- A Protocol for NMR Analysis of the Enantiomeric Excess of Chiral Diols Using an Achiral Diboronic Acid Template
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A practically simple derivatization protocol for determining the enantiopurity of chiral diols by 1H NMR spectroscopic analysis is described. Diols were treated with 0.5 equiv of 1,3-phenyldiboronic acid to afford mixtures of diastereomeric boronate esters whose homochiral/heterochiral ratios are an accurate reflection of the diol's enantiopurity.
- Tickell, David A.,Lampard, Emma V.,Lowe, John P.,James, Tony D.,Bull, Steven D.
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- A stand-alone cobalt bis(dicarbollide) photoredox catalyst epoxidates alkenes in water at extremely low catalyst load
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The cobalt bis(dicarbollide) complex, Na[3,3′-Co(η5-1,2-C2B9H11) (Na[1]), is an effective photoredox catalyst for the oxidation of alkenes to epoxides in water. Advantageous features of Na[1] include its lack of photoluminescence, high solubility and surfactant behavior in aqueous media, as well as the donor ability of the carborane ligand and high oxidizing power of the Co4+/3+ couple. These features differentiate it from the well-known and widely used photosensitizer tris (2,2′-bipyridine) ruthenium(ii) ([Ru(bpy)3]2+), which also participates in electron transfer through an outer sphere mechanism. A comparison of the catalytic performance of [Ru(bpy)3]2+ with Na[1] for alkene photo-oxidation is fully in favor of Na[1], as the former shows very low or null efficiency. With a catalyst loading of 0.1 mol% conversions between 65-97% have been obtained in short reaction times, 15 minutes, with moderate selectivity for the corresponding epoxide, due to the formation of side products as diols. But when the catalyst loading is reduced to 0.01 mol%, the selectivity for the corresponding epoxide increased considerably, being the only compound formed after 15 minutes of reaction (selectivity >99%). High TON values have been obtained (TON = 8500) for the epoxidation of aromatic and aliphatic alkenes in water. We have verified that Na[3,3′-Co(η5-1,2-C2B9H11)2] acts as a photocatalyst in both the epoxidation of alkenes and in their hydroxylation in aqueous medium with a higher rate for epoxidation than for hydroxylation. Preliminary photooxidation tests using methyl oleate as the substrate led to the selective epoxidation of the double bond. These results represent a promising starting point for the development of practical methods for the processing of unsaturated fatty acids, such as the valorisation of animal fat waste using this sustainable photoredox catalyst. This journal is
- Guerrero, Isabel,Romero, Isabel,Teixidor, Francesc,Vi?as, Clara
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supporting information
p. 10123 - 10131
(2021/12/27)
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- Electrochemically Tuned Oxidative [4+2] Annulation and Dioxygenation of Olefins with Hydroxamic Acids
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This work represents the first [4+2] annulation of hydroxamic acids with olefins for the synthesis of benzo[c][1,2]oxazines scaffold via anode-selective electrochemical oxidation. This protocol features mild conditions, is oxidant free, shows high regioselectivity and stereoselectivity, broad substrate scope of both alkenes and hydroxamic acids, and is compatible with terpenes, peptides, and steroids. Significantly, the dioxygenation of olefins employing hydroxamic acid is also successfully achieved by switching the anode material under the same reaction conditions. The study not only reveals a new reactivity of hydroxamic acids and its first application in electrosynthesis but also provides a successful example of anode material-tuned product selectivity.
- Wei, Bang-Yi,Xie, Dong-Tai,Lai, Sheng-Qiang,Jiang, Yu,Fu, Hong,Wei, Dian,Han, Bing
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supporting information
p. 3182 - 3188
(2020/12/11)
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- Iodine-Initiated Dioxygenation of Aryl Alkenes Using tert-Butylhydroperoxides and Water: A Route to Vicinal Diols and Bisperoxides
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An environment-friendly and efficient dioxygenation of aryl alkenes for the construction of vicinal diols has been developed in water with iodine as the catalyst and tert-butylhydroperoxides (TBHPs) as the oxidant. The protocol was efficient, sustainable, and operationally simple. Detailed mechanistic studies indicated that one of the hydroxyl groups is derived from water and the other one is derived from TBHP. Additionally, the bisperoxides could be obtained in good yields with iodine as the catalyst, Na2CO3 as the additive, and propylene carbonate as the solvent, instead.
- Gao, Xiaofang,Lin, Jiani,Zhang, Li,Lou, Xinyao,Guo, Guanghui,Peng, Na,Xu, Huan,Liu, Yi
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p. 15469 - 15480
(2021/11/16)
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- A One-Pot Two-Step Enzymatic Pathway for the Synthesis of Enantiomerically Enriched Vicinal Diols
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Enantiomerically enriched 1,2-diols are prominent compounds that find numerous applications in organic chemistry. They are privileged building blocks for the synthesis of APIs (Active Pharmaceutical Ingredients), broadly used as chiral ligands in asymmetric catalysis, and efficient auxiliaries employed to control the stereochemical outcome of total synthesis. Among the number of strategies developed for the preparation of these molecules, enzyme mediated reactions have gained a crucial role in the toolbox of organic chemists for their high efficiency and sustainability. Herein we describe a one-pot two-step protocol designed by combining a thiamine diphosphate (ThDP)-dependent lyase and a NADH-dependent reductase. The ThDP-dependent acetoin:dichlorophenolindophenol oxidoreductase (Ao : DCPIP OR) is exploited to produce enantioenriched α-hydroxyketones through the benzoin-type condensation of methylacetoin with either aldehydes or activated ketones. The enantioenriched α-hydroxyketones undergo the selective reduction into the corresponding 1,2-diols in the same reaction mixture due to the addition of NAD+ and of the NADH-dependent acetylacetoin reductase (AAR). Sodium formate was selected as the sacrificial reductive reactant to generate and recycle in situ the precious NADH by formate-dehydrogenase. Unprecedented reported details on the cloning and expression of the AAR are reported as well.
- Giovannini, Pier Paolo,Müller, Michel,Presini, Francesco,Baraldi, Serena,Ragno, Daniele,Di Carmine, Graziano,Jacoby, Christian,Bernacchia, Giovanni,Bortolini, Olga
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p. 973 - 978
(2021/02/01)
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- Enantioselective, Stereoconvergent Resolution Copolymerization of Racemic cis-Internal Epoxides and Anhydrides
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Unprecedented enantioselective resolution copolymerization of racemic cis-internal epoxides and anhydrides was mediated by dinuclear aluminum complexes with multiple chirality, affording optically active polyesters with two contiguous stereogenic centers, and the unreacted substrates in good enantioselectivity. Unexpected stereoconvergence is observed in this resolution copolymerization, where the selectivity factor for the enantioselective formation of copolymer significantly exceeds the kinetic resolution coefficient based on the unreacted epoxide at various conversions. Catalytic activity and copolymer enantioselectivity are strongly influenced by the phenolate ortho-substituents of the ligand set, as well as the axial linker and its chirality. An enantiopure binaphthol-linked bimetallic AlIII complex allows stereoconvergent access to the stereoregular semi-crystalline polyesters and a concomitant kinetic resolution of the epoxide substrates.
- He, Guang-Hui,Ren, Bai-Hao,Chen, Shi-Yu,Liu, Ye,Lu, Xiao-Bing
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supporting information
p. 5994 - 6002
(2021/02/11)
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- Regio- and stereoselective multi-enzymatic aminohydroxylation of β-methylstyrene using dioxygen, ammonia and formate
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We report an enzymatic route for the formal regio- and stereoselective aminohydroxylation of β-methylstyrene that consumes only dioxygen, ammonia and formate; carbonate is the by-product. The biocascade entails highly selective epoxidation, hydrolysis and hydrogen-borrowing alcohol amination. Thus, β-methylstyrene was converted into 1R,2R and 1S,2R-phenylpropanolamine in 59-63% isolated yields, and up to >99.5 : 0.5 dr and er.
- Corrado, Maria L.,Knaus, Tanja,Mutti, Francesco G.
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p. 6246 - 6251
(2019/12/03)
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- Atroposelective Synthesis of PINAP via Dynamic Kinetic Asymmetric Transformation
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The atroposelective synthesis of PINAP ligands has been accomplished via a palladium-catalyzed C?P coupling process through dynamic kinetic asymmetric transformation. These catalytic conditions allow access to a wide variety of alkoxy- and benzyloxy-substituted PINAP ligands in high enantiomeric excess. The methods described in this communication afford valuable P,N ligands in good yields and high enantioselectivity using low catalyst loading. (Figure presented.).
- Han, Seo-Jung,Bhat, Vikram,Stoltz, Brian M.,Virgil, Scott C.
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p. 441 - 444
(2018/12/14)
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- Copper-Catalyzed Tandem Hydrocupration and Diastereo- and Enantioselective Borylalkyl Addition to Aldehydes
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We report the copper-catalyzed stereoselective addition of in situ generated chiral boron-α-alkyl intermediates to various aldehydes including α,β-unsaturated aldehydes under mild conditions. This tandem and multicomponent method facilitated the synthesis of enantiomerically enriched 1,2-hydroxyboronates bearing contiguous stereocenters in good yield with high diastereo- and enantioselectivity up to a ratio greater than 98:2. In particular, α,β-unsaturated aldehydes were successfully used as electrophiles in Cu?H catalysis through 1,2-addition without significant reduction. The resulting 1,2-hydroxyboronates were used in various transformations.
- Jang, Won Jun,Yun, Jaesook
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supporting information
p. 12116 - 12120
(2018/09/11)
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- Direct, high-yielding, one-step synthesis of vic-diols from aryl alkynes
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An unprecedented, high yielding, direct, one-step synthesis of vic-diols from alkynes has been developed via metal-free, open-to-air dihydroboration with ammonia borane. The electronics of the alkyne and the reaction stoichiometry are critical for obtaining optimal yields of the 1,2-diol.
- Ramachandran, P. Veeraraghavan,Drolet, Michael P.
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supporting information
p. 967 - 970
(2018/02/14)
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- Cis -Oxoruthenium complexes supported by chiral tetradentate amine (N4) ligands for hydrocarbon oxidations
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We report the first examples of ruthenium complexes cis-[(N4)RuIIICl2]+ and cis-[(N4)RuII(OH2)2]2+ supported by chiral tetradentate amine ligands (N4), together with a high-valent cis-dioxo complex cis-[(N4)RuVI(O)2]2+ supported by the chiral N4 ligand mcp (mcp = N,N′-dimethyl-N,N′-bis(pyridin-2-ylmethyl)cyclohexane-1,2-diamine). The X-ray crystal structures of cis-[(mcp)RuIIICl2](ClO4) (1a), cis-[(Me2mcp)RuIIICl2]ClO4 (2a) and cis-[(pdp)RuIIICl2](ClO4) (3a) (Me2mcp = N,N′-dimethyl-N,N′-bis((6-methylpyridin-2-yl)methyl)cyclohexane-1,2-diamine, pdp = 1,1′-bis(pyridin-2-ylmethyl)-2,2′-bipyrrolidine)) show that the ligands coordinate to the ruthenium centre in a cis-α configuration. In aqueous solutions, proton-coupled electron-transfer redox couples were observed for cis-[(mcp)RuIII(O2CCF3)2]ClO4 (1b) and cis-[(pdp)RuIII(O3SCF3)2]CF3SO3 (3c′). Electrochemical analyses showed that the chemically/electrochemically generated cis-[(mcp)RuVI(O)2]2+ and cis-[(pdp)RuVI(O)2]2+ complexes are strong oxidants with E° = 1.11-1.13 V vs. SCE (at pH 1) and strong H-atom abstractors with DO-H = 90.1-90.8 kcal mol-1. The reaction of 1b or its (R,R)-mcp counterpart with excess (NH4)2[CeIV(NO3)6] (CAN) in aqueous medium afforded cis-[(mcp)RuVI(O)2](ClO4)2 (1e) or cis-[((R,R)-mcp)RuVI(O)2](ClO4)2 (1e?), respectively, a strong oxidant with E(RuVI/V) = 0.78 V (vs. Ag/AgNO3) in acetonitrile solution. Complex 1e oxidized various hydrocarbons, including cyclohexane, in acetonitrile at room temperature, affording alcohols and/or ketones in up to 66% yield. Stoichiometric oxidations of alkenes by 1e or 1e? in tBuOH/H2O (5:1 v/v) afforded diols and aldehydes in combined yields of up to 98%, with moderate enantioselectivity obtained for the reaction using 1e?. The cis-[(pdp)RuII(OH2)2]2+ (3c)-catalysed oxidation of saturated C-H bonds, including those of ethane and propane, with CAN as terminal oxidant was also demonstrated.
- Tse, Chun-Wai,Liu, Yungen,Wai-Shan Chow, Toby,Ma, Chaoqun,Yip, Wing-Ping,Chang, Xiao-Yong,Low, Kam-Hung,Huang, Jie-Sheng,Che, Chi-Ming
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p. 2803 - 2816
(2018/03/21)
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- Semirational Engineering of the Naphthalene Dioxygenase from Pseudomonas sp. NCIB 9816-4 towards Selective Asymmetric Dihydroxylation
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Enzyme-catalyzed asymmetric dihydroxylation is a powerful tool for the selective oxyfunctionalization of various organic compounds. By applying Rieske non-heme dioxygenases (ROs), molecular oxygen and a reduction equivalent are needed for the generation of vicinal cis-diols. We report a comprehensive mutagenesis study of the active site of the naphthalene dioxygenase from Pseudomonas sp. NCIB 9816-4 comprising 62 variants. We aimed to understand the important structure–function relationships by investigating different substituted arene substrates and the geometry of the active site. Introducing single-point mutations at positions F202, A206, V260, H295, F352, and L307 resulted in drastic shifts in the reaction specificity, regioselectivity, and stereoselectivity (≥90 %) while maintaining the residual activity towards the natural substrate naphthalene.
- Halder, Julia M.,Nestl, Bettina M.,Hauer, Bernhard
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p. 178 - 182
(2017/12/26)
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- Green Organocatalytic Dihydroxylation of Alkenes
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An inexpensive, green, metal-free one-pot procedure for the dihydroxylation of alkenes is described. H2O2 and 2,2,2-trifluoroacetophenone were employed as the oxidant and organocatalyst, respectively, in this highly sustainable protocol in which a variety of homoallylic alcohols, aminoalkenes, and simple alkenes were converted into the corresponding polyalcohols in good to excellent yields. This process takes advantage of an epoxidation reaction followed by an acidic treatment in which water participates in the ring opening of the in situ prepared epoxide to lead to the desired product.
- Theodorou, Alexis,Triandafillidi, Ierasia,Kokotos, Christoforos G.
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p. 1502 - 1509
(2017/04/01)
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- A Well-Defined Osmium-Cupin Complex: Hyperstable Artificial Osmium Peroxygenase
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Thermally stable TM1459 cupin superfamily protein from Thermotoga maritima was repurposed as an osmium (Os) peroxygenase by metal-substitution strategy employing the metal-binding promiscuity. This novel artificial metalloenzyme bears a datively bound Os ion supported by the 4-histidine motif. The well-defined Os center is responsible for not only the catalytic activity but also the thermodynamic stability of the protein folding, leading to the robust biocatalyst (Tm ≈ 120 °C). The spectroscopic analysis and atomic resolution X-ray crystal structures of Os-bound TM1459 revealed two types of donor sets to Os center with octahedral coordination geometry. One includes trans-dioxide, OH, and mer-three histidine imidazoles (O3N3 donor set), whereas another one has four histidine imidazoles plus OH and water molecule in a cis position (O2N4 donor set). The Os-bound TM1459 having the latter donor set (O2N4 donor set) was evaluated as a peroxygenase, which was able to catalyze cis-dihydroxylation of several alkenes efficiently. With the low catalyst loading (0.01% mol), up to 9100 turnover number was achieved for the dihydroxylation of 2-methoxy-6-vinyl-naphthalene (50 mM) using an equivalent of H2O2 as oxidant at 70 °C for 12 h. When octene isomers were dihydroxylated in a preparative scale for 5 h (2% mol cat.), the terminal alkene octene isomers was converted to the corresponding diols in a higher yield as compared with the internal alkenes. The result indicates that the protein scaffold can control the regioselectivity by the steric hindrance. This protein scaffold enhances the efficiency of the reaction by suppressing disproportionation of H2O2 on Os reaction center. Moreover, upon a simple site-directed mutagenesis, the catalytic activity was enhanced by about 3-fold, indicating that Os-TM1459 is evolvable nascent osmium peroxygenase.
- Fujieda, Nobutaka,Nakano, Takumi,Taniguchi, Yuki,Ichihashi, Haruna,Sugimoto, Hideki,Morimoto, Yuma,Nishikawa, Yosuke,Kurisu, Genji,Itoh, Shinobu
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supporting information
p. 5149 - 5155
(2017/05/04)
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- Assessing the stereoselectivity of: Serratia marcescens CECT 977 2,3-butanediol dehydrogenase
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α-Hydroxy ketones and vicinal diols constitute well-known building blocks in organic synthesis. Here we describe one enzyme that enables the enantioselective synthesis of both building blocks starting from diketones. The enzyme 2,3-butanediol dehydrogenase (BudC) from S. marcescens CECT 977 belongs to the NADH-dependent metal-independent short-chain dehydrogenases/reductases family (SDR) and catalyses the selective asymmetric reductions of prochiral α-diketones to the corresponding α-hydroxy ketones and diols. BudC is highly active towards structurally diverse diketones in combination with nicotinamide cofactor regeneration systems. Aliphatic diketones, cyclic diketones and alkyl phenyl diketones are well accepted, whereas their derivatives possessing two bulky groups are not converted. In the reverse reaction vicinal diols are preferred over other substrates with hydroxy/keto groups in non-vicinal positions.
- Médici, Rosario,Stammes, Hanna,Kwakernaak, Stender,Otten, Linda G.,Hanefeld, Ulf
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p. 1831 - 1837
(2017/07/15)
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- Highly Enantioselective Iron-Catalyzed cis-Dihydroxylation of Alkenes with Hydrogen Peroxide Oxidant via an FeIII-OOH Reactive Intermediate
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The development of environmentally benign catalysts for highly enantioselective asymmetric cis-dihydroxylation (AD) of alkenes with broad substrate scope remains a challenge. By employing [FeII(L)(OTf)2] (L=N,N′-dimethyl-N,N′-bis(2-methyl-8-quinolyl)-cyclohexane-1,2-diamine) as a catalyst, cis-diols in up to 99.8 % ee with 85 % isolated yield have been achieved in AD of alkenes with H2O2as an oxidant and alkenes in a limiting amount. This “[FeII(L)(OTf)2]+H2O2” method is applicable to both (E)-alkenes and terminal alkenes (24 examples >80 % ee, up to 1 g scale). Mechanistic studies, including18O-labeling, UV/Vis, EPR, ESI-MS analyses, and DFT calculations lend evidence for the involvement of chiral FeIII-OOH active species in enantioselective formation of the two C?O bonds.
- Zang, Chao,Liu, Yungen,Xu, Zhen-Jiang,Tse, Chun-Wai,Guan, Xiangguo,Wei, Jinhu,Huang, Jie-Sheng,Che, Chi-Ming
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supporting information
p. 10253 - 10257
(2016/08/24)
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- Chiral-Substituted Poly-N-vinylpyrrolidinones and Bimetallic Nanoclusters in Catalytic Asymmetric Oxidation Reactions
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A new class of poly-N-vinylpyrrolidinones containing an asymmetric center at C5 of the pyrrolidinone ring were synthesized from l-amino acids. The polymers, particularly 17, were used to stabilize nanoclusters such as Pd/Au for the catalytic asymmetric oxidations of 1,3- and 1,2-cycloalkanediols and alkenes, and Cu/Au was used for C-H oxidation of cycloalkanes. It was found that the bulkier the C5 substituent in the pyrrolidinone ring, the greater the optical yields produced. Both oxidative kinetic resolution of (±)-1,3- and 1,2-trans-cycloalkanediols and desymmetrization of meso cis-diols took place with 0.15 mol % Pd/Au (3:1)-17 under oxygen atmosphere in water to give excellent chemical and optical yields of (S)-hydroxy ketones. Various alkenes were oxidized with 0.5 mol % Pd/Au (3:1)-17 under 30 psi of oxygen in water to give the dihydroxylated products in >93% ee. Oxidation of (R)-limonene at 25 °C occurred at the C-1,2-cyclic alkene function yielding (1S,2R,4R)-dihydroxylimonene 49 in 92% yield. Importantly, cycloalkanes were oxidized with 1 mol % Cu/Au (3:1)-17 and 30% H2O2 in acetonitrile to afford chiral ketones in very good to excellent chemical and optical yields. Alkene function was not oxidized under the reaction conditions. Mechanisms were proposed for the oxidation reactions, and observed stereo- and regio-chemistry were summarized.
- Hao, Bo,Gunaratna, Medha J.,Zhang, Man,Weerasekara, Sahani,Seiwald, Sarah N.,Nguyen, Vu T.,Meier, Alex,Hua, Duy H.
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supporting information
p. 16839 - 16848
(2017/01/10)
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- Stereoselective Two-Step Biocatalysis in Organic Solvent: Toward All Stereoisomers of a 1,2-Diol at High Product Concentrations
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Biotransformations on larger scale are mostly limited to cases in which alternative chemical routes lack sufficient chemo-, regio-, or stereoselectivity. Here, we expand the applicability of biocatalysis by combining cheap whole cell catalysts with a microaqueous solvent system. Compared to aqueous systems, this permits manifoldly higher concentrations of hydrophobic substrates while maintaining stereoselectivity. We apply these methods to four different two-step reactions of carboligation and oxidoreduction to obtain 1-phenylpropane-1,2-diol (PPD), a versatile building block for pharmaceuticals, starting from inexpensive aldehyde substrates. By a modular combination of two carboligases and two alcohol dehydrogenases, all four stereoisomers of PPD can be produced in a flexible way. After thorough optimization of each two-step reaction, the resulting processes enabled up to 63 g L-1 product concentration (98% yield), space-time-yields up to 144 g L-1 d-1, and a target isomer content of at least 95%. Despite the use of whole cell catalysts, we did not observe any side product formation of note. In addition, we prove that, by using 1,5-pentandiol as a smart cosubstrate, a very advantageous cofactor regeneration system could be applied.
- Wachtmeister, Jochen,Jakoblinnert, Andre,Rother, D?rte
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p. 1744 - 1753
(2016/10/31)
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- Production Of Enantiopure alpha-Hydroxy Carboxylic Acids From Alkenes By Cascade Biocatalysis
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The invention provides compositions comprising an alkene epoxidase and a selective epoxide hydrolase, such as a recombinant microorganism comprising a first heterologous nucleic acid encoding an alkene epoxidase and a second heterologous nucleic acid encoding a selective epoxide hydrolase. Exemplary alkene epoxidases include StyAB, while exemplary selective epoxide hydrolases include epoxide hydrolases from Sphingomonas, Solanum tuberosum, or Aspergillus. The invention also provides non-toxic methods of making enantiomerically pure vicinal diols or enantiomerically pure alpha-hydroxy carboxylic acids using these compositions and microorganisms.
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-
Paragraph 0094-0096
(2016/05/02)
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- Osmium on chelate resin: Nonvolatile catalyst for the synthesis of DIOLS from alkenes
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Osmium tetraoxide (OsO4) was immobilized on a commercially available chelate resin DIAION CR11 (CR11) just by simply immersing it in a methanol solution of OsO4 at room temperature. The resulting purple solid, 5% Os/CR11, indicated no volatility, and effectively catalyzed the oxidation of various alkenes to the corresponding diols.
- Monguchi, Yasunari,Wakayama, Fumika,Takada, Hitoshi,Sawama, Yoshinari,Sajiki, Hironao
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supporting information
p. 700 - 704
(2015/03/14)
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- Regio- and enantioselective reduction of diketones: Preparation of enantiomerically pure hydroxy ketones catalysed by Candida parapsilosis ATCC 7330
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Enantiomerically enriched hydroxy ketones were prepared by the reduction of the corresponding diketones with excellent enantiomeric excess (98%) and in good yields (up to 75%) using whole cells of Candida parapsilosis ATCC 7330. Cyclic diketones, such as 1,2-cyclohexanedione and 1,4-cyclohexanedione, resulted in hydroxy ketones as products. Cyclohexane-1,3-dione and 5,5-dimethylcyclohexane-1,3-dione gave dimerised products, such as 2,2′-(ethane-1,1-diyl)bis(3-hydroxycyclohex-2-enone) and 2,2′-(ethane-1,1-diyl)bis(3-hydroxy-5,5-dimethylcyclohex-2-enone) with acetaldehyde generated in situ from whole cells of Candida parapsilosis ATCC 7330, which is reported here for the first time.
- Mahajabeen, Pula,Chadha, Anju
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p. 1167 - 1173
(2015/10/28)
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- Alkene anti-Dihydroxylation with Malonoyl Peroxides
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Malonoyl peroxide 1, prepared in a single step from the commercially available diacid, is an effective reagent for the anti-dihydroxylation of alkenes. Reaction of 1 with an alkene in the presence of acetic acid at 40 °C followed by alkaline hydrolysis leads to the corresponding diol (35-92%) with up to 13:1 anti-selectivity. A mechanism consistent with experimental findings is proposed that accounts for the selectivity observed.
- Alamillo-Ferrer, Carla,Davidson, Stuart C.,Rawling, Michael J.,Theodoulou, Natalie H.,Campbell, Matthew,Humphreys, Philip G.,Kennedy, Alan R.,Tomkinson, Nicholas C. O.
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supporting information
p. 5132 - 5135
(2015/11/03)
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- Enantio- and diastereoselective synthesis of 1,2-hydroxyboronates through Cu-Catalyzed additions of alkylboronates to aldehydes
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The first catalytic enantio- and diastereoselective synthesis of 1,2-hydroxyboronates is reported. Reactions are promoted by a readily available chiral monodentate phosphoramidite-copper complex in the presence of an alkyl 1,1-diboron reagent. Products contain two contiguous stereogenic centers and are obtained in up to 91% yield, >98:2 d.r., and 98:2 e.r. The reaction is tolerant of aryl and vinyl aldehydes, and the 1,2-hydroxyboronate products can be transformed into versatile derivatives. Mechanistic experiments indicate control of absolute stereochemistry of the α-boryl component.
- Joannou, Matthew V.,Moyer, Brandon S.,Meek, Simon J.
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supporting information
p. 6176 - 6179
(2015/06/02)
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- Ionophilic imidazolium-tagged cinchona ligand on LDH-immobilized osmium: Recyclable and recoverable catalytic system for asymmetric dihydroxylation reaction of olefins
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Abstract A catalytic system for the asymmetric dihydroxylation of olefins was developed by using an ionic-tagged biscinchona alkaloid ligand immobilized onto OsO4-exchanged layered double hydroxide (LDH) as a robust recyclable homogenous-heterogeneous catalytic system. The desired products were obtained in high yield and enantioselectivity.
- Kaur, Amanpreet,Singh, Vasundhara
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p. 1191 - 1194
(2015/06/02)
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- Osmium impregnated on magnetite as a heterogeneous catalyst for the syn-dihydroxylation of alkenes
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A new catalyst derived from osmium has been prepared, fully characterized and tested in the dihydroxylation of alkenes. The catalyst was prepared by wet impregnation methodology of OsCl3·3H2O on a commercial micro-magnetite surface. The catalyst allowed the reaction with one of the lowest osmium loadings for a heterogeneous catalyst and was selective for the monodihydroxylation of 1,5-dienes. Moreover, the catalyst was easily removed from the reaction medium by the simple use of a magnet. The selectivity of catalyst is very high with conversions up to 99%. Preliminary kinetics studies showed a first-order reaction rate with respect to the catalyst.
- Cano, Rafael,Pérez, Juana M.,Ramón, Diego J.
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p. 177 - 182
(2014/01/06)
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- Enantioselective trans-dihydroxylation of aryl olefins by cascade biocatalysis with recombinant escherichia coli coexpressing monooxygenase and epoxide hydrolase
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Cascade biocatalysis via intracellular epoxidation and hydrolysis was developed as a green and efficient method for enantioselective dihydroxylation of aryl olefins to prepare chiral vicinal diols in high ee and high yield. Escherichia coli (SSP1) coexpressing styrene monooxygenase (SMO) and epoxide hydrolase SpEH was developed as a simple and efficient biocatalyst for S-enantioselective dihydroxylation of terminal aryl olefins 1a-15a to give (S)-vicinal diols 1c-15c in high ee (97.5-98.6% for 10 diols; 92.2-93.9% for 3 diols) and high yield (91-99% for 6 diols; 86-88% for 2 diols; 67% for 3 diols). Combining SMO and epoxide hydrolase StEH showing complementary regioselectivity to SpEH as a biocatalyst for the cascade biocatalysis gave rise to R-enantioselective dihydroxylation of aryl olefins, being the first example of this kind of reversing the overall enantioselectivity of cascade biocatalysis. E. coli (SST1) coexpressing SMO and StEH was also engineered as a green and efficient biocatalyst for R-dihydroxylation of terminal aryl olefins 1a-15a to give (R)-vicinal diols 1c-15c in high ee (94.2-98.2% for 7 diols; 84.2-89.9% for 6 diols) and high yield (90-99% for 6 diols; 85-89% for 5 diols; 65% for 1 diol). E. coli (SSP1) and E. coli (SST1) catalyzed the trans-dihydroxylation of trans-aryl olefin 16a and cis-aryl olefin 17a with excellent and complementary stereoselectivity, giving each of the four stereoisomers of 1-phenyl-1,2- propanediol 16c in high ee and de, respectively. Both strains catalyzed the trans-dihydroxylation of aryl cyclic olefins 18a and 19a to afford the same trans-cyclic diols (1R,2R)-18c and (1R,2R)-19c, respectively, in excellent ee and de. This type of cascade biocatalysis provides a tool that is complementary to Sharpless dihydroxylation, accepting cis-alkene and offering enantioselective trans-dihydroxylation.
- Wu, Shuke,Chen, Yongzheng,Xu, Yi,Li, Aitao,Xu, Qisong,Glieder, Anton,Li, Zhi
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p. 409 - 420
(2014/03/21)
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- Osmium(III) and osmium(V) complexes bearing a macrocyclic ligand: A simple and efficient catalytic system for cis-dihydroxylation of alkenes with hydrogen peroxide
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A simple protocol that uses [OsIII(OH)(H2O)(L-N 4Me2)](PF6)2 (1; L-N 4Me2=N,N′-dimethyl-2,11-diaza[3.3](2,6) pyridinophane) as a catalyst and H2O2 as a terminal oxidant for efficient cis-1,2-dihydroxylation of alkenes is presented. Unfunctionalized (or aliphatic) alkenes and alkenes/styrenes containing electron-withdrawing groups are selectively oxidized to the corresponding vicinal diols in good to excellent yields (46-99 %). In the catalytic reactions, the stoichiometry of alkene:H2O2 is 1:1, and thus the oxidant efficiency is very high. For the dihydroxylation of cyclohexene, the catalytic amount of 1 can be reduced to 0.01 mol % to achieve a very high turnover number of 5500. The active oxidant is identified as the Os V(O)(OH) species (2), which is formed via the hydroperoxide adduct, an OsIII(OOH) species. The active oxidant 2 is successfully isolated and crystallographically characterized. The wizard of Os: A simple protocol that uses [OsIII(OH)(H2O)(L-N4Me 2)](PF6)2 (1) and H2O2 for efficient cis-1,2-dihydroxylation of alkenes is presented. Unfunctionalized (or aliphatic) alkenes and alkenes/styrenes containing electron-withdrawing groups were converted into the corresponding vicinal diols in good to excellent yields. It has been confirmed that the OsV(O)(OH) species (2) is the active oxidant, which is formed via the hydroperoxide adduct A. Copyright
- Sugimoto, Hideki,Ashikari, Kenji,Itoh, Shinobu
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p. 2154 - 2160
(2013/09/23)
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- An osmium(III)/osmium(V) redox couple generating OsV(O)(OH) center for cis -1,2-dihydroxylation of alkenes with H2O2: Os complex with a nitrogen-based tetradentate ligand
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For the synthesis of the 1,2-diols, cis-1,2-dihydroxylation of alkenes catalyzed by osmium(VIII) tetroxide (OsO4) is a powerful method. However, OsO4 is quite toxic due to its highly volatile and sublimable nature. Thus, the development of alternative catalysts for cis-1,2-dihydroxylation of alkenes is highly challenging. Our approach involves the use of a nitrogen-based tetradentate ligand, tris(2-pyridylmethyl)amine (tpa), for an osmium center to develop a new osmium catalyst and hydrogen peroxide (H2O2) as a cheap and environmentally benign oxidant. The new Os-tpa complex acts as a very efficient turnover catalyst for syn-selective dihydroxylation of various alkenes (turnover number ~1000) in aqueous media, and H2O2 oxidant is formally incorporated into the products quantitatively (100% atom efficiency). The reaction intermediates involved in the catalytic cycle have been isolated and characterized crystallographically as [OsIII(OH)(H 2O)(tpa)]2+ and [OsV(O)(OH)(tpa)]2+ complexes. The observed syn-selectivity, structural characteristics of the intermediates, and kinetic studies have suggested a concerted [3 + 2]-cycloaddition mechanism between [OsV(O)(OH)(tpa)]2+ and alkenes, which is strongly supported by DFT calculations.
- Sugimoto, Hideki,Kitayama, Kazuhiro,Mori, Seiji,Itoh, Shinobu
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p. 19270 - 19280
(2013/01/15)
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- Metal-free dihydroxylation of alkenes using cyclobutane malonoyl peroxide
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Cyclobutane malonoyl peroxide (7), prepared in a single step from the commercially available diacid 6, is an effective reagent for the dihydroxylation of alkenes. Reaction of a chloroform solution of 7 with an alkene in the presence of 1 equiv of water at 40 °C followed by alkaline hydrolysis leads to the corresponding diol (30-84%). With 1,2-disubstituted alkenes, the reaction proceeds with syn-selectivity (3:1 → 50:1). A mechanism consistent with experimental findings is proposed, which is supported by deuterium and oxygen labeling studies and explains the stereoselectivity observed. Alternative reaction pathways that are dependent on the structure of the starting alkene are also described leading to the synthesis of allylic alcohols and γ-lactones.
- Jones, Kevin M.,Tomkinson, Nicholas C. O.
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experimental part
p. 921 - 928
(2012/02/16)
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- Modular monodentate oxaphospholane ligands: Utility in highly efficient and enantioselective 1,4-diboration of 1,3-dienes
-
Tune it up! Tunable, chiral, monodentate oxaphospholane ligands (termed OxaPhos) are highly effective in the Pt-catalyzed title reaction, providing the 1,4-addition products in enantiomer ratios approaching 99:1 (see scheme). In the presence of enantiomerically pure cis-iBu-OxaPhos, a catalyst loading of only 0.02 mol% [Pt(dba)3] was sufficient for effective reaction. pin=pinacolato, dba=dibenzylideneacetone.
- Schuster, Christopher H.,Li, Bo,Morken, James P.
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supporting information; body text
p. 7906 - 7909
(2011/10/09)
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- Synthesis and reaction of phthaloyl peroxide derivatives, potential organocatalysts for the stereospecific dihydroxylation of alkenes
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To improve the synthesis and reactivity of phthaloyl peroxide derivatives a method has been developed using sodium percarbonate and phthaloyl chlorides. The reactions of the new phthaloyl peroxide derivatives with trans-stillbene as well as the improved reactivity of 3,4-dichlorophthaloyl peroxide with a variety of alkenes are reported.
- Yuan, Changxia,Axelrod, Abram,Varela, Michael,Danysh, Laura,Siegel, Dionicio
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supporting information; experimental part
p. 2540 - 2542
(2011/06/21)
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- A recyclable dendritic osmium catalyst for homogeneous dihydroxylation of olefins
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A series of osmate (OsO42-) core dendrimers was prepared by an ion-exchange technique through the mixing of K 2OsO4 and a bis(quaternary ammonium bromide) core dendrimer, which consisted of poly(benzyl ether) dendron. By employing an osmate core dendrimer as a homogeneous catalyst, dihydroxylation reactions of olefins proceeded rapidly, and the dendritic osmium catalyst was recovered by reprecipitation and then reused. Furthermore, a dendritic effect on the recyclability of a catalyst was observed. In the case of asymmetric dihydroxylation reactions, the corresponding diol was obtained in a high chemical yield with a fair enantiomeric excess (ee). In this case, not only the dendritic osmium catalyst but also the chiral ligand could be recovered by reprecipitation and reused efficiently up to five times.
- Fujita, Ken-Ichi,Yamazaki, Manabu,Ainoya, Taku,Tsuchimoto, Teruhisa,Yasuda, Hiroyuki
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experimental part
p. 8536 - 8543
(2010/11/18)
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- Alkene syn dihydroxylation with malonoyl peroxides
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Cyclopropyl malonoyl peroxide (1), which can be prepared in a single step from the commercially available diacid, is an effective reagent for the dihydroxylation of alkenes. Reaction of 1 with an alkene in the presence of 1 equiv of water at 40 °C followed by alkaline hydrolysis leads to the corresponding diol (40-93%). With 1,2-disubstituted alkenes, the reaction proceeds with syn selectivity (3:1 to >50:1). A mechanism consistent with the experimental findings that is supported by oxygen-labeling studies is proposed.
- Griffith, James C.,Jones, Kevin M.,Picon, Sylvain,Rawling, Michael J.,Kariuki, Benson M.,Campbell, Matthew,Tomkinson, Nicholas C. O.
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supporting information; experimental part
p. 14409 - 14411
(2010/12/24)
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- Rhodotorula minuta-mediated bioreduction of 1,2-diketones
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The reduction of cyclic and acyclic 1,2-diketones was investigated by employing whole cells of the yeast Rhodotorula minuta as biocatalyst. The reactions showed a variable degree of regio- and enantioselectivity depending on the nature of the substrate. In the case of cyclic diketones, the reduction afforded a mixture of diastereomeric diols only. The reduction of acyclic diketones allowed production of both the hydroxy ketone and the diol, in a two-step reaction. The first step was highly regio- and stereoselective, affording the hydroxy ketone of (S)-configuration with high enantiomeric excess. After longer reaction times the corresponding (S,S)-diols were obtained in high yield and diastereomeric excess.
- Monsalve, Leandro N.,Cerrutti, Patricia,Galvagno, Miguel A.,Baldessari, Alicia
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experimental part
p. 137 - 143
(2011/11/12)
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- Enantioselective hydrogenation of 1-phenyl-1,2-propanodione on Pt/ ZrO 2 catalysts
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The enantioselective hydrogenation of 1-phenyl-1,2-propanedione at 298K and pressure of 40 bar of H2 over zirconia supported Pt catalysts has been studied. Three different zirconia were prepared: i) ZrO2- P obtained by a precipitation procedure from ZrOCl2 ii) MSZrO 2 obtained by a sol-gel procedure using cetryltrimethylammonium bromide (CTMABR) as surfactant to get a mesostructured solid iii) CNTsZrO 2 obtained after impregnation of carbon nanotubes with ZrO(NO) 3 followed by pyrolisis and calcination. Pt (1wt%) was introduced on the support by impregnation of an aqueous solution of H2PtCl 6. The catalysts were characterized by nitrogen adsorption-desorption isotherms at 77 K, hydrogen chemisorption, XRD and TEM techniques. The reactions were carried out in a stainless steel batch reactor using cyclohexane as solvent and cinchonidine as chiral modifier. The presence of CD in the reaction medium is necessary to induce an enantiomeric excess (ee) of the desired product R-1phenyl-1 hydroxi-2-propanone. In all the studied systems, the relation between the enantioselectivity and the CD concentration added in situ exhibits a bell type curve; indicative of the importance of competitive adsorption between the modifier and the substrate on the catalyst surface. On the other hand, confinement effect led to an important enhancement in the activity in those catalysts supported on mesostructured supports, mainly in the Pt/CNTsZrO2 catalyst.
- Urbina, Claudia,Pecchi, Gina,Campos, Cristian,Reyes, Patricio
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experimental part
p. 25 - 30
(2010/09/05)
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- Access to enantiopure aromatic epoxides and diols using epoxide hydrolases derived from total biofilter DNA
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Metagenomic DNA is a rich source of genes encoding novel epoxide hydrolases (EHs). We retrieved two genes encoding functional EHs from total DNA isolated from biofilter-derived biomass, using PCR with EH-specific degenerate primers followed by genome-walking PCR. The degenerate primers were based on two EH-specific consensus sequences: HGWP and GHDWG. The resulting recombinant EHs, Kau2 and Kau8, were expressed in Escherichia coli, and their enantioselectivity and regioselectivity were determined using 13 different epoxide substrates. The EH Kau2 had broad substrate specificity and preferentially hydrolyzed epoxides with S-configuration. It showed high enantioselectivity towards aromatic epoxides such as styrene oxide, p-nitrostyrene oxide, and trans-1-phenyl-1,2-epoxypropane. In addition, Kau2 showed enantioconvergent hydrolysis activity. The EH Kau8 also showed broad substrate specificity and preferentially hydrolyzed epoxides with R-configuration. High enantioselectivity was observed for p-nitrostyrene oxide, and the hydrolysis activity of Kau8 was less enantioconvergent than that of Kau2. To determine the usefulness of Kau2 for synthetic applications, preparative-scale biohydrolysis reactions were performed. Specifically, two kinetic resolutions were carried out with 80 g/L of racemic trans-1-phenyl-1,2-epoxypropane, affording both (1R,2R)-epoxide and the corresponding (1R,2S)-diol in high enantiomeric excess (>99%) and good yield (>45%). In addition, a process based on enantioconvergent hydrolysis by the EH Kau2 was established for racemic cis-1-phenyl-1,2-epoxypropane at a concentration of 13 g/L, resulting in the formation of the corresponding (1R,2R)-diol with a 97% yield and an enantiomeric excess exceeding 98%.
- Kotik, Michael,Stepanek, Vaclav,Grulich, Michal,Kyslik, Pavel,Archelas, Alain
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experimental part
p. 41 - 48
(2010/12/19)
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- Osmium-catalyzed asymmetric dihydroxylation by carbon dioxide-activated hydrogen peroxide and N-methylmorpholine
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An improved process has been developed for the osmium-catalyzed dihydroxylation of olefins via in situ formation of NMO from NMM using CO2 catalysis and H2O2. All olefins examined were selectively cis-dihydroxylated to their corresponding diols in good to excellent yields, and by the use of chiral ligands, high enantiomeric excesses were obtained.
- Balagam, Bharathi,Mitra, Ranjan,Richardson, David E.
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p. 1071 - 1075
(2008/09/18)
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- A convenient procedure for the synthesis of racemic syn-1,2-diarylethane-1, 2-diols by osmate catalyzed dihydroxylation of trans-stilbenes facilitated by Troeger base
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Racemic (dl) mixture of syn-1,2-diarylethane-1,2-diols are prepared from the corresponding substituted trans-stilbenes using osmate catalyzed dihydroxylation facilitated by racemic Troeger base under ambient conditions.
- Satishkumar, Sakilam,Periasamy, Mariappan
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p. 1080 - 1083
(2008/12/23)
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- Examination of homo-[3 + 2]-dipolar cycloaddition: Mechanistic insight into regio-and diastereoselectivity
-
(Chemical Equation Presented) The reaction of 2,3-disubstituted-1,1- cyclopropanediesters with nitrones under Lewis acid conditions produces tetrahydro-1,2-oxazines in which the cis/trans relationship of the cyclopropanes is not conserved. Reacting nitrones with 2,3-cis-disubstituted cyclopropanes lead to 5,6-trans-oxazines, and 2,3-trans-disubstituted cyclopropanes lead to 5,6-cis-oxazines. This observed stereochemical inversion provides evidence for a stepwise annulation mechanism in the preparation of tetrahydro-1,2-oxazines.
- Karadeolian, Avedis,Kerr, Michael A.
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p. 10251 - 10253
(2008/03/28)
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- Highly stereoselective syn-ring opening of enantiopure epoxides with nitric oxide
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Reaction of enantiopure epoxides (1) with NO occurred highly stereoselectively, affording syn-ring opened products, nitrates (2). The configuration of 2 was confirmed to be retained by determining the configuration of reduced products 1,2-glycols (4) from 2. A possible mechanism is suggested to trace out the syn-ring opening pathway.
- Wu, Wentao,Liu, Qiang,Shen, Yinglin,Li, Rui,Wu, Longmin
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p. 1653 - 1656
(2008/02/03)
-
- Preparation, characterization and catalytic properties of polyaniline-supported metal complexes
-
Polyaniline-supported Sc, In, Pd, Os and Re catalysts were prepared by using a simple protocol and the thus prepared catalysts were well characterized using FTIR, XPS, UV-Vis/DRS, TGA-DTA. All the catalysts were successfully employed in a wide range of organic transformations such as cyanation and allylation of carbonyl compound, Suzuki coupling of aryl halides and boronic acids, and, most importantly, in asymmetric dihydroxylation of olefins to afford optically active vicinal diols. All the catalysts were separated from the reaction mixture by simple filtration and reused with consistent activity for five cycles without noticeable leaching of metal from the support.
- Choudary, Boyapati M.,Roy, Moumita,Roy, Sarabindu,Kantam, M. Lakshmi,Sreedhar, Bojja,Kumar, Karasala Vijay
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p. 1734 - 1742
(2007/10/03)
-
- Concatenated catalytic asymmetric allene diboration/allylation/ functionalization
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(Chemical Equation Presented) Palladium-catalyzed enantioselective diboration of prochiral allenes generates a reactive chiral allylboron intermediate which is a versatile reagent for the allylation of carbonyls. Experiments that improve the enantioselectivity of this process, examine the substrate scope, and are directed toward functionalization of the allylation intermediate are described.
- Woodward, Angela R.,Burks, Heather E.,Chan, Louis M.,Morken, James P.
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p. 5505 - 5507
(2007/10/03)
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- Osmium-catalyzed dihydroxylation of alkenes by H2O2 in room temperature ionic liquid co-catalyzed by VO(acac)2 or MeReO3
-
Room temperature ionic liquid [bmim]PF6 was used to immobilize a bimetallic catalytic system for H2O2-based dihydroxylation of alkenes. Osmium tetroxide was used as the substrate-selective catalyst with either VO(acac)2 or MeReO 3 as co-catalyst. The latter serve as an electron transfer mediator (ETM) and activates H2O2. For an increased efficiency N-methylmorpholine is required as an additional ETM in most cases. A range of alkenes were dihydroxylated using this robust bimetallic system and it was demonstrated that for some of the alkenes the catalytic system can be recycled and used up to five times.
- Johansson, Mikael,Lindén, Auri A.,B?ckvall, Jan-E.
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p. 3614 - 3619
(2007/10/03)
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- A novel microencapsulated osmium catalyst using cross-linked polystyrene as an efficient catalyst for asymmetric dihydroxylation of olefins in water
-
A novel microencapsulated osmium catalyst (PSresin-MC Os) was developed using cross-linked polystyrene. The concept of this method may go beyond that of microencapsulation. The catalyst was successfully used in asymmetric dihydroxylation in water, and it was recovered quantitatively by simple filtration and reused several times without loss of activity. The shape of the catalyst was maintained even after several uses. Moreover, no leaching of the Os component was detected.
- Ishida, Tasuku,Akiyama, Ryo,Kobayashi, Shu
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p. 1189 - 1192
(2007/10/03)
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- Rh-catalyzed enantioselective diboration of simple alkenes: Reaction development and substrate scope
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The rhodium-catalyzed reaction between bis(catecholato)diboron and simple alkenes results in the syn addition of the diboron across the alkene. The resulting 1,2-bis(boronate) is subsequently oxidized to provide the 1,2-diol. In the presence of enantiomerically enriched Quinap ligand, high enantioselection in the diboration can be achieved. The reaction is highly selective for trans- and trisubstituted alkenes and can be selective for some monosubstituted alkenes as well. The development of this reaction is described as is the substrate scope and experiments that are informative about the reaction mechanism and competing pathways.
- Trudeau, Stephane,Morgan, Jeremy B.,Shrestha, Mohanish,Morken, James P.
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p. 9538 - 9544
(2007/10/03)
-
- NaIO4/LiBr-mediated diastereoselective dihydroxylation of olefins: A catalytic approach to the prevost-woodward reaction
-
(Chemical Equation Presented) LiBr catalyzes efficiently the dihydroxylation of alkenes to afford syn and anti diols with excellent diastereoselectivity depending upon the use of NaIO4 (30 mol %) or PhI(OAc)2 (1 equiv), respectively, as the oxidants. The oxidation of non-benzylic halides has been achieved for the first time to afford the corresponding diols in excellent yields.
- Emmanuvel, Lourdusamy,Ali Shaikh, Tanveer Mahammad,Sudalai, Arumugam
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p. 5071 - 5074
(2007/10/03)
-
- CATALYZED ENANTIOSELECTIVE TRANSFORMATION OF ALKENES
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Enantioselective catalytic reactions that operate directly on unactivated alkenes for the preparation of chiral organic building blocks and new materials. More particularly, a catalyzed enantioselective reaction that operates on an unsaturated hydrocarbon, such as an alkene, to provide an enantiomerically enriched reactive organometallic intermediate, which can be converted to a variety of multifunctional optically active reaction products.
- -
-
Page/Page column 50
(2010/02/10)
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- Markedly enhanced recyclability of osmium catalyst in asymmetric dihydroxylation reactions by using macroporous resins bearing both residual vinyl groups and quaternary ammonium moieties
-
Markedly enhanced recyclability of osmium catalyst in asymmetric dihydroxylation has been achieved by using osmylated macroporous resins bearing both residual vinyl groups and quaternary ammonium moiety. The Royal Society of Chemistry 2005.
- Kim, Kwang Jin,Choi, Han Young,Hwang, Soon Ho,Park, Yil Sung,Kwueon, Eun Kyung,Choi, Doo Seong,Song, Choong Eui
-
p. 3337 - 3339
(2007/10/03)
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- Alkene cis-dihydroxylation by [(Me3tacn)(CF3CO 2)RuVIO2]CIO4 (Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane): Structural characterization of [3 + 2] cycloadducts and kinetic studies
-
cis-Dioxoruthenium(VI) complex [(Me3tacn)(CF3CO 2)RuVIO2]CIO4 (1, Me3tacn = 1,4,7-trimethyl-1,4,7-triazacyclononane) reacted with alkenes in aqueous tert-butyl alcohol to afford cis-1,2-diols in excellent yields under ambient conditions. When the reactions of 1 with alkenes were conducted in acetonitrile, oxidative C=C cleavage reaction prevailed giving carbonyl products in >90% yields without any cis-diol formation. The alkene cis-dihydroxylation and C=C cleavage reactions proceed via the formation of a [3 + 2] cycloadduct between 1 and alkenes, analogous to the related reactions with alkynes [Che et al. J. Am. Chem. Soc. 2000, 122, 11380], With cyclooctene and trans-β-methylstyrene as substrates, the Ru(III) cycloadducts [(Me3tacn)(CF 3CO2)RuIIIO(H)CH(CH2) 6HCO]CIO4 (4a) and [(Me3tacn)(CF 3CO2)RuIIIO(H)-PhCHCH(CH3)O]CIO 4 (4b) were isolated and structurally characterized by X-ray crystal analyses. The kinetics of the reactions of 1 with a series of p-substituted styrenes has been studied in acetonitrile by stopped-flow spectrophotometry. The second-order rate constants varied by 14-fold despite an overall span of 1.3 V for the one-electron oxidation potentials of alkenes. Secondary kinetic isotope effect (KIE) was observed for the oxidation of β-d2-styrene (kH/kD = 0.83 ± 0.04) and α-deuteriostyrene (kH/kD = 0.96 ± 0.03), which, together with the stereoselectivity of cis-alkene oxidation by 1, is in favor of a concerted mechanism.
- Yip, Wing-Ping,Yu, Wing-Yiu,Zhu, Nianyong,Che, Chi-Ming
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p. 14239 - 14249
(2007/10/03)
-
- New uses for the Burgess reagent in chemical synthesis: Methods for the facile and stereoselective formation of sulfamidates, glycosylamines, and sulfamides
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Although the Burgess reagent (methoxycarbonylsulfamoyltriethylammonium hydroxide, inner salt) has found significant use in chemical synthesis as a dehydrating agent, almost no work has been directed towards its potential in other synthetic applications. As this article will detail, we have found that the Burgess reagent is remarkably effective at accomplishing a number of non-dehydrative synthetic tasks when applied to appropriate substrates, such as the formation of sulfamidates from 1,2-diols or epoxyalcohols, α- and β-glycosylamines from carbohydrates, and cyclic sulfamides from 1,2-aminoalcohols. Beyond delineating the power of these new reaction manifolds, we also describe the construction of a group of alternative Burgess-type reagents that extends the scope of these new reactions even further.
- Nicolaou,Snyder, Scott A.,Longbottom, Deborah A.,Nalbandian, Annie Z.,Huang, Xianhai
-
p. 5581 - 5606
(2007/10/03)
-