- Total syntheses of (+)-adunctins C and D: Assignment of their absolute configurations
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The first total synthesis of (+)-adunctin C (ent-1) and (+)-adunctin D (2), two monoterpene-substitued dihydrochalcones isolated from Piper aduncum (Piperaceae), was achieved. A regioselective oxidative [3 + 2] cycloaddition of acylphloroglucinol with (-)-β-phellandrene was developed to construct their unique spirobenzofuran skeleton. The absolute configurations of natural adunctins 1 and 2 were thus assigned through these endeavors. This journal is
- Luo, Gan,Peng, Yu,Wang, Ya-Wen,Xiao, Jian,Zhao, Jun
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supporting information
p. 9840 - 9843
(2021/12/07)
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- Optimisation of a lithium magnesiate for use in the non-cryogenic asymmetric deprotonation of prochiral ketones
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A study has been conducted to determine whether lithium magnesiates are feasible candidates for the enantioselective deprotonation of 4-alkylcyclohexanones. The commercially available chiral amine (+)-bis[(R)-1-phenylethyl]amine (2-H) was utilised to indu
- Francos, Javier,Zaragoza-Calero, Silvia,O'Hara, Charles T.
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p. 1408 - 1412
(2014/01/06)
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- Enantioselective desymmetrization of prochiral ketones via an organocatalytic deprotonation process
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The first desymmetrization of 4-substituted cyclohexanones by organocatalytic asymmetric deprotonation at low catalyst loading is reported. The combination of N,O-bis(trimethylsilyl)acetamide (BSA) and chiral quaternary ammonium aryloxide salts has been u
- Claraz, Aurelie,Oudeyer, Sylvain,Levacher, Vincent
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p. 764 - 768
(2013/07/25)
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- New potentially dhelating chiral magnesium amide bases for use in enantioselective deprotonation reactions
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A series of chiral secondary amines, incorporating a five- or six-membered heterocycle, were synthesised and used to prepare novel chiral magnesium bisamide reagents. These amide bases were subsequently applied within asymmetric deprotonation reactions to
- Kerr, William J.,Middleditch, Michael,Watson, Allan J. B.
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supporting information; experimental part
p. 177 - 180
(2011/03/22)
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- Towards energetically viable asymmetric deprotonations: Selectivity at more elevated temperatures with C2-symmetric magnesium bisamides
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A novel chiral magnesium bisamide has enabled the development of effective asymmetric deprotonation protocols at substantially more elevated temperatures. This new, structurally simple, C2-symmetric magnesium complex displays excellent levels o
- Bennie, Linsey S.,Kerr, William J.,Middleditch, Michael,Watson, Allan J. B.
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supporting information; experimental part
p. 2264 - 2266
(2011/04/12)
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- Chiral and achiral lithium amides having a fluorous ponytail: Preparation and evaluation as a recycling reagent for lithium enolate generation
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Diisopropylamine derivatives bearing a perfluoroalkyl chain were prepared and converted to the corresponding lithium amides by treatment with n-butyllithium. The fluorous lithium amides reacted with ketones to efficiently produce lithium enolates. Asymmetric deprotonation of prochiral ketones was also studied using lithium amides derived from chiral fluorous amines, which gave optical yields comparable with the parent nonfluorous chiral lithium amides. These reusable fluorous amines can be easily recovered by liquid-liquid extraction or chromatographic separation. Georg Thieme Verlag Stuttgart.
- Matsubara, Hiroshi,Maeda, Louis,Sugiyama, Hiroyuki,Ryu, Ilhyong
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p. 2901 - 2912
(2008/03/13)
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- Application of polydentate chiral amines within magnesium-mediated asymmetric deprotonation reactions
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A set of polydentate secondary amines, each containing two stereogenic centres, were prepared. These were subsequently utilised in magnesium-mediated asymmetric deprotonation reactions and excellent enantiomeric ratios were obtained (up to 94:6 er). Furth
- Bassindale, Martin J.,Crawford, James J.,Henderson, Kenneth W.,Kerr, William J.
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p. 4175 - 4179
(2007/10/03)
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- Novel enantiomerically pure heteroleptic magnesium complexes for use in enantioselective deprotonation reactions
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Two classes of heteroleptic magnesium complexes, alkylmagnesium amides RMgNR2 and aryloxymagnesium amides ROMgNR2, have been prepared and subsequently shown to be efficient bases in the enantioselective deprotonation of substituted c
- Carswell, Emma L.,Hayes, Douglas,Henderson, Kenneth W.,Kerr, William J.,Russell, Claire J.
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p. 1017 - 1021
(2007/10/03)
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- Magnesium amide base-mediated enantioselective deprotonation processes
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A novel homochiral magnesium bisamide has been readily prepared and, following careful optimisation, this species has been shown to react efficiently with a series of prochiral 4-substituted cyclohexanones in the presence of TMSCl to give the corresponding silyl enol ethers in enantiomeric ratios of up to 95:5. Additionally, the same chiral base system has been shown to be highly effective in the desymmetrisation of cis-2,6-disubstituted cyclohexanones, providing excellent levels of both conversion and enantioselection (up to >99.5:0.5 er). Furthermore, the magnesium bisamide has also been shown to mediate a kinetic resolution process with the corresponding trans-disubstituted substrates, allowing access to enantioenriched enol ethers and ketones.
- Henderson, Kenneth W,Kerr, William J,Moir, Jennifer H
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p. 4573 - 4587
(2007/10/03)
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- Stereoselective reactions. XXXIV. Enantioselective deprotonation of prochiral 4-substituted cyclohexanones using chiral bidentate lithium amides having a bulky group instead of a phenyl group on the chiral carbon
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Using chiral bidentate lithium amides having a bulky group instead of a phenyl group on the chiral carbon, enantioselective deprotonation of prochiral 4-substituted cyclohexanones in the presence of excess trimethylsilyl chloride was examined in THF in th
- Toriyama,Sugasawa,Motohashi,Tokutake,Koga
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p. 468 - 472
(2007/10/03)
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- Effect of amine structure and reaction additives on enantioselective deprotonations mediated by homochiral magnesium amide bases
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A series of novel, optically pure, Mg-bisamides have been prepared and, in turn, used to mediate enantioselective deprotonations of conformationally locked ketones. The new bases exhibit a wide range of selectivities, from poor to excellent (up to 95:5 e.
- Anderson, John D,García García, Pilar,Hayes, Douglas,Henderson, Kenneth W.,Kerr, William J.,Moir, Jennifer H.,Fondekar, Kamalesh Pai
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p. 7111 - 7114
(2007/10/03)
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- Enantioselective deprotonation reactions using a novel homochiral magnesium amide base
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A novel homochiral magnesium bisamide base system has been prepared and reacted with a series of prochiral ketones in the presence of TMSCl to give efficient formation of the corresponding enol ethers in enantiomeric ratios of up to 95:5.
- Henderson, Kenneth W.,Kerr, William J.,Moir, Jennifer H.
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p. 479 - 480
(2007/10/03)
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- New Homochiral Ligands Bearing Nonstereogenic Chirotopic Centers. Lithiated N,N′-Dialkylureas as Chiral Bases and Sterically Crowded Phosphines for Asymmetric Catalysis
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The synthesis of new homochiral pseudo-C2-symmetrical ligands of type 1 bearing a nonstereogenic chirotopic center is reported. Two such structural units are combined in the ureas 2 and 10, which proved to be useful for enantioselective deprotonation and alkylation of ketones (up to 88% ee). The monophosphine 3 induced a high enantiomeric excess in the Pd-catalyzed allylation of dimethyl malonate (up to 73% ee). Furthermore, we have shown that the achiral sterically crowded alkyl diphosphine 23 efficiently stabilized Pd(0) at high temperatures.
- Graf, Claus-Dieter,Malan, Christophe,Harms, Klaus,Knochel, Paul
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p. 5581 - 5588
(2007/10/03)
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- New chiral ligands with nonstereogenic chirotopic centers for asymmetric synthesis
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Pseudo-C2-symmetrical ligands have been prepared efficiently: The attachment of the chiral alkyl group to the heteroatom (P or N) through a nonstereogenic, chirotopic carbon center facilitates their synthesis as the configuration at this carbon atom no longer needs to be controlled. Two such ligands were combined, for example, in the base 1, which is especially useful for asymmetric deprotonation of prochiral ketones [Eq. (a)].
- Graf, Claus-Dieter,Malan, Christophe,Knochel, Paul
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p. 3014 - 3016
(2007/10/03)
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- Stereoselective reactions, 25. Enantioselective deprotonation of prochiral 4-substituted cyclohexanones by chiral chelated lithium amides
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Enantioselective deprotonation of prochiral 4-substituted cyclohexanones (4a-d) by chiral chelated lithium amides (8a-k) in the presence of excess trimethylsilyl chloride was realized to give the corresponding chiral silyl enol ethers (6a-d) in up to 89% ee. It is shown that enantioselectivity of the reaction is dependent on the solvent used, but becomes almost independent on the solvent in the presence of HMPA. The sense of asymmetric induction can be correlated to the configuration at the chiral carbon bearing amide nitrogen of the lithium amide.
- Shirai, Ryuichi,Sato, Daisaku,Aoki, Kazumasa,Tanaka, Masahide,Kawasaki, Hisashi,Koga, Kenji
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p. 5963 - 5972
(2007/10/03)
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- Stereoselective reactions. 28. Effects of the alkyl group at the amide nitrogen of chiral bidentate lithium amides on enantioselective deprotonation reaction
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Enantioselective deprotonation of 4-substituted cyclohexanones (1a-d) by chiral bidentate lithium amides ((R)-2a-j) having an alkyl- or a fluoroalkyl substituent at the amide nitrogen was examined. (R)-2i having a 2,2,2-trifluoroethyl group at the amide nitrogen was found to be an excellent chiral base for the present deprotonation reaction. Structures of (R)-2i in solution and solid state are discussed.
- Aoki, Kazumasa,Tomioka, Kiyoshi,Noguchi, Hiroshi,Koga, Kenji
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p. 13641 - 13656
(2007/10/03)
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- Stereoselective reactions. 29. Lithium-hydrogen interchange between achiral tridentate lithium amides and chiral bidentate amines. An approach to catalytic enantioselective
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1H-NMR spectral studies have shown that lithium-hydrogen interchange between a chiral bidentate amine ((R)-3b) and an achiral tridentate lithium amide (5a) occurs rapidly in THF, favoring the exclusive formation of a chiral bidentate lithium am
- Yamashita, Toyoharu,Sato, Daisaku,Kiyoto, Taro,Kumar, Arvind,Koga, Kenji
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p. 16987 - 16998
(2007/10/03)
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- An approach to catalytic asymmetric deprotonation of 4-substituted cyclohexanones
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Lithium-hydrogen interchange between a chiral bidentate amine ((R)-4b) and an achiral tridentate lithium amide (8) occurs rapidly in situ, favoring the exclusive formation of a chiral bidentate lithium amide ((R)-5b). Based on this finding, catalytic asym
- Yamashita, Toyoharu,Sato, Daisaku,Kiyoto, Taro,Kumar, Arvind,Koga, Kenji
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p. 8195 - 8198
(2007/10/03)
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- Efficient and convenient syntheses of (R)-(-)-cryptone and (S)-(-)-isopropenyl-2-cyclohexen-1-one
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Starting with (+)-nopinone (3); (R)-(-)-cryptone (1) and (S)(-)-4-isopropenyl-2-cyclohexen-1-one (2) were synthesized in five steps and 42% overall yield, and four steps and 49% overall yield, respectively.
- Kato,Watanabe,Tooyama,Vogler,Yoshikoshi
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p. 1055 - 1057
(2007/10/02)
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- Efficient Preparation of (R)-(-)-Cryptone form (+)-Nopinone and Its Transformation into Noroxopenlanfuran
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Starting with (R)-(-)-cryptone, prepared in 42percent overall yield from (+)-nopinone in five steps, the first synthesis of noroxopenlanfuran was accomplished, confirming its absolute configuration.
- Kato, Michiharu,Watanabe, Masataka,Vogler, Bernhard,Tooyama, Youichi,Yoshikoshi, Akira
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p. 1706 - 1707
(2007/10/02)
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