- Remarkably Efficient Iridium Catalysts for Directed C(sp2)-H and C(sp3)-H Borylation of Diverse Classes of Substrates
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Here we describe the discovery of a new class of C-H borylation catalysts and their use for regioselective C-H borylation of aromatic, heteroaromatic, and aliphatic systems. The new catalysts have Ir-C(thienyl) or Ir-C(furyl) anionic ligands instead of the diamine-type neutral chelating ligands used in the standard C-H borylation conditions. It is reported that the employment of these newly discovered catalysts show excellent reactivity and ortho-selectivity for diverse classes of aromatic substrates with high isolated yields. Moreover, the catalysts proved to be efficient for a wide number of aliphatic substrates for selective C(sp3)-H bond borylations. Heterocyclic molecules are selectively borylated using the inherently elevated reactivity of the C-H bonds. A number of late-stage C-H functionalization have been described using the same catalysts. Furthermore, we show that one of the catalysts could be used even in open air for the C(sp2)-H and C(sp3)-H borylations enabling the method more general. Preliminary mechanistic studies suggest that the active catalytic intermediate is the Ir(bis)boryl complex, and the attached ligand acts as bidentate ligand. Collectively, this study underlines the discovery of new class of C-H borylation catalysts that should find wide application in the context of C-H functionalization chemistry.
- Chattopadhyay, Buddhadeb,Hassan, Mirja Md Mahamudul,Hoque, Md Emdadul
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supporting information
p. 5022 - 5037
(2021/05/04)
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- Rhodium(II)-Catalyzed Aryl C?H Carboxylation of 2-Pyridylphenols with CO2
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A protocol for C?H carboxylation of electron-deficient 2-pyridylphenols with CO2 through a Rh(II)-catalyzed C?H bond activation under redox-neutral conditions has been developed. A suitable phosphine ligand was crucial for this reaction. This m
- Cai, Zhihua,Li, Shangda,Gao, Yuzhen,Li, Gang
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supporting information
p. 4005 - 4011
(2018/09/20)
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- Electrochemical methoxymethylation of alcohols-a new, green and safe approach for the preparation of MOM ethers and other acetals
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A new, green, safe, cost-effective and highly efficient electrochemical approach for the methoxymethylation of alcohols and phenols was successfully developed. The methodology was also applied to the synthesis of substituted acetals.
- Luo, Xiya,Ma, Xiaofeng,Lebreux, Frédéric,Markó, István E.,Lam, Kevin
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supporting information
p. 9969 - 9972
(2018/09/11)
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- Enantioselective and Regioselective Hydroetherification of Alkynes by Gold-Catalyzed Desymmetrization of Prochiral Phenols with P-Stereogenic Centers
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The gold(I)-catalyzed enantioselective hydroetherification of alkynes was achieved via desymmetrization of prochiral bisphenols bearing P-stereogenic centers. (S)-DTBM-Segphos(AuCl)2/AgNTf2 proved to be a highly efficient catalyst system for this transformation, affording P-chiral cyclic phosphine oxides in good yields with high enantioselectivities (with up to 99% ee). The same catalyst system allowed for the enantioselective desymmetrization of dialkynes. Synthetic transformations of the cyclization products afforded other P-chiral molecules with high enantiospecificity.
- Zheng, Yin,Guo, Linna,Zi, Weiwei
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supporting information
p. 7039 - 7043
(2018/11/24)
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- Total synthesis of [13C]2-, [13C]3-, and [13C]5-isotopomers of xanthohumol, the principal prenylflavonoid from hops
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Xanthohumol [(E)-6′-methoxy-3′-(3-methylbuten-2-yl)-2′,4′,4″-trihydroxychalcone], he principal prenylated flavonoid from hops, has a complex bioactivity profile, and 13C-labeled isotopomers of this compound are of potential use as molecular probes and as analytical standards to study metabolism and mode of action. 1,3-[13C]2-Xanthohumol was prepared by an adaptation of the total synthesis of Khupse and Erhardt in 7 steps and 5.7% overall yield from phloroglucinol by a route incorporating a cascade Claisen-Cope rearrangement to install the 3′-prenyl moiety from a 5′-prenyl aryl ether and an aldol condensation between 1-[13C]-2′,4′-bis(benzyloxymethyloxy)-6′-methoxy-3′-(3-methylbuten-2-yl)acetophenone and 1′-[13C]-4-(methoxymethyloxy)benzaldehyde. The 13C-atom in the methyl ketone was derived from 1-[13C]-acetyl chloride while that in the aryl aldehyde was derived from [13C]-iodomethane. Tri- and penta-13C-labeled xanthohumols were similarly prepared by applying minor modifications to the route.
- Ellinwood, Duncan C.,El-Mansy, Mohamed F.,Plagmann, Layhna S.,Stevens, Jan F.,Maier, Claudia S.,Gombart, Adrian F.,Blakemore, Paul R.
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p. 639 - 648
(2017/11/27)
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- Bismuth trichloride–mediated cleavage of phenolic methoxymethyl ethers
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A simple and efficient method for removal of phenolic methoxymethyl ethers in the presence of 30?mol% of bismuth trichloride in acetonitrile/water is described. Notable features of the cleavage protocol entail use of an ecofriendly bismuth reagent, ease of handling, low cost, operational simplicity, and good functional group compatibility. A number of structurally varied phenolic methoxymethyl ethers were cleaved in good to excellent yields.
- Obaro-Best, Oghale,Reed, Jack,Norfadilah, Alya A. F. B.,Monahan, Ryan,Sunasee, Rajesh
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supporting information
p. 586 - 593
(2016/06/08)
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- Enantiodivergent Atroposelective Synthesis of Chiral Biaryls by Asymmetric Transfer Hydrogenation: Chiral Phosphoric Acid Catalyzed Dynamic Kinetic Resolution
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Reported herein is an enantiodivergent synthesis of chiral biaryls by a chiral phosphoric acid catalyzed asymmetric transfer hydrogenation reaction. Upon treatment of biaryl lactols with aromatic amines and a Hantzsch ester in the presence of chiral phosp
- Mori, Keiji,Itakura, Tsubasa,Akiyama, Takahiko
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supporting information
p. 11642 - 11646
(2016/10/24)
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- P4VPy–CuO nanoparticles as a novel and reusable catalyst: application at the protection of alcohols, phenols and amines
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P4VPy–CuO nanoparticles were synthesized using ultrasound irradiations. Relevant properties of the synthesized nanoparticles were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Fourier transform infrared spectroscopy. After identification, the prepared reagent was used for the promotion of different types of protection reactions of alcohols, phenols and amines. Easy workup, short reaction times, excellent yields, relatively low cost and reusability of the catalyst are the striking features of the reported methods.
- Shirini, Farhad,Fallah-Shojaei, Abdollah,Abedini, Masoumeh,Samavi, Laleh
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p. 1699 - 1712
(2016/07/27)
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- Pd-Catalyzed Cross-Coupling of Aryllithium Reagents with 2-Alkoxy-Substituted Aryl Chlorides: Mild and Efficient Synthesis of 3,3′-Diaryl BINOLs
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Palladium-catalyzed cross-coupling of aryllithium reagents with 2-alkoxy-substituted aryl chlorides is described. The reactions proceed under mild conditions with short reaction times and provide a wide range of 2-alkoxy-substituted biaryls. This new methodology is applied to the efficient preparation of 3,3′-diaryl BINOLs and represents the first synthesis of this important class of chiral compounds from the corresponding 3,3′-dichloro BINOLs. (Chemical Equation Presented).
- Castelló, Luis M.,Hornillos, Valentín,Vila, Carlos,Giannerini, Massimo,Fa?anás-Mastral, Martín,Feringa, Ben L.
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supporting information
p. 62 - 65
(2015/07/28)
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- Two novel tetracycles, cassibiphenols A and B from the flowers of Cassia siamea
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Chemical investigation of the flowers of Cassia siamea (Leguminosae), resulted in the isolation of two novel tetracycles connecting 5-(2-hydroxypropyl)benzene-1,3-diol, cassibiphenols A (1) and B (2). The structures were elucidated by analysis of the 1D, 2D NMR, and HRMS spectra. Synthesis of a tetracyclic core of 1 and 2 led to determine the absolute configuration of 1 and C-12 of 2.
- Deguchi, Jun,Sasaki, Tadahiro,Hirasawa, Yusuke,Kaneda, Toshio,Kusumawati, Idha,Shirota, Osamu,Morita, Hiroshi
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p. 1362 - 1365
(2014/03/21)
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- Expanded substrate scope and improved reactivity of ether-forming cross-coupling reactions of organotrifluoroborates and acetals
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Mixed acetals and organotrifluoroborates undergo BF3· OEt2-promoted cross-couplings to give dialkyl ethers under simple, mild conditions. A survey of reaction partners identified a hydroxamate leaving group that improves the regioselectivity and product yield in the BF 3·OEt2-promoted coupling reaction of mixed acetals and potassium alkynyl-, alkenyl-, aryl- and heteroaryltrifluoroborates to access substituted dialkyl ethers. This leaving group enables the reaction to proceed rapidly under mild conditions (0 °C, 5-60 min) and permits reactions with electron-deficient potassium aryltrifluoroborates that are less reactive with other acetal substrates. A study of the reaction mechanism and characterization of key intermediates by NMR spectroscopy and X-ray crystallography identified a role for the hydroxamate moiety as a reversible leaving group that serves to stabilize the key oxocarbenium intermediate and the need for a slight excess of organodifluoroborane to serve as a catalyst. A secondary role for the boron nucleophile as an activating ligand was also considered. These studies provide the basis for a general class of reagents that lead to dialkyl ethers by a simple, predictable cross-coupling reaction.
- Vo, Cam-Van T.,Mitchell, T. Andrew,Bode, Jeffrey W.
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supporting information; experimental part
p. 14082 - 14089
(2011/10/12)
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- 13C-isotope labelling for the facilitated NMR analysis of a complex dynamic chemical system
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13C-isotope labelling is presented as a novel tool for the study of complex chemical systems. 13C-isotope labelling permits the quantification of all 26 members of a dynamic library from a single 13C NMR spectrum without the need for advanced instrumentation or sophisticated experimental protocols.
- Dal Molin, Marta,Gasparini, Giulio,Scrimin, Paolo,Rastrelli, Federico,Prins, Leonard J.
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supporting information; experimental part
p. 12476 - 12478
(2012/02/03)
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- Synthesis of deuterium-labelled etravirine
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This study describes the synthesis of deuterium-labelled etravirine. Etravirine labelled with six deuteriums was prepared in eight steps starting from phenol with excellent chemical purity and isotopic enrichment. It provides important internal standard f
- Wang, Wei,Wu, Wenchao,Shen, Zucheng,Chen, Liqin
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experimental part
p. 371 - 373
(2012/06/01)
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- Total synthesis of the pyranoisoflavone kraussianone 1 and related isoflavones
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The first total synthesis of the pyranoisoflavone kraussianone 1 (1) is described. The key steps involved the Suzuki-Miyaura reaction for the construction of the isoflavone core and the regioselective formation of the dimethylpyran scaffolds to the phloroglucinol (ring A) and resorcinol (ring B) moieties of kraussianone 1 (1). This route also provided access to the related isoflavones eriosemaone D (2) and genistein (3) via simple structural modifications.
- Selepe, Mamoalosi A.,Drewes, Siegfried E.,Van Heerden, Fanie R.
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body text
p. 1680 - 1685
(2011/02/21)
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- A facile method for the rapid and selective deprotection of methoxymethyl (MOM) ethers
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We describe a rapid and efficient method for selective deprotection of methoxymethyl (MOM) ethers using ZnBr2 and n-PrSH, which completely removed MOM from diverse MOM ethers of primary, secondary, and tertiary alcohols or phenol derivatives. The deprotection takes less than ten minutes with both high yield and selectivity in the presence of other protecting groups. In addition, the rapid deprotection of MOM ethers of tertiary hydroxyls in high yield with no epimerization allows MOM to be a suitable protecting group for tertiary alcohols.
- Han, Jae Hyun,Kwon, Young Eun,Sohn, Jeong-Hun,Ryu, Do Hyun
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experimental part
p. 1673 - 1677
(2010/04/04)
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- PHOTOACID GENERATOR, COPOLYMER, CHEMICALLY AMPLIFIED RESIST COMPOSITION, AND METHOD OF FORMING PATTERN USING THE CHEMICALLY AMPLIFIED RESIST COMPOSITION
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Disclosed are a photoacid generator, a copolymer, a chemically amplified resist composition, and a method of forming a pattern using the chemically amplified resist composition. The photoacid is connected with a main chain of the copolymer, whereby the ph
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- Highly efficient and selective methoxymethylation of alcohols and phenols catalyzed by reusable ZrO(OTf)2 under solvent-free conditions
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Different primary, secondary, and tertiary alcohols were efficiently converted to their corresponding methoxymethyl ethers with formaldehyde dimethyl acetal in the presence of catalytic amounts of ZrO(OTf)2 at room temperature. Phenols were als
- Moghadam, Majid,Tangestaninejad, Shahram,Mirkhani, Valiollah,Mohammadpoor-Baltork, Iraj,Khajehzadeh, Mostafa
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experimental part
p. 641 - 647
(2011/05/04)
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- High-valent [SnIV(Br8TPP)(OTf)2] as a highly efficient and reusable catalyst for selective methoxymethylation of alcohols and phenols: The effect of substituted bromines on the catalytic activity
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High-valent tin(IV)octabromotetraphenylporphyrinato trifluoromethanesulfonate, [SnIV(Br8TPP)(OTf)2], was used for selective methoxymethylation of alcohols and phenols with formaldehyde dimethyl acetal (FDMA) at room temper
- Moghadam, Majid,Tangestaninejad, Shahram,Mirkhani, Valiollah,Mohammadpoor-Baltork, Iraj,Khajehzadeh, Mostafa,Kosari, Farshid,Araghi, Mehdi
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experimental part
p. 238 - 243
(2010/04/04)
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- Highly efficient and selective methoxymethylation of alcohols and phenols catalyzed by high-valent tin(IV) porphyrin
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An efficient and selective method for methoxymethylation of alcohols and phenols with formaldehyde dimethyl acetal (FDMA) catalyzed by electron deficient tin(IV)tetraphenylporphyrinato trifluoromethanesulfonate, [SnIV(TPP)(OTf)2], is
- Gharaati, Shadab,Moghadam, Majid,Tangestaninejad, Shahram,Mirkhani, Valiollah,Mohammadpoor-Baltork, Iraj,Kosari, Farshid
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experimental part
p. 1995 - 2000
(2011/01/07)
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- Light-driven rotary molecular motors on gold nanoparticles
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We report the synthesis of unidirectional light-driven rotary molecular motors based on chiral overcrowded alkenes and their immobilisation on the surface of gold nanoparticles through two anchors. Using a combination of 1H and 13C N
- Pollard, Michael M.,Ter Wiel, Matthijs K. J.,Van Delden, Richard A.,Vicario, Javier,Koumura, Nagatoshi,Van Den Brom, Coenraad R.,Meetsma, Auke,Feringa, Ben L.
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supporting information; experimental part
p. 11610 - 11622
(2009/12/09)
-
- Stereoselective ring-opening polymerization of a racemic lactide by using achiral salen- and homosalen-aluminum complexes
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Highly isotactic polylactide or poly(lactic acid) is synthesized in a ring-opening polymerization (ROP) of racemic lactide with achiral salen- and homosalen-aluminum complexes (salenH2 = N,N′-bis(salicylidene) ethylene-1,2-diamine; homosalenH2 = N,N′-bis(salicylidene) trimethylene-1,3-diamine). A systematic exploration of ligands demonstrates the importance of the steric influence of the Schiff base moiety on the degree of isotacticity and the backbone for high activity. The complexes prepared in situ are pure enough to apply to the polymerizations without purification. The crystal structures of the key complexes are elucidated by X-ray diffraction, which confirms that they are chiral. However. analysis of the 1H and 13C NMR spec tra unambiguously demonstrates that their conformations are so flexible that the chiral environment of the complexes cannot be maintained in solution at 25°C and that the complexes are achiral under the polymerization conditions. The flexibility of the back-bone in the propagation steps is also documented. Hence, the isotacticity of the polymer occurs due to a chain-end control mechanism. The highest reactivity in the present system is obtained with the homosalen ligand with 2.2-dimethyl substituents in the backbone (ArCH=NCH2CMe2CH2N=CHAr), whereas tBuMe2Si substituents at the 3-positions of the salicylidene moieties lead to the highest selectivity (Pmeso,= 0.98; T m = 210°C). The ratio of the rate constants in the ROPs of racemic lactide and L-lactide is found to correlate with the stereoselectivity in the present system. The complex can be utilized in bulk polymerization, which is the most attractive in industry, although with some loss of stereoselectivity at high temperature, and the afforded polymer shows a higher melting temperature (Pmeso = 0.92, Tm up to 189°C) than that of homochiral poly(L-lactide) (Tm = 162-180°C). The "livingness" of the bulk polymerization at 130°C is maintained even at a high conversion (97-98%) and for an extended polymerization time (1-2 h).
- Nomura, Nobuyoshi,Ishii, Ryohei,Yamamoto, Yoshihiko,Kondo, Tadao
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p. 4433 - 4451
(2008/02/09)
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- Traceless Staudinger ligation of glycosyl azides with triaryl phosphines: Stereoselective synthesis of glycosyl amides
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α-Glycosyl amides can be synthesized from the corresponding O-benzyl-α-glycosyl azides using a traceless Staudinger ligation with diphenylphosphanyl-phenyl esters 4. All the phosphines employed and their phenol precursors are stable to air at 4 °C for months. Fast intramolecular trapping of the reduction intermediates results in the direct formation of the amide link, which, in turn, prevents epimerisation and allows retention of configuration at the anomeric carbon. Yields and α-selectivity are high when the reaction is performed in polar aprotic solvents. Removal of the benzyl ether protecting groups is achieved by catalytic hydrogenation. α-Glycosyl amides represent a class of virtually unexplored nonhydrolyzable monosaccharide derivatives that may find a useful application as sugar mimics. Conformational studies by NMR spectroscopy confirm that deprotected α-glycosyl amides in the gluco, galacto, and fuco series retain the normal pyranose conformation of the monosaccharide. The reaction of phosphines 4 with tetra-O-acetyl-glycosyl azides is nonstereoconservative, and β-glycosyl amides are obtained in good yields and with complete stereoselectivity starting from both α and β azides.
- Bianchi, Aldo,Bernardi, Anna
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p. 4565 - 4577
(2007/10/03)
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- Discovery and optimization of new chromium catalysts for ethylene oligomerization and polymerization aided by high-throughput screening
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High throughput screening (HTS) of a 205 member Schiff base salicylaldimine ligand library derived from salicylaldehydes bearing bulky ortho-substituents, i.e., 9-anthracenyl, 1,4,5,8-tetramethylanthracenyl or triptycenyl, reacted in-situ with (p-tolyl)CrCl2(thf)3, identified two new classes of highly active chromium based systems for the Oligomerization and polymerization of ethylene, respectively. The polymerization system comprises bidentate ortho-substituted anthracenyl Schiff bases bearing small primary or secondary alkyl imine substituents. The Oligomerization catalysts are based upon tridentate orthotriptycenyl-substituted Schiff bases with pyridylmethyl or quinolyl substituents. Validation tests confirmed polymerization productivities of up to 3000 g·mmol-1h-1bar-1 for the polymerization catalyst systems while the oligomerization catalysts gave productivities up to 10 000 g·mmol-1h-1bar -1. Key catalyst precursors have been characterized by X-ray crystallography.
- Jones, David J.,Gibson, Vernon C.,Green, Simon M.,Maddox, Peter J.,White, Andrew J. P.,Williams, David J.
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p. 11037 - 11046
(2007/10/03)
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- Application of directed orthometalation toward the synthesis of aryl siloxanes
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A selection of ortho-substituted aryl siloxanes have been prepared by directed orthometalation protocols. These siloxanes can be prepared in high yields and purity by use of a diverse selection of ortho-directing groups and electrophilic siloxane derivatives. The siloxanes are employed in palladium-catalyzed cross-coupling reactions with aryl bromides to generate unsymmetrical orthosubstituted biaryls in good to excellent yields.
- Seganish, W. Michael,DeShong, Philip
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p. 6790 - 6795
(2007/10/03)
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- Studies towards the total synthesis of mumbaistatin: Synthesis of highly substituted benzophenone and anthraquinone building blocks
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Model compounds and building blocks for a planned total synthesis of the highly potent glucose-6-phosphate (G6P) translocase inhibitor mumbaistatin (1) and structural analogs were elaborated: compound 1 represents a lead structure in the development of po
- Kaiser, Florian,Schwink, Lothar,Velder, Janna,Schmalz, Hans-Günther
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p. 3201 - 3217
(2007/10/03)
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- Practical approach to the Meerwein-Ponndorf-Verley reduction of carbonyl substrates with new aluminum catalysts
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Simple mixing of Al(OiPr)3 with the requisite ligand 1 in CH2Cl2 at room temperature smoothly generates the new, powerful aluminum catalyst 2, which efficiently catalyzes Meerwein-Ponndorf-Verley (MPV) reduction of various carbonyl substrates under mild conditions (see scheme). Scale-up experiments highlight the potential of the new MPV reduction procedure for practical use.
- Ooi, Takashi,Ichikawa, Hayato,Maruoka, Keiji
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p. 3610 - 3612
(2007/10/03)
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- Efficient deprotection of phenol methoxymethyl ethers using a solid acid catalyst with Wells-Dawson structure
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Deprotection of various phenols from their respective methoxymethyl ethers using an heteropolyacid catalyst was studied. The catalyst was the Wells-Dawson heteropolyacid, used both in bulk or supported on silica. Yields were high to quantitative after less than one hour reaction time and the catalyst was easily recoverable and reusable.
- Romanelli,Autino,Baronetti,Thomas
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p. 1006 - 1011
(2007/10/03)
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- Methoxymethylation of alcohols, phenols, and avermectin aglycones using MOM-2-pyridylsulfide
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Methoxymethyl-2-pyridylsulfide (MOM-ON) is an effective methoxymethylating reagent when used in conjunction with AgOTf, NaOAc, and THF. A wide range of MOM ethers are produced from corresponding phenols and alcohols, including tertiary and allylic alcohols, in good yields and under mild, neutral conditions. This method is also effective for the methoxymethylation of avermectin aglycones.
- Marcune,Karady,Dolling,Novak
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p. 2446 - 2449
(2007/10/03)
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- Ring transformation of glycidic amides with ortho-metalated phenols to enantiopure 3-hydroxychromanones
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A novel access to hitherto unknown enantiopure 2-alkylchroman-4-ones 10 was found by a reaction of ortho-metalated O-MOM-protected phenols with Weinreb amides 8 of enantiopure cis- or trans-glycidic acids. Upon acidic hydrolysis, the resulting o-MOMO-benz
- Woydowski,Ziemer,Liebscher
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p. 3489 - 3491
(2007/10/03)
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- Covalent modification of cyclooxygenase-2 (COX-2) by 2-acetoxyphenyl alkyl sulfides, a new class of selective COX-2 inactivators
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All of the selective COX-2 inhibitors described to date inhibit the isoform by binding tightly but noncovalently at the substrate binding site. Recently, we reported the first account of selective covalent modification of COX-2 by a novel inactivator, 2-acetoxyphenyl hept-2-ynyl sulfide (70) (Science 1998, 280, 1268-1270). Compound 70 selectively inactivates COX-2 by acetylating the same serine residue that aspirin acetylates. This paper describes the extensive structure-activity relationship (SAR) studies on the initial lead compound 2-acetoxyphenyl methyl sulfide (36) that led to the discovery of 70. Extension of the S-alkyl chain in 36 with higher alkyl homologues led to significant increases in inhibitory potency. The heptyl chain in 2-acetoxyphenyl heptyl sulfide (46) was optimum for COX-2 inhibitory potency, and introduction of a triple bond in the heptyl chain (compound 70) led to further increments in potency and selectivity. The alkynyl analogues were more potent and selective COX-2 inhibitors than the corresponding alkyl homologues. Sulfides were more potent and selective COX-2 inhibitors than the corresponding sulfoxides or sulfones or other heteroatom-containing compounds. In addition to inhibiting purified COX-2, 36, 46, and 70 also inhibited COX-2 activity in murine macrophages. Analogue 36 which displayed moderate potency and selectivity against purified human COX-2 was a potent inhibitor of COX-2 activity in the mouse macrophages. Tryptic digestion and peptide mapping of COX-2 reacted with [1-14C-acetyl]-36 indicated that selective COX-2 inhibition by 36 also resulted in the acetylation of Ser516. That COX-2 inhibition by aspirin resulted from the acetylation of Ser516 was confirmed by tryptic digestion and peptide mapping of COX-2 labeled with [1- 14C-acetyl]salicyclic acid. The efficacy of the sulfides in inhibiting COX- 2 activity in inflammatory cells, our recent results on the selectivity of 70 in attenuating growth of COX-2-expressing colon cancer cells, and its selectivity for inhibition of COX-2 over COX-1 in vivo indicate that this novel class of covalent modifiers may serve as potential therapeutic agents in inflammatory and proliferative disorders.
- Kalgutkar, Amit S.,Kozak, Kevin R.,Crews, Brenda C.,Hochgesang Jr., G. Phillip,Marnett, Lawrence J.
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p. 4800 - 4818
(2007/10/03)
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- Synthesis of (-)-Monoterpenylmagnolol and Magnolol
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(-)-Monoterpenylmagnolol (3) was synthesized in eight steps from (+)-3,9-dibromocamphor (4) and the bis(methoxymethyl) ether (22) of 3-(4-hydroxyphenyl)-1-propanol.Fragmentation of an endo-3-aryl-9-bromocamphor (27) provided the correct absolute stereochemistry.In this total synthesis, dissolving metal conditions were developed to reduce enol phosphate and isopropenyl functions without concomitant reduction of an attached phenol.Palladium(0)-catalyzed cross-coupling of an arylzinc chloride with 4-allyl-2-iodophenyl methoxymethyl ether (34) provided the desired tricyclic 1,2,3,5-tetrasubstituted biaryl 41 in fair yield without optimization and with little isomerization of the allyl group.Magnolol (1) was also synthesized by aryl coupling of 34 and the methoxymethyl ether of 4-allyl-2-lithiophenol via the zinc chloride method as above, as well as from 5,5'-dibromo-2,2'-dimethoxybiphenyl (37) by allylation with allyltributylstannane followed by ether cleavage.
- Agharahimi, Mohamad R.,LeBel, Norman A.
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p. 1856 - 1863
(2007/10/02)
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- A Palladium-Catalyzed Intramolecular Arene-Triflate Coupling for the Synthesis of Fluoranthrenes and Benzofluoranthrenes
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A method for the preparation of fluoranthrenes and benzofluoranthrenes from aryl bromides and aryl methoxymethyl ethers is described.The key step in this synthesis is an intramolecular triflate-arene coupling mediated by bis(triphenylphosphine)palladium(II)chloride.Fluoranthrene, benzofluoranthrene, benzofluoranthrene, and indenopyrene were prepared in yields of 84-91percent.The regiospecific synthesis of substituted benzofluoranthrenes was demonstrated by the preparation of 6-fluorobenzofluoranthrene (72percent yield) and 5- and 6-methoxybenzofluoranthrene in yields of 73percent and 62percent respectively when the reaction was conducted in the presence of excess triphenylphosphine.Key Words: synthesis; palladium; triflate; fluoranthrene; benzofluoranthrene
- Rice, Joseph E.,Cai, Zhen-Wei
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p. 1663 - 1678
(2007/10/02)
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- Novel ortho-Alkoxy-Substituted Phosphorus Ylides and Their Stereoselectivity in Wittig Reactions
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The stereochemistry of the reactions between tris(2-methoxymethoxypheny)phosphonioethanide (1f), -butanide (2f), and -phenyl-methanide (3f) and a variety of aldehydes was investigated.Ylides having a β-unbranched aliphatic sidechain, such as 2f, and saturated straight-chain aldehydes give olefins with unprecedented cis-selectivity (cis/trans ca. 200:1).
- Jeganathan, Suruliappa,Tsukamoto, Masamitsu,Schlosser, Manfred
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p. 109 - 111
(2007/10/02)
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- PHOTOLACTONIZATION: A NOVEL SYNTHETIC ENTRY TO MACROLIDES
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o-Quinol acetates, hydroxyalkylated at C(6), are easily accessible from simple phenols by Wessely acetoxylation (preferentially catalyzed by BF3).On UV irradiation (in the presence of an appropriate tertiary amine), they are smoothly converted to macrocyclic lactones.Subtle conditions have been elaborated to load to high overall yields, and the scope of the conversion of phenols to macrolides has been elucidated.
- Quinkert, Gerhard,Billhardt, Uta-Maria,Jakob, Harald,Fischer, Gerd,Glenneberg, Juergen,et al.
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p. 771 - 821
(2007/10/02)
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- Preparation d'acetals fonctionnels
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Functional acetals can be prepared either by reaction of functional organomagnesium compounds with the mixed orthoformate C6H5O-CH()C2H5)2 or by reaction of carbonyl compounds with the acetylenic lithium compounds Li-CC-(CH2)n-CH(OC2H5)2 (n=0,1).
- Barbot, Francis,Miginiac, Philippe
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- Mechanism of Reactions of N-(Methoxymethyl)-N,N-dimethylanilinium Ions with Nucleophilic Reagents
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The prediction that the oxocarbonium ion derived from formaldehyde should have a "lifetime" of ca. 10-15 s that gives rise to an enforced preassociation or concerted reaction mechanism has been tested by examining the reactions of N-(methoxymethyl)-N,N-dimethylanilinium ions in water in the presence of added nucleophilic reagents.These compounds undergo well-behaved second-order reactions with nucleophiles and give the amount of substitution product that is expected from the rate increase in the presence of nucleophile.Structure-reactivity correlations exhibit behavior intermediate between that expected for SN2 (Swain-Scott) and carbonium ion (N+) reactions.The small values of s = 0.3 and βnuc = 0.14 and large values of β1g = -0.7 to -0.9 indicate a transition state that can be described either as an open transition state for SN2 displacement or as an oxocarbonium ion that is stabilized by weak interactions with the entering and leaving groups.Secondary α-deuterium isotope effects for the second-order reactions range from (kH/kD)/D = 0.99 for fluoride ion to 1.18 for iodide ion.Solvolysis and the second-order reaction with n-propylamine exhibit values of ΔS(ex) = -1.2 and -2.1 cal K-1 mol-1, respectively, and display similar changes in rate in mixed water-alcohol solvents.It is suggested that the lifetime of the carbonium ion species in the presence of nucleophiles is so short that the reaction mechanism must be concerted.
- Knier, Barry L.,Jencks, William P.
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p. 6789 - 6798
(2007/10/02)
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- Process for methoxymethylation of phenolic hydroxyl groups
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A process for preparing methoxymethyl ethers of phenols utilizing dimethoxy methane is described. The thus-protected phenols are useful as intermediates in a variety of reaction sequences.
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