- Aqueous chemoenzymatic one-pot enantioselective synthesis of tertiary α-aryl cycloketonesviaPd-catalyzed C-C formation and enzymatic C=C asymmetric hydrogenation
-
An aqueous chemoenzymatic cascade reaction combining Pd-catalyzed C-C formation and enzymatic C=C asymmetric hydrogenation (AH) was developed for enantioselective synthesis of tertiary α-aryl cycloketones in good yields and excellent enantioselectivities. The stereopreference of the enzyme in AH of α-aryl cyclohexenones was studied. An enantiocomplementary enzyme was obtained by site-directed mutation.
- Luan, Pengqian,Liu, Yunting,Li, Yongxing,Chen, Ran,Huang, Chen,Gao, Jing,Hollmann, Frank,Jiang, Yanjun
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p. 1960 - 1964
(2021/03/26)
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- The Silicon-Hydrogen Exchange Reaction: Catalytic Kinetic Resolution of 2-Substituted Cyclic Ketones
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We have recently reported the strong and confined, chiral acid-catalyzed asymmetric 'silicon-hydrogen exchange reaction'. One aspect of this transformation is that it enables access to enantiopure enol silanes in a tautomerizing σ-bond metathesis, via deprotosilylation of ketones with allyl silanes as the silicon source. However, until today, this reaction has not been applied to racemic, 2-substituted, cyclic ketones. We show here that these important substrates readily undergo a highly enantioselective kinetic resolution furnishing the corresponding kinetically preferred enol silanes. Mechanistic studies suggest the fascinating possibility of advancing the process to a dynamic kinetic resolution.
- List, Benjamin,Zhang, Pinglu,Zhou, Hui
-
supporting information
p. 1953 - 1956
(2021/11/17)
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- The Silicon-Hydrogen Exchange Reaction: A Catalytic σ-Bond Metathesis Approach to the Enantioselective Synthesis of Enol Silanes
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The use of chiral enol silanes in fundamental transformations such as Mukaiyama aldol, Michael, and Mannich reactions as well as Saegusa-Ito dehydrogenations has enabled the chemical synthesis of enantiopure natural products and valuable pharmaceuticals. However, accessing these intermediates in high enantiopurity has generally required the use of either stoichiometric chiral precursors or stoichiometric chiral reagents. We now describe a catalytic approach in which strongly acidic and confined imidodiphosphorimidates (IDPi) catalyze highly enantioselective interconversions of ketones and enol silanes. These "silicon-hydrogen exchange reactions"enable access to enantiopure enol silanes via tautomerizing σ-bond metatheses, either in a deprotosilylative desymmetrization of ketones with allyl silanes as the silicon source or in a protodesilylative kinetic resolution of racemic enol silanes with a carboxylic acid as the silyl acceptor.
- Zhou, Hui,Bae, Han Yong,Leutzsch, Markus,Kennemur, Jennifer L.,Bécart, Diane,List, Benjamin
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p. 13695 - 13700
(2020/08/24)
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- HPLC with cellulose Tris (3,5-DimethylPhenylcarbamate) chiral stationary phase: Influence of coating times and coating amount on chiral discrimination
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Coating cellulose tris (3,5-dimethylphenylcarbamate) (CDMPC) on silica gels with large pores have been demonstrated as an efficient way for the preparation of chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC). During the process, a number of parameters, including the type of coating solvent, amount of coating, and the method for subsequent solvent removing, have been proved to affect the performance of the resultant CSPs. Coating times and the concentration of coating solution, however, also makes a difference to CSPs' performance by changing the arrangement of cellulose derivatives while remaining the coating amount constant, have much less been studied before, and thereby, were systematically investigated in this work. Results showed that CSPs with more coating times exhibited higher chiral recognition and column efficiency, suggesting that resolution was determined by column efficiency herein. Afterwards, we also investigated the effect of coating amount on the performance of CSPs, and it was shown that the ability of enantio-recognition did not increase all the time as the coating amount; and four of seven racemates achieved best resolution when the coating amount reached to 18.37%. At the end, the reproducibility of CDMPC-coated CSPs were further confirmed by two methods, ie, reprepared the CSP-0.15-3 and reevaluated the effect of coating times.
- Wei, Qiuhong,Su, Hongjiu,Gao, Diannan,Wang, Shudong
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p. 164 - 173
(2019/01/18)
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- Enantioselective Protonation of Silyl Enol Ethers Catalyzed by a Chiral Pentacarboxycyclopentadiene-Based Bronsted Acid
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The enantioselective protonation of silyl enol ethers was realized in the presence of a pentacarboxycyclopenta-1,3-diene-based chiral Bronsted acid catalyst with water as an achiral proton source to give the corresponding α-aryl ketones in good yields and up to 75percent ee.
- An, Shaoyu,Li, Jun,Li, Pingfan,Yuan, Chao
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p. 1317 - 1320
(2019/06/19)
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- Safe and Scalable Aerobic Oxidation by 2-Azaadamantan-2-ol (AZADOL)/NOx Catalysis: Large-Scale Preparation of Shi's Catalyst
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A method for safe and scalable aerobic alcohol oxidation using 2-azaadamantan-2-ol (AZADOL), an azaadamantane-type hydroxylamine catalyst, with a NOx cocatalyst in a conventional batch reactor has been developed. The use of 2 mol % AZADOL and 10 mol % NaNO2 was determined to promote aerobic alcohol oxidation quantitatively within a reasonable time (8 h). Safety is ensured by controlling the reaction temperature below the flash point of the acetic acid solvent. The robustness of the developed method is demonstrated by the 500 g scale oxidation of diacetone fructose into Shi's catalyst for asymmetric epoxidation.
- Sasano, Yusuke,Sato, Hikaru,Tadokoro, Shinsuke,Kozawa, Masami,Iwabuchi, Yoshiharu
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p. 571 - 577
(2019/03/19)
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- Amino-TEMPO Grafted on Magnetic Multi-Walled Nanotubes: An Efficient and Recyclable Heterogeneous Oxidation Catalyst
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An efficient and easy recyclable heterogeneous oxidation catalyst was prepared by grafting TEMPO–NH2 moieties on the surface of magnetic multi-walled carbon nanotubes (MWCNT), first by a radical reaction introducing butyric acid moieties on carbon nanotube surface. Subsequently, carboxylic acid moieties were submitted for amidation using TEMPO–NH2. The functionalized nanotubes [MWCNT-{(CH2)3-CO-NH-TEMPO}n] were investigated as a (pre-)catalyst for the oxidation of primary and secondary alcohols for the production of aldehydes and ketones in a Montanari-type catalytic oxidation using the cheap and readily available 1,3-dichloro-5,5-dimethylhydantoin as the terminal oxidant.
- Gambarotti, Cristian,Bj?rsvik, Hans-René
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p. 1405 - 1412
(2019/01/04)
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- Cellulose type chiral stationary phase based on reduced graphene oxide@silica gel for the enantiomer separation of chiral compounds
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The graphene oxide (GO) was covalently coupled to the surfaces of silica gel (SiO2) microspheres by amide bond to get the graphene oxide@silica gel (GO@SiO2). Then, the GO@SiO2 was reduced with hydrazine to the reduced graphene oxide@silica gel (rGO@SiO2), and the cellulose derivatives were physically coated on the surfaces of rGO@SiO2 to prepare a chiral stationary phase (CSP) for high performance liquid chromatography. Under the optimum experimental conditions, eight benzene-enriched enantiomers were separated completely, and the resolution of trans-stilbene oxide perfectly reached 4.83. Compared with the blank column of non-bonded rGO, the separation performance is better on the new CSP, which is due to the existence of rGO to produce special retention interaction with analytes, such as π-π stacking, hydrophobic effect, π-π electron-donor–acceptor interaction, and hydrogen bonding. Therefore, the obtained CSP shows special selectivity for benzene-enriched enantiomers, improves separation selectivity and efficiency, and rGO plays a synergistic effect with cellulose derivatives on enantioseparation.
- Li, Yuanyuan,Li, Qiang,Zhu, Nan,Gao, Zhuxian,Ma, Yulong
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p. 996 - 1004
(2018/07/29)
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- Chiral isoxazolidine-mediated stereoselective umpolung α-phenylation of methyl ketones
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An effective asymmetric α-phenylation of methyl ketones with triphenylaluminium in the presence of (+)-benzopyranoisoxazolidine has been developed. The reaction proceeds via the in situ formation of a chiral N-alkoxyenamine and the subsequent diastereoselective nucleophilic phenylation to provide α-phenylated products in moderate to good yields, with high enantioselectivities.
- Takeda, Norihiko,Furuishi, Mizuki,Nishijima, Yuri,Futaki, Erika,Ueda, Masafumi,Shinada, Tetsuro,Miyata, Okiko
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supporting information
p. 8940 - 8943
(2018/12/10)
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- Preparation and evaluation of regioselectively substituted amylose derivatives for chiral separations
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Six novel regioselectively substituted amylose derivatives with a benzoate at 2-position and two different phenylcarbamates at 3- and 6-positions were synthesized and their structures were characterized by 1H nuclear magnetic resonance (NMR) spectroscopy. Their enantioseparation abilities were then examined as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) after they were coated on 3-aminopropyl silica gels. Investigations indicated that the substituents at the 3- and 6-positions played an important role in chiral recognition of these amylose 2-benzoate serial derivatives. The derivatives demonstrated characteristic enantioseparation and some racemates were better resolved on these derivatives than on Chiralpak AD, which is one of the most efficient CSPs, utilizing coated amylose tris(3,5-dimethylphenylcarbamate) as the chiral selector. Among the derivatives prepared, amylose 2-benzoate-3-(phenylcarbamate/4-methylphenylcarbamate)-6-(3,5-dimethylphenylcarbamate) exhibited chiral recognition abilities comparable to that of Chiralpak AD and may be useful CSPs in the future. The effect of mobile phase on chiral recognition was also studied. In general, with the decreased concentration of 2-propanol, better resolutions were obtained with longer retention times. Moreover, when ethanol was used instead of 2-propanol, poorer resolutions were often achieved. However, in some cases, improved enantioselectivity was achieved with ethanol rather than 2-propanol as the mobile phase modifier.
- Tang, Shouwan,Jin, Zhaolei,Sun, Baishen,Wang, Fang,Tang, Wenyuan
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p. 512 - 521
(2017/08/26)
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- Burgess Reagent Facilitated Alcohol Oxidations in DMSO
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The Burgess reagent ([methoxycarbonylsulfamoyl]triethylammonium hydroxide) has historically found utility as a dehydrating agent. Herein we show that, in the presence of dimethyl sulfoxide, the Burgess reagent efficiently and rapidly facilitates the oxidation of a broad range of primary and secondary alcohols to their corresponding aldehydes and ketones in excellent yields and under mild conditions, and can be combined with other transformations (e.g., Wittig olefinations). A mechanism similar to those described for the Pfitzner-Moffatt and Swern oxidations is proposed.
- Sultane, Prakash R.,Bielawski, Christopher W.
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p. 1046 - 1052
(2018/06/18)
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- First chemo-enzymatic synthesis of the (R)-Taniguchi lactone and substrate profiles of CAMO and OTEMO, two new Baeyer–Villiger monooxygenases
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Abstract: This study investigates the substrate profile of cycloalkanone monooxygenase and 2-oxo-Δ3-4,5,5-trimethylcyclopentenylacetyl-coenzyme A monooxygenase, two recently discovered enzymes of the Baeyer–Villiger monooxygenase family, used as whole-cell biocatalysts. Biooxidations of a diverse set of ketones were performed on analytical scale: desymmetrization of substituted prochiral cyclobutanones and cyclohexanones, regiodivergent oxidation of terpenones and bicyclic ketones, as well as kinetic resolution of racemic cycloketones. We demonstrated the applicability of the title enzymes in the enantioselective synthesis of (R)-(?)-Taniguchi lactone, a building block for the preparation of various natural product analogs such as ent-quinine. Graphical abstract: [Figure not available: see fulltext.]
- Rudroff, Florian,Fink, Michael J.,Pydi, Ramana,Bornscheuer, Uwe T.,Mihovilovic, Marko D.
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p. 157 - 165
(2017/01/17)
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- Synthesis of optically active poly(diphenylacetylene)s using polymer reactions and an evaluation of their chiral recognition abilities as chiral stationary phases for HPLC
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A series of optically active poly(diphenylacetylene) derivatives bearing a chiral substituent (poly-2S) or chiral and achiral substituents (poly-(2Sx-co-31-x)) on all of their pendant phenyl rings were synthesized by the reaction of poly(bis(4-carboxyphenyl)acetylene) with (S)-1-phenylethylamine ((S)-2) or benzylamine (3) in the presence of a condensing reagent. Their chiroptical properties and chiral recognition abilities as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) were investigated. Poly-2S and poly-(2Sx-co-31-x) (0.06 x-co-31-x)). Furthermore, h-poly-2S and h-poly-(2S0.36-co-30.64) emitted circularly polarized luminescence with opposite signs. h-Poly-2S showed higher chiral recognition abilities toward a larger number of racemates than poly-2S without a preferred-handed helicity and the previously reported preferred-handed poly(diphenylacetylene) derivative bearing the same chiral substituent on half of its pendant phenyl rings. h-Poly-(2S0.36-co-30.64) also exhibited good chiral recognition abilities toward several racemates, though the elution order of some enantiomers was reversed compared with h-poly-2S.
- Maeda, Katsuhiro,Maruta, Miyuki,Sakai, Yuki,Ikai, Tomoyuki,Kanoh, Shigeyoshi
-
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- Enantioselective Protonation of Silyl Enol Ether Using Excited State Proton Transfer Dyes
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Enantiopure excited state proton transfer (ESPT) dyes were used for the asymmetric protonation of silyl enol ether. Under 365 nm irradiation, with 3,3′-dibromo-VANOL as the ESPT dye, up to 49% enantioselectivity with a 68% yield of product was observed at room temperature. The reaction is effective with a range of silyl enol ethers and can also be achieved with visible light upon the addition of triplet sensitizer. The relatively low ee of the protonated product is due to the racemization/decomposition of the ESPT dye in the excited state as indicated by circular dichroism, HPLC, and UV-vis spectroscopy.
- Das, Anjan,Ayad, Suliman,Hanson, Kenneth
-
supporting information
p. 5416 - 5419
(2016/11/06)
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- Synthesis and Enantioseparation Ability of Xylan Bisphenylcarbamate Derivatives as Chiral Stationary Phases in HPLC
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Ten novel xylan bisphenylcarbamate derivatives bearing meta- and para-substituents on their phenyl groups were synthesized and their chiral recognition abilities were evaluated as the chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) after coating them on macroporous silica. The chiral recognition abilities of these CSPs depended on the nature, position, and number of the substituents on the phenyl moieties. The introduction of an electron-donating group was more attractive than an electron-withdrawing group to improve the chiral recognition ability of the xylan phenylcarbamate derivatives. Among the CSPs discussed in this study, xylan bis(3,5-dimethylphenylcarbamate)-based CSP seems to possess the highest resolving power for many racemates, and the meta-substituted CSPs showed relatively better chiral recognition than the para-substituted ones. For some racemates, the xylan bis(3,5-dimethylphenylcarbamate) derivative exhibited higher enantioselectivity than the CSP based on cellulose tris(3,5-dimethylphenylcarbamate). Chirality 27:518-522, 2015
- Li, Geng,Shen, Jun,Li, Qiang,Okamoto, Yoshio
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p. 518 - 522
(2015/08/03)
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- Influence of Helical Structure on Chiral Recognition of Poly(phenylacetylene)s Bearing Phenylcarbamate Residues of L -Phenylglycinol and Amide Linage as Pendants
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Four poly(phenylacetylene)s (PPA-1, PPA-2, PPA-3, PPA-4) bearing phenylcarbamate residues of L-phenylglycinol and amide linkage as pendants were prepared to be used as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC), and the influences of coating solvents, dimethylformamide (DMF) and tetrahydrofuran (THF), which were used for coating the polymers on silica gel, on the helical structure of the polymers and their chiral recognition abilities were investigated. The structure analysis of PPA-1, PPA-2, PPA-3, PPA-4 by 1H nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), optical rotation, and circular dichroism (CD) spectra indicated that the polymers possess the cis-transoidal structure with dynamic helical conformation. The polymers in THF seem to have shorter conjugated helical main chains along with a tighter twist conformation than those in DMF. The chiral recognition abilities of PPA-1, PPA-2, PPA-3, PPA-4 with the different helical structures induced by the coating solvents were evaluated as the CSPs in HPLC. The helical structures of PPA-1, PPA-2, PPA-3, PPA-4 induced with THF are preferable for chiral recognition for some racemates compared to those induced with DMF, and higher chiral recognition abilities of PPA-1, PPA-2, PPA-3, PPA-4 were achieved using THF.
- Zhang, Chunhong,Ma, Rui,Wang, Hailun,Sakai, Ryosuke,Satoh, Toshifumi,Kakuchi, Toyoji,Liu, Lijia,Okamoto, Yoshio
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p. 500 - 506
(2015/08/03)
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- Synthesis and chiral recognition ability of a novel fullerene-functionalized cellulose derivative
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The fullerene-functionalized cellulose derivative 1 was synthesized and coated onto silica gel as chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC). The chiral recognition ability of the obtained chiral packing material (CPM) was evaluated by HPLC with ten types of racemates 2-11. This CPM could be used in the eluents including chloroform and terahydrofuran (THF), which are usually unsuitable solvents for conventional coating-type CPMs. Hence the scope of application of this CPM is wider than conventional coating CPM.
- Gao, Bo,Xu, Zeyu,Fan, Luan,Xu, Xiaodong,Bai, Jianwei,Shen, Xiande
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p. 1479 - 1481
(2015/11/24)
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- Synthesis and chiral recognition of helical poly(phenylacetylene)s bearing L-phenylglycinol and its phenylcarbamates as pendants
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A series of novel stereoregular one-handed helical poly(phenylacetylene) derivatives (PPA-1 and PPA-1a-g) bearing L-phenylglycinol and its phenylcarbamate residues as pendants was synthesized for use as chiral stationary phases (CSPs) for HPLC, and their chiral recognition abilities were evaluated using 13 racemates. The phenylcarbamate residues include an unsubstituted phenyl, three chloro-substituted phenyls (3-Cl, 4-Cl, 3,5-Cl2), and three methyl-substituted phenyls (3-CH3, 4-CH3, 3,5-(CH3)2). The acidity of the phenylcarbamate N-H proton and the hydrogen bonds formed between the N-H groups of the phenylcarbamate residues were dependent on the type, position, and the number of substituents on the phenylcarbamate residues. The chiral recognition abilities of these polymers significantly depended on the dynamic helical conformation of the main chain with more or less regularly arranged pendants. The chiral recognition abilities seem to be improved by the introduction of substituents on the phenylcarbamate residues, and PPA-1d bearing the more acidic N-H groups due to the 3,5-dichloro substituents, exhibited a higher chiral recognition than the others. PPA-1d showed an efficient chiral recognition for some racemates, and baseline separation was possible for racemates 5, 11, 12, and 15.
- Zhang, Chunhong,Wang, Hailun,Yang, Taotao,Ma, Rui,Liu, Lijia,Sakai, Ryosuke,Satoh, Toshifumi,Kakuchi, Toyoji,Okamoto, Yoshio
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p. 809 - 821
(2015/03/04)
-
- Regio- and enantioselective Baeyer-Villiger oxidation: Kinetic resolution of racemic 2-substituted cyclopentanones
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A kinetic resolution of racemic 2-substituted cyclopentanones via highly regio- and enantioselective Baeyer-Villiger oxidation has been successfully developed. The reaction could afford the normal 6-substituted δ-lactones in up to 98% ee and >19/1 regioselectivity. Meanwhile, the unreacted ketones were recovered in excellent ee values (up to 98%). It represents the best results of the kinetic resolution of racemic 2-substituted cyclopentanones via nonenzymic asymmetric BV oxidation.
- Zhou, Lin,Liu, Xiaohua,Ji, Jie,Zhang, Yuheng,Wu, Wangbin,Liu, Yangbin,Lin, Lili,Feng, Xiaoming
-
supporting information
p. 3938 - 3941
(2014/08/18)
-
- Highly enantioselective organocatalytic oxidative kinetic resolution of secondary alcohols using chiral alkoxyamines as precatalysts: Catalyst structure, active species, and substrate scope
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The development and characterization of enantioselective organocatalytic oxidative kinetic resolution (OKR) of racemic secondary alcohols using chiral alkoxyamines as precatalysts are described. A number of chiral alkoxyamines have been synthesized, and their structure-enantioselectivity correlation study in OKR has led us to identify a promising precatalyst, namely, 7-benzyl-3-n-butyl-4-oxa-5-azahomoadamantane, which affords various chiral aliphatic secondary alcohols (ee up to >99%, krel up to 296). In a mechanistic study, chlorine-containing oxoammonium species were identified as the active species generated in situ from the alkoxyamine precatalyst, and it was revealed that the chlorine atom is crucial for high reactivity and enantioselectivity. The present OKR is the first successful example applicable to various unactivated aliphatic secondary alcohols, including heterocyclic alcohols with high enantioselectivity, the synthetic application of which is demonstrated by the synthesis of a bioactive compound.
- Murakami, Keiichi,Sasano, Yusuke,Tomizawa, Masaki,Shibuya, Masatoshi,Kwon, Eunsang,Iwabuchi, Yoshiharu
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supporting information
p. 17591 - 17600
(2015/02/19)
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- Mechanistic insight into aerobic alcohol oxidation using NOx-nitroxide catalysis based on catalyst structure-activity relationships
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The mechanism of an NOx-assisted, nitroxide(nitroxyl radical)-catalyzed aerobic oxidation of alcohols was investigated using a set of sterically and electronically modified nitroxides (i.e., TEMPO, AZADO (1), 5-F-AZADO (2), 5,7-DiF-AZADO (3), 5-MeO-AZADO (4), 5,7-DiMeO-AZADO (5), oxa-AZADO (6), TsN-AZADO (7), and DiAZADO (8)). The motivation for the present study stemmed from our previous observation that the introduction of an F atom at a remote position from the nitroxyl radical moiety on the azaadamantane nucleus effectively enhanced the catalytic activity under typical NOx-mediated aerobic-oxidation conditions. The kinetic profiles of the azaadamantane-N-oxyl-[AZADO (1)-, 5-F-AZADO (2)-, and 5,7-DiF-AZADO (3)]-catalyzed aerobic oxidations were closely investigated, revealing that AZADO (1) showed a high initial reaction rate compared to 5-F-AZADO (2) and 5,7-DiF-AZADO (3); however, AZADO-catalyzed oxidation exhibited a marked slowdown, resulting in ~90% conversion, whereas 5-F-AZADO-catalyzed oxidation smoothly reached completion without a marked slowdown. The reasons for the marked slowdown and the role of the fluoro group are discussed. Oxa-AZADO (6), TsN-AZADO (7), and DiAZADO (8) were designed and synthesized to confirm their comparable catalytic efficiency to that of 5-F-AZADO (2), providing supporting evidence for the electronic effect on the catalytic efficiency of the heteroatoms under NOx-assisted aerobic-oxidation conditions.
- Shibuya, Masatoshi,Nagasawa, Shota,Osada, Yuji,Iwabuchi, Yoshiharu
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p. 10256 - 10268
(2015/02/19)
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- A mild and highly efficient laccase-mediator system for aerobic oxidation of alcohols
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With the aid of the highly active nitroxyl radical AZADO (2-azaadamantane N-oxyl), a simple method for the aerobic catalytic oxidation of alcohols is presented. The oxidations could typically proceed under practical ambient conditions (room temperature, air atmosphere, no moisture effect, metal-free, etc.) with a broad generality of the alcohol substrates, and especially for the oxidation of complex and highly functionalized alcohols. An ionic mechanism is proposed for the present system.
- Zhu, Chenjie,Zhang, Zhi,Ding, Weiwei,Xie, Jingjing,Chen, Yong,Wu, Jinglan,Chen, Xiaochun,Ying, Hanjie
-
supporting information
p. 1131 - 1138
(2014/03/21)
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- Arene CH-O hydrogen bonding: A stereocontrolling tool in palladium-catalyzed arylation and vinylation of ketones
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Weak is powerful: For the arylation of tin enolates, the palladium catalyst engages in weak CH-O hydrogen bonds to control stereoselectivity (see scheme). Similar catalysts capable of NH-O hydrogen bonding also works well. Copyright
- Huang, Zhiyan,Lim, Li Hui,Chen, Zuliang,Li, Yongxin,Zhou, Feng,Su, Haibin,Zhou, Jianrong
-
supporting information
p. 4906 - 4911
(2013/06/05)
-
- Highly efficient Cu(I)-catalyzed oxidation of alcohols to ketones and aldehydes with diaziridinone
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A novel and efficient Cu(I)-catalyzed oxidation of alcohols has been achieved with di-tert-butyldiaziridinone as the oxidant under mild conditions. A wide variety of primary and secondary alcohols with various functional groups can be oxidized to aldehydes and ketones in high yields. The reaction proceeds under neutral conditions making it compatible with acid- or base-sensitive substrates, and it is amenable to gram scale.
- Zhu, Yingguang,Zhao, Baoguo,Shi, Yian
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supporting information
p. 992 - 995
(2013/04/10)
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- Chemoselective oxidation by electronically tuned nitroxyl radical catalysts
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Electronic tuning: Nitroxyl radical 1 is shown to be an efficient catalyst for the oxidation of secondary alcohols, and promotes oxidation through an oxoammonium species which is highly reactive because of the adjacent electron-withdrawing ester groups. Chemoselective oxidation of benzylic alcohols in the presence of aliphatic alcohols is observed and is proposed to proceed by a rate-determining hydride transfer. Copyright
- Hamada, Shohei,Furuta, Takumi,Wada, Yoshiyuki,Kawabata, Takeo
-
supporting information
p. 8093 - 8097
(2013/08/23)
-
- Influence of stereoregularity and linkage groups on chiral recognition of poly(phenylacetylene) derivatives bearing L -leucine ethyl ester pendants as chiral stationary phases for HPLC
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Stereoregular poly(phenylacetylene) derivatives bearing L-leucine ethyl ester pendants, poly-1 and poly-2a, were, respectively, synthesized by the polymerization of N-(4-ethynylphenylcarbamoyl)-L-leucine ethyl ester (1) and N-(4-ethynylphenyl-carbonyl)-L-leucine ethyl ester (2) using Rh(nbd)BPh 4 as a catalyst, while stereoirregular poly-2b was synthesized by solid-state thermal polymerization of 2. Their chiral recognition abilities for nine racemates were evaluated as chiral stationary phases (CSPs) for high-performance liquid chromatography (HPLC) after coating them on silica gel. Both poly-1 and poly-2a with a helical conformation showed their characteristic recognition depending on coating solvents and the linkage groups between poly(phenylacetylene) and L-leucine ethyl ester pendants. Poly-2a with a shorter amide linkage showed higher chiral recognition than poly-1 with a longer urea linkage. Coating solvents played an important role in the chiral recognition of both poly-1 and poly-2a due to the different conformation of the polymer main chains induced by the solvents. A few racemates were effectively resolved on the poly-2a coated with a MeOH/CHCl3 (3/7, v/v) mixture. The separation factors for these racemates were comparable to those obtained on the very popular CSPs derived from polysaccharide phenylcarbamates. Stereoirregular poly-2b exhibited much lower chiral recognition than the corresponding stereoregular, helical poly-2a, suggesting that the regular structure of poly(phenylacetylene) main chains is essential to attain high chiral recognition.
- Zhang, Chunhong,Liu, Fangbin,Li, Yufa,Shen, Xiande,Xu, Xiaodong,Sakai, Ryosuke,Satoh, Toshifumi,Kakuchi, Toyoji,Okamoto, Yoshio
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p. 2271 - 2278
(2013/05/09)
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- Enantioselective baeyer-villiger oxidation: Desymmetrization of meso cyclic ketones and kinetic resolution of racemic 2-arylcyclohexanones
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Catalytic enantioselective Baeyer-Villiger (BV) oxidations of racemic and meso cyclic ketones were achieved in the presence of chiral N,N'-dioxide-Sc III complex catalysts. The BV oxidations of prochiral cyclohexanones and cyclobutanones afforded series of optically active μ- and γ-lactones, respectively, in up to 99% yield and 95% ee. Meanwhile, the kinetic resolution of racemic 2-arylcyclohexanones was also realized via an abnormal BV oxidation. Enantioenriched 3-aryloxepan-2-ones, whose formation is counter to the migratory aptitude, were obtained preferentially. Both the lactones and the unreacted ketones were obtained with high ee values.
- Zhou, Lin,Liu, Xiaohua,Ji, Jie,Zhang, Yuheng,Hu, Xiaolei,Lin, Lili,Feng, Xiaoming
-
supporting information
p. 17023 - 17026,4
(2012/12/12)
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- Enantioselective baeyer-villiger oxidation: Desymmetrization of meso cyclic ketones and kinetic resolution of racemic 2-arylcyclohexanones
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Catalytic enantioselective Baeyer-Villiger (BV) oxidations of racemic and meso cyclic ketones were achieved in the presence of chiral N,N'-dioxide-Sc III complex catalysts. The BV oxidations of prochiral cyclohexanones and cyclobutanones afforded series of optically active μ- and γ-lactones, respectively, in up to 99% yield and 95% ee. Meanwhile, the kinetic resolution of racemic 2-arylcyclohexanones was also realized via an abnormal BV oxidation. Enantioenriched 3-aryloxepan-2-ones, whose formation is counter to the migratory aptitude, were obtained preferentially. Both the lactones and the unreacted ketones were obtained with high ee values.
- Zhou, Lin,Liu, Xiaohua,Ji, Jie,Zhang, Yuheng,Hu, Xiaolei,Lin, Lili,Feng, Xiaoming
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supporting information
p. 17023 - 17026
(2013/01/15)
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- An excellent dual recycling strategy for the hypervalent iodine/nitroxyl radical mediated selective oxidation of alcohols to aldehydes and ketones
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Using a recyclable hypervalent iodine reagent 1, the authors have constructed versatile and green methods for the hypervalent iodine and nitroxyl radical-mediated selective oxidation of alcohols to aldehydes and ketones. The recyclable reagent 1 having a unique tetraphenyladamantane structure exhibited almost the same reactivity as the ordinary reagent, phenyliodine diacetate (PIDA), in the hypervalent iodine(iii)/2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-mediated oxidation. For recycling, the reagent 1 could be nearly quantitatively recovered as the reduced tetraiodide 2 by filtration after reaction completion, utilizing the insolubility of the formed 2 in a polar solvent, specifically, methanol. Based on the confirmed reactivity and excellent recycling operation of the reagent 1, the methodology has been further extended to a greener dual recycling strategy. By combining the recyclable iodine reagent 1 and silica-supported TEPMO catalyst, a variety of alcohols were effectively oxidized to the desired aldehydes, and the two types of used reagent and catalyst, the iodine 1 and immobilized TEMPO 5, could be separately recovered by an easy workup, and both repeatedly used without any loss of their original activities for at least four cycles.
- Dohi, Toshifumi,Fukushima, Kei-Ichiro,Kamitanaka, Tohru,Morimoto, Koji,Takenaga, Naoko,Kita, Yasuyuki
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experimental part
p. 1493 - 1501
(2012/06/18)
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- Enantioselective oxidation by a cyclohexanone monooxygenase from the xenobiotic-degrading Polaromonas sp. strain JS666
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A cyclohexanone monooxygenase (CHMO) from the xenobiotic-degrading Polaromonas sp. strain JS666 was heterologously expressed in Escherichia coli, and its ability to catalyze enantio- and regiodivergent oxidations of prochiral and racemic ketones was investigated. The expression system was also used to evaluate this enzyme's potential role in the oxidation of cis-1,2-dichloroethene (cDCE), a groundwater pollutant for which strain JS666 is the only known assimilator. The substrate enantiopreference and -selectivity of the strain JS666 CHMO is similar to that of other CHMO-type enzymes; of note is this enzyme's excellent stereodiscrimination of 2-substituted cyclic ketones. The expression system exhibits no activity with ethene or cDCE as substrates under the tested conditions. Phylogenetic analysis shows that sequence variability among cyclohexanone monooxygenases could be a rich source of new enzyme activities and attributes.
- Alexander, Anne K.,Biedermann, David,Fink, Michael J.,Mihovilovic, Marko D.,Mattes, Timothy E.
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experimental part
p. 105 - 110
(2012/07/28)
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- Chiral sulfinamide/achiral sulfonic acid cocatalyzed enantioselective protonation of enol silanes
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The application of chiral sulfinamides and achiral sulfonic acids as a cocatalyst system for enantioselective protonation reactions is described. Structurally simple, easily accessible sulfinamides were found to induce moderate-to-high ee's in the formation of 2-aryl-substituted cycloalkanones from the corresponding trimethylsilyl enol ethers.
- Beck, Elizabeth M.,Hyde, Alan M.,Jacobsen, Eric N.
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p. 4260 - 4263
(2011/10/08)
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- Chiral bronsted acid from a cationic gold(I) complex: Catalytic enantioselective protonation of silyl enol ethers of ketones
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A chiral Bronsted acid has been developed from a cationic gold(I) disphosphine complex in the presence of alcoholic solvent and applied to the enantioselective protonation reaction of silyl enol ethers of ketones. Various optically active cyclic ketones were obtained in excellent yields and high enantioselectivities, including cyclic ketones bearing aliphatic substrates at the α-position. Furthermore, the application of this Bronsted acid was extended to the first Bronsted acid-catalyzed enantioselective protonation reaction of silyl enol ethers of acyclic substrates, regardless of their E/Z ratio.
- Cheon, Cheol Hong,Kanno, Osamu,Toste, F. Dean
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p. 13248 - 13251
(2011/10/10)
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- Highly efficient, organocatalytic aerobic alcohol oxidation
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5-Fluoro-2-azaadamantane N-oxyl (5-F-AZADO) realizes a simple, organocatalytic aerobic alcohol oxidation system that has a wide scope under mild conditions at ambient pressure and temperature and is weakly acidic and halogen- and transition-metal-free. The oxoammonium nitrate (5-F-AZADO +NO3-) works as a bifunctional catalyst of 5-F-AZADO and NOx that enables the catalytic aerobic oxidation of alcohols by itself (a metal-salt-free system).
- Shibuya, Masatoshi,Osada, Yuji,Sasano, Yusuke,Tomizawa, Masaki,Iwabuchi, Yoshiharu
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supporting information; experimental part
p. 6497 - 6500
(2011/06/23)
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- Rapid determination of enantiomeric excess of α-chiral cyclohexanones using circular dichroism spectroscopy
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Chemical equations presented. Ketone handedness was discriminated using circular dichroism (CD) spectroscopy by monitoring the metal-to-ligand charge transfer (MLCT) bands of complexes between [CuI((S)-1)(CH 3CN)2]PF6 and derivatized α-chiral cyclohexanones (4). This method was able to quantify the enantiomeric excess of unknown samples using a calibration curve, giving an absolute error of ±7%. The analysis was fast, allowing potential application of this assay in high-throughput screening (HTS).
- Leung, Diana,Anslyn, Eric V.
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supporting information; experimental part
p. 2298 - 2301
(2011/06/26)
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- Immobilization and chromatographic evaluation of novel regioselectively substituted amylose-based chiral packing materials for HPLC
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The regioselectively substituted amylose derivatives bearing a 4-tert-butylbenzoate or 4-chlorobenzoate group at 2-position, and 3,5-dichlorophenylcarbamate and a small amount of 3-(triethoxysilyl) propylcarbamate groups at 3- and 6-positions were synthesized by a two-step process based on the esterification of 2-position of a glucose unit. The obtained derivatives were effectively immobilized onto macroporous silica gel by intermolecular polycondensation of triethoxysilyl groups. Their chiral recognition abilities were evaluated as chiral packing materials (CPMs) for high-performance liquid chromatography. These CPMs showed high chiral recognition as well as the conventional coated-type CPM, and can be used with the eluents-containing chloroform and tetrahydrofuran. With the extended use of these eluents, improvement of chiral recognition and reversed elution orders were realized. For some racemates, the immobilized CPM exhibited ability comparable or better to the commercial immobilized amylose- or cellulose-based columns,
- Shen, Jun,Li, Pengfei,Liu, Shuangyan,Shen, Xiande,Okamoto, Yoshio
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scheme or table
p. 878 - 886
(2012/06/30)
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- Induced allostery in the directed evolution of an enantioselective Baeyer-Villiger monooxygenase
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The molecular basis of allosteric effects, known to be caused by an effector docking to an enzyme at a site distal from the binding pocket, has been studied recently by applying directed evolution. Here, we utilize laboratory evolution in a different way, namely to induce allostery by introducing appropriate distal mutations that cause domain movements with concomitant reshaping of the binding pocket in the absence of an effector. To test this concept, the thermostable Baeyer-Villiger monooxygenase, phenylacetone monooxygenase (PAMO), was chosen as the enzyme to be employed in asymmetric Baeyer-Villiger reactions of substrates that are not accepted by the wild type. By using the known X-ray structure of PAMO, a decision was made regarding an appropriate site at which saturation mutagenesis is most likely to generate mutants capable of inducing allostery without any effector compound being present. After screening only 400 transformants, a double mutant was discovered that catalyzes the asymmetric oxidative kinetic resolution of a set of structurally different 2-substituted cyclohexanone derivatives as well as the desymmetrization of three different 4-substituted cyclohexanones, all with high enantioselectivity. Molecular dynamics (MD) simulations and covariance maps unveiled the origin of increased substrate scope as being due to allostery. Large domain movements occur that expose and reshape the binding pocket. This type of focused library production, aimed at inducing significant allosteric effects, is a viable alternative to traditional approaches to designed directed evolution that address the binding site directly.
- Wu, Sheng,Acevedo, Juan Pablo,Reetz, Manfred T.
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experimental part
p. 2775 - 2780
(2010/10/03)
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- Separating agent for enantiomeric isomers
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The present invention provides a separating agent for enantiomeric isomers exhibiting high separation power. That is, the present invention provides a separating agent for enantiomeric isomers including, as an active ingredient, a polysaccharide derivative having at least part of hydrogen atoms of hydroxyl groups of a polysaccharide such as cellulose or amylose substituted by at least one of atomic groups represented by the following general formulae (I) and (II): (in the formulae, R represents a substituted or unsubstituted aromatic group, or a linear, branched, or cyclic aliphatic group).
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Page/Page column 7; 8; 9
(2010/04/23)
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- OPTICAL-ISOMER SEPARATING AGENT FOR CHROMATOGRAPHY AND PROCESS FOR PRODUCING THE SAME
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A novel optical-isomer separating agent for chromatography is provided which has, as a chiral selector, a macrocyclic amide compound having the ability to function as a chiral shift agent. The optical-isomer separating agent for chromatography is formed by bonding, with a carrier by chemical bonding, a specific ring structure containing an asymmetry recognition site, an amide group as a hydrogen-bond donor site, and a hydrogen-bond acceptor site.
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Page/Page column 16-17
(2010/12/18)
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- Catalytic asymmetric reductive animation of α-branched ketones
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Chemical equcation Presented Branching out: An organocatalytic reductive amination of -αbranched ketones using dynamic kinetic resolution is reported. The e/s-2-substituted cyclohexyl amines were obtained in high diastereoselectivity and enantioselectivit
- Wakchaure, Vijay N.,Zhou, Jian,Hoffmann, Sebastian,List, Benjamin
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scheme or table
p. 4612 - 4614
(2010/08/07)
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- Development of a new Lewis base-tolerant chiral LBA and its application to catalytic asymmetric protonation reaction
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A new Lewis base-tolerant LBA (Lewis Acid Assisted Bronsted Acid) derived from La(OTf)3 and (S)-HOP has been developed as a new chiral Bronsted acid. This acid has been successfully applied as a catalyst to asymmetric protonation reactions of silyl enol ethers of 2-substituted cyclic ketones.
- Cheon, Cheol Hong,Imahori, Tatsushi,Yamamoto, Hisashi
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supporting information; experimental part
p. 6980 - 6982
(2010/11/02)
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- Filler for Optical Isomer Separation
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A polymer compound derivative, obtained by modifying part of the hydroxy or amino groups of a polymer compound having the hydroxy or amino groups with molecules of a compound represented by the following general formula (I): A-X—Si(Y)nR3-n (I), where A represents a reactive group which reacts with a hydroxy or amino group, X represents an alkylene group which has 1 to 18 carbon atoms and which may have a branch, or an arylene group which may have a substituent, Y represents a reactive group which reacts with a silanol group to form a siloxane bond, R represents an alkyl group which has 1 to 18 carbon atoms and which may have a branch, or an aryl group which may have a substituent, and n represents an integer of 1 to 3.
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Page/Page column 9; 11
(2009/05/28)
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- Laboratory evolution of robust and enantioselective Baeyer-Villiger monooxygenases for asymmetric catalysis
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The Baeyer-Villiger Monooxygenase, Phenylacetone Monooxygenase (PAMO), recently discovered by Fraaije, Janssen, and co-workers, is unusually thermostable, which makes it a promising candidate for catalyzing enantioselective Baeyer-Villiger reactions in organic chemistry. Unfortunately, however, its substrate scope is very limited, reasonable reaction rates being observed essentially only with phenylacetone and similar linear phenyl-substituted analogs. Previous protein engineering attempts to broaden the range of substrate acceptance and to control enantioselectivity have been met with limited success, including rational design and directed evolution based on saturation mutagenesis with formation of focused mutant libraries, which may have to do with complex domain movements. In the present study, a new approach to laboratory evolution is described which has led to mutants showing unusually high activity and enantioselectivity in the oxidative kinetic resolution of a variety of 2-aryl and 2-alkylcyclohexanones which are not accepted by the wild-type (WT) PAMO and of a structurally very different bicyclic ketone. The new strategy exploits bioinformatics data derived from sequence alignment of eight different Baeyer-Villiger Monooxygenases, which in conjunction with the known X-ray structure of PAMO and induced fit docking suggests potential randomization sites, different from all previous approaches to focused library generation. Sites harboring highly conserved proline in a loop of the WT are targeted. The most active and enantioselective mutants retain the high thermostability of the parent WT PAMO. The success of the "proline" hypothesis in the present system calls for further testing in future laboratory evolution studies.
- Reetz, Manfred T.,Wu, Sheng
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supporting information; experimental part
p. 15424 - 15432
(2010/02/16)
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- Highly enantioselective organocatalytic oxidative kinetic resolution of secondary alcohols using chirally Modified AZADOs
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A highly enantioselective organocatalytic oxidative kinetic resolution (OKR) of racemic secondary alcohols has been accomplished using asymmetric organocatalysis. A panel of chirally modified 2-azaadamantane N-oxyls (AZADOs) exhibit superior catalytic act
- Tomizawa, Masaki,Shibuya, Masatoshi,Iwabuchi, Yoshiharu
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supporting information; experimental part
p. 1828 - 1831
(2009/09/06)
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- Hypervalent iodine(III)/Et4N+Br- combination in water for green and racemization-free aqueous oxidation of alcohols
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We have found that the use of the PhI(OAc)2/Et4N+Br- combination in water can significantly enhance its oxidation ability and oxidize a wide range of alcohols 1 to carbonyl compounds 2 in good to excellent yields. This clean aqueous oxidation method shows no detectable racemization processes, and even an enolizable ketone 2m could be obtained in an optically pure form from the corresponding chiral alcohol 1m. Utilization of the recyclable reagent 3 as a more practical alternative to PhI(OAc)2 is also successful in these reactions.
- Takenaga, Naoko,Goto, Akihiro,Yoshimura, Misaki,Fujioka, Hiromichi,Dohi, Toshifumi,Kita, Yasuyuki
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experimental part
p. 3227 - 3229
(2009/08/09)
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- 2-iodoxybenzenesulfonic acid as an extremely active catalyst for the selective oxidation of alcohols to aldehydes, ketones, carboxylic acids, and enones with oxone
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Electron-donating group-substituted 2-iodoxybenzoic acids (IBXs) such as5-Me-IBX (1g), 5-MeO-IBX (1h), and 4,5-Me2-IBX were superior to IBX 1a as catalysts for the oxidation of alcohols with Oxone (a trad emark of DuPont) under nonaqueous conditions, although Oxone was almost insoluble in most organic solvents. The catalytic oxidation proceeded more rapidly and cleanly in nitromethane. Furthermore, 2-iodoxybenzenesulfonic acid (IBS, 6a) was much more active than modified IBXs. Thus, we established a highly efficient and selective method for the oxidation of primary and secondary alcohols to carbonyl compounds such as aldehydes, carboxylic acids, and ketones with Oxone in nonaqueous nitromethane, acetonitrile, or ethyl acetate in the presence of 0.05-5molpercentof 6a, which was generated in situ from 2-iodobenzenesulfonic acid (7a) or its sodium salt. Cycloalkanones could be further oxidized to α,β- cycloalkenones or lactones by controlling the amounts of Oxone under the same conditions as above. When Oxone was used under nonaqueous conditions, Oxone wastes could be removed by simple filtration. Based on theoretical calculations, we considered that the relatively ionic character of the intramolecular hypervalent iodine-OSO2 bond of IBS might lower the twisting barrier of the alkoxyperiodinane intermediate 16.
- Uyanik, Muhammet,Akakura, Matsujiro,Ishihara, Kazuaki
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supporting information; experimental part
p. 251 - 262
(2009/06/28)
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- Chiral selector with multiple hydrogen-bonding sites in a macrocyclic cavity
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(Chemical Equation Presented) Chiral macrocycles with the hydrogen bond donor/acceptor sites in the cavity were synthesized and covalently bonded to silica gel to give chiral stationary phases (CSPs), which showed excellent abilities to resolve various chiral compounds, such as benzoin and Co(acac) 3, in HPLC. Various organic solvents could be used as the mobile phase to optimize the resolution efficiency of CSPs, and in some cases, even MeCN, MeOH, and CO2 could be used for the complete resolution of enantiomers.
- Ema, Tadashi,Tanida, Daisuke,Sugita, Kyoko,Sakai, Takashi,Miyazawa, Ken-Ichiro,Ohnishi, Atsushi
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supporting information; experimental part
p. 2365 - 2368
(2009/05/27)
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- A bronsted acid catalyst for the enantioselective protonation reaction
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A highly reactive and robust chiral Bronsted acid catalyst, chiral N-triflyl thiophosphoramide, was developed. The first metal-free Bronsted acid catalyzed enantioselective protonation reaction of silyl enol ethers was demonstrated using this chiral Bronsted acid catalyst. The catalyst loading could be reduced to 0.05 mol % without any deleterious effect on the enantioselectivity. Copyright
- Cheol, Hong Cheon,Yamamoto, Hisashi
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supporting information; body text
p. 9246 - 9247
(2009/02/02)
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- A light-driven stereoselective biocatalytic oxidation
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Let the sunshine in: Light can be used to drive enantioselective Baeyer-Villiger oxidations of cyclic ketones catalyzed by a flavin-dependent enzyme. Photochemical reduction of the flavin using ethylenediaminetetraacetate (EDTA) as the sacrificial electron donor closes the catalytic cycle, thus providing a means to directly regenerate reduced flavin cofactors without the need for costly nicotinamide cofactors as electron donors. (Chemical Equation Presented).
- Hollmann, Frank,Taglieber, Andreas,Schulz, Frank,Reetz, Manfred T.
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p. 2903 - 2906
(2008/03/13)
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