- Heterogeneous Hydroxyl-Directed Hydrogenation: Control of Diastereoselectivity through Bimetallic Surface Composition
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Directed hydrogenation, in which product selectivity is dictated by the binding of an ancillary directing group on the substrate to the catalyst, is typically catalyzed by homogeneous Rh and Ir complexes. No heterogeneous catalyst has been able to achieve equivalently high directivity due to a lack of control over substrate binding orientation at the catalyst surface. In this work, we demonstrate that Pd-Cu bimetallic nanoparticles with both Pd and Cu atoms distributed across the surface are capable of high conversion and diastereoselectivity in the hydroxyl-directed hydrogenation reaction of terpinen-4-ol. We postulate that the OH directing group adsorbs to the more oxophilic Cu atom while the olefin and hydrogen bind to adjacent Pd atoms, thus enabling selective delivery of hydrogen to the olefin from the same face as the directing group with a 16:1 diastereomeric ratio.
- Shumski, Alexander J.,Swann, William A.,Escorcia, Nicole J.,Li, Christina W.
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p. 6128 - 6134
(2021/05/29)
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- 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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- Stereoselective oxidation of alkanes with: M -CPBA as an oxidant and cobalt complex with isoindole-based ligands as catalysts
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Two complexes with isoindole-core ligands of general formula [M{C6H4C(NH2)NC(ONCMe2)2}2](NO3)2 (M = Co for 1 and M = Ni for 2) were studied as catalysts for the mild stereoselective alkane oxidation with m-chloroperbenzoic acid (m-CPBA) as an oxidant and cis-1,2-dimethylcyclohexane (cis-1,2-DMCH) as a main model substrate. Complex 1 disclosed a pronounced activity, with high retention of stereoconfiguration of substrates (>98% for cis-1,2-DMCH) and highest cis/trans ratio of tertiary alcohols (products) of 56, under mild conditions. The best achieved yields of tertiary cis-alcohols were of 13.7 and 50.5%, based on the substrate (cis-1,2-DMCH) and the oxidant (m-CPBA) respectively. Kinetic experiments, high bond and stereoselectivity parameters, kinetic isotope effect of 7.2(2) in the oxidation of cyclohexane, and incorporation of 18O from H218O support the involvement of CoIVO high-valent metal-oxo intermediates as main C-H attacking species.
- Nesterova, Oksana V.,Kopylovich, Maximilian N.,Nesterov, Dmytro S.
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p. 93756 - 93767
(2016/10/21)
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- P450-catalyzed regio- and stereoselective oxidative hydroxylation of disubstituted cyclohexanes: Creation of three centers of chirality in a single CH-activation event This paper is dedicated to the memory of Harry H. Wasserman
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Wild-type P450-BM3 is able to catalyze in a highly regio- and diastereoselective manner the oxidative hydroxylation of non-activated disubstituted cyclohexane derivatives lacking any functional groups, including cis- and trans-1,2-dimethylcyclohexane, cis- and trans-1,4-dimethylcyclohexane, and trans-1,4-methylisopropylcyclohexane. In all cases except chiral trans-1,2-dimethylcyclohexane as substrate, the single hydroxylation event at a methylene group induces desymmetrization with simultaneous creation of three centers of chirality. Certain mutants increase selectivity, setting the stage for future directed evolution work.
- Ilie, Adriana,Agudo, Rubén,Roiban, Gheorghe-Doru,Reetz, Manfred T.
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p. 470 - 475
(2015/02/02)
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- Cp* iridium complexes give catalytic alkane hydroxylation with retention of stereochemistry
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A series of Cp Ir complexes can catalyze C-H oxidation, with ceric ammonium nitrate as the terminal oxidant and water as the source of oxygen. Remarkably the hydroxylation of cis-decalin and 1,4-dimethylcyclohexane proceeds with retention of stereochemistry. With H2O18, cis-decalin oxidation gave 18O incorporation into the product cis-decalol.
- Zhou, Meng,Schley, Nathan D.,Crabtree, Robert H.
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supporting information; scheme or table
p. 12550 - 12551
(2010/11/16)
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- Oxidations by the system "hydrogen peroxide-[Mn2L 2O3][PF6]2 (L = 1,4,7-trimethyl-1,4, 7-triazacyclononane)-oxalic acid". Part 6. Oxidation of methane and other alkanes and olefins in water
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Oxidation of alkanes with hydrogen peroxide in water solution at 10-50 °C is efficiently catalyzed by the cationic dinuclear manganese (IV) derivative [Mn2L2O3]2+ (1, with L = 1,4,7-trimethyl-1,4,7-triazacyclononane, TMTACN) in the form of the hexafluorophosphate salt ([1][PF6]2) if oxalic acid is present as a co-catalyst. Methane gives methanol and formaldehyde (turnover numbers, TONs, were 7 and 2, respectively, after reduction of the reaction mixture with ascorbic acid) whereas cyclohexane was oxidized with TONs up to 160 affording cyclohexyl hydroperoxide, cyclohexanone and cyclohexanol (the ketone was the main product, although at room temperature almost pure alkyl hydroperoxide was formed). In contrast to the oxidation in acetonitrile, the reaction with linear n-alkanes in water exhibits an unusual distribution of oxygenates. For example, in the oxidation of n-heptane the normalized reactivity of the methylene group in position 4 of the chain is 3-7 times higher than that of the CH2 group in position 2. Dec-1-ene is epoxidized by hydrogen peroxide in water (a biphasic system) catalyzed by [1][PF6] 2 and oxalic acid in the presence of a small amount of acetonitrile with TONs up to 1000 (no epoxidation has been detected in the absence of MeCN).
- Shul'pin, Georgiy B.,Nizova, Galina V.,Kozlov, Yuriy N.,Arutyunov, Vladimir S.,Dos Santos, Ana Cláudia M.,Ferreira, Ana Carolina T.,Mandelli, Dalmo
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p. 4498 - 4504
(2007/10/03)
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- Chemospecific chromium[VI] catalyzed oxidation of C-H bonds at -40 °C
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H5IO6 in the presence of catalytic chromoyl diacetate is a powerful method for oxidation of C-H bonds. Tertiary and oxygen activated C-H bonds are oxidized to tertiary alcohols or ketones at temperatures as low as -40 °C. The putative reagent is neutral dioxoperoxy chromium[VI] which undergoes C-H oxidation with retention of stereochemistry. This reagent appears to be the first reagent capable of oxidation of a C-H bond in the presence of an olefin without concomitant epoxidation. Copyright
- Lee, Seongmin,Fuchs
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p. 13978 - 13979
(2007/10/03)
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- The selective functionalization of saturated hydrocarbons. Part 36. Stereoselectivity studies of Gif-type reactions
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The stereoselectivity of various Gif-type reactions was evaluated using trans-1,4-dimethylcyclohexane as a chemical probe. The results revealed that these reactions were moderately stereoselective. The outcome of the reactions was preferentially formed in the more stable equatorial configuration.
- Barton, Derek H. R.,Chavasiri, Warinthorn
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p. 2997 - 3004
(2007/10/03)
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- Studies on the Decomposition of Alkyl Hydroperoxides by Different Catalysts
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The catalytic decomposition of cumene, 1-methylcyclohexyl and cyclohexyl hydroperoxides was studied in cyclohexane, cis- and trans-1,4-dimethylcyclohexane and cis-pinane as the solvents.The stearates and the acetylacetonates of manganese, cobalt and chromium, the acetylacetonates of molybdenum and vanadium, n-butyl orthoborate and n-butyl metaborate were used as the catalysts.The chromium-, vanadium-, molybdenum- and boron-containing catalysts brought about some Hock-type decomposition of cumene hydroperoxide and thus proved to be acidic.Of these more of less acidic catalysts only molybdenyl acetylacetonate effected a partially stereospecific hydroxylation of the tertiary C-H-bonds in cis- and trans-1,4-dimethylcyclohexane.The well-known selectivity of chromium catalysts for the ketone formation during the decomposition of secondary hydroperoxides is caused by the catalytic oxidation of secondary alcohols by hydroperoxides in the presence of chromium compounds.In the presence of all the catalysts used the free-radical pathways of the hydroperoxide decomposition predominated, and the attack of the intermediate radicals on the starting hydroperoxide was more important than the attack on the solvent molecules.
- Lauterbach, Gerlinde,Pritzkow, W.,Tien, Tieu Dung,Voerckel, V.
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p. 933 - 946
(2007/10/02)
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- On the Mechanism of Hydroperoxide Decomposition by Boric Acid Derivatives
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Decomposition of cyclohexane and 1-methylcyclohexane hydroperoxides in cis- and trans-1,4-dimethylcyclohexane in the presence of boric acid esters results in a non-stereospecific attack at the tertiary C-H bonds of the 1,4-dimethylcyclohexanes.Mixtures of cis- and trans-1,4-dimethylcyclohexanols are formed in every case.This proves that the attack of the hydroperoxides at the tertiary C-H bonds does not proceed by an aliphatic SE2 mechanism.
- Kunzelmann, Astrid,Lauterbach, Gerlinde,Potekhin, Vyacheslav Matveevich,Pritzkow, Wilhelm,Schmidt-Renner, Wolfgang,Vasina, Larisa Fedorovna
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p. 772 - 776
(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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- STERIC AND KINETIC EFFECTS OF CHANGING SOLVENT AND REAGENT IN GRIGNARD REACTIONS ON SOME 4-SUBSTITUTED CYCLOHEXANONES
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The stereochemistry and relative rates of Grignard reactions on some 4R-substituted cyclohexanones (R = tBu, Me, OMe, CO2Me, OCOPh and Cl) have been determined under two separate reaction conditions (MeMgI in C6H6 and MeMgCl in THF).The results of our studies indicate that substrates containing an ester group have a higher reaction order in Grignard reactant than other groups when reactions were carried out in the aromatic solvent.The same is not true for reactions carried out in THF.Both stereochemical product ratios and relative reaction rates are better understood assuming that compounds containing a polar group (OMe and Cl at least) react via a transition state possessing that group in the axial conformation.
- Cianetti, Claudia,Maio, Giorgio Di,Pignatelli, Vito,Tagliatesta, Pietro,Vecchi, Elisabetta,Zeuli, Errico
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p. 657 - 666
(2007/10/02)
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