- The 13C Hyperfine Splittings in ESR Spectra of Prop-2-ynyl and 1-(Trimethylsiloxy)prop-2-ynyl Radicals
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The 13C satellite lines were observed in the 9.4 GHz ESR spectra of prop-2-ynyl and 1-trimethylsiloxyprop-2-ynyl radicals generated from precursors containing 13C in natural abundance.The 13C hfs indicate that prop-2-ynyl radicals adopt the ?-delocalized structure, not the ?-allenyl form.The hfs of 1-trimethylsiloxyprop-2-ynyl radicals indicate that there is appreciable delocalization of spin onto the trimethylsiloxy group and that the radical is essentially planar at C(1).A linear correlation of a(C) with a(H) is shown to hold for a number of neutral hydocarbon ?-delocalized radicals.The experimental hfs are compared with spin densities calculated by a variety of semiempirical and ab initio SCF MO methods.
- Walton, J. C.
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Read Online
- Chlorozincate(II) acidic ionic liquid: Efficient and biodegradable silylation catalyst
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A practical and highly efficient silylation of alcohol and phenol derivatives with hexamethyldisilazane (HMDS) using acidic ionic liquids under mild reaction conditions is described. A series of Br?nsted as well as Br?nsted–Lewis acidic ionic liquids were prepared and their performance investigated for the silylation of a wide variety of alcohols and phenols with HMDS. Imidazole- as well as N-methyl-2-pyrrolidone-based acidic ionic liquids have a higher catalytic activity for the protection of sensitive, hindered alcohols and phenols, thus providing an environmentally begin and versatile alternative to current acid catalysts. In addition, the acidic ionic liquids are reusable, being recovered easily and reused several times without significant deterioration in catalytic activity.
- Abbasi, Faezeh,Azizi, Najmedin,Abdoli-Senejani, Masumeh
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- The influence of the organolithium reagent nature on the possibility of the O→Csp migration of the R3Si group in propynes HC≡CCH2OSiR3
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A possibility of the O→Csp 1,4-migration of the R3Si group in silyl ethers of terminal acetylenic alcohols upon treatment with organolithium reagents (RLi) was studied. In the case of 3-trimethylsilyloxypropyne, depending on the nature of RLi, the heterolysis of the Si—O bond occurs either by the action of acetylide formed as a result of deprotonation with the formation of 3-trimethylsilylprop-2-yn-1-ol trimethylsilyl ether, or by the action of the metalation agent with the formation of propargyl alcohol. The realization of the O→Csp 1,4-migration of the Me3Si group requires the use of mild organolithium reagents (lithium hexamethyldisilazanide and diisopropylamide). Silyl ethers having steric hindrance at the carbon atom bonded to the reaction center or around the silicon atom do not react with the studied organolithium reagents.
- Novokshonov,Medvedeva,Mareev
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p. 2264 - 2268
(2018/03/25)
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- Preparation of nano silica supported sodium hydrogen sulfate: As an efficient catalyst for the trimethyl, triethyl and t-butyldimethyl silylations of aliphatic and aromatic alcohols in solution and under solvent-free conditions
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Nano silica supported sodium hydrogen sulfate has been prepared by mixing NaHSO4 with activated Nano silicagel. We wish to report a new method for the synthesis of trimethyl (TMS), triethyl (TES) and t-butyldimethyl silyl (TBS) ethers from benzylic, allylic, propargylic alcohols, phenols, naphtholes and some of phenolic drugs in the solution and under solvent-free conditions.
- Abri, Abdolreza,Ranjdar, Somayeh
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p. 929 - 934
(2014/10/16)
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- A mild and highly efficient method for the preparation of silyl ethers using Fe(HSO4)3/Et3N by chlorosilanes
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Avery efficient and mild procedure for preparation of silyl ethers from benzylic, allylic, propargilic alcohols, phenols, naphtoles and some of phenolic drugs with trimethylsilylchloride (TMSCl), triethylsilylchloride (TESCl) and t-buthyldimethylsilyl chloride (TDSCl) ethers in the presence of Fe(HSO 4)3/Et3N in roomtemperature in excellent yields is reported. This procedure also allows the excellent selectivity for silylation of alcohols and phenols.
- Abri, Abdolreza,Assadi, Mohammad Galeh,Pourreza, Samira
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p. 1449 - 1454
(2013/03/13)
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- An expeditious, efficient green methodology for the Boc protection of amines and silyl protection of alcohols over tungstophosphoric acid-doped mesoporous silica
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An efficient, chemoselective and eco-friendly protocol for the protection of amines as N-tert-butylcarbamate using (Boc)2O and protection of alcohols as silyl ether using HMDS over tungstophosphoric acid/SBA15 has been developed. Solventless condition, easy work-up, short reaction time, excellent yields and reusability of the catalyst are the striking features of this methodology which can be considered to be one of the better methods for the protection of amines and alcohols.
- Karmakar, Bikash,Banerji, Julie
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experimental part
p. 3855 - 3858
(2010/08/20)
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- A concise, protection-free and divergent approach for the enantioselective syntheses of two pheromonal epoxide components of the fall webworm moth and other species
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(Figure presented) On the basis of Zhous modified Sharpless asymmetric epoxidation, sequential coupling reactions, and a divergent strategy, the protection-free syntheses of two main pheromonal components 1 and 5, found in the fall webworm moth, Hyphantria cunea, and other species have been accomplished in 10 steps (for two compounds). The overall yields are 31% for 1, 28% for 5, and 25% for both 1 and 5, respectively. The ee values of the final products 1 and 5 are at least 99%.
- Du, Yu,Zheng, Jian-Feng,Wang, Zhi-Gang,Jiang, Li-Jiao,Ruan, Yuan-Ping,Huang, Pei-Qiang
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supporting information; experimental part
p. 4619 - 4622
(2010/10/03)
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- Novel and highly effective method for the trimethylsilylation of alcohols and phenols with hexamethyldisilazane (HMDS), catalyzed by I2 generated in situ using Fe(NO3)3 · 9 H 2O/NaI under heterogeneous and neutral conditions
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Structurally diverse alcohols and phenols were trimethylsilylated in a clean and efficient reaction with hexamethyldisilazane (HMDS) based on the use of I2 generated in situ from Fe(NO3)3 · 9 H2O/NaI. The reaction occurs very rapid in good-to-high yield in CH2Cl2 at room temperature, and the use of toxic and corrosive molecular I2 is avoided.
- Khazaei, Ardeshir,Rahmati, Sadegh,Rostami, Amin
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experimental part
p. 1434 - 1438
(2009/10/16)
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- SN2′ boron-mediated Mitsunobu reactions - A new one-pot three-component synthesis of substituted enamides and enol benzoates
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The conversion of (3-hydroxy-1-propen-1-yl)boronates to substituted enamides and enol benzoates is readily achieved in a one-pot procedure consisting of a regiocontrolled Mitsunobu reaction with convenient nucleophiles, followed by allylboration of aldehydes. Wiley-VCH Verlag GmbH & Co. KGaA, 2009.
- Berree, Fabienne,Gernigon, Nicolas,Hercouet, Alain,Chia, Hui Lin,Carboni, Bertrand
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supporting information; experimental part
p. 329 - 333
(2009/07/04)
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- A convenient catalyst for aqueous and protein Suzuki-Miyaura cross-coupling
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(Figure Presented) A phosphine-free palladium catalyst for aqueous Suzuki-Miyaura cross-coupling is presented. The catalyst is active enough to mediate hindered, ortho-substituted biaryl couplings but mild enough for use on peptides and proteins. The Suzuki-Miyaura couplings on protein substrates are the first to proceed in useful conversions. Notably, hydrophobic aryl and vinyl groups can be transferred to the protein surface without the aid of organic solvent since the aryl- and vinylboronic acids used in the coupling are water-soluble as borate salts. The convenience and activity of this catalyst prompts use in both general synthesis and bioconjugation.
- Chalker, Justin M.,Wood, Charlotte S. C.,Davis, Benjamin G.
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supporting information; experimental part
p. 16346 - 16347
(2010/01/29)
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- Facile method for trimethylsilylation of alcohols using hexamethyldisilazane and ammonium thiocyanate under neutral conditions
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A highly efficient method for trimethylsilylation of primary, secondary, tertiary, allylic, and a variety of sugar-derived alcohols using hexamethyldisilazane in the presence of a catalytic amount of ammonium thiocyanate under neutral conditions is reported. Copyright Taylor & Francis Group, LLC.
- Jadhav, Vrushali H.,Kumar, K. S. Ajish,Chaudhari, Vinod D.,Dhavale, Dilip D.
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p. 1363 - 1370
(2008/02/01)
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- Efficient and practical protocol for silylation of hydroxyl groups using reusable lithium perchlorate dispread in silica gel under neutral condition
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A very efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, allylic, benzylic, secondary, hindered secondary, tertiary, and phenols with hexamethyldisilazane on the surface of silica gel dispersed with LiClO4 in room temperature at few minutes in excellent yields under neutral conditions is reported. This procedure also allows the excellent selectivity under LP-SiO2 system for silylation of alcohols in the presence of amine and phenolic hydroxy groups.
- Azizi, Najmedin,Yousefi, Rozbeh,Saidi, Mohammad R.
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p. 817 - 820
(2007/10/03)
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- Internal nucleophilic termination in acid-mediated polyene cyclizations: Part 5. Synthetic access to didehydro analogues of (±)-Ambrox and diastereoisomers
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Treatment of the acyclic tetraenols (E)- and (Z)-2 with an excess of ClSO3H in 2-nitropropane at - 80° stereoselectively afforded in 30 and 43% yield, respectively, diastereoisomer mixtures of the racemic, tricyclic ethers 1c,d and 1a,b, together with 20 (Table). Under identical conditions, but with the acyclic pentaenol 10 (1:1 diastereoisomer mixture) as substrate, the tricyclic ethers 22a/22b (10:1) were isolated in 27% yield. These kinetically controlled stereospecific transformations are thought to proceed via non-concerted pathways (see Schemes 5 and 7), fully consistent with our earlier work. In contrast, another set of reaction conditions (CF 3CO2H, CH2Cl2, -15° to -10°) was used for the cyclization of the monocyclic dienols (E)-3 and (Z)-3, which resulted in the non-stereoselective formation of the major products 1c,d and 1a,b, respectively, in 35-37% yield. Representing novel didehydro analogues of the known ambergris odorant (±)-Ambrox and its diastereoisomers, the qualitative organoleptic properties of 1a-d and of the 10:1 diastereoisomer mixture of the novel tetradehydro analogues 22a/ 22b are briefly described.
- Snowden, Roger L.,Linder, Simon
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p. 3071 - 3086
(2008/01/27)
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- Zinc mediated reactions in organic synthesis: Efficient synthesis of silyl ethers under mild conditions
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General and practical method for the syn the sis of silyl ethers in the presence of zinc powder under mild conditions has been described.
- Bandgar, Babasaheb Pandurang,Chavare, Satish Navnath,Pandit, Shivaji Sandu
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p. 125 - 128
(2007/10/03)
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- Development of an end-game strategy towards apoptolidin: A sequential Suzuki coupling approach
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An end-game strategy towards the synthesis of apoptolidin has been demonstrated in a model study, in which the C(1)-C(15) fragment was successfully assembled using three consecutive Suzuki coupling reactions.
- Jin, Bohan,Liu, Qingsong,Sulikowski, Gary A.
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p. 401 - 408
(2007/10/03)
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- Fe/Cr- and Co/Cr-mediated catalytic asymmetric 2-haloallylations of aldehydes
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The first example to couple aldehydes and 3-bromo-2-halopropenes in a catalytic asymmetric manner is reported. The coupling reaction is effected by the use of a chiral sulfonamide-Cr complex (prepared in situ from 1d, CrBr3, Fe(III) or from Co(II), Et3N, and Mn), TMSCl, and 2,6-lutidine. The method reported here is operationally simple and scalable, furnishing 3-halohomoallylic alcohols with a synthetically useful level of enantiomeric excess. Copyright
- Kurosu, Michio,Lin, Mei-Huey,Kishi, Yoshito
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p. 12248 - 12249
(2007/10/03)
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- Effects of Structural Factors in Silyl Ethers Derived from Terminal Acetylenic Alcohols on 1,4-O→Csp Migration of the Silyl Group
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Effects of structural factors in silyl ethers derived from terminal acetylenic alcohols on 1,4-O-→Csp migration of the silyl group in the Iotsitch reagent were studied. The effect of steric factor at the carbon atom neighboring to the reaction center was found to be stronger than that at the silicon atom in the migrating group.
- Medvedeva,Novokshonov,Mareev,Borisova
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p. 336 - 339
(2007/10/03)
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- Hydroboration-azide alkylation as efficient tandem reactions for the synthesis of chiral non racemic substituted pyrrolidines
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The synthesis of chiral non racemic substituted pyrrolidines from homoallylic alcohols is presented. These precursors are readily converted via the azides to the corresponding pyrrolidines using hydroboration-cycloalkylation tandem reactions as key steps.
- Salmon, Anne,Carboni, Bertrand
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- Enantioselective catalysis 107: new optically active deltacyclenes as building blocks for the synthesis of expanded phosphanes
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The cobalt-catalyzed homo Diels-Alder reaction of norbornadiene and terminal acetylenes yields chiral deltacyclenes.We tried to extend the scope of this reaction to acetylenes containing a heteroatom (i) in the propargylic position, (ii) in the ortho position of phenylacetylene or (iii) directly bonded to the triple bond.The synthesis of nine new substituted deltacyclenes with cobalt cytalysts derived from CoI2 and zinc powder or Co(acac)3 and Et2AlCl is described.Using Norphos as a cocatalyst, the products are obtained in high enantiomeric excess. - Keywords: enantioselective homogeneous catalysis; homo Diels-Alder reaction; deltacyclene; terminal acetylene
- Brunner, Henri,Reimer, Alfred
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p. 307 - 314
(2007/10/03)
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- Synthesis of (±)-isoavenaciolide and of (±)-ethisolide from (±)-7-oxabicyclo|2.2.1|hept-5-en-2-one
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A short total synthesis of (±)-ethisolide and (±)-isoavenaciolide was accomplished from (±)-oxanorbornenone respectively in 11 and 12 steps, using a radical cyclization as a key step.
- Cossy, Janine,Ranaivosata, Jean-Luc,Bellosta, Veronique
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p. 629 - 638
(2007/10/03)
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- Synthesis and metal ion binding studies of enediyne-containing crown ethers
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The 3-ene-1,5-diyne crown ether 5 is a novel enediyne-containing crown ether that was designed as a model system for a class of enediynes that might undergo alkali metal ion-triggered Bergman cyclization. We report the preparation of 5 by two different routes. In the shorter and preferable route, a carbenoid coupling reaction is employed to simultaneously construct the enediyne moiety and effect a macrocyclization of an acyclic bis(propargyl)bromide 15 to the 24-membered crown ether 5. Under standard reaction conditions, this carbenoid coupling produces as the major product the isomeric 5-ene-1,3-diyne-crown ethers (Z)-16 and (E)-16. The formation of 5-ene-1,3-diynes from the carbenoid coupling of propargyl bromides is unprecedented. We present evidence that it is the polyether nature of dibromide 15 that leads to the formation of the 5-ene-1,3-diyne-crown ether products. Judicious control of the reaction conditions can be used to produce either 5 or (Z)-16 from 15 in synthetically useful yields. Both enediyne-crown ethers 5 and (Z)-16 bind alkali metal ions, as evidenced by their ability to extract alkali metal picrates into organic solvents. Enediyne-crown ether 5 undergoes Bergman cyclization at 135°C in DMSO/1,4-cyclohexadiene to produce the known o-xylyl crown ether 4. Crown ether 5 represents an enediyne in which molecular recognition of alkali metals might serve as a trigger for Bergman cyclization.
- McPhee, Mark M.,Kerwin, Sean M.
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p. 9385 - 9393
(2007/10/03)
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- TRIMETHYLSILYLATION OF ACETYLENIC ALCOHOLS AND GLYCOLS
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A universal method for trimethylsilylation of acetylenic alcohols and glycols based on reaction with hexamethyldisilazane in the presence of catalytic quantities of saccharin was developed.The rate of trimethylsilylation of acetylenic alcohols decreases in the series primary-secondary-tertiary acetylenic alcohols.Trimethylsilylation of acetylenic alcohols, except dimethylethynylcarbinol, reduces their toxicity.
- Demina, M. M.,Velikanov, A. A.,Medvedeva, A. S.,Voronkov, M. G.,Zaks, A. S.
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p. 1575 - 1579
(2007/10/02)
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- Asymmetric synthesis of the C3-C8 fragment of leucotrienes and analogues
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An asymmetric synthesis of the C3-C8 fragment of leukotrienes and analogues using the aldol-type condensation of chiral sulfinyl ester is described. Thus, starting from (3S)-3-tert-butyldimethylsiloxy-1-(2-methoxyethoxymethoxy)-5-trimethyls ilyl-4-pentyne, the corresponding methyl (2Z,4S)-hexenoate, methyl (4R)-hexanoate, (2Z,4S)- and (2E,4S)-2-hexenal derivatives were prepared. Several molecules prepared during this work were shown to be important intermediates in the synthesis of various natural products.
- Solladie,Hamdouchi
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p. 979 - 982
(2007/10/02)
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- SYNTHESIS OF DIOSPHENOL ETHERS BY MEANS OF ALKOXYTRIMETHYLSILANES
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α-Diketones may be O-alkylated with a variety of alkoxytrimethylsilanes.
- Ponaras, A. A.,Meah, Md. Younus
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p. 4953 - 4956
(2007/10/02)
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- Reagents and synthetic methods. 31. Silylations with N-trimethylsilyl-2-oxazolidinone (TMSO)
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Silylation of ketones, alcohols, mercaptans, and carboxylic acids with N-trimethylsilyl-2-oxazolidinone (TMSO) and triflic acid as catalyst has been described from synthetic and mechanistic points of view.
- Aizpurua, Jesus M.,Palomo, Claudio,Palomo, Antonio L.
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p. 336 - 340
(2007/10/02)
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- Reagents and synthetic methods. 18 : N-trimethylsilyl-2-oxazolidinone, a useful silyating agent for hydroxy compounds
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N-trimethylsilyl-2-oxazolidinone reacts rapidly with alcohols at room temperature with the catalytic assistance of chlorotrimethylsilane to give high isolated yields of trimethylsilyl ethers.
- Aizpurua, Jesus Mari,Palomo, Claudio
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p. 265 - 268
(2007/10/02)
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