14898-79-4Relevant academic research and scientific papers
Self-assembly of a homochiral nanoscale metallacycle from a metallosalen complex for enantioselective separation
Li, Gao,Yu, Weibin,Ni, Jia,Liu, Taifeng,Liu, Yan,Sheng, Enhong,Cui, Yong
, p. 1245 - 1249 (2008)
(Chemical Presented) Only half may enter: A homochiral porous nanoscale metallacycle has been efficiently self-assembled from semiflexible enantiopure metallosalen complexes with complementary coordination motifs. Single crystals of the macromolecule (see structure; C gray, Zn purple, O red, N blue) show a reversible and controllable dynamic behavior. Particularly, the metallacycle can be used to resolve small racemic alcohols with high enantioselectivity (over 99.0% ee).
Enantiomerically enriched 1,2-P,N-bidentate ferrocenyl ligands for 1,3-dipolar cycloaddition and transfer hydrogenation reactions
Utepova, Irina A.,Serebrennikova, Polina O.,Streltsova, Marina S.,Musikhina, Alexandra A.,Fedorchenko, Tatiana G.,Chupakhin, Oleg N.,Antonchick, Andrey P.
, (2018)
Novel complexes of 1,2-P,N-bidentate ferrocenyl ligands with AgOAc or with [RuCl2(PPh3)3] as catalysts have been studied in asymmetric synthesis. The catalytic activity of these systems have been studied in [3+2]-cycloaddition of azomethine ylides with olefins and the asymmetric transfer hydrogenation of ketones.
Hydroboration. 92. Investigation of Practical Methods for the Synthesis of Optically Pure Isopinocampheylchloroborane for the Asymmetric Hydroboration of Representative Prochiral Alkenes
Dhokte, Ulhas P.,Kulkarni, Shekhar V.,Brown, Herbert C.
, p. 5140 - 5148 (1996)
A quantitative study was made of the preparation of the optically pure borane reagent, isopinocampheylchloroborane (IpcBHCl), potentially valuable for asymmetric hydroboration.IpcBHCl (87-90percent) in equilibrium with 5-6.5percent of IpcBCl2 and IpcBH2, respectively, can be prepared conveniently by a number of relatively simple operations: (1) the reaction of isopinocampheylborane (IcpBH2) with anhydrous hydrochloric acid (HCl) in ethyl ether (EE); (2) the reaction of stoichiometric amounts of IpcBH2 with isopinocampheyldichloroborane (IpcBCl2) in EE; and (3) the reduction of IpcBCl2 with trimethylsilane (Me3SiH) or lithium aluminum hydride (LAH) in EE.The reduction of IpcBCl2 with Me3SiH in pentane proceeds extremely slowly to provide the desired reagent, IpcBHCl.However, in EE, the reduction proceeds much faster, providing an equilibrium mixture of 90percent IpcBHCl, 5percent IpcBH2, and 5percent IpcBCl2.We also investigated the reduction of IpcBCl2 with Me3SiH in pentane and dichloromethane (CH2CL2) in the presence of known amounts of EE, tetrahydrofuran (THF), and dimethyl sulfide (SMe2), solvents which coordinate with the dichloroboranes.A comparative study of the rate of hydroboration of the alkene, 2-methyl-2-butene, with IpcBH2 and IpcBHCl, obtained as described above, was made in representative solvents, such as pentane, CH2Cl2, EE, and THF, at 0 deg C and, in many cases, also at 25 deg C.This study revealed that the rate of hydroboration is faster in THF for IpcBH2, while for IpcBHCl, the rate is faster in EE.Asymmetric hydroboration of prochiral alkenes was achieved by two methods, viz., IpcBHCl, produced by the reaction of IpcBH2 with HCl in EE (method A), and the reduction-hydroboration reaction of IpcBCl2 with LAH (0.25 equiv) in the presence of the prochiral alkene (method B) in EE.In both methods, the temperature of the reaction mixture was maintained at -25 deg C.Almost identical results were realized in these two procedures, with the enantiomeric excess (ee) realized with IpcBHCl, in some cases, considerably better than that achieved with IpcBH2.Although, IpcBHCl was obtained in onyl 87090percent purity along with IpcBH2 and IpcBCl2 as side products, the presence of the latter compound had no observable effect on the chiral outcome of the asymmetric hydroboration.
Isopinocampheylbromoborane, a new promising reagent for the asymmetric hydroboration of prochiral alkenes
Dhokte, Ulhas P.,Brown, Herbert C.
, p. 9021 - 9024 (1996)
A new promising in situ generated hydroborating agent, isopinocampheylbromoborane (IpcBHBr), achieves the asymmetric hydroboration of representative prochiral alkenes in pentane at lower temperatures, even at -78 °C, than has been possible with isopinocampheylborane (IpcBH2) and isopinocampheylchloroborane·EE (IpcBHCl·EE) reagents, usually in higher enantioselectivities than previously achieved. This is first time that the asymmetric hydroboration of prochiral alkenes with an α-pinene-derived borane reagent (IpcBHBr) has been achieved at such low temperature, -78 °C, in a relatively short time, 4-6 h. Copyright (C) 1996 Elsevier Science Ltd.
Asymmetric reduction of simple aliphatic ketones with dried cells of Geotrichum candidum
Matsuda, Tomoko,Nakajima, Yuta,Harada, Tadao,Nakamura, Kaoru
, p. 971 - 974 (2002)
Simple aliphatic ketones such as 2-pentanone, 2-butanone, 3-hexanone, etc., were reduced with high yield and excellent enantioselectivity to the corresponding (S)-alcohols using dried cells of Geotrichum candidum.
Utilization of deep-sea microbial esterase PHE21 to generate chiral sec-butyl acetate through kinetic resolutions
Wang, Yilong,Xu, Yongkai,Zhang, Yun,Sun, Aijun,Hu, Yunfeng
, p. 1027 - 1035 (2018)
We previously identified and characterized 1 novel deep-sea microbial esterase PHE21 and used PHE21 as a green biocatalyst to generate chiral ethyl (S)-3-hydroxybutyrate, 1 key chiral chemical, with high enantiomeric excess and yield through kinetic resolution. Herein, we further explored the potential of esterase PHE21 in the enantioselective preparation of secondary butanol, which was hard to be resolved by lipases/esterases. Despite the fact that chiral secondary butanols and their ester derivatives were hard to prepare, esterase PHE21 was used as a green biocatalyst in the generation of (S)-sec-butyl acetate through hydrolytic reactions and the enantiomeric excess, and the conversion of (S)-sec-butyl acetate reached 98% and 52%, respectively, after process optimization. Esterase PHE21 was also used to generate (R)-sec-butyl acetate through asymmetric transesterification reactions, and the enantiomeric excess and conversion of (R)-sec-butyl acetate reached 64% and 43%, respectively, after process optimization. Deep-sea microbial esterase PHE21 was characterized to be a useful biocatalyst in the kinetic resolution of secondary butanol and other valuable chiral secondary alcohols.
Dilongifolylborane: A New Effective Chiral Hydroborating Agent with Intermediate Steric Requirements
Jadhav, Prabhakar K.,Brown, Herbert C.
, p. 2988 - 2990 (1981)
Dilongifolylborane, (Lgf)2BH, a new effective chiral hydroborating agent, is readily synthesized from (+)-longifolene.Thus, treatment of (+)-longifolene with borane-methyl sulfide (BH3*SMe2) in ethyl ether rapidly precipitates snow-white crystalline (Lgf)2BH: mp 160-161 deg C; dimer; IR 1565 cm-1.The new chiral dialkylborane achieves the successful asymmetric hydroboration of cis, trisubstituted acyclic, and trisubstituted cyclic prochiral olefins to provide alcohols, after oxidation of the intermediate organoboranes, with optical purities in the range of 60-78percent ee.In the cases studied, the new asymmetric center at the alcohol position is predominantly the R enantiomer.
Hydroboration. 83. Synthesis and Hydroboration of 2-Ethylapopinene. Comparison of Monoisopinocampheylborane and Its 2-Ethyl Analogue for the Chiral Hydroboration of Representative Alkenes
Brown, Herbert C.,Randad, Ramnarayan S.,Bhat, Krishna S.,Zaidlewicz, Marek,Weissman, Steven A.,et al.
, p. 5513 - 5518 (1988)
Reduction of nopol tosylate gives the new chiral ligand (-)-2-ethylapopinene (90.2percent ee) with higher steric requirements than those of α-pinene.Reaction of borane with (-)-2-ethylapopinene in THF at 0 deg C, in a molar ratio of 1:2, provides an equilibrium mixture of mono- and dialkylboranes EapBH2 and Eap2BH.With an excess of (-)-2-ethylapopinene (1:10; BMS/2-ethylapopinene), the formation of bis(2-ethylapoisopinocampheyl)borane, Eap2BH, is essentially quantitative (ca. 98percent).Treatment of the equilibrium mixture of boranes (Eap2BH, EapBH2) with TMED at 34 deg C precipitates crystalline (EapBH2)2*TMED.Treatment of the crystalline product with BF3*OEt2 gives EapBH2 (mono(2-ethylapoisopinocampheyl)borane) of essentially 100percent ee, enantiomerically purer than the (-)-2-ethylapopinene (ca. 90percent ee) utilized for the preparation.Hydroboration of a series of olefins with EapBH2, followed by oxidation of the intermediate organoborane, produces the corresponding alcohols with significantly improved enantiomeric purities over those realized with IpcBH2 under the same conditions.Liberation of the olefin from purified EapBH2 provides (-)-2-ethylapopinene (D23 -46.2 deg (neat) in high optical purity (>99percent ee).Metalation of (+)-α-pinene (D23 +51.4 deg (neat)) with the Lochmann reagent, followed by alkylation with methyl iodide, provides in high optical purity (>99percent ee) (+)-2-ethylapopinene (D23 +46.4 deg (neat)), unavailable from commercial (-)-nopol.
Chiral nanoscale metal-organic tetrahedral cages: Diastereo-selective self-assembly and enantioselective separation
Liu, Taifeng,Liu, Yan,Xuan, Weimin,Cui, Yong
, p. 4121 - 4124 (2010)
(Figure Presented) Cage rage: Chiral tetrahedral cages are diastereoselectively self-assembled from enantiopure C2-symmetric biphenyl bis(β-diketonate) linkers and C3-symmetric octahedral Fe3+ or Ca3+ ions (see picture; Fe purple, C blue, O red; cavity shown as an orange sphere). The porous polyhedra exhibit metal-dependent chiroptical behavior and act as hosts for the crystallization separation of racemic alcohols with up to 99.5% ee.
Asymmetric transfer hydrogenation of alkyl/aryl or alkyl/methyl ketones catalyzed by known C2-symmetric ferrocenyl-based chiral bis(phosphinite)-Ru(II), Rh(I) and Ir(III) complexes
Durap, Feyyaz,Karaka?, Duygu Elma,Ak, Bünyamin,Baysal, Akin,Aydemir, Murat
, p. 92 - 97 (2016)
Known Ru(II), Rh(I) and Ir(III) complexes of C2-symmetric ferrocenyl based chiral bis(phoshinite) ligands were catalyzed the asymmetric transfer hydrogenation of alkyl/aryl or alkyl methyl ketones. Corresponding secondary alcohols were obtained with high enantioselectivities up to 98% ee and reactivities using iso-propanol as the hydrogen source.
