- Synthesis and reactions of donor cyclopropanes: efficient routes to cis- and trans-tetrahydrofurans
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Abstract A detailed study on the synthesis and reactions of silylmethylcyclopropanes is reported. In their simplest form, these donor-only cyclopropanes undergo Lewis acid promoted reaction to give either cis- or trans-tetrahydrofurans, with the selectivity being reaction condition-dependant. The adducts themselves are demonstrated to be an important scaffold for structural diversification. The combination of a silyl-donor group in a donor-acceptor cyclopropane with novel acceptor groups is also discussed.
- Dunn, Jonathan,Dobbs, Adrian P.
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supporting information
p. 7386 - 7414
(2015/08/24)
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- Catalysis and chemodivergence in the interrupted, formal homo-nazarov cyclization using allylsilanes
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A chemodivergent, Lewis acid catalyzed allylsilane interrupted formal homo-Nazarov cyclization is disclosed. With catalytic amounts of SnCl4 and in the presence of allyltrimethylsilane, a formal Hosomi-Sakurai-type allylation of the oxyallyl cation intermediate is observed. A variety of functionalized donor-acceptor cyclopropanes and allylsilanes were shown to be amenable to the reaction transformation and the allyl products were formed in up to 92% yield. Under dilute reaction conditions with stoichiometric SnCl4 and at reduced temperatures, an unusual formal [3 + 2]-cycloaddition between the allylsilane and the oxyallyl cation occurred to give hexahydrobenzofuran products in up to 69% yield.
- Shenje, Raynold,Williams, Corey W.,Francois, Katherine M.,France, Stefan
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supporting information
p. 6468 - 6471
(2015/02/05)
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- Rhodium(II)-catalyzed stereoselective synthesis of allylsilanes
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The rhodium-catalyzed decomposition of 2-(triisopropylsilyl)ethyl aryl- and vinyldiazoacetates results in the stereoselective formation of Z-allylsilanes. The transformation is considered to proceed by silyl-directed intramolecular C-H functionalization to form a β-lactone intermediate followed by a silyl-activated extrusion of carbon dioxide.
- Guptill, David M.,Cohen, Carolyn M.,Davies, Huw M. L.
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supporting information
p. 6120 - 6123
(2014/01/17)
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- Donor cyclopropanes in synthesis: Utilising silylmethylcyclopropanes to prepare 2,5-disubstituted tetrahydrofurans
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The use of donor-only silylmethylcyclopropanes in the Lewis acid promoted reaction with aldehydes to generate 2,5-disubstituted tetrahydrofurans is described. The diastereoselectivity obtained in the product is very much dependent upon the temperature of
- Dunn, Jonathan,Motevalli, Majid,Dobbs, Adrian P.
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scheme or table
p. 6974 - 6977
(2012/02/13)
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- Copper-catalyzed arylation of chlorosilanes with grignard reagents
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Nucleophilic substitution reactions of chlorosilanes with aryl Grignard reagents take place efficiently in the presence of copper(I) iodide to afford tetraorganosilanes.
- Morita, Eiji,Murakami, Kei,Iwasaki, Masayuki,Hirano, Koji,Yorimitsu, Hideki,Oshima, Koichiro
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scheme or table
p. 1012 - 1014
(2011/02/26)
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- Zinc-catalyzed nucleophilic substitution reaction of chlorosilanes with organomagnesium reagents
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Zinc-catalyzed nucleophilic substitution reactions of chlo-rosilanes with organomagnesium reagents afford various tetraorganosilanes under mild reaction conditions. The reactions can be performed on large scale and allow efficient preparation of functionalized tetraorganosilanes.
- Murakami, Kei,Yorimitsu, Hideki,Oshima, Koichiro
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experimental part
p. 1415 - 1417
(2009/06/28)
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- (Triisopropylsilyl)acetaldehyde acetal as a novel protective group for 1,2-diols
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(Triisopropylsilyl)acetaldehyde dimethyl acetal (TIPS-ADMA) was synthesized from chlorotriisopropylsilane in three steps. Cyclic and acyclic 1,2-diols can be transformed to (triisopropylsilyl)ethylidene acetals (TIPS-AA). Removal of the acetal by LiBF4 regenerates the starting diol in excellent yield even in the presence of an acetonide of 1,2-diol. The TIPS-AA group can survive under the deprotection conditions of the acetonide in acetic acid at 80 °C. Selective protection of 2,3- and 4,6-diols for O-methyl d-mannoside with TIPS-ADMA and selective deprotection of the acetals have been achieved.
- Uenishi, Jun'ichi,Tanaka, Yusuke,Kawai, Nobuyuki
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p. 5553 - 5555
(2007/10/03)
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- Evaluation of β- and γ-Effects of Group 14 Elements Using Intramolecular Competition
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To evaluate β-effects and γ-effects of group 14 elements, we have devised a system in which the intramolecular competition between γ-elimination of tin and β-elimination of silicon, germanium, and tin can be examined. Thus, the reactions of α-acetoxy(arylmethyl)stannanes with allylmetals (metal = Si, Ge, Sn) in the presence of BF3·OEt2 were carried out. The reactions seem to proceed by the initial formation of an α-stannyl-substituted carbocation, which adds to an allylmetal to give the carbocation that is β to the metal and γ to tin. The β-elimination of the metal gives the corresponding allylated product, and the γ-elimination of tin gives the cyclopropane derivative. In the case of allylsilane, the cyclopropane derivative was formed as a major product, whereas in the case of allylgermane the allylated product was formed predominantly. In the case of the allystannane the allylated product was formed exclusively. These results indicate that the y-elimination of tin is faster than the β-elimination of silicon, but slower than the β-elimination of germanium and tin. The theoretical studies using ab initio molecular orbital calculations of the carbocation intermediates are consistent with the experimental results. The effect of substituents on silicon was also studied. The introduction of sterically demanding substituents on silicon disfavored the β-elimination of silicon probably because of the retardation of nucleophilic attack on silicon to cleave the carbon-silicon bond.
- Sugawara, Masanobu,Yoshida, Jun-Ichi
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p. 3135 - 3142
(2007/10/03)
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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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- HIGHLY SELECTIVE γ-ALKYLATION OF TRIISOPROPYLSILYLALLYL ANION. SYNTHESIS OF α-TRIISOPROPYLSILYL ALDEHYDES.
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The reaction of triisopropylsilylallyllithium with alkyl halides took place with considerably greater γ-selectivity than reported for trimethylsilyl allyllithium.Silica gel induced rearrangement of the epoxides 5 derived from the alkylation products 3 gave α-triisopropylsilyl aldehydes 6 by a process in which silyl group transposition occurred with predominant inversion at the migration terminus.
- Muchowski, Joseph M.,Naef, Reto,Maddox, Michael L.
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p. 5375 - 5378
(2007/10/02)
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