reductive amination of carbonyls catalyzed by a stereoselective imine reductase produces chiral amines in high yields with high enantioselectivities. The reaction efficiency is attributed to its remarkable tolerance to high concentrations of amine nucleophiles, high pH values, high chemoselectivity towards imines, and high stereoselectivity of the biocatalyst.
- Scheller, Philipp N.,Lenz, Maike,Hammer, Stephan C.,Hauer, Bernhard,Nestl, Bettina M.
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p. 3239 - 3242
(2015/10/28)
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- Disulfonimide-Catalyzed Asymmetric Reduction of N-Alkyl Imines
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A chiral disulfonimide (DSI)-catalyzed asymmetric reduction of N-alkyl imines with Hantzsch esters as a hydrogen source in the presence of Boc2O has been developed. The reaction delivers Boc-protected N-alkyl amines with excellent yields and enantioselectivity. The method tolerates a large variety of alkyl amines, thus illustrating potential for a general reductive cross-coupling of ketones with diverse amines, and it was applied in the synthesis of the pharmaceuticals (S)-Rivastigmine, NPS R-568 Hydrochloride, and (R)-Fendiline. A chiral disulfonimide (DSI)-catalyzed asymmetric reduction of N-alkyl imines with Hantzsch esters as a hydrogen source in the presence of Boc2O was developed. The reaction delivers Boc-protected N-alkyl amines with excellent yields and enantioselectivity. The method was successfully applied to the synthesis of the pharmaceuticals (S)-Rivastigmine, NPS R-568 Hydrochloride, and (R)-Fendiline.
- Wakchaure, Vijay N.,Kaib, Philip S. J.,Leutzsch, Markus,List, Benjamin
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supporting information
p. 11852 - 11856
(2015/10/05)
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- Chiral molecular tweezers: Synthesis and reactivity in asymmetric hydrogenation
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We report the synthesis and reactivity of a chiral aminoborane displaying both rapid and reversible H2 activation. The catalyst shows exceptional reactivity in asymmetric hydrogenation of enamines and unhindered imines with stereoselectivities of up to 99% ee. DFT analysis of the reaction mechanism pointed to the importance of both repulsive steric and stabilizing intermolecular non-covalent forces in the stereodetermining hydride transfer step of the catalytic cycle.
- Lindqvist, Markus,Borre, Katja,Axenov, Kirill,Kótai, Bianka,Nieger, Martin,Leskel?, Markku,Pápai, Imre,Repo, Timo
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supporting information
p. 4038 - 4041
(2015/04/14)
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- Characterization of three novel enzymes with imine reductase activity
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Imine reductases (IRED) are promising catalysts for the synthesis of optically pure secondary cyclic amines. Three novel IREDs from Paenibacillus elgii B69, Streptomyces ipomoeae 91-03 and Pseudomonas putida KT2440 were identified by amino acid or structural similarity search, cloned and recombinantly expressed in E. coli and their substrate scope was investigated. Besides the acceptance of cyclic amines, also acyclic amines could be identified as substrates for all IREDs. For the IRED from P. putida, a crystal structure (PDB-code 3L6D) is available in the database, but the function of the protein was not investigated so far. This enzyme showed the highest apparent E-value of approximately Eapp = 52 for (R)-methylpyrrolidine of the IREDs investigated in this study. Thus, an excellent enantiomeric purity of >99% and 97% conversion was reached in a biocatalytic reaction using resting cells after 24 h. Interestingly, a histidine residue could be confirmed as a catalytic residue by mutagenesis, but the residue is placed one turn aside compared to the formally known position of the catalytic Asp187 of Streptomyces kanamyceticus IRED.
- Gand,Müller,Wardenga,H?hne
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p. 126 - 132
(2015/02/19)
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- Chiral aminophosphines as catalysts for enantioselective double-michael indoline syntheses
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The bisphosphine-catalyzed double-Michael addition of dinucleophiles to electron-deficient acetylenes is an efficient process for the synthesis of many nitrogencontaining heterocycles. Because the resulting heterocycles contain at least one stereogenic center, this double-Michael reaction would be even more useful if an asymmetric variant of the reaction were to be developed. Aminophosphines can also facilitate the double-Michael reaction and chiral amines are more readily available in Nature and synthetically; therefore, in this study we prepared several new chiral aminophosphines. When employed in the asymmetric double-Michael reaction between ortho-tosylamidophenyl malonate and 3-butyn-2-one, the chiral aminophosphines produced indolines in excellent yields with moderate asymmetric induction.
- Khong, San N.,Kwon, Ohyun
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scheme or table
p. 5626 - 5650
(2012/07/03)
-
- Cyanative self-condensation of aromatic aldehydes promoted by VO(O iPr)3-Lewis base as a cooperative catalyst
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Self-condensation of aromatic aldehydes with trimethylsilyl cyanide proceeded by the cooperative catalytic effect of VO(OiPr)3 and a Lewis base to give the corresponding O-acylated cyanohydrins. The reaction conversion and selectivity were strongly dependent on the solvent used, the Lewis base, and the presence of oxygen. All the nine kinds of aromatic aldehydes considered herein afforded the O-acylated cyanohydrins with excellent selectivity under an O2 atmosphere.
- Kodama, Koichi,Kawamata, Hiroaki,Takahashi, Naoya,Hirose, Takuji
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p. 9440 - 9446
(2013/01/15)
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- Asymmetric control in Diels-Alder cycloadditions of chiral 9-aminoanthracenes by relay of stereochemical information
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Two approaches to the synthesis of chiral 9-amino anthracenes are described. The first, by nucleophilic addition of organolithium reagents to imines promoted by BF3·OEt2, unexpectedly provided stable aminoboranes as products. The second approach, using palladium catalysed cross coupling, was more successful for primary amines, and the key 9-(α-methylbenzylamino)anthracene subjected to cycloadditions with N-methyl maleimide and maleic anhydride. Excellent reactivity was achieved with good levels of diastereoselectivity, through a favourable combination of electrostatic and hydrogen bonding effects. Trial studies of the retro Diels-Alder reaction of these cycloadducts were also performed.
- Adams, Harry,Bawa, Ramadan A.,McMillan, Keith G.,Jones, Simon
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p. 1003 - 1012
(2008/02/03)
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- CATALYST COMPOSITIONS AND THEIR USE IN THE DE-ENRICHMENT OF ENANTIOMERICALLY ENRICHED SUBSTRATES
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There is provided a process for the de-enrichment of enantiomerically enriched compositions which comprises reacting an enantiomerically enriched composition comprising at least a first enantiomer or diastereomer of a substrate comprising a carbon-heteroatom bond, wherein the carbon is a chiral centre and the heteroatom is a group V heteroatom, in the presence of a catalyst system and optionally a reaction promoter to give a product composition comprising first and second enantiomers or diastereomers of the substrate having a carbon-heteroatom bond, the ratio of second to first enantiomer or disatereomer in the product composition being greater than the ratio of second to first enantiomer or disatereomer in the enantiomerically enriched composition. Preferred catalyst systems include transition metal halide complex of the formula MnXpYr wherein M is a transition metal; X is a halide; Y is a neutral optionally substituted hydrocarbyl complexing group, a neutral optionally substituted perhalogenated hydrocarbyl complexing group, or an optionally substituted cyclopentadienyl complexing group; and n, p and r are integers. The reaction promoter is preferably a halide salt.
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-
Page/Page column 13-15
(2008/06/13)
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- ASYMMETRIC IMINE HYDROGENATION PROCESSES
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A process for the catalytic hydrogenation or asymmetric hydrogenation of imines of Formula (I) to the corresponding amines of Formula (II) is provided in which R1 is aryl ; R2 is aryl, cyclic, alkyl, alkenyl or alkynyl; and R3 is alky l. The catalytic system includes a ruthenium complex containing (1) a diamine and (2) a diphosphine or two monodentate phosphines ligands. Such process also relates to the asymmetric hydrogenation of prochiral imines to the chiral amines using chiral ruthenium complexes bearing chiral diphosphines or chiral monodentate phosphines and chiral diamines.
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Page/Page column 27
(2008/06/13)
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- ortho-anisylsulfonyl as a protecting group for secondary amines: Mild Ni0-catalyzed hydrodesulfonylation
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A potentially good alternative to the tosyl group (Ts) as a protecting group for amines is N-ortho-anisylsulfonyl (Ans), which is readily cleaved under mild, Ni0-catalyzed reductive conditions (see scheme, acac = acetylacetonate). N-Anisylation of primary amines followed by alkylation and deprotection provides a route to a range of secondary amines.
- Milburn, Robert R.,Snieckus, Victor
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p. 892 - 894
(2007/10/03)
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- Asymmetric reduction of ketoxime derivatives and N-alkylketimines with borane-oxazaborolidine adducts
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Oxime ethers of acetophenone, isopropyl methyl ketone, and tert-butyl methyl ketone were reduced to the corresponding hydroxylamine ethers of 45-94% ee with borane-oxazaborolidine 1 derived from (-)-norephedrine. A one-pot reduction of acetophenone oxime with 1 to 1-phenylethylhydroxylamine of 87% ee is described. The reduction of 6-methyl-2,3,4,5-tetrahydropyridine and N-methylimines of the above mentioned ketones with borane-B-methyloxazaborolidine adduct 2, derived from (-)-diphenylprolinol, gave the corresponding amines of 40-74% ee.
- Krzeminski, Marek P.,Zaidlewicz, Marek
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p. 1463 - 1466
(2007/10/03)
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- Efficient Cs2CO3-promoted solution and solid phase synthesis of carbonates and carbamates in the presence of TBAI
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Novel solution and solid-phase methods for the synthesis of carbonates and carbamates were developed using cesium bases and TBAI via a three-component coupling. Cesium carbonate not only promoted successful carbonylations of alcohols and carbamations of amines, but also suppressed common side reactions traditionally seen using existing protocols. Various alcohols and amines were examined, using a wide array of alkyl halides, and the results demonstrated this methodology was highly chemoselective. In particular, use of either sterically demanding substrates or amino acid derivatives afforded the corresponding products exclusively, offering a wide variety of applications such as novel protecting groups and peptidomimetic syntheses.
- Salvatore, Ralph N,Chu, Feixia,Nagle, Advait S,Kapxhiu, Elona A,Cross, Richard M,Jung, Kyung Woon
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p. 3329 - 3347
(2007/10/03)
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- Diastereoselective carbozincation of propargylic amines
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The carbometalation of propargylic amines derived from methylbenzylamine takes place with good 1,3-diastereoselection in the presence of Lewis acids.
- Rezaei, Hadi,Marek, Ilan,Normant, Jean F
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p. 2477 - 2483
(2007/10/03)
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- 163. Chiral diselenides from benzylamines: Catalysts in the diethylzinc addition to aldehydes
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A series of new chiral diselenides with a N-atom in the side chain was prepared by a short synthetic sequence (Scheme 1). Only 1 mol-% of these diselenides catalyzed very effectively the diethylzinc addition to various aromatic and α,β-unsaturated aldehyd
- Wirth, Thomas,Kulicke, Klaus J.,Fragale, Gianfranco
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p. 1957 - 1966
(2007/10/03)
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- Stereoselective α-Methylation of N-Methyl Benzylamine via a Combination of Chromium Tricarbonyl and Chiral Formamidine Methodologies.
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Whereas carbanions of formamidines derived from N-methyl benzylamine and L-valinol or L-leucinol undergo electrophilic benzylic methylation with poor stereoselectivities (d.e. 17-26percent), enhanced stereoselectivities (d.e. 74-84percent) are observed for the corresponding chromium tricarbonyl complexes.
- Albert, Joan,Davies, Stephen G.
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p. 5945 - 5948
(2007/10/02)
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- Amidures de lithium chiraux; β-elimination de trityllithium a partir d'un amidure de lithium
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The synthesis of a chiral secondary amine bearing a N-CH2-trityl moiety is described.The formation of the corresponding lithium amide results in the β-elimination of trityllithium, leading to an intermediate methyleneamiine, which can react with nucleophiles.
- Plaquevent, Jean-Christophe,Ravard, Alain
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p. C51 - C53
(2007/10/02)
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- DERIVATIVES OF OPTICALLY ACTIVE (1-PHENYLETHYL)AMINE IN COMPLEXES WITH LITHIUM ALUMINUM HYDRIDE FOR THE ASYMMETRIC REDUCTION OF A CARBONYL GROUP
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(R)-1-Phenylethanol is formed preferentially in the reduction of acetophenone by the complexes of lithium aluminum hydride with (-)-(2-hydroxyethyl)(1-phenylethyl)amine and (-)-methyl(2-hydroxyethyl)(1-phenylmethyl)amine.
- Potapov, V. M.,Dem'yanovich, V. M.,Maleev, V. I.
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p. 1606 - 1609
(2007/10/02)
-
- Base Catalysed Rearrangements involving Ylide Intermediates. Part 18. Competing , , and Rearrangements of Ammonium Ylides
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The rearrangements of acyl stabilised ammonium ylides are, in several cases, accompanied by competing rearrangements and in one case by a rearrangement.For examples involving migrating benzyl or phenylethyl groups the mechanism of these rearrangements has been studied.Thus the competing , , and rearrangements of the ylide (12) are largely intramolecular, but the intermolecularity is as high as 28percent for the and rearrangements and 14percent for the rearrangement in methanol at 55 deg C.The competing and rearrangements of the optically active (29a) give products with predominant retention of the configuration of the migrating phenylethyl group, but the intramolecular stereoselectivity of the rearrangement is significantly greater than that of the rearrangement.These results are consistent with a radical pair pathway for all three modes of rearrangement.Suitably substituted acyl stabilised allylammonium ylides (55) rearrange by competing , and processes.
- Chantrapromma, Kan,Ollis, W. David,Sutherland, Ian O.
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p. 1049 - 1062
(2007/10/02)
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- Derecemization par protonation enantioselective. Application a un α-aminoacide, la phenylglycine
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This work describes the application of deracemization by enantioselective protonation to α-aminoacid derivatives.Esters of phenylglycine are readly converted into Schiff bases.Melanation of the latter by a lithium amide, followed by protonation by a chiral acid, leads to the optically active starting materials (e.e. as high as 70percent).Chiral acids can easily be retrieved after protonation with excellent yields and conservation of enantiomeric purity.A mechanism responsible for the asymmetric induction is suggested by means of a study of the parameters modifying the selectivity, such as the nature of protecting groups, chiral acid, and lithium amide.
- Duhamel, Lucette,Plaquevent, Jean-Christophe
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- STEREOCHEMICAL INVESTIGATIONS. LII. CHIRAL AMIDES OF o-HYDROXY- AND o-METHOXY-SUBSTITUTED BENZOIC ACIDS
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A number of o-hydroxy- and o-methoxybenzamides have been obtained from (-)-α-phenylamine, (+)-α-benzylethylamine, and (-)-1,2-diphenylethylamine, and their UV, IR, PMR, and CD spectra have been studied.The chiral optical properties of these amides are determined primarily by the nature of the cyclic structure which can form as a result of intramolecular hydrogen bonding.
- Solov'eva, L. D.,Dem'yanovich, V. M.,Potapov, V. M.
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p. 1099 - 1105
(2007/10/02)
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- Deracemization by enantioselective protonation IV an improved method for the enantiomeric enrichment of α-aminoacids using metalation by means of chiral amides
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Optically active α-aminoesters are obtained by metalation of the corresponding Schiff bases by chiral lithium amide followed by protonation by an achiral or a chiral acid. 70 % e.e. can be obtained.
- Duhamel, Lucette,Plaquevent, Jean-Christophe
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p. 2521 - 2524
(2007/10/02)
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