- Practical Olefin Metathesis in Protic Media under an Air Atmosphere
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The discovery that efficient olefin metathesis reactions involving previously challenging terminal olefin substrates are possible using novel and readily available catalyst systems in non-distilled, non-degassed protic media in air is reported.
- Connon, Stephen J.,Rivard, Michael,Zaja, Mirko,Blechert, Siegfried
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- Regioselective Chromatic Orthogonality with Light-Activated Metathesis Catalysts
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The ability to selectively guide consecutive chemical processes towards a preferred pathway by using light of different frequencies is an appealing concept. Herein we describe the coupling of two photochemical reactions, one the photoisomerization and consequent activation of a sulfur-chelated latent olefin-metathesis catalyst at 350nm, and the other the photocleavage of a silyl protecting group at 254nm. Depending on the steric stress exerted by a photoremovable neighboring chemical substituent, we demonstrate the selective formation of either five- or six-membered-ring frameworks by light-triggered ring-closing metathesis. The orthogonality of these light-induced reactions allows the initiation of these processes independently and in interchangeable order, according to the wavelength of light used to promote them. A guiding light: By the combination of a light-activated sulfur-chelated olefin-metathesis catalyst with a photocleavable bulky silyl protecting group, two orthogonal pathways enabled the selective synthesis of five- or six-membered heterocycles according to the order in which the starting material was irradiated with light of different wavelengths. Thus, protecting-group removal and metathesis gave either a dihydropyran or a dihydrofuran.
- Levin, Efrat,Mavila, Sudheendran,Eivgi, Or,Tzur, Eyal,Lemcoff, N. Gabriel
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- Syntheses of new carbanucleosides by pericyclic reactions
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The synthesis of heterobase-functionalized cyclopentene derivatives as valuable substrate for the introduction of suitable substituents through pericyclic reactions is reported. The structures of ene and 1,3-dipolar adducts are discussed, and the primary antiviral activities of some adenine derivatives are reported. The synthesis of heterobase-functionalized cyclopentene derivatives as valuable substrates for the introduction of suitable substituents through pericyclic reactions is reported. The structures of ene and 1,3-dipolar adducts are discussed, and the primary antiviral activities of some adenine derivatives are reported. Copyright
- Scagnelli, Luca,Memeo, Misal Giuseppe,Carosso, Serena,Bovio, Bruna,Quadrelli, Paolo
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- Making JP-10 Superfuel Affordable with a Lignocellulosic Platform Compound
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The synthesis of renewable jet fuel from lignocellulosic platform compounds has drawn a lot of attention in recent years. So far, most work has concentrated on the production of conventional jet fuels. JP-10 is an advanced jet fuel currently obtained from fossil energy. Due to its excellent properties, JP-10 has been widely used in military aircraft. However, the high price and low availability limit its application in civil aviation. Here, we report a new strategy for the synthesis of bio-JP-10 fuel from furfuryl alcohol that is produced on an industrial scale from agricultural and forestry residues. Under the optimized conditions, bio-JP-10 fuel was produced with high overall carbon yields (≈65 %). A preliminary economic analysis indicates that the price of bio-JP-10 fuel can be greatly decreased from ≈7091 US$/ton (by fossil route) to less than 5600 US$/ton using our new strategy. This work makes the practical application of bio-JP-10 fuel forseeable.
- Li, Guangyi,Hou, Baolin,Wang, Aiqin,Xin, Xuliang,Cong, Yu,Wang, Xiaodong,Li, Ning,Zhang, Tao
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- A concise synthesis of (-)-centrolobine via a diastereoselective ring rearrangement metathesis-isomerisation sequence
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A total synthesis of (-)-centrolobine (1) based on a diastereoselective ring rearrangement metathesis-double bond isomerisation sequence and a one-pot cross metathesis-hydrogenation procedure is described. The Royal Society of Chemistry 2006.
- Boehrsch, Verena,Blechert, Siegfried
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- A short stereoselective synthesis of (+)- and (-)-2-oxabicyclo[3.3.0]oct-6-en-3-one by intramolecular carbon-hydrogen insertion catalyzed by chiral dirhodium(II) carboxamidates
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The synthesis of (1S,5R)-(-)-2-oxabicyclo[3.3.0]oct-6-en-3-one, a useful synthetic precursor en route to various prostaglandins, from divinylcarbinol via catalytic metathesis and C-H insertion of 3-cyclopentenyl diazoacetate is described. Enantioselectivities of 90±1% have been achieved in the insertion process.
- Doyle, Michael P.,Catino, Arthur J.
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- A radical clock investigation of microsomal cytochrome P-450 hydroxylation of hydrocarbons. Rate of oxygen rebound
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A number of alkyl-substituted cyclopropanes for which the rates of ring opening of the corresponding cyclopropylcarbinyl radicals have been determined (see preceding paper in this issue) have been used as substrates for hydroxylation by phenobarbital-induced, rat liver microsomal cytochrome P-450 at 37 °C. Three of these compounds gave both ring-closed and ring-opened alcohols, thus allowing the rate constant, kOH, for "oxygen rebound" onto the corresponding carbon-centered radicals to be determined. In particular, both trans- (1bH) and cis- (1cH) 1,2-dimethylcyclopropane gave 4-penten-2-ol (2bOH) and 2-methyl-3-buten-1-ol (3bOH) together with the corresponding trans- (1bOH) or cis- (1cOH) 2-methylcyclopropanemethanols. Of much greater importance, for both 1bH and 1cH the ratios of the yields of the secondary-to-primary ring-opened alcohols, i.e., [2bOH]/[3bOH], were the same, within experimental error as the ratio of the rates of ring opening of the corresponding trans- (1b?) and cis- (1c?) methylcyclopropylmethyl radicals in solution at 37 °C. This indicates that when 1b? and 1c? are formed from their parent hydrocarbons by H-atom abstraction in the hydrophobic pocket of cytochrome P-450 they are not detectably constrained in their subsequent reactions by their unusual environment. From the ratio of the yields of the unrearranged alcohol to each of the rearranged alcohols we calculate kOH values of 1.5 and 1.6 × 1010 s-1 for 1bH as substrate and values of 1.9 and 1.8 × 1010 s-1 for 1cH as substrate. Consistent with these values we have obtained kOH = 2.2 × 1010 s-1 for bicyclo[2.1.0]pentane as substrate. Substrates such as methylcyclopropane and 1,1-dimethylcyclopropane, for which the corresponding cyclopropylmethyl radicals undergo relatively slow ring opening, yielded only the ring-closed alcohols on oxidation with cytochrome P-450. 1,1,2,2-Tetramethylcyclopropane gave only a trace of a ring-opened alcohol, corresponding to kOH = 2.5 × 1011 s-1 for this substrate. Hexamethylcyclopropane gave no detectable ring-opened alcohol from which observation a limit for kOH > 5 × 1011 s-1 can be calculated. Possible explanations for the unexpected behavior of these last two, relatively bulky, substrates are discussed.
- Bowry, Vincent W.,Ingold
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- Timing of the Radical Recombination Step in Cytochrome P-450 Catalysis with Ring-Strained Probes
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Notricyclane, methylcyclopropane, and bicyclopentane have been used to probe the catalytic mechanism of microsomal cytochrome P-450.Nortricyclane is oxidized by rat liver microsomes to nortricyclanol without the detectable formation of norborn-5-en-2-ol.Methylcyclopropane is similarly oxidized to cyclopropylmethanol without the detectable formation of 3-buten-1-ol or cyclobutanol.The radical pair in the hydroxylation reaction therefore collapses faster than the cyclopropylmethyl radical rearranges (1 x 108 s-1).In contrast, microsomal oxidation of bicyclopentane yields approximately a 7:1 mixture of endo-2-hydroxybicyclopentane and 3-cyclopenten-1-ol.Deuterium labeling studies indicate the endo hydrogen is predominantly or exclusively removed from, and the hydroxyl group is delivered to, the endo face in both the rearranged and unrearranged products.The results indicate that a radical pair is formed in P-450-catalyzed hydroxylations that collapses with stereochemical specificity at a rate in excess of 1 x 109 s-1.
- Montellano, Paul R. Ortiz de,Stearns, Ralph A.
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- Coordination chemistry of a hemilabile amino-tethered N-heterocyclic carbene with ruthenium(II)
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The reaction of the amine-tethered N-heterocyclic carbene ligand 2,4,6-Me3C6H2NC3H 2NCH2CH2NH-2,4,6-Me3C 6H2 (Mes[CNH]) with Ru(CHPh)(PCy 3)2Cl2 leads to the formation of Mes[CNH]Ru(CHPh)(PCy3)Cl2, which exists as a mixture of two isomers in a ratio of 7:1. While the major species was characterized by X-ray crystallography, the minor rotamer species could be characterized only in solution. Phosphine exchange kinetics and equilibrium variable-temperature measurements did not show much difference from benchmark Grubbs systems. Evidence for coordination of the amine tether was obtained by addition of pyridine, which generated the octahedral complex Mes[CNH]Ru(CHPh)(py)Cl2 with the tethered amine coordinated. Similarly, addition of PMe3 results in the formation of Mes[CNH]Ru(CHPh)(PMe3)Cl2, also having an octahedral structure with the pendant amine ligated. Attempts to benchmark the catalytic potential of the PCy3 derivative showed that it was far inferior to known Grubbs-type systems.
- Jong, Howard,Patrick, Brian O.,Fryzuk, Michael D.
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- Preparation and characterization of 2-silanorbornanes
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Four members of the new class of 2-silabicycloheptanes, or 2-silanorbornanes, were prepared: 2-silanorbornane (1), 2,2-dichloro-2-silanorbornane (2), 2-chloro-2-methyl-2-silanorbornane (3), and 2-methyl-2-silanorbornane (4); the ring-closure reaction involved a platinum-catalyzed, intramolecular hydrosilation.The silanes were chracterized by carbon and hydrogen elemental analyses and by 1H, 13C, and 29Si NMR, IR, and mass spectrometry.Isomer assigments for 3 and 4 were made on the basis of the NMR data.In the mass spectra, each compound gave an abundant molecular ion and a major mode of fragmentation peculiar to this bicyclic system.Some initial stereochemical studies of the reactions of 3 and 4 were performed, including fluoride-induced equilibration of the isomers of 4.
- Cremer, Sheldon E.,Blankenship, Craig
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- Organocatalytic Desymmetrization of Meso-Aziridines Via Asymmetric Intramolecular Rearrangement
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Herein we report the first organocatalytic method for the desymmetrization of meso-aziridines that does not require the use of an external nucleophilic reagent. The process was designed upon a base promoted rearrangement of bicyclic meso-cyclopentanone aziridines, that progresses in intramolecular fashion to provide densely functionalized cyclic ketones, key intermediates for the preparation of Active Pharmaceutical Ingredients. The key enantio-determining step proceeded under the catalysis of a bifunctional thiourea organocatalyst. The process provides an entry to a class of highly functionalized chiral amines, 4-aminocyclopentenones, not accessible with previous desymmetrization methods. The ambiphilic nature of the products makes them versatile synthetic intermediates in the preparation of natural products and popular antiviral nucleoside inhibitors, for example abacavir.
- Costanzo, Martina,Cortigiani, Mauro,Gillick-Healy, Malachi W.,Kelly, Brian G.,Monasterolo, Claudio,Adamo, Mauro F. A.
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p. 4560 - 4565
(2021/07/20)
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- One-pot chemoenzymatic reactions in water enabled by micellar encapsulation
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The use of micellar conditions to enable one-pot reactions involving both transition metal and enzymatic catalysts is reported. Representative enzymatic transformations under micellar conditions are unaffected by the presence of non-ionic surfactants, including designer surfactants such as TPGS-750-M. Furthermore, the presence of enzymes has a negligible effect on transition metal catalysis under micellar conditions in water. Finally, three one-pot chemoenzymatic reactions in water are reported in which the micelle-forming surfactant TPGS-750-M is a crucial factor for reaction efficiency.
- Adams, Nicholas P.,Bushi, Jurgen,Hastings, Courtney J.,Kolb, Samuel J.
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supporting information
p. 6187 - 6193
(2020/10/18)
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- Synthesis and antiviral evaluation of novel 2′,2′-difluoro 5′-norcarbocyclic phosphonic acid nucleosides as antiviral agents
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A very efficient synthetic route to novel 2′,2′-difluoro 5′-norcarbocyclic phosphonic acid nucleosides from but-3-en-1-ol 5 is described. The discovery of 2′-fluorinated furanose nucleoside 1 as a potent anti-HIV-1 agent has led to the synthesis and biological evaluation of 2′-modified 5′-norversions of the carbocyclic phosphonate nucleosides. The synthesized nucleoside analogues 18, 19, 23a, 23b, and 24 were tested for anti-HIV activity as well as cytotoxicity. Adenine analogue 19 shows significant anti-HIV-1 activity (EC50 = 13 μM).
- Shen, Guang Huan,Hong, Joon Hee
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- Stability and activity of cis-dichloro ruthenium olefin metathesis precatalysts bearing chelating sulfur alkylidenes
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S-Chelated Grubbs type complexes are usually found in their stable cis-dichloro conformation. These precatalysts are usually latent and necessitate external stimuli to promote olefin metathesis reactions. Herein we report the synthesis of new S-chelated ruthenium complexes, by a simple exchange of the benzylidene to an alkylidene chelating ligand. The structure of the complexes was studied by NMR spectroscopy, single crystal X-ray diffraction and DFT calculations. The new complexes were tested in a series of olefin metathesis reactions and were found to be the first cis-dichloro ruthenium precatalysts that are active at room temperature. The observed differences in reactivity and structure between the alkylidene complexes and their benzylidene counterparts highlight the important influence aromaticity may have on the stability and activity of chelated Grubbs type complexes. The findings may also have implications to develop alternative strategies to stabilize, or destabilize, other organometallic complexes bearing relevant chelating ligands.
- Tzur, Eyal,Ivry, Elisa,Diesendruck, Charles E.,Vidavsky, Yuval,Goldberg, Israel,Lemcoff, N. Gabriel
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supporting information
p. 24 - 28
(2014/08/18)
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- 4-Aminocyclopentane-1,3-diols as platforms for diversity: Synthesis of a screening library
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Trisubstituted cyclopentanes have a discrete shapely curvature. While the central ring of these compounds is devoid of rotatable bonds, the pseudo rotation of the cyclopentane ring leads to a desirable disruption of planarity. This is favorable for aqueous solubility and enables addressing of wide-ranging conformational space. The sp3-rich framework of 4-aminocyclopentane- 1,3-diols offers stereochemically defined attachment points for substituents and renders these fragment-like molecules good platforms for molecular diversity. By using an established N-selective polymer-assisted acylation protocol, these scaffolds with natural product-like properties were transformed into a screening library by attachment of substituents at defined positions. Here we describe the synthesis and characterization of these molecular platforms and their use as starting points for the construction of an 80-member library of 4-amidocyclopentane-1,3-diol monoethers. Five of the compounds displayed cytotoxicity in a tumor cell line assay with IC50 values in the low micromolar range.
- Zohrabi-Kalantari,Wilde,Grünert,Bednarski,Link
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p. 203 - 213
(2014/03/21)
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- 4-aminocyclopentane-1,3-diols as platforms for diversity: Synthesis of anandamide analogs
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Starting from cyclopentadiene, two racemic mixtures of 4-aminocyclopentane- 1,3-diols were prepared in 8 steps and characterized. Structure determination proved the anticipated trans-orientation of the two oxygen atoms with respect to the plane of the ring. The fragment-like new compounds are small and hydrophilic, devoid of rotatable bonds, and offer stereochemically defined attachment points for substituents. Thus, these platforms for diversity are suitable starting points for the construction of combinatorial libraries of lead-like 4-amidocyclopentane-1,3-diols or natural product analogs. As a proof of concept, cyclopentanoid anandamide analogs were prepared using these molecular platforms and evaluated as tools for the investigation of unresolved issues in the molecular biology of anandamide.
- Zohrabi-Kalantari, Vida,Jarrahian, Abbas,Bissantz, Caterina,Bergstrom, Donald E.,Barker, Eric L.,Link, Andreas
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p. 881 - 888
(2013/09/23)
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- FUSED HETEROAROMATIC PYRROLIDINONES
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Disclosed are compounds of Formula 1, and pharmaceutically acceptable salts thereof, wherein G, L1, L2, R1, R2, R3, and R4 are defined in the specification. This disclosure also relates to materials and methods for preparing compounds of Formula 1, pharmaceutical compositions containing them, and their use for treating disorders, diseases, and conditions involving the immune system and inflammation, including rheumatoid arthritis, hematological malignancies, epithelial cancers (i.e., carcinomas), and other disorders, diseases, and conditions for which inhibition of SYK is indicated.
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Page/Page column 76
(2011/07/06)
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- Weil-defined silica-supported olefin metathesis catalysts
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Two triethoxysilyl-functionalized N-heterocyclic carbene ligands have been synthesized and used to prepare the corresponding second-generation ruthenium olefin metathesis catalysts. These complexes were then grafted onto silica gel, and the resulting materials were efficient heterogeneous catalysts for a number of metathesis reactions. The solid-supported catalysts were shown to be recyclable over a number of reaction cycles, and no detectable levels of ruthenium were observed in reaction filtrates (ruthenium concentration of filtrate 5 ppb).
- Allen, Daryl P.,Wingerden, Matthew M. Van,Grubbs, Robert H.
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supporting information; experimental part
p. 1261 - 1264
(2009/09/25)
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- Scope and mechanism of intramolecular aziridination of cyclopent-3-enyl- methylamines to 1-azatricyclo[2.2.1.02,6]heptanes with lead tetraacetate
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A series of seven cyclopent-3-en-1-ylmethylamines bearing one, two, or three methyl substituents at the C2, C3, C4, or Cα positions, including the unsubstituted parent, was accessed by ring-closing metatheses of α,α-diallylacetonitrile (or methallyl variants) and α,α-diallylacetone followed by hydride reductions or reductive amination, or by Curtius degradations of α,α-dimethyl- and 2,2,3-trimethylcyclopent-3-enylacetic acids. Oxidation of the primary amines with Pb(OAc)4 in CH2Cl2, CHCl3 or benzene in the presence of K2CO3 effected efficient intramolecular aziridinations, in all cases except the α-methyl analogue (16), to form the corresponding 1-azatricyclo[2.2.1.02,6]heptanes, including the novel monoterpene analogues, 1-azatricyclene and the 2-azatricyclene enantiomers. The cumulative rate increases of aziridination reactions observed by 1H NMR spectroscopy in CDCl3 resulting from the presence of one or two methyl groups on the cyclopentene double bond, in comparison to the rate of the unsubstituted parent amine (1:17.5:>280), indicate a highly electrophilic intermediate as the nitrene donor and a symmetrical aziridine-like transition state. A mechanism is outlined in which the amine displaces an acetate ligand from Pb(OAc)4 to form a lead(IV) amide intermediate RNHPb(OAc)3 proposed as the actual aziridinating species.
- Hu, Huayou,Faraldos, Juan A.,Coates, Robert M.
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supporting information; experimental part
p. 11998 - 12006
(2009/12/08)
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- Metathesis catalysts
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The invention relates to polymeric transition metal catalysts, to processes for preparing them, to intermediates and also to the use of the transition metal catalysts as catalysts in organic reactions, in particular in olefin metathesis reactions.
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Page/Page column 8-9
(2008/12/06)
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- Cage escape competes with geminate recombination during alkane hydroxylation by the diiron oxygenase AlkB
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(Chemical Presented) AlkBstops the radical clock: Three structurally analogous radical-clock substrates with a large span in their rearrangement rates are hydroxylated by AlkB to afford similar amounts of rearranged (2) and unrearranged products (1). Such a result is in accord with radical rebound competing with cage escape of the geminate substrate radical. The results show that radical clocks can measure both the radical lifetime and the kinetics of cage escape.
- Austin, Rachel N.,Luddy, Kate,Erickson, Karla,Pender-Cudlip, Marilla,Bertrand, Erin,Deng, Dayi,Buzdygon, Ryan S.,Van Beilen, Jan B.,Groves, John T.
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supporting information; experimental part
p. 5232 - 5234
(2009/04/04)
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- Unsubstituted bicyclo[1.1.0]but-2-ylcarbinyl cations
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A synthesis for the unsubstituted bicyclo[1.1.0]but-2-ylmethanols (endo- and exo-9) from 1,3-butadiene has been developed. Solvolyses of their sulfonates 10 and 11 took entirely different courses, as the endo compound 10 gave rise exclusively to rearranged products such as cyclopent-3-en-1-ol (14), while the exo compound 11 underwent only the substitution of the tosylate group with complete retention of the exo-bicyclo[1.1.0]but-2-ylmethyl skeleton. Under solvolytic conditions, 10 reacted at very similar rates to the corresponding monocyclic substrate, that is, cyclopropylcarbinyl mesylate (19); in contrast, 11 reacted only three times as fast as n-butyl tosylate and about 1000-fold slower than 10. The nature of the bicyclo[1.1.0]but-2-ylcarbinyl cations has been probed by quantum chemical calculations. Whereas, the exo isomer (exo-18) corresponds to a local energy minimum, the endo isomer is only a transition state [endo-l8(TS)] for an automerization of the nonclassical cyclopent-3-en-1-yl cation (13) and converts into 13 by a Wagner-Meerwein rearrangement. The most favorable isomerization of exo-18 also leads to 13 but via a transition state resembling the 2-vinylcycloprop-1-yl cation [25(TS)]. On the introduction of methyl groups at positions 1 and 3 of exo-18, the cation is no longer an energy minimum and it becomes a transition state [27(TS)] for an automerization of the nonclassical 1,3-dimethylcyclopent-3-en-1-yl cation (28). The large effect of the methyl substitution rationalizes the puzzling results of the previous product and rate studies, which utilized various substituted derivatives of bicyclo[1.1.0]but-2-ylcarbinyl sulfonates as substrates.
- Bentley, T. William,Engels, Bernd,Hupp, Thomas,Bogdan, Elena,Christl, Manfred
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p. 1018 - 1026
(2007/10/03)
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- NOVEL BENSOPHENONE DERIVATIVES OR SALTS THEREOF
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A benzophenone derivative represented by the following formula: whereinR1 represents, for example, an optionally substituted heterocyclic group, or a substituted phenyl group; Z represents, for example, an alkylene group; R2 represents, for example, a carboxyl group optionally protected with alkyl;R3 represents, for example, an optionally protected hydroxyl group; R4 represents, for example, an optionally substituted cycloalkyloxy group; and R5 represents, for example, a hydrogen atom, ???or a salt thereof has anti-arthritic activity, inhibits bone destruction caused by arthritis, and provides high safety and excellent pharmacokinetics and thus is useful as therapeutic agent for arthritis. These compounds have inhibitory effect on AP-1 activity and are useful as preventive or therapeutic agent for diseases in which excessive expression of AP-1 is involved.
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Page 136-137
(2010/02/07)
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- Scope of the directed dihydroxylation: Application to cyclic homoallylic alcohols and trihaloacetamides
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The synthesis and directed dihydroxylation of a range of cyclic alkenes was investigated. Both homoallylic alcohols and homoallylic trihaloacetamides were found to be efficient directing groups, giving rise to good to excellent levels of remote asymmetric induction with OsO4-TMEDA. Interestingly, in all cases examined, trifluoroacetamides were found to be superior to trichloroacetamides as directing groups and an argument is presented which rationalises this observation.
- Donohoe, Timothy J.,Mitchell, Lee,Waring, Michael J.,Helliwell, Madeleine,Bell, Andrew,Newcombe, Nicholas J.
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p. 2173 - 2186
(2007/10/03)
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- A solid-supported phosphine-free ruthenium alkylidene for olefin metathesis in methanol and water.
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The synthesis and olefin metathesis activity in protic solvents of 7, a phosphine-free ruthenium alkylidene bound to a hydrophilic solid support are reported. This heterogeneous catalyst promotes relatively efficient ring closing- and cross-metathesis reactions in both methanol and water. The potential utility of homogeneous catalyst 2 for olefin metathesis in methanol is also demonstrated.
- Connon, Stephen J,Blechert, Siegfried
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p. 1873 - 1876
(2007/10/03)
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- A self-generating, highly active, and recyclable olefin-metathesis catalyst
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Sequential ring-opening-metathesis polymerization and cross-metathesis reactions allow a one-pot synthesis of the illustrated ruthenium catalyst. This conceptually novel polymer-bound catalyst shows excellent metathesis activity and recyclability.
- Connon, Stephen J.,Dunne, Aideen M.,Blechert, Siegfried
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p. 3835 - 3838
(2007/10/03)
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- Microwave-Accelerated Ruthenium-Catalyzed Olefin Metathesis
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(matrix presented) Microwave heating is an efficient method for the acceleration of ring-closing metathesis reactions using ruthenium-based catalysts. The reaction can be rapidly conducted in either ionic liquids, such as 1-butyl-3-methylimidazolium tetrafluoroborate (bmim), or in a microwave transparent solvent (MTS) such as dichloromethane.
- Mayo, Kelly G.,Nearhoof, Eliza H.,Kiddle, James J.
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p. 1567 - 1570
(2007/10/03)
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- Towards chiral non-racemic cis-1,3-disubstituted cyclopentane 1,4-diphosphines
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Reaction of dialkyl- or diaryl-trans-(3,4-epoxycyclopentyl)phosphine oxides 2 with the lithium derivative of methyldiphenylphosphine oxide gives a mixture of (±)-t-4- and (±)-c-4-(disubstituted phosphinoyl)-t-2-(diphenylphosphinoylmethyl)-r-1-cyclopentanol derivatives 13a-c and 16a-c, which could be obtained in pure form by separation of the corresponding acetates 14a-c and 17a-c followed by methanolysis. Compounds 13b and 16b were transformed into the corresponding dehydroxy derivatives 19 and 21 through the Barton procedure. Additionally, 16a was transformed into a diastereomeric mixture of carbamates 22 and 23 on reaction with (S)-α-phenylethylisocyanate which could be separated by repeated crystallization. The relative configuration of compounds 13b, 17a, 21 and 22 was established by X-ray diffraction analysis.
- Camps, Pelayo,Colet, Gisela,Font-Bardia, Merce,Muoz-Torrero, Victoria,Solans, Xavier,Vazquez, Santiago
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p. 759 - 778
(2007/10/03)
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- Desymmetrisation of dialdehydes: (+)-(S) and (-)-(R) nor-methyl mevaldate as versatile synthetic intermediates
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Desymmetrisation of 3-(t-butyldimethylsilyloxy)pentanedial 2 may be carried out by monoacetalisation with (R)- or (S)-2-phenylethanol. The products may be elaborated to nor-methyl mevaldate derivatives.
- Buckley, Shirley L.J.,Drew, Michael G.B.,Harwood, Laurence M.,Macías-Sánchez, Antonio J.
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p. 3593 - 3596
(2007/10/03)
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- Mechanistic studies of olefin metathesis by ruthenium carbene complexes using electrospray ionization tandem mass spectrometry
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The olefin metathesis reaction of the Grubbs ruthenium carbene complexes has been investigated in the gas phase by electrospray ionization tandem mass spectrometry. Relative rates of reaction for substituted ruthenium benzylidenes and alkylidenes after removal of one phosphine ligand were interpreted with the aid of linear free energy analysis and kinetic isotope effects. The experimental observations are consistent with a reaction profile in which the metallacyclobutane structure is a transition state rather than an intermediate, although alternative explanations cannot be wholly ruled out. Electron withdrawal on the carbene moiety is found to accelerate the metathesis reaction when only the metathesis step itself is examined. Quantum chemical calculations at a variety of levels were performed to check for the consistency of the interpretation.
- Adlhart, Christian,Hinderling, Christian,Baumann, Harold,Chen, Peter
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p. 8204 - 8214
(2007/10/03)
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- Synthesis and activity of a new generation of ruthenium-based olefin metathesis catalysts coordinated with 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene ligands.
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[formula: see text] A new family of 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene-substituted ruthenium-based complexes 9a-c has been prepared starting from RuCl2(=CHPh)(PCy3)2 2. These air- and water-tolerant complexes were shown to exhibit an increased ring-closing metathesis activity at elevated temperature when compared to that of the parent complex 2 and the previously developed complex 3. In many instances the activity of these complexes also rivaled or exceeded that of the alkoxy-imido molybdenum complex 1. Catalyst loadings of as low as 0.05 mol% could be used.
- Scholl,Ding,Lee,Grubbs
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p. 953 - 956
(2008/02/09)
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- Syntheses with organoboranes. VII, monohydroboration of conjugated dienes with catecholborane catalyzed by complexes of Nickel(II) chloride and Cobalt(II) chloride with diphosphines
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The monohydroboration of representative conjugated dienes 1-7 with catecholborane in the presence of SmI3, t-BuOSmI2, LaI3, Ti(OPr(i))4, iron(II), nickel(II) and cobalt(II) chloride complexes with dppe, dppp and dppb was examined. NiCl2(dppe), NiCl2(dppp) and CoCl2(dppp) shoned catalytic activity. The 1,2-addition products were obtained, no 1,4-addition was observed. The reactivity in the presence of NiCl2(dppe) decreased in the order acyclic dienes > cyclic dienes >>1-decene.
- Zaidlewicz, Marek,Meller, Jerzy
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p. 7279 - 7282
(2007/10/03)
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- Asymmetric microbial hydrolysis of epoxides
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Kinetic resolution of 2-mono- and 2,2-disubstituted epoxides was accomplished using epoxide hydrolases from bacterial and fungal origin by employing lyophilized whole microbial cells. In all cases investigated, the biocatalytic hydrolysis was shown to proceed with retention of configuration at the stereogenic center leading to 1,2-diols and remaining epoxides. The selectivity of the reaction was dependent on the substrate structure and the strain used with E-values ranging from low or moderate (with 2-monosubstituted epoxides) to excellent (E >100, with 2,2-disubstituted oxiranes).
- Mischitz,Kroutil,Wandel,Faber
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p. 1261 - 1272
(2007/10/03)
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- A study of the aluminum hydride reduction of unsaturated cyclic epoxides
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The aluminum hydride reduction of 3,4-epoxycyclopentene to 3-cyclopentenol has been previously observed1 and the complete regiospecificity of the reaction is confirmed here. A mechanism is proposed involving initial complexation of the aluminum hydride anion with the double bond followed by hydride transfer to the 3-Carbon. Analysis of the atomic charges determined from semiempirical electrostaic potentials support the proposed mechanism. Spectroscopic analysis of the resultant alcohol indicates the presence of an O-H''''''π intramolecular hydrogen bonded interaction.
- Healy, Eamonn F.,Lewis,Minniear, Amy B.
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p. 6647 - 6648
(2007/10/02)
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- Asymmetric Catalysis by Vitamin B12. The Mechanism of the Cob(I)alamin-Catalyzed Isomerization of 1,2-Epoxycyclopentane to (R)-Cyclopent-2-enol
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The isomerization of 1,2-epoxycyclopentane (1) to enantiomerically enriched (R)-cyclopent-2-enol (2) in protic solvents is catalyzed by cob(I)alamin.The enantiomeric excess (e.e.) of (R)-2 is usually ca. 60percent; it is only slightly dependent on the temperature, but increases with decreasing dielectric constant ε of the solvent.Standard kinetic methods show the reaction to be first order in vitamine B12 and zero order in 1.The rate constant increases exponentially with increasing ε of the solvent.An Arrhenius plot at ε = 40 gives activation parameters ΔH(excit.) = 78 +/- 4 kJ*mol-1 and ΔS(excit.) = -49 +/- 1 J*mol-1*K-1.The isomerization 1 --> 2 proceeds in two steps (Schemes 2 and 7): i) The epoxide ring is first opened by the proton-assisted fast and irreversible nucleophile attack of the chiral CoI catalyst to form diastereomeric (1R,2R)- and (1S,2S)-(2-hydroxycyclopentyl)cob(III)alamins 6 in a ratio of ca. 4:1 which are the dominant species in the steady state; ii) The intermediates 6 then decompose in the rate limiting step to form 2 and recycled catalyst.Experiments with specifically 2H-labeled 1 showed the hydro-cobalt elimination 6 --> 2 to be non-stereoselective.It proceeds via reversible Co-C bond homolysis to a free 2-hydroxycyclopentyl radical from which stereoelectronically controlled H-abstraction by CoII takes place.
- Bonhote, Pierre,Scheffold, Rolf
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p. 1425 - 1444
(2007/10/02)
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- Palladium-catalyzed allylic acetoxylation: an exploratory study of the influence of added acids
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In order to investigate the possibility of improving the selectivity in palladium-catalyzed acetoxylation of substituted cycloalkenes and linear alkenes, the influence of added strong acids has been studied.It was found that the product selectivity can be increased in some cases, but also that side reactions lower the total yields when trifluoroacetic or stronger acids are used.The improvement of the selectivity may possibly be due to a change in mechanism for the acetoxylation.
- Akermark, Bjoern,Hansson, Sverker,Rein, Tobias,Vagberg, Jan,Heumann, Andreas,Baeckvall, Jan-Erling
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p. 433 - 444
(2007/10/02)
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- ORGANOTINS AS ETHERIFICATION CATALYSTS. III. ETHERIFICATIONS AND HYDRO-HYDROXY-ELIMINATIONS PROMOTED BY BUTYLTIN TRICHLORIDE
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Butyltin trichloride, as a catalyst precursor, promotes the following processes: (i) etherification of 2,3-unsaturated alcohols, (ii) etherification of functional diols, (iii) cyclization of 2,5-hexanedione, and (iv) dehydration of cyclic diols.Many examples are reported.
- Marton, Daniele,Slaviero, Pierangelo,Tagliavini, Giuseppe
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p. 7099 - 7108
(2007/10/02)
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- Prostaglandin Endoperoxide Model Compounds. Part 2. Stereospecific Synthesis of Isomeric 5-Bromo-2,3-dioxabicycloheptanes and 2-Bromo-6,7-dioxabicyclooctanes
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Cyclopent-3-enyl hydroperoxide (9) has been prepared from cyclopentadiene via hydroboration and autoxidation, and converted by bromination into trans-3,cis-4-dibromocyclopentyl hydroperoxide (10).Reaction of compound (10) with silver oxide has afforded endo-5-bromo-2,3-dioxabicycloheptane (11) (42percent), whereas treatment of compound (10) with silver trifluoroacetate has provided exo-5-bromo-2,3-dioxabicycloheptane (15) (6percent) and exo-5-trifluoroacetoxy-2,3-dioxabicycloheptane (16) (14percent).The exo-bromide (15) (11percent) has also been prepared from cyclopent-3-enyl bromide by trans-hydroperoxybromination and ring closure with silver oxide.The configurations of the peroxides have been confirmed by catalytic hydrogenation.Cyclohex-3-enyl hydroperoxide (26) has been prepared from anisole by a 5-step procedure ending with oxidation of N-cyclohex-3-enyl-N'-tosylhydrzide, and converted by bromination into a mixture of two diastereoisomeric 3,4-dibromocyclohexyl hydroperoxides.Treatment of the trans-3,cis-4-dibromide (27) with silver oxide has afforded endo-2-bromo-6,7-dioxabicyclooctane (29) (40percent), whereas reaction of the cis-3,trans-4-dibromide (28) with silver trifluoroacetate has provided exo-2-bromo-6,7-dioxabicyclooctane (30) (18percent).Treatment of compound (27) with silver trifluoroacetate yielded a 9:1 mixture of peroxides (30) and (29) (19percent), but compound (28) did not react with silver oxide.It is suggested that the silver oxide-induced dioxabicyclizations proceed by an SN2 mechanism whereas the silver trifluoroacetate reactions involve a bromonium ion intermediate.
- Bloodworth, A. J.,Eggelte Henny J.
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p. 3272 - 3278
(2007/10/02)
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- CONVERSION OF 3-CYCLOPENTENYL HYDROPEROXIDE INTO 5-SUBSTITUTED-2,3-DIOXABICYCLOHEPTANES
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3-Cyclopentenyl hydroperoxide 8 has been prepared from cyclopentadiene via hydroboration and autoxidation.Bromination of 8 followed by treatment with an appropriate silver salt has afforded the 5-substituted-2,3-dioxabicycloheptanes 11 (endo-bromo), 13 (exo-bromo), and 12 (exo-trifluoroacetoxy).
- Bloodworth, A. J.,Eggelte, H. J.
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p. 2001 - 2004
(2007/10/02)
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