- COMPARAISON ENTRE LE ROLE DE L'EAU ET CELUI D'UN ETHER COURONNE DANS LE CADRE DE LA REACTION DE WITTIG REALISEE EN MILIEU HETEROGENE : LIQUIDE-SOLIDE
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The similar results issued from the use of water and the 18-crown-6 ether for the Wittig reaction (in liquid-solid two-phase system) allowed us to obtain vary high yields in olefin starting from aromatic as well as aliphatic aldehydes.
- Delmas, M.,Bigot, Y. Le,Gaset, A.
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- Synthesis of renewable alkylated naphthalenes with benzaldehyde and angelica lactone
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Herein, we report a new route for the synthesis of renewable alkylated naphthalenes (ANs) with benzaldehyde and angelica lactone, two platform compounds that can be derived from lignocellulose.
- Cong, Yu,Li, Guangyi,Li, Ning,Wang, Aiqin,Wang, Ran,Wang, Xiaodong,Xu, Jilei,Zhang, Tao
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supporting information
p. 5474 - 5480
(2021/08/16)
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- Stereoselective Rhodium-Catalyzed Isomerization of Stereoisomeric Mixtures of Arylalkenes
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A new efficient method for the synthesis of a high ratio of E -alkenes from E / Z mixtures of alkenes with B 2pin 2in the presence of a rhodium catalyst is described. This reaction features mild reaction conditions, broad functional group tolerance, and highly great application potential.
- Yang, Hongxuan,Dong, Wenke,Wang, Wencan,Li, Tao,Zhao, Wanxiang
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supporting information
p. 2833 - 2840
(2020/10/06)
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- Highly Selective and Potent Human β-Secretase 2 (BACE2) Inhibitors against Type 2 Diabetes: Design, Synthesis, X-ray Structure and Structure–Activity Relationship Studies
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Herein we present the design, synthesis, and biological evaluation of potent and highly selective β-secretase 2 (memapsin 1, beta-site amyloid precursor protein cleaving enzyme 2, or BACE 2) inhibitors. BACE2 has been recognized as an exciting new target for type 2 diabetes. The X-ray structure of BACE1 bound to inhibitor 2 a {N3-[(1S,2R)-1-benzyl-2-hydroxy-3-[[(1S,2S)-2-hydroxy-1-(isobutylcarbamoyl)propyl]amino]propyl]-5-[methyl(methylsulfonyl)amino]-N1-[(1R)-1-phenylpropyl]benzene-1,3-dicarboxamide} containing a hydroxyethylamine isostere was determined. Based on this structure, a computational docking study was performed which led to inhibitor 2 a-bound BACE2 models. These were used to optimize the potency and selectivity of inhibitors. A systematic structure–activity relationship study led to the identification of determinants of the inhibitors’ potency and selectivity toward the BACE2 enzyme. Inhibitors 2 d [N3-[(1S,2R)-1-benzyl-2-hydroxy-3-[[(1S,2S)-2-hydroxy-1-(isobutylcarbamoyl)pentyl]amino]propyl]-N1-methyl-N1-[(1R)-1-phenylpropyl]benzene-1,3-dicarboxamide; Ki=0.031 nm, selectivity over BACE1: ≈174 000-fold] and 3 l [N1-((2S,3R)-3-hydroxy-1-phenyl-4-((3-(trifluoromethyl)benzyl)amino)butan-2-yl)-N3,5-dimethyl-N3-((R)-1-phenylethyl)isophthalamide; Ki=1.6 nm, selectivity over BACE1: >500-fold] displayed outstanding potency and selectivity. Inhibitor 3 l is nonpeptide in nature and may pave the way to the development of a new class of potent and selective BACE2 inhibitors with clinical potential.
- Ghosh, Arun K.,Brindisi, Margherita,Yen, Yu-Chen,Lendy, Emma K.,Kovela, Satish,Cárdenas, Emilio Leal,Reddy, Bhavanam Sekhara,Rao, Kalapala Venketeswara,Downs, Deborah,Huang, Xiangping,Tang, Jordan,Mesecar, Andrew D.
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p. 545 - 560
(2019/02/13)
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- New Insights into the Reaction Capabilities of Ionic Organic Bases in Cu-Catalyzed Amination
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The application of ionic organic bases in the copper-catalyzed amination reaction (Ullmann reaction) has been studied at room temperature, with sub-mol-% catalyst loadings, and with more challenging amines at elevated temperatures. The cation present in the base has been shown to have little effect on the reaction at standard catalyst and ancillary ligand loadings, whereas the choice of anion is crucial for good reactivity. A substrate scope carried out at room temperature with the best performing bases, TBAM and TBPM, showed both bases to be highly effective under these mild reaction conditions. Moreover, under sub-mol % catalyst loadings and room temperature conditions, TBPM gave good to excellent yields for a number of different amines and functionalized aryl iodides (14 examples). However, reactions involving more challenging amines gave little or no yield. By using more forceful conditions (120 °C) moderate to excellent yields of cross-coupled products containing more challenging amines was achievable using TBPM and to a lesser extent with TBAM. As part of this work a study on the stability of the organic bases at 120 °C was undertaken. TBAM is shown to decompose to give nBu3N and mono-butylmalonate at higher temperatures, and this can be correlated to a decrease in performance in the coupling reaction. The phosphonium cations in TBPM did not undergo analogous reactivity but were shown instead to experience some degree of deprotonation at the α-CH2 to generate phosphonium ylides. This however did not lead to a significantly degradation in the activity of the TBPM in the cross-coupling reaction.
- Lo, Quintin A.,Sale, David,Braddock, D. Christopher,Davies, Robert P.
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p. 1944 - 1951
(2019/02/19)
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- Alkene functionalization for the stereospecific synthesis of substituted aziridines by visible-light photoredox catalysis
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A novel strategy involving visible-light-induced functionalization of alkenes for the synthesis of substituted aziridines was developed. The readily prepared N-protected 1-aminopyridinium salts were used for the generation of N-centered radicals. This approach allowed the synthesis of aziridines bearing various functional groups with excellent diastereoselectivity under mild conditions. Moreover, this protocol was successfully applied to prepare structurally diverse nitrogen-containing frameworks.
- Yu, Wan-Lei,Chen, Jian-Qiang,Wei, Yun-Long,Wang, Zhu-Yin,Xu, Peng-Fei
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supporting information
p. 1948 - 1951
(2018/03/01)
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- Thiol Treatment Creates Selective Palladium Catalysts for Semihydrogenation of Internal Alkynes
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Surface and interfacial engineering of heterogeneous metal catalysts is effective and critical for optimizing selective hydrogenation for fine chemicals. By using thiol-treated ultrathin Pd nanosheets as a model catalyst, we demonstrate the development of stable, efficient, and selective Pd catalysts for semihydrogenation of internal alkynes. In the hydrogenation of 1-phenyl-1-propyne, the thiol-treated Pd nanosheets exhibited excellent catalytic selectivity (>97%) toward the semihydrogenation product (1-phenyl-1-propene). The catalyst was highly stable and showed no obvious decay in either activity or selectivity for over ten cycles. Systematic studies demonstrated that a unique Pd-sulfide/thiolate interface created by the thiol treatment was crucial to the semihydrogenation. The high catalytic selectivity and activity benefited from the combined steric and electronic effects that inhibited the deeper hydrogenation of C=C bonds. More importantly, this thiol treatment strategy is applicable to creating highly active and selective practical catalysts from commercial Pd/C catalysts for semihydrogenation of internal alkynes. The development of next-generation catalytic materials requires a methodological shift from trial-and-error to mechanism-directed design. It is highly desirable to build model catalyst systems with simplified structures to ensure maximized utilization of both state-of-the-art characterization tools and computational chemistry methods. In this work, thiol-treated palladium nanosheets are adopted as a model catalyst for the selective semihydrogenation of internal alkynes. Unexpectedly, thiol treatment created highly selective palladium catalysts with high activity toward the semihydrogenation reaction. The ultrathin nature of the as-prepared catalysts allows for the application of a variety of surface science and computational methods to resolve the complexity of metal-organic interfaces and thus elucidate the underlying mechanism. Driven by atomic-level understanding, we have realized practical, lead-free catalysts for semihydrogenation. Thiol treatment is demonstrated as a highly effective strategy for promoting the catalytic selectivity of Pd nanocatalysts in the hydrogenation of internal alkynes to alkenes.
- Zhao, Xiaojing,Zhou, Lingyun,Zhang, Wuyong,Hu, Chengyi,Dai, Lei,Ren, Liting,Wu, Binghui,Fu, Gang,Zheng, Nanfeng
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supporting information
p. 1080 - 1091
(2018/04/30)
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- Concavity Tuning of Intermetallic Pd-Pb Nanocubes for Selective Semihydrogenation Catalysis
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Although considerable studies on pursuing high-performance Pd-based catalysts for the semihydrogenation of alkynes have been carried out, the creation of catalyst with high activity, selectivity and stability simultaneously toward semihydrogenation reactions remains a significant challenge. Herein, for the first time we report a facile synthetic strategy to realize the intermetallic Pd-Pb nanocubes with different concave degree by selectively utilizing small molecules. These obtained Pd-Pb nanocrystals exhibit high activity in the semihydrogenation of alkynes, where their performances are highly shape- and composition-dependent with Pd-Pb concave nanocubes showing the optimized alkene selectivity of 94.6% and activity of 179.2 h-1, much higher than those of 10% Pd/C. Detailed X-ray photoelectron spectroscopy results show that the higher ratio of metallic Pd results in the higher activity for semihydrogenation of phenylacetylene and the higher ratio of Pb2+ and Pb/Pd contribute to higher styrene selectivity. The density functional theory calculations further reveal that the favorable adsorption energy of phenylacetylene and desirable desorption energy of styrene on the Pd3Pb surface are critical for the phenylacetylene semihydrogenation with excellent activity and high selectivity. Furthermore, the Pd-Pb concave nanocube can endure at least five cycles with very limited conversion and selectivity decays, representing an efficient Pd-based catalyst for selective hydrogenation and beyond.
- Zhang, Junbo,Xu, Weiwei,Xu, Lai,Shao, Qi,Huang, Xiaoqing
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p. 6338 - 6345
(2018/09/20)
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- CATALYSTS AND METHODS FOR FORMING ALKENYL AND ALKYL SUBSTITUTED ARENES
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Embodiments of the present disclosure provide for Rh(I) catalysts, methods of making alkenyl substituted arenes (e.g., allyl arene, vinyl arene, and the like), methods of making alkyl substituted arenes, and the like.
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Paragraph 0155
(2018/03/25)
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- A Pd-Cu2O nanocomposite as an effective synergistic catalyst for selective semi-hydrogenation of the terminal alkynes only
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A new type lead-free catalyst of a Pd-Cu2O nanocomposite was developed for highly selective semi-hydrogenation of alkynes. With unprecedented selectivity for the semi-hydrogenation of terminal alkynes to alkenes, we show for the first time that the catalyst only hydrogenated the terminal alkynes, i.e. did not hydrogenate the internal alkynes.
- Yang, Shuliang,Cao, Changyan,Peng, Li,Zhang, Jianling,Han, Buxing,Song, Weiguo
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supporting information
p. 3627 - 3630
(2016/03/05)
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- Improvements and Applications of the Transition Metal-Free Asymmetric Allylic Alkylation using Grignard Reagents and Magnesium Alanates
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Two new N-heterocyclic carbene (NHC) ligands have been synthesized and employed in the transition metal-free asymmetric allylic alkylation (AAA) mediated by Grignard reagents and magnesium alanates. The employment of these ligands showed high yields and improved regio- and enantioselectivity in the formation of tertiary and quaternary stereocenters. Moreover, the low catalyst loading (up to 0.3 mol%) and high scalability (up to 10 mmol) of this improved methodology provide a convenient access to biologically active compounds and synthetically valuable intermediates.
- Grassi, David,Alexakis, Alexandre
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supporting information
p. 3171 - 3186
(2015/11/03)
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- Study of the Structure-Activity Relationship in a Heterogeneous Copper-Palladium Catalysed Suzuki-Miyaura Coupling
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Abstract Copper-palladium bimetallic catalyst supported on 4 ? molecular sieve prepared with two-step wet impregnation was successfully applied in the Suzuki-Miyaura reaction. The reaction took place with a variety of substituted boronic acids as well as with a collection of iodo- and bromobenzene derivatives. In some cases steric effects had influence on the reaction, ortho-substituted iodo- or bromobenzenes gave lower yield independently from the substituent. But most m- and p-substituted iodo- and bromobenzenes showed good to excellent activity. Several biphenyls were obtained by two or even three pathways: either the boronic acid or the respective iodo- or bromobenzene was functionalised.
- Fodor, Anna,Magyar, gnes,Barczikai, Dra,Pirault-Roy, Laurence,Hell, Zoltn
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p. 834 - 839
(2015/08/06)
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- Alkene isomerization-hydroarylation tandem catalysis: Indole c2-alkylation with aryl-substituted alkenes leading to 1,1-diarylalkanes
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A cobalt-N-heterocyclic carbene catalyst generated from CoBr2, imidazolium salt, and cyclohexylmagnesium bromide was found to promote the imine-directed C2-alkylation of indoles with nonconjugated arylalkenes through a tandem alkene isomerization-hydroarylation process, affording 1,1-diarylalkanes with exclusive regioselectivity. The feasibility of the tandem catalysis was demonstrated for allyl-, homoallyl-, and bishomoallylbenzene derivatives. The catalytic system is also applicable to a variety of β-substituted styrene derivatives. Mechanistic experiments using deuterium-labeled indole substrate and Grignard reagent provided insight into the cobalt-mediated C -H activation step, which likely involves exchange of the C2-hydrogen atom of the former and the β-hydrogen atoms of the latter. ...? but thats secondary: A catalytic system consisting of CoBr2, N-heterocyclic carbene, and cyclohexylmagnesium bromide promotes the imine-directed addition of indoles to nonconjugated aryl-substituted alkenes through tandem alkene isomerization-hydroarylation, affording 1,1-diarylalkane derivatives with exclusive regioselectivity. Deuterium-labeling experiments revealed the involvement of the secondary alkyl Grignard reagent in the cobalt-mediated C -H activation process.
- Yamakawa, Takeshi,Yoshikai, Naohiko
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supporting information
p. 1242 - 1246
(2014/05/06)
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- Rhodium-on-carbon catalyzed hydrogen scavenger- and oxidant-free dehydrogenation of alcohols in aqueous media
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The efficient and catalytic dehydrogenation of alcohols is a clean approach for preparing carbonyl compounds accompanied only by the generation of hydrogen gas. We have accomplished the heterogeneous rhodium-on-carbon catalyzed dehydrogenation of secondary, as well as primary, alcohols to the corresponding ketones and carboxylic acids in water under basic conditions. This journal is the Partner Organisations 2014.
- Sawama, Yoshinari,Morita, Kosuke,Yamada, Tsuyoshi,Nagata, Saori,Yabe, Yuki,Monguchi, Yasunari,Sajiki, Hironao
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supporting information
p. 3439 - 3443
(2014/07/08)
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- Highly practical iron-catalyzed C-O cleavage reactions
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Facile iron-catalyzed cleavage of various allyl, cinnamyl and benzyl C-O linkages has been effected in the presence of ethylmagnesium chloride. The protocol is operationally simple (xylene-THF, r.t., 1 h), requires low catalyst loading (1 mol% FeCl2) and tolerates halides, esters, amines, ethers and olefins. The allyl moiety is converted to volatile hydrocarbons which renders laborious product separation unnecessary.
- Gaertner, Dominik,Konnerth, Hannelore,Von Wangelin, Axel Jacobi
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p. 2541 - 2545
(2013/09/24)
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- Bidentate hydroxyalkyl NHC ligands for the copper-catalyzed asymmetric allylic substitution of allyl phosphates with grignard reagents
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Demonstrating their potential: Bidentate alkoxy NHC ligands have been used in the copper-catalyzed asymmetric allylic alkylation of allyl phosphates with Grignard reagents (see scheme). The method provides access to tertiary and quaternary chiral centers with high regio- and enantioselectivity. The system is also applied to the synthesis of chiral E,E-dienes, a key structural motif prevalent in natural products. Copyright
- Magrez, Magaly,Le Guen, Yann,Basle, Olivier,Crevisy, Christophe,Mauduit, Marc
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supporting information
p. 1199 - 1203
(2013/02/25)
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- Copper-free asymmetric allylic alkylation with a grignard reagent: Design of the ligand and mechanistic studies
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The Cu-free asymmetric allylic alkylation, catalysed by NHC, with Grignard reagents is reported on allyl bromide derivatives with good results. The enantioselectivity was quite homogeneous (around 85 % ee) on large and various substrates, regardless of the nature of the Grignard reagent. The formation of stereogenic quaternary centres was highly regioselective for both aliphatic and aromatic derivatives with good enantiomeric excess (up to 92 % ee). The methodology developed was found to be complementary with the Cu-catalysed version. Several new NHCs were tested with improved efficiency. In addition, mechanistic studies, using NMR spectroscopy, led to the discovery of the catalytically active species. Copyright
- Grassi, David,Dolka, Chrysanthi,Jackowski, Olivier,Alexakis, Alexandre
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supporting information
p. 1466 - 1475
(2013/02/25)
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- Furanoside phosphite-phosphoroamidite and diphosphoroamidite ligands applied to asymmetric Cu-catalyzed allylic substitution reactions
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A phosphite-phosphoroamidite and diphosphoroamidite ligand library was applied in the Cu-catalyzed allylic substitution of a range of cinnamyl-type substrates using several organometallic nucleophiles. Results indicated that selectivity depended strongly on the ligand parameters (position of the phosphoroamidite group at either C-5 or C-3 of the furanoside backbone, as well as the configuration of C-3, the introduction of a second phosphoroamidite moiety, the substituents and configurations in the biaryl phosphite/ phosphoroamidite moieties), the nature of the leaving group of the substrate and the alkylating reagent. Good enantioselectivities (up to 76%) and activity combined with high regioselectivities were obtained.
- Magre, Marc,Mazuela, Javier,Dieguez, Montserrat,Pamies, Oscar,Alexakis, Alexandre
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scheme or table
p. 67 - 71
(2012/05/20)
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- Pyridazine-based N-heterocyclic carbene complexes and ruthenium-catalyzed oxidation reaction of alkenes
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[Ru2Cl(L)(CH3CN)4](PF6) 3 (1, L = 3,6-bis(N-(pyridylmethyl)imidazolylidenyl)pyridazine), [Cu3La3](PF6)3 (2, L a = 3-(N-(pyridylmethyl)imidazolylidenyl)-6-(N-(pyridylmethyl) imidazolylonyl)pyridazine), [Pd2(allyl)2L](PF 6)2 (3), [Pd2(allyl)2L b2](PF6)2 (4, Lb = N-pyridylmethylimidazole), and [NiLc2](PF 6)2 (5, Lc = 3-(N-(pyridylmethyl) imidazolylidenyl)-6-methoxylpyridazine) have been synthesized and fully characterized by NMR spectroscopy, elemental analysis, and X-ray diffraction analysis. In complex 1, ligand L binds to two Ru(II) centers, forming a well-behaved Ru2(L)Cl plane with a five-membered metallocyclic ring. Complex 2 is trinuclear, containing a triangular Cu3 unit bonded together by three 3-(N-(pyridylmethyl)imidazolylidenyl)-6-(N-(pyridylmethyl) imidazolylonyl)pyridazine, where one imidazolylidene was oxidized into imidazolone. Deprotonation reaction with Ag2O in CH3CN and CH3OH resulted in C-N cleavage of the imidazolium salt, and subsequent reaction with [Pd(allyl)Cl]2 and Ni(PPh3) 2Cl2 gave 4 and 5, respectively. Dinuclear Ru(II)-NHC complex 1 exhibits excellent catalytic activity for the oxidation of alkenes into diketones.
- Liu, Xiaolong,Chen, Wanzhi
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p. 6614 - 6622
(2012/11/06)
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- Enantioselective synthesis of tertiary and quaternary stereogenic centers: Copper/phosphoramidite-catalyzed allylic alkylation with organolithium reagents
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An efficient and highly enantioselective copper-catalyzed allylic alkylation of disubstituted allyl halides with primary and secondary organolithium reagents using phosphoramidite ligands is reported. The use of trisubstituted allyl bromides allows, for the first time, the enantioselective synthesis of all-carbon quaternary stereogenic centers with these reactive organometallic reagents.
- Fananas-Mastral, Martin,Perez, Manuel,Bos, Pieter H.,Rudolph, Alena,Harutyunyan, Syuzanna R.,Feringa, Ben L.
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supporting information; experimental part
p. 1922 - 1925
(2012/04/17)
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- Iron-catalyzed reductive dehydroxylation of benzylic alcohols using polymethylhydrosiloxane (PMHS)
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The combination of FeCl3 and PMHS is an efficient reducing system for the selective dehydroxylation of secondary benzylic alcohols, even in the presence of carbonyls, under very mild conditions. Georg Thieme Verlag Stuttgart · New York.
- Chan, Li Yan,Lim, Jazreel Seh Kai,Kim, Sunggak
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experimental part
p. 2862 - 2866
(2012/01/11)
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- Catalytic asymmetric carbong-carbon bond formation via allylic alkylations with organolithium compounds
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Carbon-carbon bond formation is the basis for the biogenesis of nature's essential molecules. Consequently, it lies at the heart of the chemical sciences. Chiral catalysts have been developed for asymmetric C-C bond formation to yield single enantiomers from several organometallic reagents. Remarkably, for extremely reactive organolithium compounds, which are among the most broadly used reagents in chemical synthesis, a general catalytic methodology for enantioselective C-C formation has proven elusive, until now. Here, we report a copper-based chiral catalytic system that allows carbon-carbon bond formation via allylic alkylation with alkyllithium reagents, with extremely high enantioselectivities and able to tolerate several functional groups. We have found that both the solvent used and the structure of the active chiral catalyst are the most critical factors in achieving successful asymmetric catalysis with alkyllithium reagents. The active form of the chiral catalyst has been identified through spectroscopic studies as a diphosphine copper monoalkyl species.
- Perez, Manuel,Fananas-Mastral, Martin,Bos, Pieter H.,Rudolph, Alena,Harutyunyan, Syuzanna R.,Feringa, Ben L.
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experimental part
p. 377 - 381
(2012/01/06)
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- DEHYDROGENATION OF CYCLOHEXANONE TO PRODUCE PHENOL
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In a process for the dehydrogenation of cyclohexanone to produce phenol, a feed comprising cyclohexanone is contacted with a dehydrogenation catalyst under dehydrogenation conditions comprising a temperature of less than 4000C and a pressure of less than 690 kPa, gauge, such 0.1 to 50 wt% of the cyclohexanone in said feed is converted to phenol and the dehydrogenation product contains less than 100 ppm by weight of alkylbenzenes.
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Page/Page column 23; 25
(2011/09/14)
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- Enantioselective copper-catalysed allylic alkylation of cinnamyl chlorides by Grignard reagents using chiral phosphine-phosphite ligands
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The copper(I)-catalysed SN2'-type allylic substitution of E-3-aryl-allyl chlorides (cinnamyl chlorides) using Grignard reagents represents a powerful method for the synthesis of compounds carrying a benzylic stereocentre. By screening a small library of modular chiral phosphine-phosphite ligands a new copper(I)-based catalyst system was identified which allows the performance of such reactions with exceptional high degrees of regio- and enantioselectivity. Best results were obtained using TADDOLderived ligands (3 mol%), copper(I) bromide?dimethyl sulfide (CuBr?SMe2) (2.5 mol%) and methyl tert-butyl ether (MTBE) as a solvent. Various (1- alkyl-allyl)benzene derivatives were prepared with up to 99% ee (GC) in isolated yields of up to 99%. In most cases the product contained less than 3% of the linear regioisomer (except for ortho-substituted substrates). Both electron-rich and electron-deficient cinnamyl chlorides were successfully employed. The absolute configuration of the products was assigned by comparison of experimental and calculated CD spectra. The substrates were prepared from the corresponding alcohols by reaction with thionyl chloride. Initially formed mixtures of regioisomeric allylic chlorides were homogenised by treatment with CuBr?SMe2 (2.5 mol%) in the presence of triphenyl phosphine (PPh3) (3 mol%) in MTBE at low temperature to give the pure linear isomers. In reactions with methylmagnesium bromide (MeMgBr) an ortho-diphenylphosphanyl-arylphosphite ligand with an additional phenyl substituent in ortho'-position at the aryl backbone proved to be superior. In contrast, best results were obtained in the case of higher alkyl Grignard reagents (such as ethyl-, n-butyl-, isopropyl-, and 3-butenylmagnesium bromides) with a related ligand carrying an isopropyl substituent in ortho'-position. The method was tested on a multimmol scale and is suited for application in natural product synthesis.
- Loelsberg, Wibke,Ye, Shute,Schmalz, Hans-Guenther
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supporting information; experimental part
p. 2023 - 2031
(2010/10/21)
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- Chelating hydroxyalkyl NHC as efficient chiral ligands for room-temperature copper-catalyzed asymmetric allylic alkylation
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The application of chiral chelating hydroxy NHC in copper-catalyzed asymmetric allylic alkylation (Cu-AAA) involving various dialkylzincs and allylic phosphate substrates is reported here. From a library of 11 chiral chelating hydroxyalkyl NHC, a fine-tuning has been done to identify the best architectural features enabling to produce the expected γ-adducts in total regioselectivity, good isolated yields, and excellent enantioselectivities (ranging from 93% to >98% ee). Georg Thieme Verlag Stuttgart New York.
- Jennequin, Thomas,Wencel-Delord, Joanna,Rix, Diane,Daubignard, Julien,Crevisy, Christophe,Mauduit, Marc
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supporting information; experimental part
p. 1661 - 1665
(2010/08/22)
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- Copper-free asymmetric allylic alkylation with grignard reagents
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(Chemical Equation Presented) Open wide and say AAA: The copper-free asymmetric allylic alkylation reaction of Crignard reagents, catalyzed by N-heter-ocyclic carbenes, is reported for allyl bromide derivatives. This reaction offers good enantioselectivit
- Jackowski, Olivier,Alexakis, Alexandre
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scheme or table
p. 3346 - 3350
(2010/07/15)
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- Highly enantioselective copper-catalyzed allylic alkylation with atropos phosphoramidites bearing a D2-symmetric biphenyl backbone
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A novel class of atropos dibridged biphenyl phosphoramidites bearing a D2-symmetric biphenyl backbone was prepared and applied as chiral ligands in the copper-catalyzed allylic alkylation with Grignard reagent. The alkylation products were obtained in quantitative yields with high regioselectivities up to 94:6 of SN2′/SN2 ratio and enantiomeric excesses up to 91.1% for SN2′ products. The unique D2-symmetric backbone ligands have the advantages of easy preparation and sufficient reusability of their key intermediates from the undesired isomers.
- Fang, Fang,Zhang, Hui,Xie, Fang,Yang, Guoqiang,Zhang, Wanbin
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experimental part
p. 3593 - 3598
(2010/06/21)
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- Copper-catalyzed asymmetric allylic substitution with aryl and ethyl Grignard reagents
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Phenyl- and ethyl-magnesium bromides undergo regioselective asymmetric allylic substitution with high enantioselectivity under the catalysis of chiral amidophosphane-copper(i) complexes. The Royal Society of Chemistry.
- Selim, Khalid B.,Yamada, Ken-Ichi,Tomioka, Kiyoshi
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supporting information; experimental part
p. 5140 - 5142
(2009/03/11)
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- Catalytic enantioselective synthesis of vicinal dialkyl arrays
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(Chemical Equation Presented) With a consecutive "asymmetric allylic alkylation (AAA)/cross-metathesis (CM)/conjugate addition (CA)" protocol it is possible to synthesize either stereoisomer of compounds containing a vicinal dialkyl array with excellent stereoselectivity. The versatility of this protocol in natural product synthesis is demonstrated in the preparation of the ant pheromones faranal and lasiol.
- Van Zijl, Anthoni W.,Szymanski, Wiktor,Lopez, Ferrnando,Minnaard, Adriaan J.,Feringa, Ben L.
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supporting information; experimental part
p. 6994 - 7002
(2009/05/09)
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- 3,5-Bis(trifluoromethyl)phenyl sulfones in the direct Julia-Kocienski olefination
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3,5-Bis(trifluoromethyl)phenyl (BTFP) sulfones 7 have been employed in the Julia-Kocienski olefination reaction with carbonyl compounds. Sulfones 7 are readily prepared in high yields (64-97%) from commercially available 3,5-bis(trifluoromethyl)thiophenol through an alkylation/oxidation two-step sequence. The stability of metalated BTFP sulfones has been studied and compared with heteroaryl benzothiazol-2-yl (BT), 1-phenyl-1H-tetrazol-5-yl (PT), and 1-tert-butyl-1H-tetrazol-5-yl (TBT) sulfones 9-11 under different reaction conditions. The Julia-Kocienski olefination between alkyl BTFP sulfones 7 and a wide variety of aldehydes affords the corresponding 1,2-disubstituted alkenes and dienes in good yields and stereoselectivities. This one-pot protocol can be performed using KOH at room temperature or the phosphazene bases P2-Et and P4-t-Bu at -78 °C or rt and has been successfully used in a high-yielding and stereoselective synthesis of various methoxylated stilbenes such as trimethylated resveratrol. These new reaction conditions for the Julia-Kocienski olefination reaction have been also studied with BT, PT, and TBT sulfones, giving poorer results. Methylenation of aliphatic and aromatic aldehydes, ketones, and 1,2-dicarbonyl compounds is carried out through the modified Julia olefination using BTFP methyl sulfone 7d to give terminal alkenes and dienes. Mechanistic studies of the olefination reaction between benzyl BTFP sulfone 7a and aromatic aldehydes performed by KOH-induced Smiles rearrangement of stereodefined syn- and anit-β-hydroxyalkyl BTFP sulfones indicate that the stereocontrol of the reaction is determined in the elimination step. 2005 American Chemical Society.
- Alonso, Diego A.,Fuensanta, Monica,Najera, Carmen,Varea, Montserrat
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p. 6404 - 6416
(2007/10/03)
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- Cu-catalyzed asymmetric allylic alkylations of aromatic and aliphatic phosphates with alkylzinc reagents. An effective method for enantioselective synthesis of tertiary and quaternary carbons
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Efficient enantioselective Cu-catalyzed allylic alkylations of aromatic and aliphatic allylic phosphates bearing di- and trisubstituted olefins are disclosed. Enantioselective C-C bond forming reactions are promoted in the presence of 10 mol % readily available chiral amino acid-based ligand (5 steps, 40% overall yield synthesis) and 5 mol % (CuOTf)2·C 6H6. Reactions deliver tertiary and quaternary stereogenic carbon centers regioselectively and in 78-96% ee. Data regarding the effect of variations in ligand structure on the efficiency and enantioselectivity of the alkylation process, as well as a mechanistic working model, are presented. The suggested model involves a dual role for the chiral Cu complex: association of the Cu(I) center to the olefin is facilitated by a two-point binding between the carbonyl of the ligand's amide terminus and the P=O of the substrate.
- Kacprzynski, Monica A.,Hoveyda, Amir H.
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p. 10676 - 10681
(2007/10/03)
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- Fluorous solvent as a new phase-screen medium between reagents and reactants in the bromination and chlorination of alcohols
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(Matrix presented) A perfluorohexane layer regulates the rate of reagent transport in the bromination and chlorination of alcohols. A fluorous triphasic U-tube method is effective for lighter reagents; the thionyl chloride layer (yellow) vanishes, and the chlorides are obtained from the right top organic layer in the chlorination of alcohols.
- Nakamura, Hiroyuki,Usui, Taikou,Kuroda, Hirokazu,Ryu, Ilhyong,Matsubara, Hiroshi,Yasuda, Shinji,Curran, Dennis P.
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p. 1167 - 1169
(2007/10/03)
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- Sequestered alkyllithiums: Why phenyllithium alone is suitable for betaine-ylide generation
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The key step in the trans-selective modification of the Wittig reaction is the α-lithiation of the lithium bromide coordinated ylide - aldehyde adduct (the so-called "P-betaine"). Only phenyllithium effects this deprotonation rapidly and cleanly. Alkyllithiums (in particular, butyl-, sec-butyl-, and tert-butyllithium) react only sluggishly and incompletely, being tied up in very stable mixed aggregates with the lithium alkoxide part of the betaines.
- Wang, Qian,Deredas, Dariusz,Huynh, Cyril,Schlosser, Manfred
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p. 570 - 574
(2007/10/03)
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- Reaction of trialkyl(dibromomethyl)silanes or 1,2-bis(dibromomethyl)benzene with triorganomanganates. A facile and selective synthesis of alkenylsilanes and 1,2-diaryl-1,2-dihydrobenzocyclobutenes
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Treatment of trialkyl(dibromomethyl)silanes with trialkylmanganates, derived from manganese(II) chloride and three molar amounts of Grignard reagents or alkyllithiums, provided (E)-1-trialkylsilyl-1-alkenes with high stereoselectivity in good yields. The reaction of trialkyl(dibromomethyl)silanes with alkylmagnesium halides proceeded in the presence of a catalytic amount of manganese(II) chloride. Treatment of 1,2-bis(dibromomethyl)benzene with triphenylmanganate gave 1,2-diphenyl-1,2-dihydrobenzocyclobutene.
- Kakiya,Shinokubo,Oshima
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p. 2139 - 2147
(2007/10/03)
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- Alkyl migrations in phosphonium compounds with α,β-unsaturated groups
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Alkaline hydrolysis of tributylstyrylphosphonium bromide along with the usual products yields dibutyl(1-butyl-2-phenylethyl)phosphine oxide and 1-phenyl-1-pentene. The results confirm the previously suggested scheme of the reaction of tributylphosphine with phenylacetylene in the presence of water. The reaction of tributylphosphine with diphenylacetylene in the presence of water and also the alkaline hydrolysis of tributyl(phenylethynyl)phosphonium bromide are not accompanied by α-butyl migration. Phosphobetaine formed from tributylphosphine and isopropenylacetylene by the reaction with water transforms into two isomeric phosphine oxides via protonation of β- and δ-carbon atoms. Stereospecific synthesis of E and Z isomers of (diphenyl)(methyl)(2-phenylvinyl)phosphonium bromide is carried out.
- Ovakimyan,Barsegyan,Indzhikyan
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p. 1594 - 1597
(2007/10/03)
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- Zinc-promoted reactions. 8. The effect of ring strain in the reduction of 1,2-dibenzoylcycloalkanes
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Ring cleavage was the main route in the Zn reduction of 1 in neat AcOH, while selective carbonyl reduction predominated in the presence of LiCl. The less strained 2 underwent only carbonyl reduction with Zn/AcOH. The Clemmensen reduction of both 1 and 2 resulted mainly in acyclic products. The unstrained 3 was fairly resistant towards reduction, and did not undergo ring cleavage.
- Di Vona, Maria Luisa,Luchetti, Luciana,Rosnati, Vittorio
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p. 2949 - 2954
(2007/10/02)
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- A Dynamic Equilibrium of Oxaphosphetanes
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The course of the Wittig reaction was investigated by rapid injection NMR spectroscopy.Rate constants for the formation of oxaphosphetanes were determined.A new dynamic equilibrium of oxaphosphetanes was observed for the first time.The solvent and substituent dependence of the new effect was investigated.By labeling various oxaphosphetanes with 13C and 17O the lithium salt dependence of the new equilibrium was shown.A lithium adduct of oxaphosphetanes under these conditions is proposed. - Key Words: Wittig reaction / Rapid injection NMR / Dynamic NMR / Oxaphosphetanes
- Geletneky, Christian,Foersterling, Frank-Holger,Bock, Willi,Berger, Stefan
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p. 2397 - 2402
(2007/10/02)
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- Untersuchungen im Wittig-System nach einem ordnenden Konzept auf der Basis alternativer Prinzipien
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Our results show that the stereoselectivity of the Wittig-reaction can be controlled by the variation of substituents in accord with the ORDERING CONCEPT OF ALTERNATIV PRINCIPLES (individual pairs, known and unknown classes of alternatives).The "all-phenyl Wittig-system" having three phenyl groups on phosphorous two in ylid- and aldehyd-position was chosen as a standard for our investigations.Differentiation in ylid-position and compensation on phosphorous and aldehyd-position were observed by the comparison of "patterns".Consequently, most of the selectivity rules of Wittig-reactions can be explained by the differentiation through alternatives in the ylid-position.Inversion or conservation of the "patterns" of measured data points to the variation in structure of starting materials, reaction rates and selectivities.Amount-controls were also described in certain systems.
- Bandmann, Heinz,Bartik, Tamas,Bauckloh, Sylvia,Behler, Ansgar,Brille, Frank,et al.
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p. 193 - 204
(2007/10/02)
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- Palladium-Assisted (Z)-(E) Isomerization of Styrenes
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It is shown that treatment of stereoisomeric mixtures of styrenes with a catalytic amount of bis(acetonitrile)dichloropalladium(II) achieves smooth stereoisomerization of the (Z)-isomers to the (E)-isomers.
- Giles, Robin G. F.,Son, Vanessa R. Lee,Sargent, Melvyn V.
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p. 777 - 781
(2007/10/02)
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- Norrish Type I and Type II Reactions of Ketones as Photochemical Probes of the Interior of Zeolites
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The Norrish type I and type II reactions of alkylbenzoin ethers, alkyldeoxybenzoins and α-alkyldibenzyl ketones included within the microporous structures of zeolites X and Y have been investigated.Product distributions varied significantly from that observed in benzene.In addition, it differed between various alkali-metal cation-exchanged samples.These variations are interpreted to result from the restriction offered by the zeolite micropores on the motions of the adsorbed organic molecule.Although this study is restricted to ketones, the knowledge gained is expected to be of general value.
- Ramamurthy, V.,Corbin, D. R.,Eaton, D. F.
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p. 5269 - 5278
(2007/10/02)
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- MODIFICATION OF PHOTOCHEMICAL REACTIVITY BY ZEOLITES: ROLE OF CATIONS IN CONTROLLING THE BEHAVIOR OF RADICALS GENERATED WITHIN FAUJASITES.
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α-Alkyldibenzylketones included in cation exchanged faujasite type zeolites show photobehavior different from that in isotropic organic solvents.Rearrangement and disproportionation which do not contribute in solution are the major processes within the cavities of faujasites.Cation size plays a major role in controlling the pathway pursued by the primary and the secondary radical pair.
- Ramamurthy, V.,Corbin, D. R.,Eaton, D. F.,Turro, N. J.
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p. 5833 - 5836
(2007/10/02)
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- 3,5-DIMETHYL-4-ISOTHIAZOLYLMAGNESIUM IODIDE AND ITS REACTIONS WITH SOME ELECTROPHILIC REAGENTS
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As a route to 4-alkyl-, 4-alkenyl- and 4-hydroxyalkyl-isothiazoles, 3,5-dimethyl-4-isothiazolylmagnesium iodide has been obtained, and its reactions with organic halides, oxocompounds and nitriles have been studied.
- Alberola, Angel,Alonso, Felisa,Cuadrado, Purificacion,Sanudo, Maria Carmen
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p. 1207 - 1216
(2007/10/02)
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- Synthesis of Alkenes via Peterson Reaction
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The α-phenylthiosilanes (2) have been used to prepare the α-silyl anions (1) by reaction with lithium naphthalenide; subsequent condensation with a carbonyl compound gave the alkene (8) via the Peterson reaction.The α-phenylthiosilanes (2) were prepared from n,n-bis(phenylthio)acetals (4) by reaction with lithium naphthalenide and chlorotrimethylsilane.The n,n-bis(phenylthio)acetals (4) were obtained, in turn, from 1,1-bis(phenylthio)acetals (5) by anion formation with butyl-lithium-N,N,N',N'-tetramethylethylenediamine complex in hexane followed by reaction with an alkyl halide.The Peterson reaction was also used to prepare vinyl sulphides (9) and vinyl sulphones (13).
- Ager, David J.
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p. 183 - 194
(2007/10/02)
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- Dramatic Concentration Depedence of Stereochemistry in the Wittig Reaction. Examination of the Lithium Salt Effect
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The stereochemistry for Wittig reactions of butylidenetriphenylphosphorane (1) with benzaldehyde and hexanal was examined in detail with regard to concentration effects.For the reaction of 1 and benzaldehyde in the presence of LiBr, the proportion of trans-oxaphosphetane (measured by low-temperature 31P NMR) and (E)-alkene increased with respect to increasing reaction concentration in THF, approaching limiting values in a hyperbolic manner.Stereochemical drift, i.e., exaggerated production of (E)-alkene relative to trans-oxaphosphetane intermediate, was also concentration dependent, being more pronounced at higher concentrations.Experiments with varying amounts of lithium cation, and with NaBr instead of LiBr, demonstrated that this phenomenon is associated with the concentration of Li ion, which is increasingly sequestered by the THF solvent at higher dilution.In Me2SO, the dependence of alkene stereochemistry on concentration was greatly attenuated.In toluene, the concentration effect was inverted to some extent; more (E)-alkene was formed at higher dilution ( no betaines were observed by 31P NMR at low temperature).The reaction of 1 with hexanal in THF, in the presence of LiBr, exhibited a concentration depedence similar to that observed for the reaction with benzaldehyde ( at the oxaphosphetane stage).The rates of the lithium-dependent ("catalyzed") and lithium-independent ("uncatalyzed") reactions in the original carbon-carbon bond-forming step are ranked relative to each other, based on their concentration dependence in THF.For 1 and benzaldehyde in THF (with LiBr present), the catalyzed (k'') and uncatalyzed (k') rates constant have the following relative order: k1'' = 5.2 and k2'' = 2.5 mol-2*dm6*s-1; k1' = 1.0 and k2' -1*dm3*s-1 (see Scheme I and Appendix).Thus, at the representative concentrations of 0.05, 0.20, and 0.50 M, the original carbon-carbon bond-forming step in this Wittig reaction is 27percent, 61percent, and 79percent lithium catalyzed, respectively.
- Reitz, Allen B.,Nortey, Samuel O.,Jordan, Alfonzo D.,Mutter, Martin S.,Maryanoff, Bruce E.
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p. 3302 - 3308
(2007/10/02)
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- Decomposition et proprietes electrophiles des carbenoides monohalogenes non fonctionnels
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Geminal substitution of a carbon atom by a halogen atom and a lithium atom gives rise to electrophilic properties and great instability to the corresponding α-monohalogenoalkyllithium.From NMR data, it appears that the functional carbon atom exhibits an electron deficiency in connection with an intramolecular halogen-lithium coordination.This description is in agreement with the structure proposed for LiCH2F on the basis of "ab initio" calculations.Electronic and steric effects of the other substituents of the functional carbon atom and the influence of the reaction medium (basicity of solvents, Lewis acidity of associated salts) on the variation of electrophilic and nucleophilic behaviour and stability of carbenoids (mono, di, trihalogeno) can be rationalized on the basis of this metallocarbenium halogenide structure.
- Villieras, J.,Rambaud, M.,Kirschleger, B.,Tarhouni, R.
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p. 837 - 843
(2007/10/02)
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- A SIMPLIFIED WITTIG SYNTHESIS USING A SOLID-LIQUID TRANSFER PROCESS: V - THE USE OF FORMAMIDE AS CATALYST FOR THE SYNTHESIS OF ALKENES FROM CARBONYL COMPOUNDS.
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A new synthetic metod of preparation of alkenes with good yields, using formamide as phase transfer catalyst is described.
- Bigot, Y. Le,Hajjaji, N.,Rico, I.,Lattes, A.,Delmas, M.,Gaset, A.
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p. 495 - 498
(2007/10/02)
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- STEREOCHEMICAL OBSERVATIONS ON THE WITTIG REACTION OF OXIDO PHOSPHONIUM YLIDES WITH ALDEHYDES
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The reaction of aldehydes with oxido ylides shows a dramatic dependence of alkene stereochemistry on the distance between oxygen and phosphorus atoms; ylides with proximal O and P atoms favor production of E alkenes.The high E stereoselectivity with γ-oxido ylides is not mainly attributable to intramolecular proton-exchange in a Wittig intermediate.
- Maryanoff, Bruce E.,Reitz Allen B.,Duhl-Emswiler, Barbara A.
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p. 2477 - 2480
(2007/10/02)
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- Anwendungen der Phasentransfer-Katalyse 17. Wittig-Reaktionen in verschiedenen Zweiphasen-Systemen
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EINE vergleichende Untersuchung von Wittig-Reaktionen unter Phasentransfer-Katalyse (PTC) bei verschiedenen Bedingungen wurde durchgefuehrt.Es erwies sich als unnoetig, ausser den Phosphoniumsalzen einen PTC-Katalysator zu verwenden.Mechanistische Konsequenzen dieses Befundes werden diskutiert.Als ein besonders geeignetes Basensystem stellte sich Kalium-tert-butoxid in Benzol heraus.Erstmals gelang die Umzetzung von Ketonen und aliphatischen Aldehyden.Einige sehr hohe Literaturausbeuten von PTC-Wittig-Reaktionen konnten unter praeparativen Bedingungen nicht reproduziert werden.
- Dehmlow, Eckehard V.,Barahona-Naranjo, Simon
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p. 1748 - 1762
(2007/10/02)
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