- Nonheme Fe(IV) Oxo Complexes of Two New Pentadentate Ligands and Their Hydrogen-Atom and Oxygen-Atom Transfer Reactions
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Two new pentadentate {N5} donor ligands based on the N4Py (N4Py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) framework have been synthesized, viz. [N-(1-methyl-2-benzimidazolyl)methyl-N-(2-pyridyl)methyl-N-(bis-2-pyridyl methyl)amine] (L1) and [N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), where one or two pyridyl arms of N4Py have been replaced by corresponding (N-methyl)benzimidazolyl-containing arms. The complexes [FeII(CH3CN)(L)]2+ (L = L1 (1); L2 (2)) were synthesized, and reaction of these ferrous complexes with iodosylbenzene led to the formation of the ferryl complexes [FeIV(O)(L)]2+ (L = L1 (3); L2 (4)), which were characterized by UV-vis spectroscopy, high resolution mass spectrometry, and M?ssbauer spectroscopy. Complexes 3 and 4 are relatively stable with half-lives at room temperature of 40 h (L = L1) and 2.5 h (L = L2). The redox potentials of 1 and 2, as well as the visible spectra of 3 and 4, indicate that the ligand field weakens as ligand pyridyl substituents are progressively substituted by (N-methyl)benzimidazolyl moieties. The reactivities of 3 and 4 in hydrogen-atom transfer (HAT) and oxygen-atom transfer (OAT) reactions show that both complexes exhibit enhanced reactivities when compared to the analogous N4Py complex ([FeIV(O)(N4Py)]2+), and that the normalized HAT rates increase by approximately 1 order of magnitude for each replacement of a pyridyl moiety; i.e., [FeIV(O)(L2)]2+ exhibits the highest rates. The second-order HAT rate constants can be directly related to the substrate C-H bond dissociation energies. Computational modeling of the HAT reactions indicates that the reaction proceeds via a high spin transition state.
- Mitra, Mainak,Nimir, Hassan,Demeshko, Serhiy,Bhat, Satish S.,Malinkin, Sergey O.,Haukka, Matti,Lloret-Fillol, Julio,Lisensky, George C.,Meyer, Franc,Shteinman, Albert A.,Browne, Wesley R.,Hrovat, David A.,Richmond, Michael G.,Costas, Miquel,Nordlander, Ebbe
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Read Online
- A novel chemiluminescence from the reaction of dioxiranes with alkanes. Proposed mechanism of oxygen-transfer chemiluminescence
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Oxidation of adamantane and 2,3-dimethylbutane by methyl(trifluoromethyl)dioxirane is accompanied by chemiluminescence (CL); formation of the emitter of CL, triplet excited trifluoropropanone, is proposed to occur via a concerted oxenoid mechanism of oxygen insertion into C-H bond of the hydrocarbons.
- Kazakov,Barzilova,Kazakov
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Read Online
- OH Radical Induced Oxidation of 2,3-Dimethylbutane in Air
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The product distribution resulting from the OH induced oxidation of 2,3-dimethylbutane in air was measured and compared with predictions based on a general reaction mechanism.Relative rates derived for the abstraction of primary and tertiary hydrogen atoms by OH radicals from the parent compound are 17percent and 83percent, respectively.The branching ratio for the alcohol versus alkoxyl radical producing pathsways of the self-reaction of 2-propylperoxy radicals was determined to be (0.61 +/- 0.08):(0.39 +/- 0.08); the corresponding ratio for the self-reaction of primary 2,3-dimethylbutylperoxy radicals is (0.56 +/- 0.07): 0.44 +/- 0.07).Large amounts of 2,3-dimethyl-2-hydroperoxybutane and small amounts of 2,3-dimethyl-2-butanol were found, the latter as a product of the cross combination reactions of 2,3-dimethyl-2-butylperoxy with 2-propylperoxy and 2,3-dimethyl-1-butylperoxy radicals.Rate constants of 3.5 * 10-17 and 2 * 10-16 cm-3/(molecule s), respectively, were estimated for these reactions with the help of computer simulations.
- Heimann, Gerald,Warneck, Peter
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Read Online
- A crystalline, internally-coordinated chloroborane for asymmetric hydroboration
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Asymmetric hydroboration is an important method in the preparation of enantiomerically-enriched compounds that are necessary in many areas of chemistry. Here is reported the preparation of a unique chiral chloroborane-internal ether complex and its applic
- von Dollen, Breanna,Wood, John L.,Savage, Quentin R.,Jones, Andrew J.,Garner, Charles M.
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supporting information
(2022/02/01)
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- 3-PHENYL-4-HEXYNOIC ACID DERIVATIVES AS GPR40 AGONISTS
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A compound of the formula (I)wherein R represents a straight or branched, primary or secondary acyclic hydrocarbyl C3–C15 group, which can be saturated or unsaturated, or a straight or branched, primary or secondary acyclic hydrocarbyl C3–C15 group, which can be saturated or unsaturated and wherein one or more of hydrogen atoms is replaced with fluorine atom; X represents hydrogen atom or halogen atom,and* denotes chiral center, and salts thereof. The compound is useful for the treatment of diseases mediated by GPR40, in particular type II diabetes. (I)
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Page/Page column 47; 48
(2019/07/23)
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- Ligand-Controlled Direct Hydroformylation of Trisubstituted Olefins
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The direct hydroformylation of trisubstituted olefins has been achieved with a combination of a Rh(I) catalyst and a π-acceptor phosphorus (briphos) ligand. A sterically bulky briphos ligand with a large cone angle that forms a 1:1 complex with Rh(I) is found to be reactive for the hydroformylation of trisubstituted olefins. The aldehyde products were obtained with high diastereoselectivity (>99:1) and regioselectivity (49%-81%).
- Shin, Taeil,Kim, Hyungsoo,Kim, Sungmin,Lee, Ansoo,Seo, Min-Seob,Choi, Jonghoon,Kim, Hyungjun,Kim, Hyunwoo
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p. 5789 - 5792
(2019/06/24)
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- Copper-catalyzed enantioselective hydroboration of unactivated 1, 1-disubstituted alkenes
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We report an efficient and highly enantioselective hydroboration of aliphatic 1, 1-disubstituted alkenes with pinacolborane using a phosphine-Cu catalyst. The method allows facile preparation of enantiomerically enriched β-chiral alkyl pinacolboronates from a range of 1, 1-disubstituted alkenes with high enantioselectivity up to 99% ee. Unprecedented enantiodiscrimination between the geminal alkyl substituents was observed with functional group compatibility in the hydroboration. Furthermore, a catalyst loading as low as 1 mol % furnished the desired product without a decrease in yield or selectivity, demonstrating its efficiency in gram scale synthesis.
- Jang, Won Jun,Song, Seung Min,Moon, Jong Hun,Lee, Jin Yong,Yun, Jaesook
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supporting information
p. 13660 - 13663
(2017/11/07)
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- Rational Design of Thermodynamic and Kinetic Binding Profiles by Optimizing Surface Water Networks Coating Protein-Bound Ligands
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A previously studied congeneric series of thermolysin inhibitors addressing the solvent-accessible S2′ pocket with different hydrophobic substituents showed modulations of the surface water layers coating the protein-bound inhibitors. Increasing stabilization of water molecules resulted in an enthalpically more favorable binding signature, overall enhancing affinity. Based on this observation, we optimized the series by designing tailored P2′ substituents to improve and further stabilize the surface water network. MD simulations were applied to predict the putative water pattern around the bound ligands. Subsequently, the inhibitors were synthesized and characterized by high-resolution crystallography, microcalorimetry, and surface plasmon resonance. One of the designed inhibitors established the most pronounced water network of all inhibitors tested so far, composed of several fused water polygons, and showed 50-fold affinity enhancement with respect to the original methylated parent ligand. Notably, the inhibitor forming the most perfect water network also showed significantly prolonged residence time compared to the other tested inhibitors.
- Krimmer, Stefan G.,Cramer, Jonathan,Betz, Michael,Fridh, Veronica,Karlsson, Robert,Heine, Andreas,Klebe, Gerhard
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p. 10530 - 10548
(2016/12/16)
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- Sensing remote chirality: Stereochemical determination of β-, γ-, and δ-chiral carboxylic acids
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Determining the absolute stereochemisty of small molecules bearing remote nonfunctionalizable stereocenters is a challenging task. Presented is a solution in which appropriately substituted bis(porphyrin) tweezers are used. Complexation of a suitably derivatized β-, γ-, or δ-chiral carboxylic acid to the tweezer induces a predictable helicity of the bis(porphyrin), which is detected as a bisignate Cotton Effect (ECCD). The sign of the ECCD curve is correlated with the absolute stereochemistry of the substrate based on the derived working mnemonics in a predictable manner.
- Tanasova, Marina,Anyika, Mercy,Borhan, Babak
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supporting information
p. 4274 - 4278
(2015/04/14)
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- Chiral propargylic cations as intermediates in SN1-type reactions: Substitution pattern, nuclear magnetic resonance studies, and origin of the diastereoselectivity
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Nine propargylic acetates, bearing a stereogenic center (-C*HXR 2) adjacent to the electrophilic carbon atom, were prepared and subjected to SN1-type substitution reactions with various silyl nucleophiles employing bismuth trifluoromethanesulfonate [Bi(OTf)3] as the Lewis acid. The diastereoselectivity of the reactions was high when the alkyl group R2 was tertiary (tert-butyl), irrespective of the substituent X. Products were formed consistently with a diastereomeric ratio larger than 95:5 in favor of the anti-diastereoisomer. If the alkyl substitutent R2 was secondary, the diastereoselectivity decreased to 80:20. The reaction was shown to proceed stereoconvergently, and the relative product configuration was elucidated. The reaction outcome is explained by invoking a chiral propargylic cation as an intermediate, which is preferentially attacked by the nucleophile from one of its two diastereotopic faces. Density functional theory (DFT) calculations suggest a preferred conformation in which the group R2 is almost perpendicular to the plane defined by the three substituents at the cationic center, with the nucleophile approaching the electrophilic center opposite to R2. Transition states calculated for the reaction of allyltrimethylsilane with two representative cations support this hypothesis. Tertiary propargylic cations with a stereogenic center (-C* HXR2) in the α position were generated by ionization of the respective alcohol precursors with FSO3H in SO2ClF at -80 C. Nuclear magnetic resonance (NMR) spectra were obtained for five cations, and the chemical shifts could be unambiguously assigned. The preferred conformation of the cations as extracted from nuclear Overhauser experiments is in line with the preferred conformation responsible for the reaction of the secondary propargylic cations.
- Nitsch, Dominik,Huber, Stefan M.,Poethig, Alexander,Narayanan, Arjun,Olah, George A.,Prakash, G. K. Surya,Bach, Thorsten
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supporting information
p. 2851 - 2857
(2014/03/21)
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- Bis(phosphine)cobalt dialkyl complexes for directed catalytic alkene hydrogenation
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Planar, low-spin cobalt(II) dialkyl complexes bearing bidentate phosphine ligands, (P - P)Co-(CH2SiMe3)2, are active for the hydrogenation of geminal and 1,2-disubstituted alkenes. Hydrogenation of more hindered internal and endocyclic trisubstituted alkenes was achieved through hydroxyl group activation, an approach that also enables directed hydrogenations to yield contrasteric isomers of cyclic alkanes.
- Friedfeld, Max R.,Margulieux, Grant W.,Schaefer, Brian A.,Chirik, Paul J.
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supporting information
p. 13178 - 13181
(2015/03/30)
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- From olefins to alcohols: Efficient and regioselective ruthenium-catalyzed domino hydroformylation/reduction sequence
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Exploring the alternatives: Ruthenium imidazoyl phosphine complexes catalyze the domino hydroformylation/reduction of alkenes to alcohols in good yields and with good selectivities (see scheme). Linear aliphatic alcohols are synthesized under reaction conditions typically used in industrial hydroformylations. Copyright
- Fleischer, Ivana,Dyballa, Katrin Marie,Jennerjahn, Reiko,Jackstell, Ralf,Franke, Robert,Spannenberg, Anke,Beller, Matthias
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supporting information
p. 2949 - 2953
(2013/04/10)
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- Steric effects and mechanism in the formation of hemi-acetals from aliphatic aldehydes
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Some physical properties (pKa, log POW, boiling points) of hexanoic acid 1 (X = COOH) and its seven isomers 2, 3, 4, 5, 6, 7, 8 (X = COOH) are reported. Hexanal 1 (X = CHO) and its seven isomeric aldehydes 2, 3, 4, 5, 6, 7, 8 (X = CHO) are shown to equilibrate, in methanol solution, with their hemi-acetals. Logarithms of equilibrium constants correlate with values of Es for the isomeric C5H11 substituents, and with logs of relative rates for saponification of the corresponding methyl esters with ρ = 0.52, reflecting the reduced steric demand of hydrogen compared to oxygen in the quaternization of ester and aldehydic carbonyl groups. Rates of equilibration have also been measured in buffered methanol. For hexanal, with a 2:1 Et3N:AcOH buffer, the buffer-independent contribution is dominated by the methoxide catalysed pathway. Rates in this medium have been determined for isomers 1, 2, 3, 4, 5, 6, 7, 8 (X = CHO), and their logarithms do not correlate with logarithms of equilibrium constants for hemi-acetal formation or with substituent steric parameters derived from ester formation or saponification, indicating that the steric changes associated with full quaternization of the carbonyl group are not mirrored in the transition structures for hemi-acetal formation. It is suggested that transition states for hemi-acetal formation are relatively early so that steric interactions are effectively those between the nucleophile and ground state conformations of the aldehydes. A comparison of the entropies of hemi-acetal formation with entropies of activation has provided a basis for a suggested transition structure. Comparisons with acid chloride hydrolyses are made. Copyright 2013 John Wiley & Sons, Ltd. Logarithms of equilibrium constants for formation hemi-acetals of hexanal and its seven isomeric aldehydes correlate well with values of Es for the isomeric C5H11 substituents, and with logs of relative rates for saponification of the corresponding methyl esters. Logarithms of rate constants for hemi-acetal formation do not, indicating that the steric changes associated with full quaternization of the carbonyl group are not mirrored in the transition structures for hemi-acetal formation. The reasons for this are discussed. Copyright
- Daw, Graham,Regan, Andrew C.,Watt, C. Ian F.,Wood, Evan
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p. 1048 - 1057
(2014/01/06)
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- Syntheses and evaluation of anticonvulsant activity of novel branched alkyl carbamates
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A novel class of 19 carbamates was synthesized, and their anticonvulsant activity was comparatively evaluated in the rat maximal electroshock (MES) and subcutaneous metrazol (scMet) seizure tests and pilocarpine-induced status epilepticus (SE) model. In spite of the alkyl-carbamates' close structural features, only compounds 34, 38, and 40 were active at the MES test. The analogues 2-ethyl-3-methyl-butyl-carbamate (34) and 2-ethyl-3-methyl-pentyl- carbamate (38) also exhibited potent activity in the pilocarpine-SE model 30 min postseizure onset. Extending the aliphatic side chains of homologous carbamates from 7 to 8 (34 to 35) and from 8 to 9 carbons in the homologues 38 and 43 decreased the activity in the pilocarpine-SE model from ED50 = 81 mg/kg (34) to 94 mg/kg (35) and from 96 mg/kg (38) to 114 mg/kg (43), respectively. The most potent carbamate, phenyl-ethyl-carbamate (47) (MES ED50 = 16 mg/kg) contains an aromatic moiety in its structure. Compounds 34, 38, 40, and 47 offer the optimal efficacy-safety profile and, consequently, are promising candidates for development as new antiepileptics.
- Hen, Naama,Bialer, Meir,Yagen, Boris
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experimental part
p. 2835 - 2845
(2012/06/15)
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- Synthetic routes to campesterol and dihydrobrassicasterol: A first reported synthesis of the key phytosterol dihydrobrassicasterol
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Phytosterols are increasingly used as health supplements in functional foods and are associated with having both positive and negative effects on health. Given this disparity, an investigation of their full individual biological profile is imperative in order to assure food safety. This paper describes the de novo synthesis of pure phytosterols in multigram scale and we report the first synthesis of the key phytosterol dihydrobrassicasterol along with a comparison of routes to campesterol. A detailed spectroscopic analysis is included with full assignment of the 13C NMR spectroscopic data of both compounds, mixtures and their precursors leading to the potential use of NMR spectroscopy as a tool for analysis of these sterol mixtures.
- O'Connell,O'Callaghan,O'Brien,Maguire,McCarthy
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experimental part
p. 4995 - 5004
(2012/08/28)
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- Synthesis of secasterol and 24-episecasterol and their toxicity for MCF-7 cells
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The convergent synthesis of biosynthetic precursors of brassinosteroids with a Δ2-bond in cycle A-secasterol and 24-episecasterol-was performed. The key stages in the construction of the side chain in these compounds were the Julia olefination of the steroid 22-aldehyde followed by the Sharpless asymmetric dihydroxylation of the intermediate Δ22- olefin. The cytotoxicity of the synthesized compounds for breast carcinoma MCF-7 cells was assessed.
- Khripach,Zhabinskii,Gulyakevich,Konstantinova,Misharin, A. Yu.,Mekhtiev,Timofeev,Tkachev, Ya. V.
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experimental part
p. 746 - 754
(2011/10/03)
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- Enantioselective synthesis of 2-substituted alcohols using (+)-(1S,2S)-pseudoephedrine as chiral auxiliary
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An improved method for the selective synthesis of enantiopure 2-substituted alcohols is described. Highly diastereoselective alkylation of pseudoephedrine-derived amides and subsequent oxidation of the hydroxyl group in the amide side chain, leads to oxoamides. These oxoamides can be purified by crystallization or preparative HPLC to obtain diastereomeric ratios of >99:1. The following reductive cleavage of the modified auxiliary allows the epimerization-free formation of enantiopure 2-substituted alcohols with up to 99.9% ee. Georg Thieme Verlag Stuttgart.
- Tietze, Lutz F.,Raith, Christian,Brazel, C. Christian,Hoelsken, Soeren,Magull, Joerg
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p. 229 - 236
(2008/12/20)
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- 9-Borabicyclo[3.3.2]decanes and the asymmetric hydroboration of 1,1-disubstituted alkenes
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The syntheses of the optically pure asymmetric hydroborating agents 1 (a, R = Ph; b, R = TMS) in both enantiomeric forms are reported. These reagents are effective for the hydroboration of cis-, trans- and trisubstituted alkenes. More significantly, they exhibit unprecedented levels of selectivity in the asymmetric hydroboration of 1,1-disubstituted alkenes (28-92% ee), a previously unanswered challenge in the nearly 50 year history of this reagent-controlled process. For example, the hydroboration of α-methylstyrene with 1a produces the corresponding alcohol 6f in 78% ee (cf., Ipc2BH, 5% ee). Suzuki coupling of the intermediate adducts 5 produces the nonracemic products 7 very effectively (50-84%) without loss of optical purity. Copyright
- Gonzalez, Ana Z.,Roman, Jose G.,Gonzalez, Eduvigis,Martinez, Judith,Medina, Jesus R.,Matos, Karl,Soderquist, John A.
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supporting information; experimental part
p. 9218 - 9219
(2009/02/02)
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- A Convenient Synthesis of (22S)-22-Hydroxycampesterol and Some Related Steroids
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As possible candidates for intermediates in brassinolide biosynthesis, (22S)-22-hydroxycampesterol 1 and its related new steroids 5-7 are conveniently synthesized by employing the Grignard reaction of a known steroidal 22-aldehyde 8 with 2,3-dimethylbutylmagnesium bromide as a key reaction.
- Takatsuto, Suguru,Watanabe, Tsuyoshi,Gotoh, Chiharu,Kuriyama, Hiroki,Noguchi, Takahiro,Fujioka, Shozo
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p. 844 - 852
(2007/10/03)
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- Photodeoxygenation of dibenzothiophene sulfoxide: Evidence for a unimolecular S-O cleavage mechanism
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Photolysis of dibenzothiophene sulfoxide results in the formation of dibenzothiophene and oxidized solvent. Though quantum yields are low, chemical yields of the sulfide are quite high. Yields of the oxidized solvents can also be high. Typical products are phenol from benzene, cyclohexanol, and cyclohexene from cyclohexane and 2-cyclohexenol and epoxycyclohexane from cyclohexene. A number of experiments designed to elucidate the mechanism of the hydroxylation were carried out, including measurements of quantum yields as a function of concentration, solvent, quenchers, and excitation wavelength. These data are inconsistent with a mechanism involving a sulfoxide dimer, which also does not properly account for the solvent oxidations. It is suggested hbat the active oxidizing agent may be atomic oxygen O(3P) or a closely related noncovalent complex, based on the nature of the oxidation chemistry, comparison to known rate constants for O(3P) reactivity, and the quantum yield data.
- Gregory, Daniel D.,Wan, Zehong,Jenks, William S.
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- SYNTHESIS OF BRASSINOLIDE AND ITS ANALOGS
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A new version of the synthesis of brassinosteroids of the 28C series is described.It is based on stigmasterol and uses the reaction of steroidal 22-aldehydes with aryl sulfones.
- Khripach, V. A.,Zhabinskii, V. N.,Ol'khovik, V. K.,Lakhvich, F. A.
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p. 1699 - 1706
(2007/10/02)
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- Alkane Functionalization on a Preparative Scale by Mercury-Photosensitized Cross-Dehydrodimerization
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Alkanes can be functionalized with high conversions and in high chemical and quantum yields on a multigram scale by mercury-photosensitized reaction between an alkane and alcohols, ethers, or silanes to give homodimers and cross-dehydrodimers.The separation of the product mixtures is often particulary easy because of a great difference in polarity of the homodimers and cross-dimers.It is also possible to bias the product composition when the ratio of the components in the vapor phase is adjusted by altering the liquid composition.This is useful either to maximize chemical yield or to ease separation by favoring the formation of the most easily separated pair of compounds.The mechanistic basis of the reaction is discussed and a number of specific types of syntheses, for example of 2,2-disubstituted carbinols, are described in detail.The selectivity of cross-dimerization is shown to exceed that for homodimerization and reasons are discussed.Relative reactivities of different compounds and classes of compound are MeOHp-dioxanecyclohexane1,3,5-trioxacyclohexaneethanolisobutaneTHFEt3SiH.The observed selectivities generally parallel those for homodimerization, reported in the preceding paper, but certain differences are noted, and reasons for the differences are proposed.The bond-dissociation energy of Et3SiH is estimated from the reactivity data to be 90 kcal/mol.Eleven new carbinols are synthesized.
- Brown, Stephen H.,Crabtree, Robert H.
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p. 2946 - 2953
(2007/10/02)
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- Photoinduced Nitrene, Carbene, and Atomic Oxygen Transfer Reactions Starting from the Corresponding Pyridinium N-, C-, and O-Ylides
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Ultraviolet irradiation of the pyridinium ylides 1, 2, and 3 led to fragmentation of the exocyclic polar bonds, as well as to skeletal rearrangements.The photoinduced fragmentation processes gave the corresponding pyridines and highly reactive intermediates, i. e. ethoxycarbonylnitrene, dicyanocarbene and atomic oxygen (oxene), respectively.Trapping of the reactive intermediates by alkanes and alkenes permitted the determination of their spin multiplicity.Ethoxycarbonylnitrene was in its triplet ground state at the moment of its formation.Dicyanocarbene occurred as a mixture of singlet and triplet, as determined by dilution experiments with variable amounts of alkenes.As to atomic oxygen, all collected data point to its formation in solution in its triplet ground state.
- Strub, Henri,Strehler, Christiane,Streith, Jacques
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p. 355 - 364
(2007/10/02)
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- Enantioselective Synthesis of Useful Chiral Precursors, Unsymmetrical Propane-1,3-diol Derivatives, from Malonic acid
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Syntheses of chiral synthons via monosubstituted malonic chiral half esters were studied and chiral 3-silyloxy propanols were enantioselectively synthesised.
- Ihara, Masataka,Takahashi, Masanobu,Taniguchi, Nobuaki,Fukumoto, Keiichiro,Kametani, Tetsuji
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p. 619 - 620
(2007/10/02)
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- Shape Selective Alkane Hydroxylation by Metalloporphyrin Catalysts
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A series of manganese and iron porphyrins with sterically protected pockets are shown to be shape selective alkane hydroxylation catalysts.With iodosobenzene as oxidant, good regioselectivity is observed for hydroxylation of alkanes at the least hindered methyl group by using the very sterically hindered (5,10,15,20-tetrakis(2',4',6'-triphenylphenyl)porphyrinato)manganese(III) acetate (MnTTPPP(OAc)) as catalyst; The moderately hindered (5,10,15,20-tetrakis(2',4',6'-trimethoxyphenyl)porphyrinato)manganese(III) acetate shows little selectivity toward terminal CH3 hydroxylation but does show enhancement for the adjacent, ω - 1, CH2 site.Primary selectivity is dependent on the size and shape of the alkane substrate, with more bulky substituents giving greater primary selectivity.Substituting pentafluoroiodosobenzene or m-chloroperbenzoic acid as oxidants yields similar selectivity, thus conclusively demonstrating metal based oxidation via a common intermediate for these three systems.In contrast, tert-butyl hydroperoxide or 2,2,2-trifluoroethanol solubilized pentafluoroiodosobenzene show no primary carbon selectivity, and reaction product ratios are independent of the metalloporphyrin catalyst; this demonstrates that the site of oxidation with these oxidants is not metal based.The iron porphyrin derivatives also show good primary selectivity, although to a lesser degree than with the Mn derivatives, proving that these oxidations too are metal based.The regioselectivities for alkane hydroxilation shown by TTPPP derivatives are comparable to or better than those found for some isozymes of cytochrome P-450 which are responsible for primary alcohol biosynthesis from steroids, fatty acids, and alkanes.
- Cook, Bruce R.,Reinert, Thomas J.,Suslick, Kenneth S.
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p. 7281 - 7286
(2007/10/02)
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- Shape-selective Alkane Hydroxylation
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A series of sterically hindered manganese porphyrins have been used to catalyse shape-selective alkane hydroxylation, increasing the production of primary alcohols.
- Suslick, Kenneth,Cook, Bruce,Fox, Mary
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p. 580 - 582
(2007/10/02)
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- Hydroboration of Sterically Hindered Olefins under High Pressure
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Hydroboration of sterically hindered olefins such as tetramethylethylene, tetraisopropylethylene, trans-1,2-di-tert-butylethylene, and 1,2-dimethyldi-tert-butylethylene has been investigated at high pressure (6000 atm).The previously unknown trithexylborane was prepared.The boron of trithexylborane was found to be isomerized much faster to a terminal carbon than that of dithexyl- and thexylboranes. trans-1,2-Di-tert-butylethylene yields a monoalkylborane at both 1 atm and high pressure (5000-6000 atm).Evidence is presented that is consistent with the hypothesis thata multialkylborane is formed at high pressure that dissociates without an isomerization upon releasing the pressure to 1 atm.Tetraisopropylethylene was found to give no hydroborated products at 1 atm or at high pressure (3500-6000 atm). (E)- and (Z)-1,2-Dimethyldi-tert-butylethylene was prepared, characterized, and hydroborated.A monoalkylborane is formed at 1 atm.At high pressure a trialkylborane is formed, which after returning to 1 atm, yields mainly the isomerized borane. 5β-Chol-9(11)-ene was synthesized from deoxycholic acid.This was found to yield a monoalkylborane after hydroboration at 1 atm or high pressure, in contrast to a literature report for a structurally similar steroid.An isomerized olefin was isolated after oxidation of the steroidal borane.
- Rice, Joseph E.,Okamoto, Yoshiyuki
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p. 4189 - 4194
(2007/10/02)
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- Stereochemistry of Aliphatic Carbocations, 14. Alkyl Shifts from Secondary to Primary Carbon Atoms
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Alkyl shifts from secondary to primary carbon atoms have been induced by the nitrous acid deamination of suitable amines (4, 22, 39, 51); they include sequential rearrangements (-CH3,CH3 and -CH3,H).Predominant although incomplete inversion at the migration origin has been observed (Me 70percent, Et 62-64percent, nPr 65percent, iPr 64percent, tBu 55percent).Our results require the intervention of open secondary carbocations which may be preceded by less stable bridged intermediates.
- Kirmse, Wolfgang,Guenther, Bernd-Rainer,Knist, Johannes,Kratz, Sigrid,Loosen, Karin,et al.
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p. 2127 - 2139
(2007/10/02)
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