- 33. The Halide-Promoted Fragmentation of 1-Chloro-1-fluori-2(α-silylalkyl)cyclopropanes: A new entry to Fluorodienes
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When heated in the presence of tetrabutylammonium fluoride or chloride, 1-chloro-1-fluoro-2-(trimethylsilyl)methyl-cyclopropanes (1,2, and 3) undergo smooth ringopening fragmentation to afford 2-fluoro-butadienes (4, 5 and 6, resp.)with high yields.Despite unfavorable geometries, the reaction is converted and the inversion mode of rotation dominates over the retention mode by y factor of roughly 100.
- Schlosser, Manfred,Dahan, Rachel,Cottens, Sylvain
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- ENE-REACTIVITE D'ALLYLSILANES: FONCTIONNALISATION ET REGIOCHIMIE
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The hydroperoxidation of various allylsilanes by singlet oxygen has been studied.The regioselectivity of this reaction compared to those of ethyl azodicarboxylate and 4-phenyl-1,2,4-triazoline-3,5-dione, is discussed.Mechanisms are considered in the general field of the ene reaction applied to allylic organometallic Group IVB compounds.The structures of the new products (alcohols, urazoles, hydrazines) have been determined, directly or after transformations, by NMR spectroscopy.
- Dubac, J.,Laporterie, A.,Iloughmane, H.,Pillot, J. P.,Deleris, G.,Dunogues, J.
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- Synthesis of γ-amino- and δ-amino-functionalised ethers, amines, or silanes by hydroaminomethylation of heterofunctionalised allylic compounds
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Heterofunctionalised allylic ethers 1, silanes 5, and amines 9 are hydroformylated in the presence of primary or secondary amines 2 to form the corresponding γ-amino- and δ-amino-functionalised compounds. The rhodium(I)-catalysed reaction sequence proceeds by aldehyde formation and subsequent reductive amination to generate the corresponding functionalised secondary or tertiary amines. This selective one-pot hydroaminomethylation procedure establishes access to γ-amino- and δ-amino-functionalised ethers, amines or silanes with potential biological activity.
- Rische, Thorsten,Baerfacker, Lars,Eilbracht, Peter
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- Synthesis and Applications of Silyl 2-Methylprop-2-ene-1-sulfinates in Preparative Silylation and GC-Derivatization Reactions of Polyols and Carbohydrates
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Trimethylsilyl, triethylsilyl, tert-butyldimethylsilyl, and triisopropylsilyl 2-methylprop-2-ene-1-sulfinates were prepared through (CuOTf)2C6H6-catalyzed sila-ene reactions of the corresponding methallylsilanes with SO2 at 50 °C. Sterically hindered, epimerizable, and base-sensitive alcohols gave the corresponding silyl ethers in high yields and purities at room temperature and under neutral conditions. As the byproducts of the silylation reaction (SO2+isobutylene) are volatile, the workup was simplified to solvent evaporation. The developed method can be employed for the chemo- and regioselective semiprotection of polyols and glycosides and for the silylation of unstable aldols. The high reactivity of the developed reagents is shown by the synthesis of sterically hindered per-O-tert-butyldimethylsilyl-α-d-glucopyranose, the X-ray crystallographic analysis of which is the first for a per-O-silylated hexopyranose. The per-O-silylation of polyols, hydroxy carboxylic acids, and carbohydrates with trimethylsilyl 2-methylprop-2-ene-1-sulfinate was coupled with the GC analysis of nonvolatile polyhydroxy compounds both qualitatively and quantitatively. Regio- and chemoselective silylation of polyols and carbohydrates has been achieved by employing silyl sulfinates (see the picture; TBS=tert-butyldimethylsilyl, TES=triethylsilyl, TIPS=triisopropylsilyl, TMS=trimethylsilyl). The silylation reactions proceed in high yield because the reactions are mild and fast and produce only volatile byproducts. Furthermore, the silyl sulfinates are used as new derivatization reagents for the GC analysis of nonvolatile polyhydroxy compounds.
- Markovic, Dean,Tchawou, Wandji Augustin,Novosjolova, Irina,Laclef, Sylvain,Stepanovs, Dmitrijs,Turks, Maris,Vogel, Pierre
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p. 4196 - 4205
(2016/03/16)
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- The Reaction of Polyhalides with Allylsilanes Catalyzed by Copper(I) Chloride
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Allyltrimethylsilane reacted with polyhalogen compounds in the presence of copper species, such as copper(I) chloride, copper(II) chloride or metallic copper, to form polyhalo compounds containing an allyl group. Other allylsilane derivatives than allyltrimethylsilane were also subjected to a reaction with carbon tetrachloride. 3-Chloro- or 3-bromo-3-trimethylsilyl-1-propene gave 4,4,4-trichloro-1-trimethylsilyl-1-butene. Ethyl 1-trimethylsilylallyl carbonate afforded ethyl 4,4,4-trichloro-1-butenyl carbonate along with a hydrotrichloromethylation product. 2-Methyl-3-trimethylsilyl-1-propene yielded a product based on the addition of a trichloromethyl group followed by hydrogen-elimination from a 2-methyl group.
- Mitani, Michiharu,Hujita, Shigenori
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p. 3055 - 3060
(2007/10/03)
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- Catalytic asymmetric allylation using a chiral (acyloxy)borane complex as a versatile Lewis acid catalyst
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In the presence of 20 mol % of a chiral (acyloxy)borane (CAB) complex prepared from (2R,3R)-2-O-(2,6-diisopropoxybenzoyl)tartaric acid and borane-tetrahydrofuran, various allyltrimethylsilanes react with achiral aldehydes to afford the corresponding homoa
- Ishihara, Kazuaki,Mouri, Makoto,Gao, Qingzhi,Maruyama, Tohru,Furuta, Kyoji,Yamamoto, Hisashi
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p. 11490 - 11495
(2007/10/02)
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- Regioselective alkylation of 1-silyl-2-methylallyl carbanions
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Regioselective alkylations of 1-silyl-2-methylallyl carbanions were achieved by changing the substituents on silicon. γ-Alkylation was favoured by dialkylamino group on silicon, whereas α-alkylation was favoured by an alkoxy substituent on silicon.
- Li,Wang d.
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p. 2879 - 2882
(2007/10/02)
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- Kinetics of the reactions of allylsilanes, allylgermanes, and allylstannanes with carbenium ions
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Second-order rate constants for the reactions of para-substituted diarylcarbenium ions (ArAr'CH+ = 1) with allylsilanes 2, allylgermanes 3, and allylstannanes 4 have been determined in CH2Cl2 solution at -70 to -30°C. Generally, the attack of ArAr'CH+ at the CC double bond of the allylelement compounds 2-4 is rate-determining and leads to the formation of the β-element-stabilized carbenium ions 5, which subsequently react with the negative counterions to give the substitution products 6 or the addition products 7. For compounds H2C = CHCH2MPh3, the relative reactivities are 1 (M = Si), 5,6 (M = Ge), and 1600 (M = Sn). From the relative reactivities of compounds H2C=CHCH2X (X = H, SiBu3, SnBu3), the activating effect of an allylic trialkylsilyl (5 × 105) and trialkylstannyl group (3 × 109) is derived. This effect is strongly reduced, when the alkyl groups at Si or Sn are replaced by inductively withdrawing substituents, and an allylic SiCl3 group deactivates by a factor of 300 (comparison isobutene/2k). A close analogy between the reactions of alkenes and allylelement compounds with carbenium ions is manifested, and the different reaction series are connected by well-behaved linear free energy relationships. The relative reactivities of terminal alkenes and allylelement compounds are almost independent of the electrophilicities of the reference carbenium ions (constant selectivity relationship), thus allowing the construction of a general nucleophilicity scale for these compounds.
- Hagen, Gisela,Mayr, Herbert
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p. 4954 - 4961
(2007/10/02)
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- Homolytic Reactions of Ligated Boranes. Part 14. ESR Studies of Ring Opening of Cycloalkylaminyl-Borane Radicals and Reactions of Aminyl-Borane Radicals with Silicon-containing Compounds
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ESR spectroscopy has been used to characterise reactions of the aminyl-borane radicals RN.H->BH3 (2) in solution.The relative rates of β-hydrogen-atom transfer from s, ButC(H)Me, or But> to 2,3-dimethylbut-2-ene and to furan depend on the nature of the group R, confirming that H-atom transfer is bimolecular and does not involve prior β-scission of (2) to give a free hydrogen atom.Because of favourable polar factors, β-H-atom transfer from (2) to the allylsilanes Me3SiCH2CH=CH2 and Me3SiCH2CMe=CH2 are particularly rapid.The cycloalkylaminyl-borane radicals (2; R=cyclo-C3H5 or cyclo-C4H7) undergo rapid ring opening at 282 K, while no spectroscopic evidence was found for opening of the cyclopentyl or cyclohexyl analogues.Alkylaminyl-borane radicals transfer a β-hydrogen atom to hexamethyldisilane to bring about homolytic Si-Si bond cleavage.These radicals also react with trialkylsilanes R3SiH to give R3Si. .Approximate absolute rate coefficients for the reactions of (2) have been determined at 282 or 292 K.Of the primary amine-boranes investigated, s-butylamine- and cyclopentylamine-boranes appear to be the most suitable complexes for ESR spectroscopic work in liquid solution.
- Johnson, Karen M.,Kirwan, J. Nicholas,Roberts, Brian P.
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p. 1125 - 1132
(2007/10/02)
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- SYNTHESIS OF 7-ALKYL-CYCLOHEPTATRIENES FROM ALLYLIC SILANES AND TROPYLIUM TETRAFLUOROBORATE
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The regiospecific substitution of some allylic silanes using tropylium tetrafluoroborate gives 7-alkyl-cycloheptatrienes.
- Picotin, G.,Miginiac, Ph.
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p. 5897 - 5898
(2007/10/02)
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- Ether cleavage by activated metals II.* Cleavage of allyl and benzyl ethers by activated magnesium
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Activated magnesium (prepared by reduction of magnesium halides with potassium) reacts with allyl and benzyl ethers to give the corresponding allyl or benzyl magnesium compounds.
- Bartmann, Ekkehard
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- Catalytic Conversion of Allylic Esters to Corresponding Allylic Silanes with Hexamethyldisilane and Palladium(0) or Rhodium(I) Complexes
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Treatment of allylic esters (R1CH=CR2CH2OCOR3:R1=H,Ar;R2=H, alkyl; and R3=Me,Ph) with hexamethyldisilane in the presence of catalytic amounts of PdL4 (L=PPh3 or P(OPh)3) or RhCl(PPh3)3 gives the corresponding allylic silanes in the excellent yield.
- Urata, Hisao,Suzuki, Hiroharu,Moro-oka, Yoshihiko,Ikawa, Tsuneo
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p. 607 - 608
(2007/10/02)
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- Silicon-Assisted Ring Opening of Cyclopropyl Ketones with Boron Trifluoride-Acetic Acid Complex
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2-(Trimethylsilylmethyl)cyclopropyl ketones were smoothly cleaved with boron trifluoride-acetic acid complex under mild reaction conditions with the assistance of the trimethylsilyl group to give γ,δ-enones in good yields.The major effect of the trimethylsilyl group in the ring opening of the cyclopropyl ketones was unambiguously confirmed in the dicyclopropyl ketone 15: one of its two cyclopropyl rings, which has a trimethylsilylmethyl group, was selectively cleaved.Furthermore, the reaction was applied to the formal total synthesis of cis-jasmone.Keywords - ring opening of cyclopropyl ketone; trimethylsilyl group; γ,δ-enone; cis-jasmone; allylsilane; boron trifluoride-acetic acid
- Ochiai, Masahito,Sumi, Kenzo,Fujita, Eiichi
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p. 3931 - 3938
(2007/10/02)
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- REGIO- AND STEREO-SELECTIVE ALKYLATION OF 3-TRIMETHYLSILYLMETHYL DIENOLATES. A NOVEL SYNTHESIS OF 3-ALKYLATED 2-METHALLYLSILANES.
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Lithium and copper 3-trimethylsilylmethyl dienolate anions derived from easily available 3-trimethylsilylmethyl-3-butenoic acid and its methyl ester underwent regio- and stereo-selective alkylation. α-Alkylated products were readily transformed to 3-alkylated 2-methallylsilanes by pyrolysis.
- Nishiyama, Hisao,Itagaki, Kazuyoshi,Takahashi, Kaoru,Itoh, Kenji
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p. 1691 - 1694
(2007/10/02)
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