- Heteroleptic enantiopure Pd(ii)-complexes derived from halogen-substituted Schiff bases and 2-picolylamine: Synthesis, experimental and computational characterization and investigation of the influence of chirality and halogen atoms on the anticancer acti
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Seven enantiomeric pairs of palladium complexes, [Pd(pic)(R or S)-N-1-(phenyl)ethyl-2,4-X1,X2-salicylaldiminate)]NO3, [Pd(pic)(R or S)]NO3 (X1 = X2 = Cl, Br, I, H; X1/X2 = Br/Cl), were synthesized by the reaction of enantiopure halogen-substituted Schiff
- Kordestani, Nazanin,Amiri Rudbari, Hadi,Correia, Isabel,Valente, Andreia,C?rte-Real, Leonor,Islam, Mohammad Khairul,Micale, Nicola,Braun, Jason D.,Herbert, David E.,Tumanov, Nikolay,Wouters, Johan,Enamullah, Mohammed
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p. 9163 - 9180
(2021/06/06)
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- A Practical Electrophilic Nitrogen Source for the Synthesis of Chiral Primary Amines by Copper-Catalyzed Hydroamination
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A mild and practical method for the catalytic installation of the amino group across alkenes and alkynes has long been recognized as a significant challenge in synthetic chemistry. As the direct hydroamination of olefins using ammonia requires harsh conditions, the development of suitable electrophilic aminating reagents for formal hydroamination methods is of importance. Herein, we describe the use of 1,2-benzisoxazole as a practical electrophilic primary amine source. Using this heterocycle as a new amino group delivery agent, a mild and general protocol for the copper-hydride-catalyzed hydroamination of alkenes and alkynes to form primary amines was developed. This method provides access to a broad range of chiral α-branched primary amines and linear primary amines, as demonstrated by the efficient synthesis of the antiretroviral drug maraviroc and the formal synthesis of several other pharmaceutical agents.
- Guo, Sheng,Yang, Jeffrey C.,Buchwald, Stephen L.
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p. 15976 - 15984
(2018/11/23)
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- Aggregation-induced emission enhancement of chiral boranils
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New boranils based on chiral benzylamines have been synthesized and their photophysical properties studied. These BF2-complexes exhibit a bright blue fluorescence in solution and in the solid state, and exhibit aggregation-induced emission enhancement. The chirality of the ligand, even if it is not directly located at the boron center, has consequences on the circular dichroism of the complexes.
- Vaz, Patrícia A. A. M.,Rocha, Jo?o,Silva, Artur M. S.,Guieu, Samuel
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p. 18166 - 18171
(2018/11/23)
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- Synthesis, characterization and crystal structures of ruthenium complexes with bidentate chiral salicylaldiminato ligands
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Condensations of salicylaldehyde and 4-chlorosalicylaldehyde with (R)-α-methylbenzylamine in refluxing ethanol afforded the chiral Schiff base ligands (R)-N-(1-phenylethyl)salicylidene (HL1?) and (R)-N-(1-phenylethyl)(4-chlorosalicylidene) (HL2?), respectively. Similarly, reaction of 3,5-di-tert-butylsalicylaldehyde and (S)-2-amino-3-methylbutan-1-ol gave the chiral Schiff base ligand (S)-N-(1-hydroxymethylisobutyl)(3,5-di-tert-butylsalicylidene) (HL3?). Treatment of (Et4N)[RuCl4(MeCN)2] and [RuCl3(NO)(PPh3)2] with HL1? in the presence of triethylamine afforded an anionic ruthenium(III) complex (R,R)-(Et4N)[Ru(κ2-N,O-L1?)2Cl2] (1) and a neutral ruthenium(II) nitrosyl complex (R)-[Ru(κ2-N,O-L1?)(NO)Cl2(PPh3)] (2), respectively. Interaction of [RuCl2(PPh3)3] and 2 equiv. HL2? led to isolation of a ruthenium(III) complex (R,R)-[Ru(κ2-N,O-L2?)2Cl(PPh3)] (3). Reaction of [Ru(NO)Cl3·xH2O] and HL3? gave an anionic ruthenium(II) nitrosyl complex (S)-(Et3NH)[Ru(κ2-N,O-L3?)(NO)Cl3] (4). The molecular structures of ligands HL1? HL2? and ruthenium complexes 1–4 have been determined by single-crystal X-ray crystallography.
- Tang, Li-Hua,Chen, Xin,Jia, Ai-Quan,Xin, Zhi-Feng,Zhang, Qian-Feng
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p. 120 - 127
(2018/05/09)
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- Asymmetric induction in the addition of enantiomerically pure H-phosphinate to chiral aldimines: diastereoselective generation of α-amino phosphinates with P,C-stereogenic centers
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α-Amino phosphinates with P,C-stereogenic centers were prepared from a P-retained addition of (RP)-(?)-menthyl H-phenylphosphinate to (R)-aldimines with up to 86:14 dr under catalyst and solvent free condition at ambient temperature; the single
- Yang, Meng,Xu, Hao,Zhou, Zhong-Yang,Zhang, He,Liu, Li-Juan,Sun, Yong-Ming,Nie, Shao-Zhen,Zhao, Chang-Qiu
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supporting information
p. 815 - 822
(2016/09/02)
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- Stereoselective addition of dialkyl phosphites to di-salicylaldimines bearing the (R,R)-1,2-diaminocyclohexane moiety
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The addition of dialkyl phosphites to the azomethine bond of N,N′-disalicylidene-1,2-diaminocyclohexane imines, catalyzed by sodium hydride led to bis-aminophosphonates in a high diastereoselectivity. One of the bis-aminophosphonates was analyzed by X-ray
- Lewkowski, Jaros?aw,Tokarz, Pawe?,Lis, Tadeusz,?lepokura, Katarzyna
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p. 810 - 816
(2014/01/23)
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- Chiroptical inversion induced by rotation of a carbon-carbon single bond: An experimental and theoretical study
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We propose a new strategy to construct chiral molecular switches with highly reversible and sensitive chiroptical responses to variations in the external environment. Its fundamental concept involves a stimuli-triggered exchange of two conformations presenting significantly different chiroptical properties through the rotation of a carbon-carbon single bond, as demonstrated by chiral Schiff bases s-1, s-2, and a salicylamide analogue s-3. Upon addition of base in solution, the circular dichroism (CD) spectra of these molecular switches displayed unique changes featuring an inversion of the Cotton effect's signs, and the original CD profiles can be recoverd by acidification. Various spectroscopic studies as well as the conformational analysis combining with TDDFT computations allowed clear elucidation of the chiroptical inversion mechanism. It is expected that this kind of chiroptical switches is of great interest for molecular recognition, chemosensing, and the construction of molecular-scale devices. Furthermore, the present study indicates that the use of the conformational transition about a single bond may serve as the basis for designing chiroptical inversion systems.
- Lu, Wei,Du, Ganhong,Liu, Keyuan,Jiang, Liming,Ling, Jun,Shen, Zhiquan
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p. 283 - 292
(2014/02/14)
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- Design of chiral sulfoxide-Schiff base hybrids and their application in Cu-catalyzed asymmetric Henry reactions
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A new class of chiral sulfoxide-Schiff base ligands has been developed by the rational combination of two privileged chiral backbones. These sulfoxide-Schiff base ligands were found to be highly efficient for Cu-catalyzed asymmetric Henry reactions (up to
- Cheng, Hong-Gang,Lu, Liang-Qiu,Wang, Tao,Chen, Jia-Rong,Xiao, Wen-Jing
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supporting information; experimental part
p. 5596 - 5598
(2012/07/03)
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- Chiral discrimination asserted by enantiomers of Ni (II), Cu (II) and Zn (II) Schiff base complexes in DNA binding, antioxidant and antibacterial activities
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Chiral Schiff base ligands (S)-H2L and (R)-H2L and their complexes (S-Ni-L, R-Ni-L, S-Cu-L, R-Cu-L, S-Zn-L and R-Zn-L) were synthesized, characterized and examined for their DNA binding, antioxidant and antibacterial activities. The
- Khan, Noor-Ul Hasan,Pandya, Nirali,Prathap, K. Jeya,Kureshy, Rukhsana Ilays,Abdi, Sayed Hasan Razi,Mishra, Sandhya,Bajaj, Hari Chandra
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experimental part
p. 199 - 208
(2011/11/29)
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- Rapid, in situ synthesis of bidentate ligands: Chromatography-free generation of catalyst libraries
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The parallel synthesis of chiral bidentate ligands and their subsequent use in situ for a catalytic process is described. The ligands thus prepared gave comparable results to those obtained when the ligands were synthesized and purified by conventional means. This includes oxazolines and other compounds of similar complexity, meaning that for the first time these valuable compounds have been brought into the field of combinatorial catalysis.
- Frauenlob, Robin,McCormack, Martha M.,Walsh, Carolyn M.,Bergin, Enda
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supporting information; experimental part
p. 6934 - 6937
(2011/11/04)
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- Robust chiral zirconium alkoxide initiators for the room-temperature stereoselective ring-opening polymerisation of rac-lactide
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Chiral Schiff bases (1H to 4H) and a series of their Group 4 metal alkoxide complexes [(R-1)2Ti(OiPr)2, (R-2) 2Ti(OiPr)2, (R-1)2Zr(O iPr)2, (R-2)2/sub
- Chmura, Amanda J.,Cousins, David M.,Davidson, Matthew G.,Jones, Matthew D.,Lunn, Matthew D.,Mahon, Mary F.
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p. 1437 - 1443
(2008/09/19)
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- Benzaldimines as ligands for palladium in Suzuki-Miyaura reactions
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Schiff bases derived from substituted benzaldehydes are effective ligands for palladium(0) in the Suzuki-Miyaura coupling of phenylboronic acid with aryl, benzyl and allyl bromides under mild conditions.
- Srimani, Dipankar,Sarkar, Amitabha
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supporting information; experimental part
p. 6304 - 6307
(2009/04/06)
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- Syntheses, spectroscopy and crystal structures of (R)-N-(1-Aryl-ethyl) salicylaldimines and [Rh{(R)-N-(1-aryl-ethyl)salicylaldiminato} (η4-cod)] complexes
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Condensation of salicylaldehyde with enantiopure (R)-(1-aryl-ethyl)amines yields the enantiopure Schiff bases (R)-N-(1-aryl-ethyl)salicylaldimine (HSB*; aryl = phenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl (4), 4-bromophenyl (5), 2-naphthyl). These Schiff bases readily react with dinuclear (acetato)(η4-cycloocta-1,5-diene)rhodium(I), [Rh(μ-O2CMe)(η4-cod)]2, to afford the mononuclear complexes, cyclooctadiene-((R)-N-(1-aryl-ethyl)salicylaldiminato- κ2N,O)-rhodium(I), [Rh(SB*)(η4-cod)] (SB* = deprotonated chiral Schiff base = salicylaldiminate; aryl = phenyl (7), 2-methoxyphenyl, 4-methoxyphenyl, 4-bromophenyl, 2-naphthyl). The complexes have been characterized by IR, UV/vis, 1H/13C NMR and mass spectrometry, optical rotation as well as by single-crystal X-ray structure determination for 4, 5 and 7. The structure of 5 shows C-Br π contacts. Compound 7 is only the second example of a Rh(η4-cod) complex with a six-membered Rh-N,O-chelate ring.
- Enamullah, Mohammed,Uddin, A. K. M. Royhan,Chamayou, Anne-Christine,Janiak, Christoph
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p. 807 - 817
(2008/09/21)
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- Synthesis, isolation and structural investigation of Schiff-base alkoxytitanium complexes: Steric limitations of ligand coordination
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This paper reports the reaction of Ti(OiPr)4 with a series of Schiff-base ligands. The Schiff-base proligands 1a-1 are synthesised by the condensation of salicylaldehyde with a range of primary alkylamine and aniline derivatives. The treatment of 1a-f with Ti(OiPr)4 yields the octahedral bis(aryloxyimine)Ti(OiPr)2 complexes 2a-f. X-ray crystal structure analysis of 2c, 2d and 2e reveals complexes with a trans-aldiminato oxygen atom and cis-N,cis-alkoxide ligand arrangement about the central metal atom. The reactions of Ti(OiPr)4 with the ligands 1g and 1h result in a sterically induced ligand rearrangement to form the octahedral complexes 2g and 2h, also characterised by X-ray diffraction experiments, in which the nitrogen atoms of the O,N-chelate are now trans-orientated at the titanium centre. 1H NMR analysis reveals significant deshielding of the isopropoxide methine proton, induced by this coordination mode. In contrast, reactions of 1i and 1j with Ti(OiPr)4 result in the formation and isolation of the complexes 2i and 2j. X-ray crystal structure analysis shows complex 2j to have a previously unobserved ligand orientation, in which both ligands are trans-orientated, with respect to the aldiminato oxygen atoms, about the titanium centre, but steric bulk of the ligand inhibits the bidentate coordination of both O,N-ligands. Further increase in the steric bulk of the imine substituent results in a reduced reactivity for ligands 1k and 1l, such that Ti(OiPr)4 reacts with 1k to form the dimeric mono(Schiff-base) complex 2k (characterised by X-ray analysis). No reaction is observed for 11. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
- Johnson, Andrew L.,Davidson, Matthew G.,Lunn, Matthew D.,Mahon, Mary F.
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p. 3088 - 3098
(2007/10/03)
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- New Schiff base zinc(II) complexes exhibiting second harmonic generation
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Four bis(salicylaldiminato)zinc(II) complexes have been synthesized from four Schiff bases obtained by the condensation of chiral (R)-(+)-1-phenylethylamine with salicylaldehyde (1), 5-nitrosalicylaldehyde (2), 3,5-dichlorosalicylaldehyde (3) and 5-methox
- Evans, Cara,Luneau, Dominique
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- Ready N-alkylation of enantiopure aminophenols: Synthesis of tertiary aminophenols
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A regioselective indirect alkylation of aminophenols to enantiopure tertiary aminophenols, which are useful chiral ligands for metal-catalysed asymmetric reactions, is reported. This very simple synthetic methodology, through reduction or alkylation of an intermediate benzoxazine, was performed in mild conditions, suitable for the conservation of the configuration of the stereogenic centres. Some crystalline aminophenols show the phenomenon of 'crystallization-induced asymmetric transformation'.
- Cimarelli, Cristina,Palmieri, Gianni,Volpini, Emanuela
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p. 6089 - 6096
(2007/10/03)
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- Kinetic and mechanistic study with optically active, four-coordinate nickel(II) complexes: Stereoselectivity in ligand substitution
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Conventional and rapid scan stopped-flow spectrophotometry as well as polarimetry was used to study the kinetics of ligand substitution in six chiral bis N-alkylsalicylaldiminato nickel(II) complexes NiA2 by different chiral salen-type ligands H2B, according to NiA2 + H2B → NiB + 2HA, in acetone at 298 K and, partly, at variable temperature. In most cases ligand substitution was found to follow monophasic second-order kinetics, rate = k x [NiA2] x [H2B]. Second-order rate constant k, lying in the range 10-2 - 400 M-1S-1 at 298 K, was determined for the various combinations of enantiomers in a given system NiA2/H2B, namely, R-NiA2/R-H2B, S-NiA2/R-H2B, R-NiA2/S-H2B, and S-NiA2/S-H2B. It was found that ligand substitution is subject to chiral discrimination. The ratio of second-order rate constants, k(fast)/k(slow), with k(fast) being rate constant k for the faster reacting pair of enantiomers and vice versa, lies in the range 1.0-3.0, depending on the nature of the N-alkyl groups in NiA2 and organic groups attached to the ethylene bridge in the salen ligands H2B. The rate discrimination factor of 3.0, as obtained for NiA2 = bis[N-dehydroabietylsalicylaldiminato]nickel(II) reacting with the R- and with the S-enantiomer of H2B = N,N'-disalicylidene-1,2-diamino-4-methylpentane, appears to be the highest stereoselectivity reported so far for ligand substitution in nickel(II) complexes. With NiA2 = R- and S-bis[N-(1-phenylethyl)-5-nitrosalicylaldiminato]nickel(II) and H2B = R- and S-N,N'-disalicylidene-1,2-diamino-4-methylpentane, the kinetics of ligand substitution are biphasic, describing initial adduct formation between NiA2 and H2B (equilibrium constant K) and stepwise loss of the two bidentate ligands HA (first-order rate constants k1 and k2). The data for K, k1, and k2 for one of the combinations of enantiomers were determined at variable temperature, and the corresponding activation parameters are presented.
- Haus,Raidt,Link,Elias
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p. 5111 - 5117
(2008/10/08)
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- Difference in the rate of photo-induced unimolecular motion of chiral salicylideneamines in the chiral crystal environments
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From the kinetic investigation on the photochromic process of chiral N-salicylidene-1-phenylethylamine it was revealed that the rate of unimolecular asymmetric motion was influenced by the neighboring asymmetric crystal environments.
- Kawato, Toshio,Koyama, Hiroyuki,Kanatomi, Hajime,Shigemizu, Hideki
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p. 401 - 402
(2007/10/03)
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- Copper(II) in organic synthesis. VIII enantioselective Michael reactions with chiral copper(II) complexes as catalysts
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Using copper(II) chiral complexes as catalysts, enantioselective Michael reactions were performed. The degree of enantioselectivity depended on the design of the catalyst and the best results (70% e.e.) were obtained with tetradentate ligands.
- Desimoni,Quadrelli,Righetti
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p. 2927 - 2934
(2007/10/02)
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- Asymmetric Catalyses, 13 . Chelate Ligands and their Rhodium Complexes with Lateral Asymmetric Centers and their Use in Enantioselective Catalysis
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The chelate ligands 1-3 with lateral asymmetric centers at the nitrogen atoms were prepared and characterized.In the Rh complexes 4 and 5 the asymmetric centers directly interact with those coordination positions where during enantioselective catalysis pr
- Brunner, Henri,Rahman, A. F. M. Mokhlesur
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p. 1332 - 1338
(2007/10/02)
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