- 2-Hydroxylation of 1,3-Diketones with Atmospheric Oxygen
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An efficient method for the 2-hydroxylation of 1,3-diketones by using atmospheric oxygen as an oxidant under transition-metal-free condition is described. The protocol has the advantages of using an inexpensive and stable oxidant, producing high yields, and requiring ecofriendly conditions.
- Li, Zheng,Li, Tianpeng,Li, Jiasheng,He, Lili,Jia, Xianggui,Yang, Jingya
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p. 2863 - 2865
(2015/12/18)
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- DDQ-mediated oxidation of sp3 C-H bond for the direct synthesis of vicinal tricarbonyl compounds Dedicated to academician Li-Xin Dai on the occasion of his 90th birthday
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A facile and direct synthetic method was developed for the construction of vicinal tricarbonyl compounds (VTCs) in moderate to excellent yields (46-92%), by treating the readily available 1,3-dicarbonyl compounds with 2,2,6,6-tetramethylpiperidine-1-oxyl
- Wang, Zheng-Lin,An, Xing-Lan,Ge, Li-Shi,Jin, Jing-Hai,Luo, Xiaoyan,Deng, Wei-Ping
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p. 3788 - 3792
(2014/05/20)
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- Regioselective aliphatic carbon-carbon bond cleavage by a model system of relevance to iron-containing acireductone dioxygenase
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Mononuclear Fe(II) complexes ([(6-Ph2TPA)Fe(PhC(O)C(R)C(O)Ph)]X (3-X: R = OH, X = ClO4 or OTf; 4: R = H, X = ClO4)) supported by the 6-Ph2TPA chelate ligand (6-Ph2TPA = N,N-bis((6-phenyl-2-pyridyl)methyl)-N-(2-pyridylmethyl)amine) and containing a β-diketonate ligand bound via a six-membered chelate ring have been synthesized. The complexes have all been characterized by 1H NMR, UV-vis, and infrared spectroscopy and variably by elemental analysis, mass spectrometry, and X-ray crystallography. Treatment of dry CH3CN solutions of 3-OTf with O2 leads to oxidative cleavage of the C(1)-C(2) and C(2)-C(3) bonds of the acireductone via a dioxygenase reaction, leading to formation of carbon monoxide and 2 equiv of benzoic acid as well as two other products not derived from dioxygenase reactivity: 2-oxo-2- phenylethylbenzoate and benzil. Treatment of CH3CN/H2O solutions of 3-X with O2 leads to the formation of an additional product, benzoylformic acid, indicative of the operation of a new reaction pathway in which only the C(1)-C(2) bond is cleaved. Mechanistic studies show that the change in regioselectivity is due to the hydration of a vicinal triketone intermediate in the presence of both an iron center and water. This is the first structural and functional model of relevance to iron-containing acireductone dioxygenase (Fe-ARD′), an enzyme in the methionine salvage pathway that catalyzes the regiospecific oxidation of 1,2-dihydroxy-3-oxo-(S)- methylthiopentene to form 2-oxo-4-methylthiobutyrate. Importantly, this model system is found to control the regioselectivity of aliphatic carbon-carbon bond cleavage by changes involving an intermediate in the reaction pathway, rather than by the binding mode of the substrate, as had been proposed in studies of acireductone enzymes.
- Allpress, Caleb J.,Grubel, Katarzyna,Szajna-Fuller, Ewa,Arif, Atta M.,Berreau, Lisa M.
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p. 659 - 668
(2013/03/14)
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- Formation of α-hydroxy-β-diketones through hydroxylation of isoxazolium salts: Stereoselective approach to angular cis-diols in polycyclic systems
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Only two steps were needed for the unprecedented oxidation of isoxazoles, which is exploited in the stereocontrolled introduction of an "angular cis-diol" characteristic of polyketide-derived polycyclic natural products, suchas 3. In this two-step process, 1) N-methylation of isoxazole 1 and 2) stereoselective epoxidation of isoxazolium salt 2 withsodium hypochlorite followed by hydrolysis are carried out (Bn: benzyl). (Chemical Equation Presented)
- Takikawa, Hiroshi,Takada, Akiomi,Hikita, Katsuyoshi,Suzuki, Keisuke
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supporting information; experimental part
p. 7446 - 7449
(2009/03/12)
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- The RuO4-catalyzed ketohydroxylation. Part 1. Development, scope, and limitation
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A new straightforward oxidation of C,C-double bonds to unsymmetrical α-hydroxy ketones using catalytic amounts of RuCl3 and stoichiometric amounts of Oxone under buffered conditions has been developed, a reaction for which we coined the expression "ketohydroxylation". The transformation allows the direct formation of α-hydroxy ketones (acyloins) from olefins without intermediate formation of syn-diols. The present paper will provide detailed information starting with the underlying concept and the subsequent development of the reaction. The effect of base, solvent stoichiometry, and temperature will be discussed resulting in an improved mechanistic model that might help to explain the influence of different reaction parameters on reactivity and selectivity in RuO4-catalyzed oxidations of C,C-double bonds. Furthermore, an improved workup procedure allows the recovery of the ruthenium catalyst by precipitation while simplifying the overall product purification. The second part of the paper focuses on exploration of scope and limitation. A variety of substituted olefins are oxidized to α-hydroxy ketones in good to excellent regioselectivities and yield. Cyclic substrates proved to be problematic to oxidize; however, a careful analysis of temperature effects resulted in the development of a successful protocol for the ketohydroxylation of cyclic substrates by simply decreasing the reaction temperature.
- Plietker, Bernd
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p. 8287 - 8296
(2007/10/03)
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- RuO4-catalyzed ketohydroxylation of olefins
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A new mild method for the oxidation of a variety of olefins to α-hydroxy ketones is described. Using the concept of a nucleophilic reoxidant, different olefins were ketohydroxylated with high regioselectivity in good to excellent yields.
- Plietker, Bernd
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p. 7123 - 7125
(2007/10/03)
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