- Well-defined Cp*Co(III)-catalyzed Hydrogenation of Carbonates and Polycarbonates
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We herein report the catalytic hydrogenation of carbonates and polycarbonates into their corresponding diols/alcohols using well-defined, air-stable, high-valent cobalt complexes. Several novel Cp*Co(III) complexes bearing N,O-chelation were isolated for the first time and structurally characterized by various spectroscopic techniques including single crystal X-ray crystallography. These novel Co(III) complexes have shown excellent catalytic activity to produce value added diols/alcohols from carbonate and polycarbonates through hydrogenation using molecular hydrogen as sole reductant or iPrOH as transfer hydrogenation source. To demonstrate the developed methodology's practical applicability, we have recycled the bisphenol A monomer from compact disc (CD) through hydrogenation under the established reaction conditions using phosphine-free, earth-abundant, air- and moisture-stable high-valent cobalt catalysts.
- Dahiya, Pardeep,Gangwar, Manoj Kumar,Sundararaju, Basker
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p. 934 - 939
(2020/12/15)
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- Catalytic Diastereo- and Enantioconvergent Synthesis of Vicinal Diamines from Diols through Borrowing Hydrogen
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We present herein an unprecedented diastereoconvergent synthesis of vicinal diamines from diols through an economical, redox-neutral process. Under cooperative ruthenium and Lewis acid catalysis, readily available anilines and 1,2-diols (as a mixture of diastereomers) couple to forge two C?N bonds in an efficient and diastereoselective fashion. By identifying an effective chiral iridium/phosphoric acid co-catalyzed procedure, the first enantioconvergent double amination of racemic 1,2-diols has also been achieved, resulting in a practical access to highly valuable enantioenriched vicinal diamines.
- Feng, Wei,Gao, Taotao,Lau, Kai Kiat,Lin, Yamei,Pan, Hui-Jie,Yang, Binmiao,Zhao, Yu
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supporting information
p. 18599 - 18604
(2021/08/09)
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- An Amphiphilic (salen)Co Complex – Utilizing Hydrophobic Interactions to Enhance the Efficiency of a Cooperative Catalyst
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An amphiphilic (salen)Co(III) complex is presented that accelerates the hydrolytic kinetic resolution (HKR) of epoxides almost 10 times faster than catalysts from commercially available sources. This was achieved by introducing hydrophobic chains that increase the rate of reaction in one of two ways – by enhancing cooperativity under homogeneous conditions, and increasing the interfacial area under biphasic reaction conditions. While numerous strategies have been employed to increase the efficiency of cooperative catalysts, the utilization of hydrophobic interactions is scarce. With the recent upsurge in green chemistry methods that conduct reactions ‘on water’ and at the oil-water interface, the introduction of hydrophobic interactions has potential to become a general strategy for enhancing the catalytic efficiency of cooperative catalytic systems. (Figure presented.).
- Solís-Mu?ana, Pablo,Salam, Joanne,Ren, Chloe Z.-J.,Carr, Bronte,Whitten, Andrew E.,Warr, Gregory G.,Chen, Jack L.-Y.
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supporting information
p. 3207 - 3213
(2021/06/01)
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- The formyloxyl radical: Electrophilicity, C-H bond activation and anti-Markovnikov selectivity in the oxidation of aliphatic alkenes
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In the past the formyloxyl radical, HC(O)O, had only been rarely experimentally observed, and those studies were theoretical-spectroscopic in the context of electronic structure. The absence of a convenient method for the preparation of the formyloxyl radical has precluded investigations into its reactivity towards organic substrates. Very recently, we discovered that HC(O)O is formed in the anodic electrochemical oxidation of formic acid/lithium formate. Using a [CoIIIW12O40]5- polyanion catalyst, this led to the formation of phenyl formate from benzene. Here, we present our studies into the reactivity of electrochemically in situ generated HC(O)O with organic substrates. Reactions with benzene and a selection of substituted derivatives showed that HC(O)O is mildly electrophilic according to both experimentally and computationally derived Hammett linear free energy relationships. The reactions of HC(O)O with terminal alkenes significantly favor anti-Markovnikov oxidations yielding the corresponding aldehyde as the major product as well as further oxidation products. Analysis of plausible reaction pathways using 1-hexene as a representative substrate favored the likelihood of hydrogen abstraction from the allylic C-H bond forming a hexallyl radical followed by strongly preferred further attack of a second HC(O)O radical at the C1 position. Further oxidation products are surmised to be mostly a result of two consecutive addition reactions of HC(O)O to the CC double bond. An outer-sphere electron transfer between the formyloxyl radical donor and the [CoIIIW12O40]5- polyanion acceptor forming a donor-acceptor [D+-A-] complex is proposed to induce the observed anti-Markovnikov selectivity. Finally, the overall reactivity of HC(O)O towards hydrogen abstraction was evaluated using additional substrates. Alkanes were only slightly reactive, while the reactions of alkylarenes showed that aromatic substitution on the ring competes with C-H bond activation at the benzylic position. C-H bonds with bond dissociation energies (BDE) ≤ 85 kcal mol-1 are easily attacked by HC(O)O and reactivity appears to be significant for C-H bonds with a BDE of up to 90 kcal mol-1. In summary, this research identifies the reactivity of HC(O)O towards radical electrophilic substitution of arenes, anti-Markovnikov type oxidation of terminal alkenes, and indirectly defines the activity of HC(O)O towards C-H bond activation.
- Iron, Mark A.,Khenkin, Alexander M.,Neumann, Ronny,Somekh, Miriam
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p. 11584 - 11591
(2020/11/23)
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- One-Pot Three-Step Consecutive Transformation of L-α-Amino Acids to (R)- and (S)-Vicinal 1,2-Diols via Combined Chemical and Biocatalytic Process
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Optically pure vicinal 1,2-diols are versatile chiral building blocks in the fine chemical and pharmaceutical industries. L-α-amino acid is a good feedstock source for high value-added product production since it is inexpensive and renewable. However, conversion of L-α-amino acids to enantioenriched vicinal 1,2-diols remains a significant challenge. In this study, combining a simple chemical process and a three-enzyme cascade biocatalysis system, we have successfully implemented a one-pot sequential process for the transformation of L-α-amino acids into enantiopure vicinal 1,2-diols in aqueous medium. Firstly, the NaBH4-H2SO4 system converted L-α-amino acids to (S)-amino alcohols via amino acid carboxyl reduction. Secondly, the three-enzyme (transaminase, carbonyl reductase and glucose dehydrogenase) cascade biocatalysis system converted amino alcohols to enantiopure vicinal 1,2-diols via amino alcohol deamination, α-hydroxy ketone asymmetric reduction and cofactor regeneration. Taking advantage of the two different reaction systems, chiral vicinal 1,2-diols could be obtained from L-α-amino acids with high yields (69–90 %) and excellent ee values (91–>99 % ee).
- Zhang, Jian-Dong,Zhao, Jian-Wei,Gao, Li-Li,Zhao, Jing,Chang, Hong-Hong,Wei, Wen-Long
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p. 5032 - 5037
(2019/10/28)
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- Aromatic Donor-Acceptor Interaction-Based Co(III)-salen Self-Assemblies and Their Applications in Asymmetric Ring Opening of Epoxides
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Aromatic donor-acceptor interaction as the driving force to assemble cooperative catalysts is described. Pyrene/naphthalenediimide functionalized Co(III)-salen complexes self-assembled into bimetallic catalysts through aromatic donor-acceptor interactions and showed high catalytic activity and selectivity in the asymmetric ring opening of various epoxides. Control experiments, nuclear magnetic resonance (NMR) spectroscopy titrations, mass spectrometry measurement, and X-ray crystal structure analysis confirmed that the catalysts assembled based on the aromatic donor-acceptor interaction, which can be a valuable noncovalent interaction in supramolecular catalyst development.
- Liang, Jian,Soucie, Luke N.,Blechschmidt, Daniel R.,Yoder, Aaron,Gustafson, Addie,Liu, Yu
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supporting information
p. 513 - 518
(2019/01/14)
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- Hydrogenation of CO2-Derived Carbonates and Polycarbonates to Methanol and Diols by Metal–Ligand Cooperative Manganese Catalysis
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The first base-metal-catalysed hydrogenation of CO2-derived carbonates to alcohols is presented. The reaction proceeds under mild conditions in the presence of a well-defined manganese complex with a loading as low as 0.25 mol %. The non-precious-metal homogenous catalytic system provides an indirect route for the conversion of CO2 into methanol with the co-production of value-added (vicinal) diols in yields of up to 99 %. Experimental and computational studies indicate a metal–ligand cooperative catalysis mechanism.
- Zubar, Viktoriia,Lebedev, Yury,Azofra, Luis Miguel,Cavallo, Luigi,El-Sepelgy, Osama,Rueping, Magnus
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supporting information
p. 13439 - 13443
(2018/09/21)
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- Mechanistically Driven Development of an Iron Catalyst for Selective Syn-Dihydroxylation of Alkenes with Aqueous Hydrogen Peroxide
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Product release is the rate-determining step in the arene syn-dihydroxylation reaction taking place at Rieske oxygenase enzymes and is regarded as a difficult problem to be resolved in the design of iron catalysts for olefin syn-dihydroxylation with potential utility in organic synthesis. Toward this end, in this work a novel catalyst bearing a sterically encumbered tetradentate ligand based in the tpa (tpa = tris(2-methylpyridyl)amine) scaffold, [FeII(CF3SO3)2(5-tips3tpa)], 1 has been designed. The steric demand of the ligand was envisioned as a key element to support a high catalytic activity by isolating the metal center, preventing bimolecular decomposition paths and facilitating product release. In synergistic combination with a Lewis acid that helps sequestering the product, 1 provides good to excellent yields of diol products (up to 97% isolated yield), in short reaction times under mild experimental conditions using a slight excess (1.5 equiv) of aqueous hydrogen peroxide, from the oxidation of a broad range of olefins. Predictable site selective syn-dihydroxylation of diolefins is shown. The encumbered nature of the ligand also provides a unique tool that has been used in combination with isotopic analysis to define the nature of the active species and the mechanism of activation of H2O2. Furthermore, 1 is shown to be a competent synthetic tool for preparing O-labeled diols using water as oxygen source.
- Borrell, Margarida,Costas, Miquel
-
supporting information
p. 12821 - 12829
(2017/09/25)
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- SUBSTITUTED 4-AMINOBENZAMIDES AS KCNQ2/3 MODULATORS
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The invention relates to substituted 4-aminobenzamides, to pharmaceutical compositions containing these compounds and also to these compounds for use in the treatment and/or prophylaxis of pain and further diseases and/or disorders.
- -
-
Page/Page column 147; 149
(2013/11/05)
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- SUBSTITUTED 4-AMINOBENZAMIDES AS KCNQ2/3 MODULATORS
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Substituted 4-aminobenzamides, pharmaceutical compositions containing these compounds and also methods of using these compounds in the treatment and/or prophylaxis of pain and further diseases and/or disorders.
- -
-
Paragraph 0721
(2013/11/05)
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- Scope and mechanism of the Pt-catalyzed enantioselective diboration of monosubstituted alkenes
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The Pt-catalyzed enantioselective diboration of terminal alkenes can be accomplished in an enantioselective fashion in the presence of chiral phosphonite ligands. Optimal procedures and the substrate scope of this transformation are fully investigated. Reaction progress kinetic analysis and kinetic isotope effects suggest that the stereodefining step in the catalytic cycle is olefin migratory insertion into a Pt-B bond. Density functional theory analysis, combined with other experimental data, suggests that the insertion reaction positions platinum at the internal carbon of the substrate. A stereochemical model for this reaction is advanced that is in line both with these features and with the crystal structure of a Pt-ligand complex.
- Coombs, John R.,Haeffner, Fredrik,Kliman, Laura T.,Morken, James P.
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supporting information
p. 11222 - 11231
(2013/08/23)
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- A flexible synthesis of C33-C39 polyketide region of apratoxin: Synthesis of natural and unnatural analogues
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A flexible synthesis sequence toward the synthesis of the polyketide region of apratoxin has been developed. The common step of the synthesis is a crotylation reaction. Stereospecific aldolisation, sulfate ring opening or Jacobsen HKR is also highlighted. This synthetic scheme led to the synthesis of several analogues. These examples raise the possibility of synthesising numerous analogues of this portion of apratoxins. Then, together with our supported strategy to synthesise the oxazoline analogue of apratoxin A, this paper opens the possibility to provide easily oxoapratoxin analogues for future SAR studies of this potent antitumoral compound.
- Gilles, Arnaud,Martinez, Jean,Cavelier, Florine
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scheme or table
p. 437 - 440
(2012/03/22)
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- Pt-catalyzed enantioselective diboration of terminal alkenes with B 2(pin)2
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(Chemical Equation Presented) The Pt-catalyzed enantioselective addition of bis(pinacolato)diboron to simple monosubstituted alkenes is described. This reaction occurs in the presence of a readily available chiral phosphonite ligand and is effective with a variety of terminal alkene substrates. Importantly, the reaction can operate with catalyst loadings of only 1 mol % Pt. While oxidation of the intermediate 1,2-bis(boronate) ester provides the chiral 1,2-diol as the reaction product, the intermediate may also be subjected to homologation/oxidation to furnish a chiral 1,4-diol as the reaction product.
- Kliman, Laura T.,Mlynarski, Scott N.,Morken, James P.
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supporting information; experimental part
p. 13210 - 13211
(2010/01/30)
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- Highly diastereoselective synthesis of orthoquinone monoketals through λ13-iodane-mediated oxidative dearomatization of phenols
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(Chemical Equation Presented) Versatile chiral substrates for asymmetric synthesis are formed through the spiroketalization of phenols with a chiral substituted ethanol unit O-tethered to the ortho position upon treatment with PhI-(OAc)2 (see example; TFE = 2,2,2-tri-fluoroethanol). Intermediates with a six-membered iodine(III)-containing ring (the natural localized molecular orbitals associated with the I-C6 bond are shown) undergo ligand coupling to give the spiroketals.
- Pouysegu, Laurent,Chassaing, Stefan,Dejugnac, Delphine,Lamidey, Anne-Marie,Miqueu, Karinne,Sotiropoulos, Jean-Marc,Quideau, Stephane
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supporting information; experimental part
p. 3552 - 3555
(2009/02/07)
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- Stereoselective functionalisation of SuperQuat enamides: asymmetric synthesis of homochiral 1,2-diols and α-benzyloxy carbonyl compounds
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Homochiral (E)- and (Z)-enamides derived from SuperQuat (S)-4-phenyl-5,5-dimethyl-oxazolidin-2-one undergo highly diastereoselective epoxidation upon treatment with dimethyldioxirane. Subsequent epoxide opening with meta-chlorobenzoic acid proceeds via a stereoselective SN1-type process, with retention of configuration, to give the corresponding 1′-m-chlorobenzoyl-2′-hydroxy derivatives. Treatment of the SuperQuat enamides with mCPBA effects this two-step transformation in one pot. Reductive cleavage of the isolated 1′-m-chlorobenzoyl-2′-hydroxy derivatives (≥96% de) generates homochiral 1,2-diols in ≥96% ee. Alternatively, regioselective lithiation of the enamide at C(1′) with tBuLi followed by reaction with an aromatic aldehyde and in situ O-benzylation generates a 1′-(benzyloxy-aryl-methyl) substituted enamide with high diastereoselectivity. Subsequent oxidative cleavage of the enamide C{double bond, long}C bond with NaIO4/RuCl3 followed by methanolysis of the resultant N-acyl fragment furnishes an O-benzyl protected α-hydroxy methyl ester in high ee.
- Aciro, Caroline,Davies, Stephen G.,Garner, A. Christopher,Ishii, Yutaka,Key, Min-Suk,Ling, Kenneth B.,Prasad, R. Shyam,Roberts, Paul M.,Rodriguez-Solla, Humberto,O'Leary-Steele, Catherine,Russell, Angela J.,Sanganee, Hitesh J.,Savory, Edward D.,Smith, Andrew D.,Thomson, James E.
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p. 9320 - 9344
(2008/12/22)
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- Multifaceted palladium catalysts towards the tandem diboration-arylation reactions of alkenes
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Novel Pd26+ compounds have been synthesized in high yield. These compounds and their Pd24+ counterparts as synthetic precursors mediate the diboration of vinylarenes and aliphatic 1-alkenes, and under mild and basic reaction conditions they produce a variety of 1,2-diboronate esters with excellent conversions and chemo-selectivities. The presence of bis(catecholato)diboron (B2cat2) favours the reduction of PdIII to PdII, while the catalytic precursor of PdII is transformedinto Pd0-nanoparticles. An "in situ" catalytic tandem reaction has been designed to transform the diboronate intermediates into the monoarylated product, which after oxidative workup, provides the carbohydroxylated adduct. Eventually, the same catalyst performs both sequences with total conversion from the alkene.
- Penno, Dirk,Lillo, Vanesa,Koshevoy, Igor O.,Sanau, Mercedes,Ubeda, M. Angeles,Lahuerta, Pascual,Fernandez, Elena
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supporting information; experimental part
p. 10648 - 10655
(2009/12/01)
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- Ring-expanding olefin metathesis: A route to highly active unsymmetrical macrocyclic oligomeric co-salen catalysts for the hydrolytic kinetic resolution of epoxides
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In the presence of the third generation Grubbs catalyst, the ring-expanding olefin metathesis of a monocyclooct-4-en-1-yl functionalized salen ligand and the corresponding Co(II)(salen) complex at low monomer concentrations results in the exclusive formation of macrocyclic oligomeric structures with the salen moieties being attached in an unsymmetrical, flexible, pendent manner. The TOF-MALDI mass spectrometry reveals that the resulting macrocyclic oligomers consist predominantly of dimeric to tetrameric species, with detectable traces of higher homologues up to a decamer. Upon activation under aerobic and acidic conditions, these Co(salen) macrocycles exhibit extremely high reactivities and selectivities in the hydrolytic kinetic resolution (HKR) of a variety of racemic terminal epoxides under neat conditions with very low catalyst loadings. The excellent catalytic properties can be explained in terms of the new catalyst's appealing structural features, namely, the flexible oligomer backbone, the unsymmetrical pendent immobilization motif of the catalytic sites, and the high local concentration of Co(salen) species resulting from the macrocyclic framework. This ring-expanding olefin metathesis is suggested to be a simple way to prepare tethered metal complexes that are endowed with key features - (i) a high local concentration of metal complexes and (ii) a flexible, single point of attachment to the support - that facilitate rapid and efficient catalysis when a bimetallic transition state is required.
- Zheng, Xiaolai,Jones, Christopher W.,Weck, Marcus
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p. 1105 - 1112
(2007/10/03)
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- Hydrolytic kinetic resolution of epoxides catalyzed by chromium(III)-endo, endo-2,5-diaminonorbornane-salen [Cr(III)-DIANANE-salen] complexes. Improved activity, low catalyst loading
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The hydrolytic kinetic resolution (HKR) of terminal epoxides, using chiral chromium(III)-salen catalysts based on DIANANE (endo,endo-2,5-diaminonorbornane) , was studied. A broad substrate scope was found for the chromium(III)-DIANANE catalysts, and very low loadings (down to 0.05 mol%) were needed to achieve high enantiomeric purities of both the remaining epoxides and the product diols (up to >99% ee). Besides monosubstituted epoxides, 2-methyl-2-n-pentyloxirane, which is an example for 2,2-disubstituted epoxides, could be ring-opened in an asymmetric fashion with water in the presence of an electronically tuned chromium-(III)-DIANANE complex.
- Berkessel, Albrecht,Ertuerk, Erkan
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p. 2619 - 2625
(2007/10/03)
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- P2-P3 conformationally constrained ketoamide-based inhibitors of cathepsin K
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An orally bioavailable series of ketoamide-based cathepsin K inhibitors with good pharmacokinetic properties has been identified. Starting from a potent inhibitor endowed with poor drug properties, conformational constraint of the P2-P3 linker and modifications to P1′ elements led to an enhancement in potency, solubility, clearance, and bioavailability. These optimized inhibitors attenuated bone resorption in a rat TPTX hypocalcemic bone resorption model.
- Barrett, David G.,Boncek, Virginia M.,Catalano, John G.,Deaton, David N.,Hassell, Anne M.,Jurgensen, Cynthia H.,Long, Stacey T.,McFadyen, Robert B.,Miller, Aaron B.,Miller, Larry R.,Payne, J. Alan,Ray, John A.,Samano, Vicente,Shewchuk, Lisa M.,Tavares, Francis X.,Wells-Knecht, Kevin J.,Willard Jr., Derril H.,Wright, Lois L.,Zhou, Hui-Qiang Q.
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p. 3540 - 3546
(2007/10/03)
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- Rh-catalyzed enantioselective diboration of simple alkenes: Reaction development and substrate scope
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The rhodium-catalyzed reaction between bis(catecholato)diboron and simple alkenes results in the syn addition of the diboron across the alkene. The resulting 1,2-bis(boronate) is subsequently oxidized to provide the 1,2-diol. In the presence of enantiomerically enriched Quinap ligand, high enantioselection in the diboration can be achieved. The reaction is highly selective for trans- and trisubstituted alkenes and can be selective for some monosubstituted alkenes as well. The development of this reaction is described as is the substrate scope and experiments that are informative about the reaction mechanism and competing pathways.
- Trudeau, Stephane,Morgan, Jeremy B.,Shrestha, Mohanish,Morken, James P.
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p. 9538 - 9544
(2007/10/03)
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- Regioselective homologation of bis(boronate) intermediates derived from rhodium-catalyzed diboration of simple alkenes
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Regioselective homologation of alkyl-1,2-bis(catecholboronates) may be accomplished by treatment of these reactive intermediates with TMSCHN 2. A convenient process is reported where alkene diboration and the subsequent homologation reaction are accomplished in the same reaction flask. Georg Thieme Verlag Stuttgart.
- Kalendra, Diane M.,Due?es, Rebecca A.,Morken, James P.
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p. 1749 - 1751
(2007/10/03)
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- Catalytic enantioselective hydrogenation of vinyl bis(boronates)
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Catalytic enantioselective hydrogenation of prochiral vinylmetallic reagents can provide an attractive alternative to hydrometalation and bismetalation of alkenes. In this contribution, the first highly enantioselective hydrogenation of vinyl boronic esters is described. The chiral reduction products are versatile intermediates for chemical synthesis. Copyright
- Morgan, Jeremy B.,Morken, James P.
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p. 15338 - 15339
(2007/10/03)
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- Enantioselective reduction of α-keto esters to 1,2-diols using the NaBH4/Me3SiCl system catalyzed by polymer-supported chiral sulfonamide
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In the presence of 25mol% of a polymer-supported chiral sulfonamide, a variety of α-keto esters can be reduced into the corresponding 1,2-diols in good yields and high enantioselectivities using the NaBH4/Me 3SiCl reducing system.
- Wang, Guang-Yin,Hu, Jian-Bing,Zhao, Gang
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p. 807 - 810
(2007/10/03)
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- Mechanistic Investigation Leads to a Synthetic Improvement in the Hydrolytic Kinetic Resolution of Terminal Epoxides
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The mechanism of the hydrolytic kinetic resolution (HKR) of terminal epoxides was investigated by kinetic analysis using reaction calorimetry. The chiral (salen)Co-X complex (X = OAc, OTs, Cl) undergoes irreversible conversion to (salen)Co-OH during the course of the HKR and thus serves as both precatalyst and cocatalyst in a cooperative bimetallic catalytic mechanism. This insight led to the identification of more active catalysts for the HKR of synthetically useful terminal epoxides. Copyright
- Nielsen, Lars P. C.,Stevenson, Christian P.,Blackmond, Donna G.,Jacobsen, Eric N.
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p. 1360 - 1362
(2007/10/03)
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- Catalytic Asymmetric Carbohydroxylation of Alkenes by a Tandem Diboration/Suzuki Cross-Coupling/Oxidation Reaction
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(Equation presented) Chiral nonsymmetric 1,2-diboron adducts are generated by catalytic enantioselective diboration. Oxidation of these adducts provides 1,2-diols in good yield. Alternatively, 1,2-diboron compounds may be reacted, in situ, with aryl halides wherein the less hindered C-B bond participates in cross-coupling. The remaining C-B bond is then oxidized in the reaction workup thereby allowing for net asymmetric carbohydroxylation of alkenes in a tandem one-pot diboration/Suzuki coupling/oxidation sequence.
- Miller, Steven P.,Morgan, Jeremy B.,Nepveux V, Felix J.,Morken, James P.
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p. 131 - 133
(2007/10/03)
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- Oxidative functionalisation of superquat enamides: Asymmetric synthesis of homochiral 1,2 diols
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Homochiral (E)-enamides derived from (S)-4-phenyl-5,5-dimethyl-oxazolidin-2-one undergo highly diastereoselective epoxidation upon treatment with dimethyldioxirane (DMDO). Treatment with m-chloroperbenzoic acid (MCPBA) produces syn-(4S, 1′R,2′)-1′ -acyloxy-2′-hydroxy derivatives with high diastereoselectivity, consistent with a mechanism involving initial epoxidation and subsequent in situ SN1 type epoxide opening and trapping with m-chlorobenzoic acid. Reductive cleavage of the isolated 1′-acyloxy-2′-hydroxy derivatives generates 1,2-diols in high yields and in high ee.
- Davies, Stephen G.,Key, Min-Suk,Rodriguez-Solla, Humberto,Sanganee, Hitesh J.,Savory, Edward D.,Smith, Andrew D.
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p. 1659 - 1662
(2007/10/03)
-
- A new practical method for the osmium-catalyzed dihydroxylation of olefins using bleach as the terminal oxidant
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A general procedure for the osmium-catalyzed dihydroxylation of various olefins using bleach as oxidant is reported for the first time. Aromatic and aliphatic olefins yield the corresponding cis-1,2-diols in the presence of dihydroquinine or dihydroquinidine derivatives (Sharpless ligands) with good to excellent chemo- and enantioselectivities under optimized pH conditions. In the presence of a small excess of bleach as reoxidant fast dihydroxylation takes place even at 0°C. Under optimum reaction conditions it is possible to dihydroxylate terminal aliphatic and aromatic olefins as well as internal olefins. The low price of the oxidant and the simple handling of bleach make this dihydroxylation variant attractive for further applications.
- Mehltretter, Gerald M.,Bhor, Santosh,Klawonn, Markus,D?bler, Christian,Sundermeier, Uta,Eckert, Markus,Militzer, Hans-Christian,Beller, Matthias
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p. 295 - 301
(2007/10/03)
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- Highly selective hydrolytic kinetic resolution of terminal epoxides catalyzed by chiral (salen)CoIII complexes. Practical synthesis of enantioenriched terminal epoxides and 1,2-diols
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The hydrolytic kinetic resolution (HKR) of terminal epoxides catalyzed by chiral (salen)CoIII complex 1·OAc affords both recovered unreacted epoxide and 1,2-diol product in highly enantioenriched form. As such, the HKR provides general access to useful, highly enantioenriched chiral building blocks that are otherwise difficult to access, from inexpensive racemic materials. The reaction has several appealing features from a practical standpoint, including the use of H2O as a reactant and low loadings (0.2-2.0 mol %) of a recyclable, commercially available catalyst. In addition, the HKR displays extraordinary scope, as a wide assortment of sterically and electronically varied epoxides can be resolved to ≥ 99% ee. The corresponding 1,2-diols were produced in good-to-high enantiomeric excess using 0.45 equiv of H2O. Useful and general protocols are provided for the isolation of highly enantioenriched epoxides and diols, as well as for catalyst recovery and recycling. Selectivity factors (krel) were determined for the HKR reactions by measuring the product ee at ca. 20% conversion. In nearly all cases, krel values for the HKR exceed 50, and in several cases are well in excess of 200.
- Schaus, Scott E.,Brandes, Bridget D.,Larrow, Jay F.,Tokunaga, Makoto,Hansen, Karl B.,Gould, Alexandra E.,Furrow, Michael E.,Jacobsen, Eric N.
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p. 1307 - 1315
(2007/10/03)
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- A practical method for synthesis of terminal 1,2-diols in high enantiomeric excess via oxazaborolidine-catalyzed asymmetric reduction
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Asymmetric borane reduction of α-hydroxy ketones protected with a tetrahydropyranyl (THP) group catalyzed by Corey's CBS reagent using N- phenylamine-borane complexes as the hydride source provided the corresponding terminal 1,2-diols with a very high enantiomeric excess.
- Cho, Byung Tae,Chun, Yu Sung
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p. 1843 - 1846
(2007/10/03)
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- N-(α-chloroalkyloxycarbonyl)pyrrolidines as a source of oxygenated d1- reagents
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Reaction of the N-(α-chloroalkyloxycarbonyl)pyrrolidines 1 with lithium powder and a catalytic amount of 4,4'-di-tertbutylbiphenyl (DTBB, 2.5 mol-%) in the presence of different electrophiles [iBuCHO, tBuCHO, PhCHO, Et2CO, (CH2)5CO, PhCOMe, Ph2CO, MeaSiCl], in THF at temperatures ranging between -78 and -60°C leads after hydrolysis with water, to the expected functionalized carbamates 2. Deprotection of compounds 2, derived from carbonyl compounds, with lithium hydroxide in a mixture of ethanol and water at 80°C affords the corresponding 1,2-diols 3.
- Ortiz, Javier,Guijarro, Albert,Yus, Miguel
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p. 3005 - 3012
(2007/10/03)
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- Methylation-ring opening of 3,3-disubstituted 2,3-epoxy alcohols. Synthesis of chiral quaternary fragments for assembly of briaran diterpenes
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Two chiral quaternary carbon-containing fragments suitable for elaboration to the briaran diterpenes were obtained by regioselective methylation of functionalized 3,3-disubstituted 2,3-epoxy-1-ols. The factors which favor methylation at the more hindered position of a trisubstituted 2,3-epoxy alcohol were determined.
- Balasubramaniam, Rajiv P.,Moss, David K.,Wyatt, Justin K.,Spence, John D.,Gee, Arvin,Nantz, Michael H.
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p. 7429 - 7444
(2007/10/03)
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- New polymer supported cinchona alkaloids for heterogeneous catalytic asymmetric dihydroxylation of olefins
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Two new polymeric cinchona alkaloid derived ligands were synthesized and utilized in the asymmetric dihydroxylation of olefins, exhibiting high enantioselectivities in the case of aliphatic terminal olefins under heterogeneous phase.
- Nandanan,Sudalai,Ravindranathan
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p. 2577 - 2580
(2007/10/03)
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- Asymmetric dihydroxylation with silica-anchored alkaloids
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Diols with excellent enantiomeric excesses are obtained from unfunctionalised alkenes in high yields by osmium-catalysed dihydroxylationsusingsilica-boundpyrimidineandpyrazino-pyridazine ligands.
- Bolm, Carsten,Maischak, Astrid,Gerlach, Arne
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p. 2353 - 2354
(2007/10/03)
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- N-(chloromethyloxycarbonyl)pyrrolidine as a source of the HOCH2- synthon
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The reaction of N-(chloromethyloxycarbonyl)pyrrolidine (1) with lithium powder and a catalytic amount of DTBB (2.5 mol %) in the presence of different electrophiles [Me3SiCl, Bu(i)CHO, Bu(t)CHO, PhCHO, Et2CO, (CH2)5CO, PhCOMe, Ph2CO] in THF at -78°C leads, after hydrolysis with water, to the expected functionalised carbamates 2. Deprotection of the acetophenone derivative 2g with DIBALH at THF reflux yields, after hydrolysis, the corresponding 1,2-diol 3g.
- Guijarro, Albert,Yus, Miguel
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p. 5593 - 5596
(2007/10/03)
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- Synthesis of 1,1-dibromo-3-hydroxyalkanes via opening of cyclic sulfates
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3-Alkoxy-1,1-dibromoalkanes are interesting substrates for diastereoselective bromine/lithium exchange reactions. A general route to the precursor 1,1-dibromo-3-hydroxyalkanes is described here via reaction of dibromomethyllithium with cyclic sulfates of 1,2-diols.
- Stiasny, Hans Christian
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p. 259 - 264
(2007/10/03)
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- Nucleophilic reactions between cyclic 1,2-sulfites and chloride ions
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When cyclic 1,2-sulfites are ring opened by chloride ion, the chlorohydrins are formed with low regio- and stereo-selectivity. The mechanisms involved in the process were investigated by measuring the stereochemical outcome of the reactions. The results showed that reversible inversion pathways (SN2 reactions) and a retention pathway (SN2i reaction) gave rise to the loss in ee in both the chlorohydrins and in the cyclic 1,2-sulfites. Acta Chemica Scandinavica 1996.
- Nymann, Kirsten,Jensen, Linda,Svendsen, John S.
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p. 832 - 841
(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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- Dispiroketals in synthesis (part 9): Resolution of 1,2-diols using a C2-symmetric diphenyltetrahydrobipyran
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A series of 1,2-diols were resolved by the enantioselective formation of the thermodynamically most stable dispiroketal using (2R,2'R) and (2S,2'S) 2,2'-diphenyl-3,3',4,4'-tetrahydro-6,6'-bi-2H-pyran 2 and 3. Deprotection was achieved using a metal ammonia reduction to liberate the resolved diols.
- Edwards,Entwistle,Ley,Owen,Perry
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p. 553 - 556
(2007/10/02)
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- Improved Enantioselectivity in Asymmetric Dihydroxylation of Terminal Olefins Using Pyrimidine Ligands
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Bis-cinchona alkaloid substituted pyrimidine ligands were found to give improved enantioselectivity in the osmium-catalyzed asymmetric dihydroxylation (AD) of monosubstituted terminal olefins.
- Crispino, Gerard A.,Jeong, Kyu-Sung,Kolb, Hartmuth C.,Wang, Zhi-Min,Xu, Daqiang,Sharpless, K. Barry
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p. 3785 - 3786
(2007/10/02)
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- New Ligands Double the Scope of the Catalytic Asymmetric Dihydroxylation of Olefins
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Improved ligands render terminal olefins good substrates for the osmium-catalyzed asymmetric dihydroxylation (ADH) process, and the amounts of chiral ligand and osmium catalyst required diminish dramatically.
- Sharpless, K. Barry,Amberg, Willi,Beller, Matthias,Chen, Hou,Hartung, Jens,et al.
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p. 4585 - 4588
(2007/10/02)
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- Substrate Enantioselection in the Microsomal Epoxide Hydrolase Catalyzed Hydrolysis of Monosubstituted Oxiranes. Effects of Branching of Alkyl Chains
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The hydrolysis of racemic 1,2-epoxyhexane (1a), 1,2-epoxydecane (1b), 4,4-dimethyl-1,2-epoxypentane (1c), and 3,3-dimethyl-1,2-epoxybutane (1d) catalyzed by rabbit liver microsomal epoxide hydrolase (MEH) has been investigated in order to further clarify the enantioselecting ability of this enzyme.Both enantiomers of all four epoxides were good substrates.The alkyl chain showed, however, a remarkable effect on the enantiomeric excess of the diols 2 produced during the course of the hydrolysis under enzyme saturation conditions.Linear-chain epoxides gave diols with very low enantiomeric excesses even at very low conversions, whereas branched-chain epoxides gave enantiomerically enriched diols.Furthermore, the ee obtained with the latter epoxides increased with increasing ratio of substrate to microsomal protein.R configurations were demonstrated for the excess enantiomers of diols 2c and 2d by CD and NMR measurements of their dibenzoate esters.In the case of 1c nucleophilic attack by water was proved using 18OH2 followed by MS analysis of the produced diol to occur 95percent at the unsubstituted oxirane carbon.A markedly biphasic profile was found for the time course of the hydrolysis of (+/-)-1d.A mechanistic explanation for the observed substrate enantioselection is proposed.
- Bellucci, Giuseppe,Chiappe, Cinzia,Conti, Luca,Marioni, Franco,Pierini, Gloria
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p. 5978 - 5983
(2007/10/02)
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- ASYMMETRIC REACTIONS BASED ON 1,3-OXATHIANES-3. SECONDARY α-HYDROXYACIDS, RCHOHCO2H AND GLYCOLS RCHOHCH2OH
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Reduction of the previously prepared chiral 2-acyl-1,3-oxathianes derived from (+)-pulegone with various metal hydride combinations proceeds stereoselectively, with diastereomer excess (d.e.) of as much as 97percent in the case of reduction of phenyl ketons with lithium tri-sec. butylborohydride.Lesser selectivity (maximum 82percent d.e.) is achived with primary or tertiary alkyl ketones: the predominant diastereomer is readily purified by chromatography.The major product in these cases is that predicted by Cram's chelate rule.The product ratio is reversed with diisobutylaluminium hydride and also in the reduction of secondary alkyl ketones with lithium sec. butylborohydride, where stereoselectivity is low.The 2-hydroxyalkyl-1,3-oxathines are cleaved to α-hydroxyaldehydes with N-chlorosuccinimide-silver nitrate and the aldehydes reduced to glycols, RCHOHCH2OH with sodium borohydride with little or no racemization.Esters, RCHOHCO2CH3, are obtained in high enantiomeric purity by O-benzylating the 2-hydroxyalkyl-1,3-oxathianes prior to cleavage, oxidizing with sodium chlorite following cleavage, esterifying and debenzylating.A method for measuring the enantiomeric purity of glycols RCHOHCH2OH by conversion to 2-phenyl-1,3-dioxolanes with benzaldehyde, followed by proton NMR analysis of the resulting 2-phenyl-4-alkyl-1,3-dioxolane diastereomer pair in the presence of a chiral europium shift reagent is described.
- Ko, Kwang-Youn,Frazee, William J.,Eliel, Ernest L.
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p. 1333 - 1344
(2007/10/02)
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- Doubly Metalated Methanol. - Alcohol d1- and d3-Reagents
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The nucleophilic counterpart of the electrophilic hydroxymethylating protonated formaldehyde B is the hypothetical tautomer A, R = H, of methoxide.Experiments are described in which the generation of doubly metalated methanol C (= formaldehyde ketyl dianion) and its use as methanol d1-reagent are attempted.Treatment of stannylated methanol 1 with two equivalents of butyllithium furnishes a pentane-soluble reagent which hydroxymethylates electrophilic centers in moderate yields (umpolung of the formaldehyde a1-reactivity), see eq. (1) and table 3.Attempted isolation, 1H- and 13C-NMR measurements, and careful product analysis of the reaction with benzaldhyde (scheme 1 and table 2) support the view that the new reagent is actually not free lithium lithiomethoxide (2) but a tin derivative, see for instance 9 in eq. (2). - The O-silylated derivative 18 (= A, R = SiMe3) is likewise generated by Sn-Li-transmetallation, but cannot be trapped externally by electrophiles due to rapid Wittig rearrangement (-> 19 -> 20).The readily accessible dilithio derivatives 21a and 23a can be employed as direct propanol and allyl alcohol d3-reagents, respectively.
- Meyer, Norbert,Seebach, Dieter
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p. 1290 - 1303
(2007/10/02)
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