- A Ball-Milling-Enabled Reformatsky Reaction
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An operationally simple one-jar one-step mechanochemical Reformatsky reaction using in situ generated organozinc intermediates under neat grinding conditions has been developed. Notable features of this reaction protocol are that it requires no solvent, no inert gases, and no pre-activation of the bulk zinc source. The developed process is demonstrated to have good substrate scope (39–82 % yield) and is effective irrespective of the initial morphology of the zinc source.
- Cao, Qun,Stark, Roderick T.,Fallis, Ian A.,Browne, Duncan L.
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p. 2554 - 2557
(2019/06/17)
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- 1,4-Bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadienes as strong salt-free reductants for generating low-valent early transition metals with electron-donating ligands
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Electron-rich organosilicon compounds, such as 1,4-bis(trimethylsilyl)-1,4- diaza-2,5-cyclohexadiene (2a), 2,5-dimethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2, 5-cyclohexadiene (2b), 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2, 5-cyclohexadiene (
- Saito, Teruhiko,Nishiyama, Haruka,Tanahashi, Hiromasa,Kawakita, Kento,Tsurugi, Hayato,Mashima, Kazushi
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supporting information
p. 5161 - 5170
(2014/04/17)
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- Scope and mechanism of the electrochemical Reformatsky reaction of α-haloesters on a graphite powder cathode in aqueous anolyte
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Six α-haloesters and eighteen carbonyl compounds were submitted to electrochemical coupling on a graphite powder cathode using aqueous anolyte free of organic solvents. Preparative yields of coupling products could be obtained with ethyl 2-bromoisobutyrate and aromatic aldehydes. Ethyl 2-bromopropionate was much less efficient. Extensive variation of applied potential, electrolyte composition, stoichiometry, catalyst, leaving halogen and activating substituents on the carbonyl compound led to the conclusion that the reaction mechanism in most cases proceeds via a radical intermediate generated from the halide reduction. Ethyl chloroacetate produced only trace amounts of coupling product, most probably by a carbanionic mechanism.
- De Souza, Carlos A.,Navarro, Marcelo,Bieber, Lothar W.,Areias, Madalena C.C.
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p. 118 - 126
(2014/05/06)
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- MNBA-mediated β-lactone formation: Mechanistic studies and application for the asymmetric total synthesis of tetrahydrolipstatin
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Various β-lactones were prepared from β-hydroxycarboxylic acids by intramolecular dehydration condensation using MNBA, an effective coupling reagent, along with a nucleophilic catalyst. The transition state that provides the desired 4-membered ring model system is disclosed by density functional theory (DFT) calculations, and the structural features of the transition form are discussed. This method was successfully applied to the asymmetric total synthesis of tetrahydrolipstatin (THL), an antiobestic drug used in clinical treatment to inhibit the activity of pancreatic lipase.
- Shiina, Isamu,Umezaki, Yuma,Kuroda, Nobutaka,Iizumi, Takashi,Nagai, Shunsuke,Katoh, Takashi
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experimental part
p. 4885 - 4901
(2012/07/30)
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- Generation of carbanions through stibine-metal and bismuthine-metal exchange reactions and its applications to precision synthesis of ω-end-functionalized polymers
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Generation of carbanions from organostibines and organobismuthines through heteroatom-metal exchange reactions was examined from synthetic and mechanistic viewpoints. The exchange reaction proceeded spontaneously upon treatment with various organometallic reagents, such as alkyl lithiums, tetraalkyl zincates, and alkyl magnesium halides to afford the corresponding carbanions quantitatively. Due to the high reactivity of these heteroatom compounds, the exchange reactions took place exclusively even in the presence of various polar functional groups, which potentially react with organometallic species. The advantage of this method was exemplified by the end-group transformation of living polymers that bear these heteroatom species at the ω-polymer end, prepared by using organostibine and bismuthine-mediated living radical polymerizations. Various polymers that bear polar functional groups and acidic hydrogen-for example, poly(methyl methacrylate), poly(butyl acrylate), poly(N-isopropyl acrylamide), and poly(2-hydroxyethyl methacrylate)-could be used in the exchange reactions, and subsequent trapping with electrophiles afforded the corresponding polymers with controlled molecular weights, molecular weight distributions, and end-group functionalities. Competition experiments showed that organostibines and organobismuthines were among the most reactive heteroatom compounds towards organometallic reagents and that their high reactivity was responsible for the high chemoselectivity in the exchange reaction. All's well that ends well: The generation of carbanions from organostibine and -bismuthine compounds was achieved thorough a heteroatom-metal exchange reaction (see scheme). The highly chemoselective exchange reaction could be applied to precision synthesis of varieties of ω-end- functionalized polymers that possess a polar functional group.
- Kayahara, Eiichi,Yamada, Hiroto,Yamago, Shigeru
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supporting information; experimental part
p. 5272 - 5280
(2011/06/20)
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- Highly enantioselective mukaiyama aldol reactions catalyzed by a chiral oxazaborolidinium ion: Total synthesis of (-)-inthomycin C
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A cationic oxazaborolidinium-catalyzed asymmetric Mukaiyama aldol reaction of (1-methoxy-2-methyl-propenyloxy)-trimethylsilane with various aldehydes including α,β-disubstituted acroleins has been developed in high yields and enantioselectivities. The synthetic utility of this methodology was demonstrated in the first short synthesis of naturally occurring inthomycin C in high enantiopurity.
- Senapati, Bidyut Kumar,Gao, Lizhu,Lee, Sung Il,Hwang, Geum-Sook,Ryu, Do Hyun
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supporting information; scheme or table
p. 5088 - 5091
(2011/01/05)
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- Enantioselective aldol reaction of silyl ketene acetals promoted by a Lewis base-activated Lewis acid catalyst
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The enantioselective aldol reaction of a silyl ketene acetal was promoted by chiral phosphine oxide-activated tetrachlorosilane to afford the corresponding adduct in high yield with moderate enantioselectivity.
- Shimoda, Yasushi,Tando, Teppei,Kotani, Shunsuke,Sugiura, Masaharu,Nakajima, Makoto
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experimental part
p. 1369 - 1370
(2009/11/30)
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- Asymmetric hydrogenation of tert-alkyl ketones
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A combined system of RuCl2(tolbinap)(pica) and an alkaline or organic phosphazene base catalyzes asymmetric hydrogenation of sterically congested tert-alkyl ketones (TolBINAP = 2,2-bis(di-4-tolylphosphino)-1,1-binaphthyl, PICA = α-picolylamine). Hydrogenation with RuH(η1-BH4)(tolbinap)(pica) does not require any strong base. Alcoholic solvents strongly affect the catalytic efficiency. The reaction proceeds smoothly in ethanol under 1-20 atm of H2 and at room temperature with a substrate to catalyst molar ratio of up to 100000. Various aliphatic, aromatic, heteroaromatic, and olefinic tert-alkyl ketones are convertible to the corresponding chiral carbinols in high enantiomeric purity. Olefinic and heteroaromatic functions are left intact. Certain cyclic ketones are also usable. The mode of enantioface selection is consistent and predictable. Copyright
- Ohkuma, Takeshi,Sandoval, Christian A.,Srinivasan, Rajagopal,Lin, Quinghong,Wei, Yinmao,Muniz, Kilian,Noyori, Ryoji
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p. 8288 - 8289
(2007/10/03)
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- Lewis acid-aldehyde-solvent interactions. A computational approach for determining the critical amount of THF molecules necessary for achieving a high enantioselection in chiral oxazaborolidinone-promoted asymmetric aldol reactions
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The effect of THF as a solvent on the enantioselectivity of oxazaborolidinone-promoted asymmetric aldol reactions of aldehydes with silylketene acetals was investigated. The use of 4-5 M equiv of THF, relative to the chiral borane, was required to achieve
- Fujiyama, Ryoji,Goh, Kazuki,Kiyooka, Syun-Ichi
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p. 1211 - 1215
(2007/10/03)
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- Metal chloride-promoted aldol reaction of α-dimethylsilylesters with aldehydes, ketones, and α-enones
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In the presence of a catalytic amount of LiCl, α-dimethylsilylesters (α-DMS-esters) 1 smoothly reacted with various aldehydes at 30°C to give aldols in good to high yields. On the other hand, the aldol reaction with ketones was effectively promoted by MgCl2 rather than by LiCl. α-Enones also underwent the metal chloride-promoted addition of 1 at the carbonyl carbon or β-carbon. Georg Thieme Verlag Stuttgart.
- Miura, Katsukiyo,Nakagawa, Takahiro,Hosomi, Akira
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p. 1917 - 1921
(2007/10/03)
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- Synthesis of β-hydroxy esters using highly active manganese
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A modified Reformatsky reaction is reported using highly reactive manganese (Mn*). The active manganese was found to readily react with α-haloester in the presence of aldehydes and ketones to yield the corresponding β-hydroxy esters. The reaction is carried out at room temperature in the absence of Lewis acid or trapping agents.
- Suh, YoungSung,Rieke, Reuben D.
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p. 1807 - 1809
(2007/10/03)
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- Synthesis and use of α-silyl-substituted α-hydroxyacetic acids
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(matrix presented) Rhodium-catalyzed oxygen transfer was used to generate benzyl 2-silyl-2-oxoacetates in good yields. The hydrogenation of these compounds led to chiral α-silyl-substituted α-hydroxyacetic acids. Resolution by means of HPLC using a chiral stationary phase afforded an enantiomerically pure representative of this class of compounds, which was successfully applied as a chiral ligand in an asymmetric aldol-type reaction.
- Bolm, Carsten,Kasyan, Andrey,Heider, Peter,Saladin, Sandra,Drauz, Karlheinz,Guenther, Kurt,Wagner, Christoph
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p. 2265 - 2267
(2007/10/03)
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- Oxovanadium(IV) complex-mediated catalysis in Mukaiyama-type aldol additions
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Condensation of vanadyl sulfate with 2,2'-biphenol in the presence of N- containing ligands provides oxovanadium(IV) complexes which serve as efficient catalysts in Mukaiyama aldol reactions to afford aldol products in 52-100% yields with diastereoselecti
- Chen, Chien-Tien,Hon, Sang-Wen,Weng, Shiue-Shien
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p. 816 - 818
(2007/10/03)
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- Uncatalyzed aldol reaction using a dimethylsilyl enolate and α- dimethylsilyl ester in N,N-dimethylformamide
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Dimethylsilyl enolates and α-dimethylsilyl esters reacted with aldehydes in N,N-dimethyl-formamide without an activator to give aldol adducts in moderate to good yields. Under the same conditions, the corresponding trimethylsilyl derivatives exhibited lower reactivities toward the aldol reaction.
- Miura, Katsukiyo,Sato, Hiroshi,Tamaki, Kentaro,Ito, Hajime,Hosomi, Akira
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p. 2585 - 2588
(2007/10/03)
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- Unusual conformational aspects of some novel chiral non-racemic pyridinyl-2-phosphonates
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Reaction of pyridinyl-2-phosphonyl dichloride (6) with 1-phenyl-2,2- dimethylpropane-1,3-diol (9) leads to the two epimeric 2-oxo-2-(2-pyridinyl)- 4-phenyl-5,5-dimethyl-1,3,2-dioxaphosphorinanes (10a,b). These can be separated and the stereochemistry assigned on the basis of 31P NMR spectroscopy. For 10a the pyridinyl substituent is arranged axially at phosphorus. Arguments derived from 2D NMR experiments indicated that the nitrogen of pyridine is locked in a conformation whereby the pyridinyl nitrogen points over the six-membered ring; in other words it is locked between the two ting oxygen substituents. This conclusion is substantiated by an X-ray crystal determination. Oxidation of 10a with hydrogen peroxide leads to the N-oxide (12). The crystal structure of 12 reveals that despite serious steric overcrowding the N-O bond is also oriented over the six-membered ring. Methylation of 10a with methyl trifluoromethanesulfonate affords the N- methyl pyridinium salt (13). NMR experiments indicate that in this case the methylated nitrogen has turned 'outside' of the six-membered ring. The borane adduct of 10a appears on the basis of NMR data to have a conformation wherein the complexed borane is located just outside of the six-membered ring. Although crystal structures have not been obtained the pyridinyl-2- thiophosphonates (15a,b) obtained from treatment of 10a and 10b with [(4- MeOC6H4)2PS]2 appear to have the same conformational properties as 10a and 10b. Restricted HartreeFock geometry optimizations have been carried out to aid in clarifying this unexpected conformational behaviour. These calculational results are in excellent accord with the experimental observations, and provide insight into the reasons for the conformational behaviour.
- Dros,Zijlstra,Van Duijnen,Spek,Kooijman,Kellogg
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p. 7787 - 7812
(2007/10/03)
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- Enantioselective aldol reaction using bornane-2,3-diol-aluminum complex as a chiral Lewis acid
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β-Hydroxy ester was formed in high enantiomeric excess by the reaction of ketene silyl acetal with aldehyde in the presence of a chiral Lewis acid prepared from diethylaluminum chloride and chiral diol derived from (+)-camphor.
- Shimizu, Makoto,Kawamoto, Manabu,Yamamoto, Yasushi,Fujisawa, Tamotsu
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p. 501 - 502
(2007/10/03)
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- Reformatsky Reaction in Water: Evidence for a Radical Chain Process
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The Reformatsky reaction of 2-bromo esters and carbonyl compounds in the presence of zinc can be carried out in concentrated aqueous salt solutions without any cosolvent. The reaction of bromoacetates is greatly enhanced by catalytic amounts of benzoyl peroxide or peracids and gives satisfactory yields with aromatic aldehydes. Preparative yields comparable to those of the traditional procedure are obtained with ethyl 2-bromoisobutyrate. This ester needs no catalyst and reacts even with saturated aldehydes and aromatic ketones, although in low yields. A radical chain mechanism, initiated by electron abstraction from the organometallic Reformatsky reagent, is proposed. Two nonchain pathways, involving radicals directly produced on the metal surface, may compete, especially in the case of secondary and tertiary halides.
- Bieber, Lothar W.,Malvestiti, Ivani,Storch, Elisabeth C.
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p. 9061 - 9064
(2007/10/03)
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- Asymmetric Synthesis of Functionalized Secondary Alcohols by Catalytic Ring-Cleavage Reactions of Cyclic Acetals Derived from (R)-1,3-Butanediol
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In the presence of a catalytic amount (0.1-0.2 molar amount) of a 2-phenyl-1,3,2-oxazaborolidin-5-one, prepared by the reaction of dichlorophenylborane and N-(trifluoromethylsulfonyl)-L- phenylalanine, and enol silyl ethers ((R2)2C=C-(R3)OTMS; R3 = t-BuS, EtS, EtO, Ph) (1.1-1.5 molar amount), chiral cyclic acetals 6 derived from (R)-1,3-butanediol and aldehydes undergo an efficient ring-cleavage reaction with the inversion of the stereochemistry at the acetal carbon to give the anti isomer of the corresponding products with high stereoselectivity. The reaction is applicable to acetals derived from aromatic, aliphatic, and α,β-unsaturated aldehydes. Not only enol silyl ethers, but also methallyltrimethylsilane and allyltributyltin, can be employed as nucleophiles, leading to the selective formation of the anti isomer of the corresponding allylated ring-cleavage products. Removal of the chiral auxiliary from these ring-cleavage products by a two-step sequence ((i) PCC (ii) Bn2NH2(CF3CO2)) furnishes enantiomerically enriched β-hydroxy carbonyl compounds and homoallyl alcohols. A modest level of kinetic resolution is observed in the ring cleavage of a racemic acetal catalyzed by a phenylboron compound derived from N-mesyl-L-phenylalanine.
- Kinugasa, Motoharu,Hanada, Toshiro,Egusa, Takayuki,Fujita, Katsuhiro,Oku, Akira
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p. 3639 - 3650
(2007/10/03)
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- A novel nitroaldol reaction catalyzed by rhodium complex in the presence of a silyl ketene acetal
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A rhodium complex, [{Rh(C5Me5)Cl}2(μ-Cl)2], catalyzed smoothly the nitroaldol reaction of nitroethane with aldehydes in the presence of a silyl ketene acetal. This reaction is the first example of transition met
- Kiyooka, Syun-Ichi,Tsutsui, Takanori,Maeda, Hirofumi,Kaneko, Yuichi,Isobe, Kiyoshi
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p. 6531 - 6534
(2007/10/02)
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- Polymer-supported Chiral Borane Promoters for the Asymmetric Aldol Reaction of Benzaldehyde with Silyl Ketene Acetal
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Chiral polymers (A and B) having pendant α-amino acid moiety were prepared by suspension copolymerization.A polymer-supported chiral borane, formed from chiral polymer A and BH3*THF, effectively promoted by aldol reaction in THF of benzaldehyde with silyl
- Kiyooka, Syun-ichi,Kido, Yuichi,Kaneko, Yuichi
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p. 5243 - 5246
(2007/10/02)
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- Synthesis of α,α,β,β-Tetrasubstituted β-Lactones from Ketones, Ethyl α-Bromoisobutyrate, and Indium or Zinc. Factors Influencing the β-Lactone Formation in the Electrochemical and the Classical Procedure of the Reformatsky Reaction
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An efficient synthesis of α,α,β,β-tetrasubstituted β-lactones is achieved by an electrochemically supported Reformatsky reaction of aliphatic and aromatic ketones with ethyl α-bromoisobutyrate at a sacrificial indium anode.Under these conditions, in most
- Schick, Hans,Ludwig, Ralf,Schwarz, Karl-Heinz,Kleiner, Katharina,Kunath, Annamarie
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p. 3161 - 3164
(2007/10/02)
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- The catalytic asymmetric aldol reaction of silyl ketene acetals with aldehydes in the presence of a chiral borane complex. Nitroethane as a highly effective solvent for catalytic conditions
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Catalytic asymmetric aldol reactions of silyl ketene acetals with aldehydes in the presence of 20 mol % of the chiral borane reagent, prepared in situ from the p-nitrobenzenesulfonamide of (S)-valine and BH3-THF complex, gave β-hydroxy carboxylic acid esters in good chemical yields along with excellent enantioselectivity under conditions that employ nitroethane as an effective solvent.
- Kiyooka, Syun-Ichi,Kaneko, Yuichi,Kume, Ken-Ichi
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p. 4927 - 4930
(2007/10/02)
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- Boron Trifluoride Promoted Aldol Reaction of Silyl Ketene Acetals with the Intermediate Generated by the DIBALH Reduction of Carboxylic Acid Esters
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The intermediate generated by the DIBALH reduction of carboxylic acid esters undergoes a boron trifluoride promoted aldol reaction with silyl ketene acetals to afford the corresponding β-hydroxy carboxylic acid esters in good yield.
- Kiyooka, Syun-ichi,Shirouchi, Masashi
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- ACTIVATION OF KETENE SILYL ACETALS BY 10-METHYLACRIDINIUM PERCHLORATE: A NOVEL CATALYSIS IN MUKAIYAMA REACTION
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10-Methylacridinium perchlorate (1) effectively promotes various reactions of ketene silyl acetals: aldol and Michael addition products are obtained with aldehydes, ketones, acetals, and α-enones.The reactions exhibit unusual dependency upon 1, namely the yields are excellent when a catalytic amount of 1 is employed whereas no desired products are accessible by the use of 1 in a stoichiometric quantity.A novel catalytic cycle is proposed.
- Otera, Junzo,Wakahara, Yoshiyuki,Kamei, Hidenobu,Sato, Tsuneo,Nozaki, Hitosi,Fukuzumi, Shunichi
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p. 2405 - 2408
(2007/10/02)
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- A convenient procedure for the preparation of reactive zinc for the Reformatsky Reaction
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A reactive zinc powder is obtained by addition of ZnCl2 to a lithium dispersion suspended in ether. Reformatsky Reactions with the zinc powder are described.
- Bouhlel,Rathke
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p. 133 - 136
(2007/10/02)
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- Iron complexes as catalysts in aldol additions
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(Dicarbonyl)(η5-cyclopentadienyl) iron halides function as catalysts for the aldol addition of enosilanes to aldehydes.
- Colombo,Ulgheri,Prati
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p. 6435 - 6436
(2007/10/02)
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- Photoreduction of 2-Benzoylalkanoates
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2-Benzoylalkanoates 1 undergo photoreduction with 2-propanol.The photoreduction products are classified into three types according to their origin: the homo-pinacol-type products 2, 5, 7, and 8, the mixed-pinacol-type product 3, and the β-hydroxy ester 6.
- Yoshioka, Michikazu,Aoki, Satoshi,Shimizu, Toshio,Hasegawa, Tadashi
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p. 2230 - 2233
(2007/10/02)
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- A NEW METHOD FOR THE SYNTHESIS OF β-HYDROXYESTERS BY USING METALLIC TIN
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Metallic tin or activated metallic tin, prepared by reduction of stannous chloride with lithium aluminum hydride, smoothly reacts with α-haloesters to yield tin enolates, which in turn react with carbonyl compounds under mild conditions to give, after hydrolysis, β-hydroxyesters in high yields.
- Harada, Taira,Mukaiyama, Teruaki
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p. 161 - 164
(2007/10/02)
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