- The efficient synthesis of alkoxy-esters from hydroxy carboxylic acids using dimsyllithium in dimethylsulfoxide followed by alkylation with an alkyl halide
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Hydroxy acids are converted directly into the related alkyl ether-alkyl esters in high yields in a single operation by double deprotonation using dimsyllithium in dimethylsulfoxide followed by treatment with an alkyl halide.
- Page, Philip C. Bulman,Chan, Yohan,Heaney, Harry,McGrath, Matthew J.,Moreno, Eduardo
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Read Online
- N-SUBSTITUTED ALPHA-AMINO AND ALPHA-HYDROXY CARBOXAMIDE DERIVATIVES
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Disclosed are N-substituted α-amino and α-hydroxy carboxamides, pharmaceutical compositions comprising them, and methods of using them.
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Paragraph 130-131
(2021/10/30)
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- Silylium-Catalyzed Carbon–Carbon Coupling of Alkynylsilanes with (2-Bromo-1-methoxyethyl)arenes: Alternative Approaches
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The catalytic activation of alkynylsilanes towards 2-halo-1-alkoxyalkyl arenes gives β-halo-substituted alkynes. It involves the chemoselective substitution of an alkoxide by an alkyne in the presence of a neighboring C(sp3)–Br bond in a cationic C–C bond-forming event. Two complementary protocols to accomplish this new transformation are reported. The outcome of a direct approach based on mixing the precursors with a freshly prepared solution of the active catalytic species (TMSNTf2) is compared with an alternative based on smooth release of the required silylium ions upon selective activation of the alkyne by gold(I) (JohnPhosAuNTf2). The two approaches gave satisfactory results to access this otherwise elusive alkynylation process, which furnishes 4-bromo-substituted alkynes and tolerates various functional groups.
- Rubial, Belén,Ballesteros, Alfredo,González, José M.
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p. 6194 - 6198
(2018/07/31)
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- Highly efficient and chemoselective zinc-catalyzed hydrosilylation of esters under mild conditions
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A mild and highly efficient catalytic hydrosilylation protocol for room-temperature ester reductions has been developed using diethylzinc as the catalyst. The methodology is operationally simple, displays high functional group tolerance and provides for a facile access to a broad range of different alcohols in excellent yields.
- Kovalenko, Oleksandr O.,Adolfsson, Hans
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supporting information
p. 2785 - 2788
(2015/02/05)
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- Sensing remote chirality: Stereochemical determination of β-, γ-, and δ-chiral carboxylic acids
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Determining the absolute stereochemisty of small molecules bearing remote nonfunctionalizable stereocenters is a challenging task. Presented is a solution in which appropriately substituted bis(porphyrin) tweezers are used. Complexation of a suitably derivatized β-, γ-, or δ-chiral carboxylic acid to the tweezer induces a predictable helicity of the bis(porphyrin), which is detected as a bisignate Cotton Effect (ECCD). The sign of the ECCD curve is correlated with the absolute stereochemistry of the substrate based on the derived working mnemonics in a predictable manner.
- Tanasova, Marina,Anyika, Mercy,Borhan, Babak
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supporting information
p. 4274 - 4278
(2015/04/14)
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- The diastereoselective formation of tetraalkoxy[4]resorcinarenes derived from (-)-(2R)-2-methoxy-2-phenylethanol and proof of absolute configurations
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The preparation of optically pure (-)-3-[(2R)-2-methoxy-2-phenylethoxy] phenol from resorcinol monobenzoate and its conversion into diastereoisomeric tetraalkoxyresorcin[4]arenes together with proof of the absolute configurations of the products is reported. The results of the study indicate that diastereoselective ring closure of linear tetrameric intermediates is controlled by the steric demand of the alkyl group in the precursor 3-alkoxyphenol.
- Bulman Page, Philip C.,Chan, Yohan,Heaney, Harry,McGrath, Matthew J.,Moreno, Eduardo
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scheme or table
p. 5347 - 5354
(2011/11/13)
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- Chiral induction by Cinchona alkaloids in the rhodium(II) catalyzed O-H insertion reaction
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Cinchona alkaloids are effective additives for enantioselective O-H insertion of α-phenyldiazoacetate and water by rhodium(II) complexes. Addition of silica gel promotes O-H insertion in the reaction rate and the reaction proceeds smoothly at less than the freezing point of water, e.g., -10°C, and provided mandelate in up to 50% ee. The results reported here are the highest asymmetric inductions obtained to date for O-H insertions via a Rh-carbenoid.
- Saito, Hiroaki,Iwai, Ryo,Uchiyama, Taketo,Miyake, Muneharu,Miyairi, Shinichi
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scheme or table
p. 872 - 874
(2010/09/04)
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- Kinetic resolution of (R,S)-pyrazolides containing substituents in the leaving pyrazole for increased lipase enantioselectivity
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With hydrolysis of (R,S)-azolides in water-saturated methyl tert-butyl ether (MTBE) via Candida antarctica lipase B (CALB) as the model system, (R,S)-pyrazolides containing a leaving 3-, 4- or 3,4-substituted-pyrazole moiety are selected as the best substrates for preparing various optically pure carboxylic acids containing an α-chiral center. Great improvements of enzyme activity for the (R)-enantiomers with excellent enantioselectivity (VR/VS > 100) are obtainable, if (R,S)-pyrazolides containing a leaving 3- or 3,4-substituted-pyrazole moiety are employed for the hydrolysis or alcoholysis by methanol in anhydrous MTBE. A detailed kinetic analysis for (R,S)-N-2-phenylpropionylpyrazoles indicates that a bulky 3-substituent such as 3-(3-bromophenyl) or 3-(2-pyridyl) in the leaving pyrazole moiety has profound effects on decreasing the nucleophilic attack and proton transfer of catalytic serine for the slow-reacting enantiomer in anhydrous MTBE, as well as that and substrate affinity for both enantiomers in water-saturated MTBE. The resolution platform is also successfully applied to the hydrolysis of (R,S)-pyrazolides in water-saturated cyclohexane via Candida rugosa lipase (Lipase MY) having opposite enantioselectivity to CALB.
- Wang, Pei-Yun,Wu, Chia-Hui,Ciou, Jyun-Fen,Wu, An-Chi,Tsai, Shau-Wei
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experimental part
p. 113 - 119
(2011/02/21)
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- Enantioselective iron-catalysed O-H bond insertions
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The ready availability, low price and environmentally benign character of iron mean that it is an ideal alternative to precious metals in catalysis. Recent growth in the number of iron-catalysed reactions reported reflects an increasing demand for sustainable chemistry. Only a limited number of chiral iron catalysts have been reported and these have, in general, proven less enantioselective than other transition-metal catalysts, thus limiting their appeal. Here, we report that iron complexes of spiro-bisoxazoline ligands are highly efficient catalysts for asymmetric O-H bond insertion reactions. These complexes catalyse insertions into the O-H bond of a wide variety of alcohols and even water, with exceptional enantioselectivities under mild reaction conditions. The selectivities surpass those obtained with other transition-metal catalysts. This study should inspire and encourage the use of iron instead of traditional precious metals in the development of greener catalysts for catalytic asymmetric synthesis.
- Zhu, Shou-Fei,Cai, Yan,Mao, Hong-Xiang,Xie, Jian-Hua,Zhou, Qi-Lin
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experimental part
p. 546 - 551
(2010/10/04)
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- An improved bouveault-blanc ester reduction with stabilized alkali metals
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Significantly improved Bouveault-Blanc conditions for ester reduction have been developed using sodium in silica gel (Na-SG), a free-flowing powder that can be easily handled in the open atmosphere. Primary alcohols were prepared in excellent yield from a variety of aliphatic esters under mild reaction conditions. The chemistry presented here is far safer than the classic Bouveault-Blanc reduction and is competitive with more modern hydride reduction methods.
- Bodnar, Brian S.,Vogt, Paul F.
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supporting information; experimental part
p. 2598 - 2600
(2009/08/07)
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- Lewis acid-mediated highly regioselective SN2-type ring-opening of 2-Aryl-N-tosylazetidines and aziridines by alcohols
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(Chemical Equation Presented) Lewis acid-mediated highly regioselective SN2-type ring-opening of 2-aryl-N-tosylazetidines with alcohols to afford various 1,3-amino ethers in excellent yields with good enantiomeric excess is described. Similar S
- Ghorai, Manas K.,Das, Kalpataru,Shukla, Dipti
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p. 5859 - 5862
(2008/02/09)
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- First synthesis of (+)-8-methoxygoniodiol and its analogue, 8-deoxygoniodiol, using a three component strategy
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We have described the first total synthesis of the natural product, (+)-8-methoxygoniodiol, and its analogue, 8-deoxygoniodiol using a catalytic asymmetric hetero-Diels-Alder/allylboration sequence involving three partners. The cytotoxic activity of these
- Carreaux, Fran?ois,Favre, Annaick,Carboni, Bertrand,Rouaud, Isabelle,Boustie, Joel
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p. 4545 - 4548
(2007/10/03)
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- Bulky diarylammonium arenesulfonates as mild and extremely active dehydrative ester condensation catalysts
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More environmentally benign alternatives to current chemical processes, especially large-scale, fundamental reactions like ester condensations, are highly desirable for many reactions. Bulky diarylammonium pentafluorobenzenesulfonates and tosylates serve as extremely active dehydration catalysts for the ester condensation reaction of carboxylic acids with equimolar amounts of sterically demanding alcohols and acid-sensitive alcohols. Typically, the esterification reaction is performed in heptane by heating at 80°C in the presence of 1 mol% of the catalyst without removing water. Esterification with primary alcohols proceeds without solvents even at room temperature. Furthermore, 4-(N-mesitylamino)polystyrene resin-bound pentafluorobenzenesulfonate can be recycled more than 10 times without a loss of activity.
- Sakakura, Akira,Nakagawa, Shoko,Ishihara, Kazuaki
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p. 422 - 433
(2007/10/03)
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- Enantioselective homoallyl-cyclopropanation of dibenzylideneacetone by modified allylindium halide reagents-rapid access to enantioenriched 1-styryl-norcarene
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Dibenzylideneacetone (8) reacts with in situ-generated allylindium halide reagents to yield the product of a homoallyl-cyclopropanation reaction: 2-(3″-butenyl)-1,1-bis[(E)-2′-phenylethenyl]cyclopropane (9), which proceeds via step-wise cleavage of the C{double bond, long}O bond and delivery of two allyl fragments from the reagent. A range of enantiomerically enriched ligands have been tested as stoichiometric asymmetric modifiers for this process. Enantiopure compounds such as cinchona alkaloids, ephedra, aminoalcohols and tartaric acid derivatives, which have proven of utility as asymmetric modifiers for the indium-mediated allylation of aldehydes and ketones, were very inefficient in the process 8→9. However, mandelic acid derivatives, in particular mandelates, were found to be of significant potential. The absolute stereochemistry of the cyclopropane 9 has been determined by degradation to 1,1-dicarboxymethyl-2-butylcyclopropane, converging with an independent enantioselective synthesis starting from hexene. Under optimised conditions, viz. using allylindium iodide reagents and working-up with aqueous Na2SO3 to avoid iodine-mediated polymerisation, (S)-9 can be generated in 86% yield and with (S)-methyl mandelate as modifier useful enantiopurity (94/6 er) was observed. The cyclopropane product ((S)-9) undergoes RCM using standard conditions to afford a norcarene unit ((1S,6S)-1-(E)-2′-(phenylethenyl)-bicyclo[4.1.0]hept-2-ene) without loss of enantiopurity.
- Lloyd-Jones, Guy C.,Wall, Philip D.,Slaughter, Jennifer L.,Parker, Alexandra J.,Laffan, David P.
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p. 11402 - 11412
(2007/10/03)
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- The first asymmetric catalytic halo aldol reaction of β-iodo allenoates with aldehydes by using chiral salen catalyst
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The first asymmetric catalytic halo aldol reaction of β-iodo allenoates with aldehydes was established. The reaction was successfully achieved by using (R,R)-SalenAlCl as the chiral catalyst and LiI as an additive at 0°C in dichloromethane. Moderate to good yields and up to 62% ee were obtained. The new system showed a good substrate scope in which both aromatic aldehydes and aliphatic aldehydes can be employed. The reaction provided the first catalytic and enantioselective approach to chiral β-iodo Baylis-Hillman ester adducts.
- Chen, Dianjun,Guo, Li,Kotti, S. R. S. Saibabu,Li, Guigen
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p. 1757 - 1762
(2007/10/03)
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- Chemo-enzymatic synthesis of enantiomerically pure (R)-2-naphthylmethoxyacetic acid
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Enantiomerically pure (R)-2-naphthylmethoxyacetic acid (2-NMA) was synthesized from 2-naphthaldehyde via an integrated chemo-enzymatic procedure. The one-pot, successive use of SnBr2-TMSCN and AcBr worked effectively to give a racemic cyanohydrin acetate. Lipase from Burkholderia cepacia then mediated the highly enantioselective hydrolysis of the (S)-enantiomer of the racemate, leaving the (R)-acetate with an e.e. of >99.9%. The resulting product of this enzyme-catalyzed hydrolysis, an (S)-cyanohydrin, spontaneously decomposed into naphthaldehyde, the starting material of this synthetic route, which could be recycled. The hydration of nitrile to amide as well as the hydrolysis of the acetate was performed with a microorganism, Rhodococcus rhodochrous, under very mild conditions without any loss of the enantiomeric purity. The amide group was hydrolyzed with nitrosylsulfuric acid, and the product was isolated as an α-hydroxy ester. The α-hydroxyl group was methylated with diazomethane-silica gel and the final task, hydrolysis of the ester, was accomplished under conditions as mild as neutral pH with an esterase from Krebsiella oxytoca to give enantiomerically pure 2-NMA.
- Kimura, Mayumi,Kuboki, Atsuhito,Sugai, Takeshi
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p. 1059 - 1068
(2007/10/03)
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- The asymmetric catalytic aldol reaction of allenolates with aldehydes using N-fluoroacyl oxazaborolidine as the catalyst
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matrix presented The asymmetric catalytic aldol reaction of silyl allenolates with aldehydes has been achieved by using N-C3F7CO oxazaborolidine as the catalyst. The fluoroacyl group of the catalyst was found to be crucial for control of enantioselectivity. The reaction provides the first enantioselective approach to β-halo Baylis-Hillman-type adducts.
- Li, Guigen,Wei, Han-Xun,Phelps, Brian S.,Purkiss, David W.,Kim, Sun Hee
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p. 823 - 826
(2007/10/03)
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- Enantioselective protonation of silyl enol ethers and ketene disilyl acetals with Lewis acid-assisted chiral Bronsted acids: Reaction scope and mechanistic insights
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Enantioselective protonation is a potent and efficient way to construct chiral carbons. Here we report details of the reaction using Lewis acid-assisted chiral Bronsted acids (chiral LBAs). The 1:1 coordinate complex of tin tetrachloride and optically active binaphthol ((R)- or (S)-BINOL) can directly protonate various silyl enol ethers and ketene disilyl acetals to give the corresponding α-aryl ketones and α-arylcarboxylic acids, respectively, with high enantiomeric excesses (up to 98% ee). A catalytic version of enantioselective protonation has also been achieved using stoichiometric amounts of 2,6-dimethylphenol and catalytic amounts of monomethyl ether of optically active BINOL in the presence of tin tetrachloride. This protonation is also effective for producing α-halocarbonyl compounds (up to 91% ee). DFT calculations on the B3LYP/LANL2DZ level show that the conformational structure of the chiral LBA and the orientation of activated proton on (R)-BINOLs are important for understanding the absolute stereochemistry of the products.
- Nakamura, Shingo,Kaneeda, Masanobu,Ishihara, Kazuaki,Yamamoto, Hisashi
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p. 8120 - 8130
(2007/10/03)
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- Improved Cs2CO3 promoted O-alkylation of acids
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Cesium carbonate mediated O-alkylation of carboxylic acids was efficiently carried out under mild in situ conditions to give the corresponding esters exclusively. Chiral templates including α-hydroxy and α-alkoxy acids were also converted to their corresponding esters with no observed racemization.
- Parrish, Jay P.,Dueno, Eric E.,Kim, Seok-In,Jung, Kyung Woon
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p. 2687 - 2700
(2007/10/03)
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- Enantioselective carboxylation of α-methoxybenzyllithium generated via asymmetric lithiation with a t-BuLi/chiral bis(oxazoline) complex
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Treatment of benzyl methyl ether with a t-BuLi/chiral bis(oxazoline) complex followed by carboxylation is shown to afford α-methoxy phenylacetic acid in high % ee (up to 95%). The asymmetric induction was proved to occur at the post-lithiation step.
- Komine, Nobuyuki,Wang, Lan-Fang,Tomooka, Katsuhiko,Nakai, Takeshi
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p. 6809 - 6812
(2007/10/03)
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- Cesium promoted O-alkylation of alcohols for the efficient ether synthesis
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Efficient Williamson type O-alkylation of alcohols was developed using cesium bases in the presence of tetrabutylammonium iodide (TBAI) and molecular sieves. Various substrates including unreactive primary and secondary alcohols were converted smoothly to
- Dueno,Chu,Kim,Kyung Woon Jung
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p. 1843 - 1846
(2007/10/03)
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- Lewis acid-promoted carbonyl addition of lithium (α- carbalkoxyvinyl)cuprates to aldehydes provides a novel asymmetric synthesis of β,β-disubstituted α-(hydroxyalkyl)acrylates
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A new anionic addition process has been developed for the asymmetric synthesis of unusual Baylis-Hillman adducts, β,β-disubstituted α- (hydroxyalkyl)acrylates. The new process involves conjugate addition of R2CuLi to β-substituted α,β-acetylenic ester to give lithium (α- carbalkoxyvinyl)cuprate which was then subjected to the carbonyl addition to aldehyde promoted by Et2AlCl. Modest to good diastereoselectivity (50.0- 87.7%de) has been obtained by using (1R,2S,5R)-(-)-menthol as the chiral auxiliary (59.0-94.0% yield). The absolute configuration was unambiguously assigned by transforming the product to methyl (R)-α-methoxyphenylacetate.
- Wei, Han-Xun,Willis, Steven,Li, Guigen
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p. 8203 - 8206
(2007/10/03)
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- Enantioselective Allylic Substitution Catalyzed by Chiral palladium Complexes: Catalyst Structure and Possible Mechanism of Enantioselection
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Allylpalladium complexes with chiral bis(dihydrooxazole) ligands were studied as catalysts for the enantioselective allylic substitution reaction of rac-1,3-diphenylprop-2-enyl acetate (rac-5) with the anion of dimethyl malonate (Scheme 1).Using enantiome
- Matt, Peter von,Lloyd-Jones, Guy C.,Minidis, Alexander B. E.,Pfaltz, Andreas,Macko, Ludwig,et al.
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p. 265 - 284
(2007/10/02)
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- Applications of Optically Active Aryl Cyanohydrins in the Synthesis of α-Hydroxy Aldehydes, α-Hydroxy Ketones and β-Hydroxy Amines
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Cyanohydrins, prepared in high optical purity from aryl aldehydes, have been converted into α-hydroxy aldehydes, α-hydroxy ketones and β-hydroxy amines without any racemization and frequently with good stereoselectivity for the erythro-diastereoisomer (>90percent) at the newly introduced stereogenic centre.
- Jackson, W. Roy,Jacobs, Howard A.,Jayatilake, Gamini S.,Matthews, Barry R.,Watson, Keith G.
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p. 2045 - 2062
(2007/10/02)
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- MODEL STUDIES FOR THE TOTAL SYNTHESIS OF THE MAYTANSINOIDS BASED ON THE INTRAMOLECULAR NITRILE OXIDE-OLEFIN CYCLOADDITION REACTION
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The macrocyclization of the olefinic nitrile oxide 30 to the ansa-macrolide skeleton 37, a model for a novel approach to the maytansinoids, is described.
- Ko, Soo Sung,Confalone, Pat N.
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p. 3511 - 3518
(2007/10/02)
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- THE INTRAMOLECULAR NITRILE OXIDE-OLEFIN CYCLOADDITION ROUTE TO THE MAYTANSINOIDS
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The macrocyclization of the olefinic nitrile oxide 24 to the ansa-macrolide skeleton 26, a model for a novel approach to the maytansinoids, is described.
- Confalone, Pat N.,Ko, Soo S.
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p. 947 - 950
(2007/10/02)
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