- Iridium Azocarboxamide Complexes: Variable Coordination Modes, C-H Activation, Transfer Hydrogenation Catalysis, and Mechanistic Insights
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Azocarboxamides, a special class of azo ligands, display intriguing electronic properties due to their versatile binding modes and coordination flexibility. These properties may have significant implications for their use in homogeneous catalysis. In the present report, half-sandwich Ir-Cp? complexes of two different azocarboxamide ligands are presented. Different coordination motifs of the ligand were realized using base and chloride abstracting ligand to give N∧N-, N∧O-, and N∧C-chelated monomeric iridium complexes. For the azocarboxamide ligand having methoxy substituted at the phenyl ring, a mixture of N∧C-chelated mononuclear (Ir-5) and N∧N,N∧C-chelated dinuclear complexes (Ir-4) were obtained by activating the C-H bond of the aryl ring. No such C-H activation was observed for the ligand without the methoxy substituent. The molecular identity of the complexes was confirmed by spectroscopic analyses, while X-ray diffraction analyses further confirmed three-legged piano-stool structure of the complexes along with the above binding modes. All complexes were found to exhibit remarkable activity as precatalysts for the transfer hydrogenation of carbonyl groups in the presence of a base, even at low catalyst loading. Optimization of reaction conditions divulged superior catalytic activity of Ir-3 and Ir-4 complexes in transfer hydrogenation over the other catalysts. Investigation of the influence of binding modes on the catalytic activity along with wide range substrates, tolerance to functional groups, and mechanistic insights into the reaction pathway are also presented. These are the first examples of C-H activation in azocarboxamide ligands.
- Albold, Uta,Chandra, Shubhadeep,Hazari, Arijit Singha,Kelm, Ola,Ko?mrlj, Janez,Sarkar, Biprajit,Urankar, Damijana
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supporting information
p. 3907 - 3916
(2021/12/03)
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- CuBr2-catalyzed ring opening/formylation reaction of cyclopropyl carbinols with DMF to synthesize formate esters
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An unprecedented protocol for the synthesis of formate esters has been developed by employing N,N-dimethylformamide (DMF) as both the source of CHO and solvent. This reaction undergoes ring opening of the cyclopropyl carbinols and in situ formation of homoallylic alcohols, which reacts with DMF to give the desired products. The substrate cyclopropyl carbinols with different groups participate smoothly in this process and the desired products are obtained in moderate to good yields.
- Zhuang, Daijiao,Gatera, Tharcisse,Yan, Rulong
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supporting information
(2020/10/19)
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- σ-Bond Hydroboration of Cyclopropanes
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Hydroboration of alkenes is a classical reaction in organic synthesis in which alkenes react with boranes to give alkylboranes with subsequent oxidation resulting in alcohols. The double bond (π-bond) of alkenes can be readily reacted with boranes owing to its high reactivity. However, the single bond (σ-bond) of alkanes has never been reacted. To pursue the development of σ-bond cleavage, we selected cyclopropanes as model substrates since they present a relatively weak σ-bond. Herein, we describe an iridium-catalyzed hydroboration of cyclopropanes, resulting in β-methyl alkylboronates. These unusually branched boronates can be derivatized by oxidation or cross-coupling chemistry, accessing "designer"products that are desired by practitioners of natural product synthesis and medicinal chemistry. Furthermore, mechanistic investigations and theoretical studies revealed the enabling role of the catalyst.
- Arifin,Itami, Kenichiro,Kato, Hiroki,Kobayashi, Chisa,Kondo, Hiroki,Matsushita, Kaoru,Miyamura, Shin,Yamaguchi, Junichiro,Yokogawa, Daisuke
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supporting information
p. 11306 - 11313
(2020/07/13)
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- Enantioselective Hydrogenation of Ketones using Different Metal Complexes with a Chiral PNP Pincer Ligand
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The synthesis of different metal pincer complexes coordinating to the chiral PNP ligand bis(2-((2R,5R)-2,5-dimethyl-phospholanoethyl))amine is described in detail. The characterized complexes with Mn, Fe, Re and Ru as metal centers showed good activities regarding the reduction of several prochiral ketones. Comparing these catalysts, the non-noble metal complexes produced best selectivities not only for aromatic substrates, but also for different kinds of aliphatic ones leading to enantioselectivities up to 99% ee. Theoretical investigations elucidated the mechanism and rationalized the selectivity. (Figure presented.).
- Garbe, Marcel,Wei, Zhihong,Tannert, Bianca,Spannenberg, Anke,Jiao, Haijun,Bachmann, Stephan,Scalone, Michelangelo,Junge, Kathrin,Beller, Matthias
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supporting information
p. 1913 - 1920
(2019/03/13)
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- Cooperative Mn(i)-complex catalyzed transfer hydrogenation of ketones and imines
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The synthesis and reactivity of Mn(i) complexes bearing bifunctional ligands comprising both the amine N-H and benzimidazole fragments are reported. Among the various ligands, the N-((1H-benzimidazol-2-yl)methyl)aniline ligand containing Mn(i) complex presented higher reactivity in the transfer hydrogenation (TH) of ketones in 2-propanol. Experimentally, it was established that both the benzimidazole and amine N-H proton played a vital role in the enhancement of the catalytic activity. Utilizing this system a wide range of aldehydes and ketones were reduced efficiently. Notably, the TH of several imines, as well as chemoselective reduction of unsaturated ketones, was achieved in the presence of this catalyst. DFT calculations were carried out to understand the plausible reaction mechanism which disclosed that the transfer hydrogenation reaction followed a concerted outer-sphere mechanism.
- Ganguli, Kasturi,Shee, Sujan,Panja, Dibyajyoti,Kundu, Sabuj
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p. 7358 - 7366
(2019/06/06)
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- Efficient and Practical Transfer Hydrogenation of Ketones Catalyzed by a Simple Bidentate Mn?NHC Complex
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Catalytic reductions of carbonyl-containing compounds are highly important for the safe, sustainable, and economical production of alcohols. Herein, we report on the efficient transfer hydrogenation of ketones catalyzed by a highly potent Mn(I)?NHC complex. Mn?NHC 1 is practical at metal concentrations as low as 75 ppm, thus approaching loadings more conventionally reserved for noble metal based systems. With these low Mn concentrations, catalyst deactivation is found to be highly temperature dependent and becomes especially prominent at increased reaction temperature. Ultimately, understanding of deactivation pathways could help close the activity/stability-gap with Ru and Ir catalysts towards the practical implementation of sustainable earth-abundant Mn-complexes.
- van Putten, Robbert,Benschop, Joeri,de Munck, Vincent J.,Weber, Manuela,Müller, Christian,Filonenko, Georgy A.,Pidko, Evgeny A.
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p. 5232 - 5235
(2019/07/18)
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- Manganese N-Heterocyclic Carbene Complexes for Catalytic Reduction of Ketones with Silanes
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Well-defined manganese(I) carbonyl complexes bearing bis-N-heterocyclic carbene (NHC) ligands are shown to be effective catalysts for the reduction of carbonyl groups through hydrosilylation reactions. A wide variety of ketones are selectively reduced to the corresponding alcohols by using phenylsilane, and the cheap and readily abundant polymethylhydrosiloxane (PMHS) in the presence of catalytic amounts of MnI organometallic complexes. Interestingly, α,β-unsaturated ketones and dialkyl ketones are selectively reduced. Mechanistic studies based on radical scavengers suggest the involvement of radical species in the catalytic reaction.
- Pinto, Mara,Fri?es, Sofia,Franco, Federico,Lloret-Fillol, Julio,Royo, Beatriz
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p. 2734 - 2740
(2018/07/24)
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- Total Synthesis of ent-Pregnanolone Sulfate and Its Biological Investigation at the NMDA Receptor
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A unique asymmetric total synthesis of the unnatural enantiomer of pregnanolone, as well as a study of its biological activity at the NMDA receptor, is reported. The asymmetry is introduced by a highly atom-economic organocatalytic Robinson annulation. A new method for the construction of the cyclopentane D-ring consisting of CuI-catalyzed conjugate addition and oxygenation followed by thermal cyclization employing the persistent radical effect was developed. ent-Pregnanolone sulfate is surprisingly only 2.6-fold less active than the natural neurosteroid.
- Kapras, Vojtech,Vyklicky, Vojtech,Budesinsky, Milos,Cisarova, Ivana,Vyklicky, Ladislav,Chodounska, Hana,Jahn, Ullrich
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supporting information
p. 946 - 949
(2018/02/23)
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- Constructing reactive Fe and Co complexes from isolated picolyl-functionalized N-heterocyclic carbenes
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We report the isolation of free picolyl-functionalized N-heterocyclic carbenes (NHCs), which serve as versatile precursors to access low coordinate iron and cobalt complexes. The reactivities of these new iron and cobalt complexes towards catalytic hydrosilylation of ketones have also been explored. For example, low loadings (0.05-1 mol%) of a four-coordinate iron complex bearing two deprotonated picolyl-NHC ligands can effect the fast catalytic reduction of ketones using the inexpensive industrial byproduct polymethylhydrosiloxane (PMHS) as the reductant at ambient temperature.
- Liang, Qiuming,Liu, Nina Jiabao,Song, Datong
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supporting information
p. 9889 - 9896
(2018/08/06)
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- Hydrogenation of Carbonyl Derivatives Catalysed by Manganese Complexes Bearing Bidentate Pyridinyl-Phosphine Ligands
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Manganese(I) catalysts incorporating readily available bidentate 2-aminopyridinyl-phosphine ligands achieve a high efficiency in the hydrogenation of carbonyl compounds, significantly better than parent ones based on more elaborated and expensive tridentate 2,6-(diaminopyridinyl)-diphosphine ligands. The reaction proceeds with low catalyst loading (0.5 mol%) under mild conditions (50 °C) with yields up to 96%. (Figure presented.).
- Wei, Duo,Bruneau-Voisine, Antoine,Chauvin, Téo,Dorcet, Vincent,Roisnel, Thierry,Valyaev, Dmitry A.,Lugan, No?l,Sortais, Jean-Baptiste
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supporting information
p. 676 - 681
(2017/12/26)
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- Hydrogenation of Carbonyl Derivatives with a Well-Defined Rhenium Precatalyst
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The first efficient and general rhenium-catalyzed hydrogenation of carbonyl derivatives was developed. The key to the success of the reaction was the use of a well-defined rhenium complex bearing a tridentate diphosphinoamino ligand as the catalyst (0.5 mol %) at 70 °C in the presence of H2 (30 bar). The mechanism of the reaction was investigated by DFT(PBE0-D3) calculations.
- Wei, Duo,Roisnel, Thierry,Darcel, Christophe,Clot, Eric,Sortais, Jean-Baptiste
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- Synthesis and kinetic regularities of the thermal decomposition of new hydrotrioxides of cyclic alcohols
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Cyclic hydrotrioxides were synthesized by low-temperature (?78 °C) ozonolysis of a series of cyclic alcohols and identified using 1H NMR spectra. The kinetic regularities of the thermal decomposition of the synthesized hydrotrioxides were studied. The experimental proof of the induced decomposition of alcohol hydrotrioxides was obtained for the first time using cyclohexanol hydrotrioxide as an example. The influence of cyclic substituents on the thermal stability of the hydrotrioxides is shown.
- Grabovskiy,Khalitova,Fedorova,Lobov,Rol’nik,Kabal’nova
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p. 464 - 468
(2017/03/08)
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- Peripheral mechanism of a carbonyl hydrosilylation catalysed by an SiNSi iron pincer complex
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Combined experimental and theoretical analysis of the carbonyl hydrosilylation catalysed by an iron(0) pincer complex reveals an unprecedented mechanism of action. The iron(0) complex is in fact a precatalyst that is converted into an iron(ii) catalyst through oxidative addition of a hydrosilane. Neither the hydrogen atom nor the silicon atom bound to the iron(ii) centre are subsequently transferred onto the carbonyl acceptor, instead remaining at the sterically inaccessible iron(ii) atom throughout the catalytic cycle. A series of labelling, crossover and competition experiments as well as the use of a silicon-stereogenic hydrosilane as a stereochemical probe suggest that the iron(ii) site is not directly involved in the hydrosilylation. Strikingly, it is the silyl ligand attached to the iron(ii) atom that acts as a Lewis acid for carbonyl activation in this catalysis. The whole catalytic process occurs on the periphery of the transition metal. Computation of the new peripheral as well as plausible alternative inner and outer sphere mechanisms support the experimental findings.
- Mets?nen, Toni T.,Gallego, Daniel,Szilvási, Tibor,Driess, Matthias,Oestreich, Martin
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p. 7143 - 7149
(2015/11/24)
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- Reduction of ketones with silanes catalysed by a cyclopentadienyl- functionalised N-heterocyclic iron complex
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The well-defined piano-stool iron(II) complex (Cp-NHC)Fe(CO)I bearing a bidentate cyclopentadienyl-functionalised N-heterocyclic carbene ligand is shown to catalyse the reduction of ketones under mild conditions (1-2 h at room temperature) when combined with catalytic amounts of potassium tert-butoxide, and using Ph2SiH2 and the inexpensive and less reactive polymethylhydrosiloxane as reducing agents. The stoichiometric reaction of (Cp-NHC)Fe(CO)I with potassium tert-butoxide generates an iron-hydroxo complex, which seems to be the active species in the reduction of ketones.
- Lopes, Rita,Cardoso, Joao M.S.,Postigo, Lorena,Royo, Beatriz
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p. 1061 - 1066
(2013/11/19)
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- N-heterocyclic carbene complexes of nickel as efficient catalysts for hydrosilylation of carbonyl derivatives
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Well-defined nickel(II) complexes bearing bidentate tetramethylcyclopentadienyl-functionalised N-heterocyclic carbene ligands (Cp*- NHCMe)NiX (X=Cl, O-t-Bu) have been prepared and applied as efficient catalysts for the hydrosilylation of carbonyl groups. The nickel-alkoxide (Cp*- NHCMe)NiACHTUNGTRENUNG(O-t-Bu) complex displayed remarkable catalytic activity in the reduction of aldehydes, affording quantitative conversion to the corresponding alcohols in 5 min at 25 °C. Mechanistic studies, based on stoichiometric reactions, revealed that the transient nickel hydride (Cp*-NHCMe)NiH complex is the active species in the hydrosilylation of carbonyls.
- Postigo, Lorena,Royo, Beatriz
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p. 2613 - 2618
(2013/01/15)
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- METHOD FOR TREATING ANXIETY
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The present invention provides a method for treating anxiety in humans using azacyclic or azabicyclic compounds.
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- HETEROCYCLIC COMPOUNDS AND THEIR PREPARATION AND USE
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The present invention relates to therapeutically active azacyclic or azabicyclic compounds, a method of preparing the same and to pharmaceutical compositions comprising the compounds. The novel compounds are useful in treating diseases in the central nervous system caused by malfunctioning of the muscarinic cholinergic system.
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- A facile entry to secondary cyclopropylcarbinols: Further developments in the stereospecific synthesis of (E)-homoallylic bromides
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Cyclopropanecarboxaldehyde has been used in an improved synthesis of secondary cyclopropylcarbinols, thus allowing for further developments in the stereospecific ring opening leading to (E)-homoallylic bromides.
- Ferreri,Ambrosone,Chatgilialoglu
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p. 3351 - 3356
(2007/10/03)
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- Studies on the Catalytic Oxidation of Alkanes and Alkenes by Titanium Silicates
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Titanium containing, aluminum-free ZSM-5 (TS-1) and amorphous TiO2-SiO2 coprecipitate are investigated as catalysts for the selective oxidation of alkanes and alkenes using a variety of oxidants at temperatures below 100 deg C. Comparisons between the activities of TS-1 and the TiO2-SiO2 coprecipitate for alkane oxidation and alkene epoxidation using nonaqueous H2O2 indicate that the absence of water is crucial for the catalytic activity of silica-supported titanium. Due to the hydrophobicity of TS-1, the concentration of water surrounding the titanium is maintained at a low value, and thus TS-1 can be used as an oxidation catalyst with aqueous H2O2 as oxidant. Alkyl hydroperoxides are active as oxidants for alkene epoxidation on the TiO2-SiO2 coprecipitate but not for alkane oxidation reactions on both TS-1 and the TiO2-SiO2 coprecipitate. A plausible explanation for the above results is provided. The presence of stereoscrambling without any "radical clock" rearrangement during alkane oxidation on TS-1 indicates that the radicals formed may have a very short life-time, or their movements are restricted such that no rearrangement can occur. A proposal for the mechanism of alkane oxidation on TS-1 is given and compared to a mechanism suggested for alkene epoxidation on TS-1 and the TiO2-SiO2 coprecipitate.
- Khouw, C. B.,Dartt, C. B.,Labinger, J. A.,Davis, M. E.
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p. 195 - 205
(2007/10/02)
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- Gas-Phase Protonation of Spiropentane. A Novel Entry into the C5H9+ Potential Energy Surface
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The structures, stabilities, and isomerization patterns of C5H9+ ions arising from the gas-phase protonation of spiropentane have been investigated by nuclear-decay, radiolytic, and FT-ICR techniques combined with ab initio calculations.The experimental and theoretical results are consistent with the initial formation of a corner-protonated spiropentane intermediate 17, whose lifetime in the gas phase exceeds 7E-9 s.This local C5H9+ minimum is separated from ca. 30 kcal mol-1 more stable cyclopentyl cation as well as from dimethylallyl open-chain isomers by significant energy barriers.Persistency of 17 in the gas phase does not find any correspondence in solution.Solvation and ion-pairing effects may explain the failure to detect C5H9+ structures retaining the spirobicyclic framework of spiropentane in the condensed phase.
- Cecchi, Patrizio,Pizzabiocca, Adriano,Renzi, Gabriele,Grandinetti, Felice,Sparapani, Cinzia,et al.
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p. 10338 - 10347
(2007/10/02)
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- An Internally Activated Tin Hydride with Enhanced Reducing Ability
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Tin hydride 1 is activated for nucleophilic hydride transfer and also for radical chain reduction, depending on solvent.The nucleophilic hydride pathway is favored in methanol, and 1 can be used as a selective reducing agent for ketones.Simple ketones are not reduced in aprotic solvents, but β-hydroxy ketones are activated internally by the hydroxyl group and can be reduced in THF with good control of stereochemistry, as in the conversion from 7 to 9 (30:1 9:8).A catalytic version of the nucleophilic hydride reductions in methanol has been developed using PhSiH3 as the stoichiometric hydride source.Radical chain dehalogenations can also be achieved with 1 at room temperature and without added radical initiators.Simple xanthates are not reduced efficiently in the absence of an initiator, but the reaction proceeds in the presence of AIBN.
- Vedejs, E.,Duncan, S. M.,Haight, A. R.
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p. 3046 - 3050
(2007/10/02)
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- Characteristic Reduction of Ketones by Bu3SnH-Bu4NX System
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Various ketones were reduced cleanly by Bu3SnH-Bu4NX (X=halogen) combined systems.The reaction proceeds effectively under mild conditions.Chemoselective reduction was performed in bifunctional compounds, and marked diastereoselective reduction was noted for α-methoxy propiophenone.
- Shibata, Ikuya,Yoshida, Tomoyuki,Baba, Akio,Matsuda, Haruo
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p. 307 - 310
(2007/10/02)
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- Calcium in Liquid Ammonia for the Reduction of Benzyl Ethers. Mechanistic Clues Derived from Chemoselectivity Studies
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Extremely high selectivity was provided by calcium in liquid ammonia in the cleavage of the benzylic carbon-oxygen bond in benzyl ethers containing various other functionalities.Results of controlled experiments indicate that the selectivities offered by the Ca -> Ca+ + e- and the Ca+ -> Ca2+ + e- processes are 4.6 and 47 times greater, respectively, than that afforded by the Li -> Li+ + e- process.
- Hwu, Jih Ru,Chua, Vincent,Schroeder, Jean E.,Barrans, Richard E.,Khoudary, Kevin P.,et al.
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p. 4731 - 4733
(2007/10/02)
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- Diels-Alder Reaction of 1-Azadienes. A Total Synthesis of Deoxynupharidine
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The Diels-Alder reaction of a N-acyl-1-azadiene was a key step in the total synthesis of the quinolizidine alkaloid (-)-deoxynupharidine.
- Hwang, Yuying C.,Fowler Frank W.
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p. 2719 - 2726
(2007/10/02)
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- Silver Nitrate-Alumina: A Chromatographic Reaction Medium for Conversion of 5-Halogenopent-2-enes into 1-Cyclopropylethyl Nitrate
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A chromatography column of 30percent silver nitrate-neutral alumina provides a reactive surface for the ready conversion of 5-halogenopent-2-enes (1) into 1-cyclopropylethyl nitrate (2) upon elution with pentane.By this technique 5-bromopent-2-ene (1a) and 5-iodopent-2-ene (1b) are converted into (2) in 74 and 94percent yield, respectively, in less than five minutes. 5-chloropent-2-ene (1c) was unreactive under the same conditions.Reduced yields of (2) were observed when (1a) or (1b) were stirred, neat, with powdered silver nitrate.When acidic alumina was used to prepare the chromatography column and only partially dried, an efficient medium for hydrolysis to the corresponding alcohol resulted.Elution of (1a) with diethyl ether therefore gave 1-cyclopropylethanol (5) in 31percent yield and elution of (2) with diethyl ether gave (5) in ca. 100percent yield.
- Hrubiec, Robert T.,Smith, Michael B.
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p. 107 - 110
(2007/10/02)
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- Effect of 3- and 4-Methyl Substituents on the Photocyclization of N-(3-Alkenyl)phthalimides: Synthesis of Pyrroloisoindoles and Pyridoisoindoles
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Photolysis of N-(3-alkenyl)phthalimides 2 in methanol gave tetrahydro-5H-pyrroloisoindol-5-ones 3 and/or tetrahydropyridoisoindol-6(2H)-ones 4 depending on the degree of substitution at the olefin carbons of 2.Electron transfer followed by the anti-Markownikoff addition of methanol is proposed as a possible pathway.Keywords - N-(3-alkenyl)phthalimide; photocyclization; pyrroloisoindole; pyridoisoindole; electron transfer; anti-Markownikoff addition
- Machida, Minoru,Oda, Kazuaki,Kanaoka, Yuichi
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- Regioselective Route to Sterically Hindered Cyclopropylcarbinyl Halides
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Reaction of cyclopropylcarbinyl alcohols 1 with hexachloroacetone and triphenylphosphine resulted in 80 - 90 percent yields of the corresponding cyclopropylcarbinyl chlorides 4 regioselectively, with no trace of the homoallylic chloride 2 or the chlorocyclobutane derivative 6a.Similar reaction of 1 with bromine and triphenylphosphine, in dimethylformamide, gave 65 - 80 percent yields of the cyclopropylcarbinyl bromide 5 with trace amounts of the homoallylic bromide 3 but no detectable bromocyclobutane derivative 6b.These reactions are amenable to the preparation of very sterically hindered cyclopropylcarbonyl halides, heretofore inaccessible, regioselectively and in a facile manner.
- Hrubiec, Robert T.,Smith, Michael B.
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p. 431 - 435
(2007/10/02)
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- Latent Inhibitors. Part 3. The Inhibition of Lactate Dehydrogenase and Alcohol Dehydrogenase by Cyclopropane-containing Compounds
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A series of monocyclic and bicyclic cyclopropylmethanols typified by bicycloheptan-7-ylmethanol is shown to comprise latent irreversible inhibitors of horse liver alcohol dehydrogenase (E.C.1.1.1.1) with inhibitory properties related to the ability of the inhibitor to bind to the enzyme.The time course of inhibition is biphasic, a property shared by a number of unsaturated aldehydes, ketones, and alcohols.Kinetic studies also suggest that inhibition occurs most effectively during the removal of hydride from the inhibitor as oxidation takes place.Analogous properties were found for the inhibition of lactate dehydrogenase (E.C.1.1.1.27) by cyclopropylglycolic acid.
- Maclnnes, Iain,Nonhebel, Derek C.,Orszulik, Stefan T.,Suckling, Colin J.,Wrigglesworth, Roger
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p. 2771 - 2776
(2007/10/02)
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- Annelative Ring Expansion via Intramolecular Photocycloaddition of α,β-Unsaturated γ-Lactones and Reductive Cleavage: Synthesis of Hydrocyclopentacyclooctene-5-carboxylates
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A new approach for annelative, two-carbon ring expansion via intramolecular photocycloaddition of fused α,β-unsaturated γ-lactones onto γ-alkenyl side chains, oxidation to γ-keto acids, and reductive cleavage of the cyclobutane ring is applied to the synthesis of hydrocyclopentacyclooctene-5-carboxylates. α,β-Unsaturated γ-lactones fused to cyclohexene and bearing 3-butenyl (4), 3-pentenyl (5), 3,4-pentadienyl (7), and 4-chloro-3-pentenyl (9) side chains in the γ-positions were prepared (Schemes II and III) either by addition of Grignard reagents to 2-bromo-1-cyclohexenecarboxaldehyde (1) followed by lihiation and carboxylation (method A) or by lithiation of N,N-dimethyl-2-bromo-1-cyclohexenecarboxamide (6) and subsequent addition to aldehydes (method B).Irradiation of the four unsaturated lactones effected mainly the fused mode of intramolecular cycloaddition, forming 2-hydroxytricycloundecane-7-carboxylic acid lactones (13-15 and 17).Oxidation of the sodium salts of the hydroxy acids with sodium ruthenate and esterification afforded a series of tricyclic γ-keto acids (20a and 21a) and esters (20b and 22).Reduction of the keto acids or esters with lithium in ammonia lead to reductive scission of the cyclobutane ring and formation of methyl decahydro- and octahydro-1-oxo-1H-cyclopentacyclooctene-5-carboxylates (24-26).
- Coates, Robert M.,Senter, Peter D.,Baker, William R.
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p. 3597 - 3607
(2007/10/02)
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- Chemistry of gem-Dihalocyclopropanes. XVII. Cyclopropylidene Incertion. Formation and Ring Opening of Bicyclobutan-2-olate
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Reactions of gem-dibromocyclopropanemethanol derivatives 3a-3e with methyllithium lead to allenic alcohols 4a-4h and products which derive from ring opening of an intermediate bicyclobutan-2-olate (17).The latter is formed by insertion of the respective cyclopropylidene into a C-H bond.Evidence for 17 was obtained from deuterium labelling experiments.This ring opening generally occurs by a carbanion mechanism, but in the case of 3d the intermediate bicyclobutanolate rearranged to the acyclic aldehyde 10, apparently by a thermal mechanism.The secondary alcohols 3f-3h reacted with methyllithium to give the corresponding allenes exclusively, which was also the case with ethers 3i-3l derived from the primary alcohols.
- Nilsen, Nils O.,Skattebol, Lars,Sydnes, Leiv K.
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p. 587 - 592
(2007/10/02)
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