- Site-Selective and Product Chemoselective Aliphatic C-H Bond Hydroxylation of Polyhydroxylated Substrates
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Site-selective and product chemoselective aliphatic C-H bond oxidation of 1,2-diols and of polyhydroxylated substrates using iron and manganese catalysts and hydrogen peroxide as terminal oxidant is described. The reaction capitalizes on the use of fluorinated alcohol solvents such as 2,2,2-trifluoroethanol (TFE) and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP), which exert a strong polarity reversal in the hydroxyl moieties of 1,2-diols via hydrogen bonding, in turn translating into a strong deactivation of proximal C-H bonds against a HAT initiated oxidation by the putative high-valent and electrophilic metal-oxo species. As a result, site-selective and product chemoselective oxidation of complex polyfunctional molecules such as steroids, sugars, and pharmaceuticals is described, where exclusive or predominant C-H bond hydroxylation at a remote and nonactivated site takes place. The current report discloses HAT initiated hydroxylations in fluorinated alcohol solvents as methods displaying orthogonal chemoselectivity to contemporary alcohol oxidations providing a useful tool for synthetic planning in densely functionalized molecules.
- Bietti, Massimo,Borrell, Margarida,Costas, Miquel,Gil-Caballero, Sergio
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p. 4702 - 4709
(2020/05/19)
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- One-Pot Enzymatic Synthesis of Cyclic Vicinal Diols from Aliphatic Dialdehydes via Intramolecular C?C Bond Formation and Carbonyl Reduction Using Pyruvate Decarboxylases and Alcohol Dehydrogenases
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An enzymatic cascade reaction was developed for one-pot enantioselective conversion of aliphatic dialdehydes to chiral vicinal diols using pyruvate decarboxylases (PDCs) and alcohol dehydrogenases (ADHs). The PDCs showed promiscuity in catalysing the cyclization of aliphatic dialdehydes through intramolecular stereoselective carbon-carbon bond formation. Consequently, 1,2-cyclopentanediols in three different stereoisomeric forms and 1,2-cyclohexanediols in two different stereoisomeric forms could be prepared with high conversion and stereoisomeric ratio from the respective initial substrates, glutaraldehyde and adipaldehyde. These cascade reactions represent a promising approach to the biocatalytic synthesis of important chiral vicinal diols. (Figure presented.).
- Zhang, Yan,Yao, Peiyuan,Cui, Yunfeng,Wu, Qiaqing,Zhu, Dunming
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p. 4191 - 4196
(2018/09/25)
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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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- Enantioselective enzymatic approach to (+)- and (-)-2-acetoxy/hydroxycyclopentanones
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A new practical enzymatic approach to (+)- and (-)-2-acetoxy/hydroxycyclopentanones with 96-98% ee has been described via enzymatic hydrolysis of the meso-diacetate 2, Swern oxidation of the thus formed (±)-hydroxy acetates 3 and 4, followed by re-enzymatic resolution. Enantiomerically pure (+)- and (-)-2-hydroxycyclopentanones are in equilibrium with enediol 9 and slowly undergo racemisation, a process which could be arrested by protecting the hydroxyl group as the acetate.
- Easwar, Srinivasan,Desai, Shrivallabh B.,Argade, Narshinha P.,Ganesh, Krishna N.
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p. 1367 - 1371
(2007/10/03)
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- Kinetic resolution of vic-diols by Bacillus stearothermophilus diacetyl reductase
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The kinetic resolution of several racemic syn- and anti-1,2-diols by enzymatic oxidation with Bacillus stearothermophilus diacetyl reductase is described. The enantiomerically pure (R,R)- and (R,S)-diols are recovered in almost quantitative yield.
- Bortolini, Olga,Casanova, Elena,Fantin, Giancarlo,Medici, Alessandro,Poli, Silvia,Hanau, Stefania
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p. 647 - 651
(2007/10/03)
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- Oxidation of homochiral ketals by rhenium(VII) oxide. V
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2-Hydroxyethyl enol ethers react with Re2O7 to produce 2-hydroxyketals. Where homochiral starting enol ethers are employed, greater than 99:1 diastereoselectivities are obtained. The stereocontrol is rationalized by invoking a transition state that approximates the geometry of a metallaoxetane. Finally, homochiral ketals are themselves oxidized to provide 2-hydroxyketals with high diastereoselectivity.
- Tang,Kennedy
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p. 7823 - 7826
(2007/10/02)
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- Preparation of Optically Active 1,2-Diols and α-Hydroxy Ketones Using Glycerol Dehydrogenase as Catalyst: Limits to Enzyme-Catalyzed Synthesis due to Noncompetitive and Mixed Inhibition by Product
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Glycerol dehydrogenase (GDH, EC 1.1.1.6, from Enterobacter aerogenes or Cellulomonas sp.) catalyzes the interconversion of analogues of glycerol and dihydroxyacetone.Its substrate specificity is quite different from than of horse liver alcohol dehydrogenase (HLADH), yeast alcohol dehydrogenase, and other alcohol dehydrogenases used in enzyme-catalyzed organic synthesis and is thus a useful new enzymic catalyst for the synthesis of enantiomerically enriched and isotopically labeled organic molecules.This paper illustrates synthetic applications of GDH as a reduction catalyst by the enantioselective reduction of 1-hydroxy-2-propanone and 1-hydroxy-2-butanone to the corresponding R 1,2-diols (ee = 95-98percent). (R)-1,2-Butanediol-2-d1 was prepared by using formate-d1 as the ultimate reducing agent.Comparison of (R)-1,2-butanediol prepared by reduction of 1-hydroxy-2-butanone enzymatically and with actively fermenting bakers' yeast indicated than yield and enantiomeric purity were similar by the two procedures.Reactions proceeding in the direction of substrate oxidation usually suffer from slow rates and incomplete conversions due to product inhibition.The kinetic consequences of product inhibition (competitive, noncompetitive, and mixed) for practical synthetic applications of GDH, HLADH, and other oxidoreductases are analyzed.In general, product inhibition seems the most serious limitation to the use of these enzymes as oxidation catalysts in organic synthesis.
- Lee, Linda G.,Whitesides, George M.
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