- Selective C-H bond hydroxylation of cyclohexanes in water by supramolecular control
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A new approach for selective hydroxylation of non-activated cyclohexanes using dioxirane generated in situ in water through supramolecular control has been developed. Using β-CD and γ-CD as the supramolecular hosts, selective hydroxylation of cyclohexane substrates, including trans/cis-1,4-, 1,3-and 1,2-dimethylcyclohexanes and trans/cis-decahydronaphthalene, was achieved in up to 54% yield in water. Furthermore, site-selective C-H bond hydroxylation of (+)-menthol was achieved by obstructing the approach of dioxirane to the C-H bond with higher steric hindrance through inclusion complexation with β-CD and γ-CD in water.
- Yang, Bin,Cui, Jian-Fang,Wong, Man Kin
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p. 30886 - 30893
(2017/07/07)
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- Catalytic Oxidation of Alkanes and Alkenes by H2O2 with a μ-Oxido Diiron(III) Complex as Catalyst/Catalyst Precursor
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A new μ-oxo diiron(III) complex of the lithium salt of the pyridine-based unsymmetrical ligand 3-[(3-{[bis(pyridin-2-ylmethyl)amino]methyl}-2-hydroxy-5-methylbenzyl)(pyridin-2-ylmethyl)amino]propanoate (LiDPCPMPP), [Fe2(μ-O)(LiDPCPMPP)2](ClO4)2, has been synthesized and characterized. The ability of the complex to catalyze oxidation of several alkanes and alkenes has been investigated by using CH3COOH/H2O2 (1:1) as an oxidative system. Moderate activity in cyclohexane oxidation (TOF = 33 h-1) and good activity in cyclohexene oxidation (TOF = 72 h-1) were detected. Partial retention of configuration (RC = 53%) in cis- and trans-1,2-dimethylcyclohexane oxidation, moderate 3/2 selectivity (4.1) in adamantane oxidation, and the observation of a relatively high kinetic isotope effect for cyclohexane oxidation (KIE = 3.27) suggest partial metal-based oxidation, probably in tandem with free-radical oxidation. Low-temperature UV/Vis spectroscopy and mass spectrometric studies in the rapid positive detection mode indicate the formation of a transient peroxido species, [Fe2(O)(O2)(LiDPCPMPP)2]2+, which might be an intermediate in the metal-based component of the oxidation process. A μ-oxido diiron(III) complex, [Fe2(μ-O)(LiDPCPMPP)2](ClO4)2, was synthesized and characterized. This complex was used as catalyst in C-H bond oxidation with CH3COOH-H2O2 as chemical oxidant. Reactivity studies indicate that the oxidation process goes through a metal-based mechanism concomitant with a radical process.
- Das, Biswanath,Al-Hunaiti, Afnan,Haukka, Matti,Demeshko, Serhiy,Meyer, Steffen,Shteinman, Albert A.,Meyer, Franc,Repo, Timo,Nordlander, Ebbe
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p. 3590 - 3601
(2015/08/06)
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- Synthesis and structure-affinity relationships of 1,3,5-alkylsubstituted cyclohexylamines binding at NMDA receptor PCP site
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A series of 1,3,5-alkylsubstituted cyclohexylamines 2 were synthesized as ligands for the N-methyl-D-aspartate (NMDA) receptor phencyclidine (PCP) binding site. Pure diastereomers with defined configuration of amino group 2- ax and 2-eq were obtained. The optimal size of 1,3,5-substituents was determined for cyclohexylamines 2 with an equatorial amino group in the lowest energy conformation using Hansch analysis. According to the data, the lipophilic part of cyclohexylamines 2 does not discriminate between hydrophobic regions of the PCP binding site but rather recognizes this site as a whole lipophilic pocket. (C) 2000 Editions scientifiques et medicales Elsevier SAS.
- Jirgensons, Aigars,Kauss, Valerjans,Kalvinsh, Ivars,Gold, Markus R.,Danysz, Wojciech,Parsons, Chris G.,Quack, Gunter
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p. 555 - 565
(2007/10/03)
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- Unprecedented Stereoselectivity in the Addition of Organoiron(II) Reagents to Cyclohaxanone Derivatives
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Various organoiron(II) reagents undergo Grignard-type additions to substituted cyclohexanone derivatives, C-C bond formation occurring stereoselectively from the equatorial direction (97 - 100percent selectivity).
- Reetz, Manfred T.,Stanchev, Stephan
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p. 328 - 330
(2007/10/02)
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- Diastereoselective Addition of Organoytterbium Reagents to Carbonyl Substrates
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Organoytterbium reagents, prepared by the addition of organolithiums or organomagnesiums to ytterbium(III) triflate, react in a highly diastereoselective fashion with a variety of chiral aldehydes and ketones.
- Molander, Gary A.,Burkhardt, Elizabeth R.,Weinig, Peter
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p. 4990 - 4991
(2007/10/02)
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- Amphiphilic Reactions by Means of Exceptionally Bulky Organoaluminum Reagents. Rational Approach for Obtaining Unusual Equatorial, Anti-Cram, and 1,4 Selectivity in Carbonyl Alkylation
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Exceptionally bulky, oxygenophilic organoaluminum reagents, methylaluminum bis(2,6-di-tert-4-alkylphenoxide) (MAD and MAT), have been successfully utilized for stereoselective activation of carbonyl moiety.Combination of MAD or MAT with carbon nucleophiles such as organolithiums or Grignard reagents generates a new amphiphilic reaction system in which the alkylation may be interpreted as the nucleophilic addition of a reactive organometallic compound to an electrophilically activated carbonyl substrate in order to account for the regio- and stereochemical consequences.In contrast to the ordinary alkylations, the amphilic alkylation disclosed herein would be categorized into the new, yet unexplored class of alkylation that exhibits high chemoselectivity to carbonyl compounds, and more significantly it allows excellent equatorial and anti-Cram selectivity in carbonyl alkylations, hitherto difficult by the existing methodologies.Further, unusual conjugate addition of organolithium reagents to α,β-unsaturated carbonyl compounds has been accomplished by using the amphiphilic reaction system.
- Maruoka, Keiji,Itoh, Takayuki,Sakurai, Minoru,Nonoshita, Katsumasa,Yamamoto, Hisashi
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p. 3588 - 3597
(2007/10/02)
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- CH3Li/TiCl4: A NON-BASIC AND HIGHLY SELECTIVE GRIGNARD ANALOGUE
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Treatment of CH3Li or CH3MgCl with TiCl4 results in quantitative formation of CH3TiCl3, a non-basic reagent which reacts chemo- and stereoselectively with carbonyl compounds.It is considerably more reactive than the alkoxy analogue CH3Ti(OCHMe2)3.This means that selective addition to ketones in the presence of such a functionality as nitro, cyano and ester groups is possible.Addition to enolizable ketones is smooth.The stereoselectivity is comparable to that observed for CH3Ti(OCHMe)3.
- Reetz, M. T.,Kyung, S. H.,Huellmann, M.
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p. 2931 - 2935
(2007/10/02)
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- Stereoselective Addition of Organotitanium Reagents to Carbonyl Compounds
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Titanation of alkyllithium or -magnesium compounds using ClTi(OR)3 results in reagents which show markedly increased diastereofacial selectivity (80 - 90percent) in reactions with α-chiral aldehydes or ketones.Titanation is also the method of choice in Grignard-type additions to substituted cyclohexanones; CH3Ti(OCHMe2)3 (6a) adds predominantly from the equatorial direction, while allyltitanium reagents 11b and 12 show axial preference.Crotyltitanium compounds react with carbonyl compounds to afford primarily adducts having anti-configuration, a process which is of particular value in case of ketones (anti/syn ratios up to 99:1).Titanation of (trimethylsilyl)allyllithium (48) with Ti(OCHMe2)4 reverses regioselectivity in reactions with aldehydes and ketones, β-hydroxy silanes 50 being the only observed products.These have anti-configuration and can be converted either into Z- or E-dienes using the Peterson elimination under basic or acidic conditions, respectively.
- Reetz, Manfred T.,Steinbach, Rainer,Westermann, Juergen,Peter, Roland,Wenderoth, Bernd
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p. 1441 - 1454
(2007/10/02)
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- Mechanistic and Preparative Studies on the Regio- and Stereoselective Paraffin Hydroxylation with Peracids
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Reactions of more than 20 hydrocarbons with p-nitro- or, e.g., 3,5-dinitroperbenzoic acid in chloroform show regioselectivities of Rst = 90 (relative rates of attack at tertiary and secondary C-H bonds, after statistical correction) to 500 and configurational retention, if applicable, of typically 97-99.7percent.Radical side reactions are recognized by concomitant formation of, e.g., nitrobenzene and are responsible for a decrease in regio- and stereoselectivity.Steric effects are observed in attack at axial tertiary C-H bonds and at bridgehead positions.Electronegative and hydrogen-bonding substituents in the alkane diminish, and alkyl groups enhance the rates; the observed Taft ρ* value of -2.2 indicates substantial positive charge accumulation in the transition state in agreement with the high regioselectivity.A Hammett reaction constant of +0.63 is obtained from substituted perbenzoic acids; activation parameters of ΔH* = 15-19 kcal mol-1 and ΔS* = -22 to -29 eu with three alkanes of different flexibility and an isotope effect of kH/kD = 2.2 with methylcyclohexane are measured.Aromatic rings are usually not attacked but lead to deactivation of the peracid even at remote alkane C-H positions; similar deactivation is found in hydrogen-bonding solvents.Androstanes yield preferentially 9α- and 5α-hydroxy products, if, e.g., a 17β-acetoxy substituent is used to steer the reaction.Diols usually are only observed as a result of a proximity effect of a peracid associated at the first formed hydroxy group.The results point to relatively late and oxenoid transition states with substantial charge separation in the substrate.Attempts to achieve selective oxidations using macrocyclic azacyclophanes with attached carboxylic functions were not successful, although the host compounds showed selective complexation of hydrocarbons.
- Schneider, Hans-Joerg,Mueller, Walter
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p. 4609 - 4615
(2007/10/02)
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