- Cycloalkylmethyl Radicals. 5. 6- to 15-Membered Rings: EPR Studies of Ring Conformations and Stereodynamics
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Cycloalkylmethyl radicals having 7- to 15-membered rings (excluding cyclotetradecylmethyl) have been generated and examined by EPR spectroscopy.All the cycloalkylmethyl radicals from the 9-membered ring upward show two distinguishable conformers, though there may be additional conformers present with cyclodecylmethyl and cyclopentadecylmethyl radicals.All the cycloalkylmethyl radicals from the 10-membered ring upward have one conformer, the quasi-equatorial, QE, with an Hβ hfs in the range 27.7-32.0 G at 140 K and one conformer, the quasi-axial, QA, with an Hβ hfs in the range 38.3-40.4 G at 140 K.The QE and QA conformers have been assigned to species in which the CH2. group occupies "outer-edge" and "corner" sites, respectively, in the preferred conformations of the cycloalkanes.The EPR results indicated that the preferred conformations of the C9, C10, C11, C12, C13, and C15 rings were , , , , , and , respectively.Arrhenius parameters for ring-atom site exchange in the cycloalkylmethyl radicals have been determined from the exchange broadening in the EPR spectra.These EPR barriers are compared with literature data on cycloalkane free energy barriers measured by NMR and enthalpic barriers estimated by force field and related methods.
- Ingold, K. U.,Walton, J. C.
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- Reactivity studies of a zirconium methylidene complex: Group transfer and methylenation reactions
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The zirconium methylidene complex (PNP)-Zr=CH2(OAr) (1; PNP = N[2-PiPr2-4-methylphenyl]2-, Ar = 2,6-iPr2C6H3), prepared from photolysis of (PNP)Zr-(CH3)2(OAr), can engage in incomplete and complete methylidene group transfer reactions with CO, CDCl3, cyclododecanone, and benzophenone. When CO was treated with 1, methylenation occurred via the putative metalloketene adduct [(PNP)Zr(OCCH2)(OAr)], which ultimately afforded t h e C-C coupled eno l a t e dimer [(PNP)Zr-(OAr)]2(OCH2C=CCH2O) (2). Addition of CDCl3 to 1 rapidly resulted in formation of (PNP)ZrCl2(OAr) (3) along with liberation of d1-vinyl chloride, H2C=CDCl. Complex 3 could be readily prepared independently from (PNP)ZrCl3 and 1 equiv of NaOAr. Wittig reactivity was observed between 1 and cyclododecanone to afford methylenecyclododecane. Similarly, treating 1 with the ketone OCPh2 resulted in methylenation of the ortho position followed by tautomerization to produce the chelated alkyloxide complex (PNP)Zr(OAr)[OCHPh(C6H4)-CH2] (4). In addition to the isolation of 4, complex 1 also engages in a cross-metathesis reaction involving the methylidene and ketone oxygen of benzophenone, as well as in olefin metathesis involving the formed olefin H2C=CPh2. Complexes 2-4 have been fully characterized, including solid-state structural analysis, and proposed mechanisms for the formation of species such as 2-4 are presented and discussed.
- Kurogi, Takashi,Kamitani, Masahiro,Manor, Brian C.,Carroll, Patrick J.,Mindiola, Daniel J.
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- Dearomative Cyclopropanation of Naphthols via Cyclopropene Ring-Opening
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The dearomatization of 2-naphthols represents a simple method for the construction of complex 3D structures from simple planar starting materials. We describe a cyclopropanation of 2-naphthols that proceeds via cyclopropene ring-opening using rhodium and acid catalysis under mild conditions. The vinyl cyclopropane molecules were formed with high chemoselectivity and scalability, which could be further functionalized at different sites. Both computational and experimental evidence were used to elucidate the reaction mechanism.
- Baker, Rachel J.,Ching, Justin,Franzoni, Ivan,Hou, Teh Ren,Lautens, Mark
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supporting information
(2022/01/13)
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- Titanium and Cobalt Bimetallic Radical Redox Relay for the Isomerization of N -Bz Aziridines to Allylic Amides
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Herein a bimetallic radical redox-relay strategy is employed to generate alkyl radicals under mild conditions with titanium(III) catalysis and terminated via hydrogen atom transfer with cobalt(II) catalysis to enact base-free isomerizations of N-Bz aziridines to N-Bz allylic amides. This reaction provides an alternative strategy for the synthesis of allylic amides from alkenes via a three-step sequence to accomplish a formal transpositional allylic amination.
- Wood, Devin P.,Guan, Weiyang,Lin, Song
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supporting information
p. 4213 - 4220
(2021/08/10)
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- Oxidative Cleavage of Alkenes by O2with a Non-Heme Manganese Catalyst
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The oxidative cleavage of C═C double bonds with molecular oxygen to produce carbonyl compounds is an important transformation in chemical and pharmaceutical synthesis. In nature, enzymes containing the first-row transition metals, particularly heme and non-heme iron-dependent enzymes, readily activate O2 and oxidatively cleave C═C bonds with exquisite precision under ambient conditions. The reaction remains challenging for synthetic chemists, however. There are only a small number of known synthetic metal catalysts that allow for the oxidative cleavage of alkenes at an atmospheric pressure of O2, with very few known to catalyze the cleavage of nonactivated alkenes. In this work, we describe a light-driven, Mn-catalyzed protocol for the selective oxidation of alkenes to carbonyls under 1 atm of O2. For the first time, aromatic as well as various nonactivated aliphatic alkenes could be oxidized to afford ketones and aldehydes under clean, mild conditions with a first row, biorelevant metal catalyst. Moreover, the protocol shows a very good functional group tolerance. Mechanistic investigation suggests that Mn-oxo species, including an asymmetric, mixed-valent bis(μ-oxo)-Mn(III,IV) complex, are involved in the oxidation, and the solvent methanol participates in O2 activation that leads to the formation of the oxo species.
- Bennett, Elliot L.,Brookfield, Adam,Guan, Renpeng,Huang, Zhiliang,Mcinnes, Eric J. L.,Robertson, Craig M.,Shanmugam, Muralidharan,Xiao, Jianliang
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supporting information
p. 10005 - 10013
(2021/07/19)
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- Direct Synthesis of Unprotected 2-Azidoamines from Alkenes via an Iron-Catalyzed Difunctionalization Reaction
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Unprotected, primary 2-azidoamines are versatile precursors to vicinal diamines, which are among the most common motifs in biologically active compounds. Herein, we report their operationally simple synthesis through an iron-catalyzed difunctionalization of alkenes. A wide array of alkene substrates are tolerated, including complex drug-like molecules and a tripeptide. Facile derivatizations of the azidoamine group demonstrate the versatility of this masked diamine motif in chemoselective, orthogonal transformations. Applications of the methodology in the concise synthesis of RO 20-1724 as well as in the formal total syntheses of both (±)-hamacanthin B and (±)-quinagolide further demonstrate the broad synthetic potential of this highly functional-group-tolerant reaction.
- Makai, Szabolcs,Falk, Eric,Morandi, Bill
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supporting information
p. 21548 - 21555
(2021/01/11)
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- Rhodium-Catalyzed Intermolecular Cyclopropanation of Benzofurans, Indoles, and Alkenes via Cyclopropene Ring Opening
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The generation of metal carbenoids via ring opening of cyclopropenes by transition metals offers a simple entry into highly reactive intermediates. Herein, we describe a diastereoselective intermolecular rhodium-catalyzed cyclopropanation of heterocycles and alkenes using cyclopropenes as carbene precursors with a low loading of a commercially available rhodium catalyst. The reported method is scalable and could be performed with catalyst loadings as low as 0.2 mol %, with no impact to the reaction yield or selectivity.
- Jeyaseelan, Rubaishan,Lautens, Mark,Ross, Rachel J.
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supporting information
(2020/06/29)
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- Stereoselective Synthesis of Vinylcyclopropa[ b]indolines via a Rh-Migration Strategy
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A mild rhodium catalytic system has been developed to synthesize vinylcyclopropa[b]indolines through cyclopropanation of indoles with vinyl carbenoids generated from ring opening of cyclopropenes in situ. By employing a Rh-migration strategy, the products can be obtained with good to excellent E:Z ratios (≤99:1) and complete diastereoselectivity (≤99:1). This method is easy, has a low catalyst loading, and works for a broad range of functionalities.
- Guo, Pan,Sun, Wangbin,Liu, Yu,Li, Yong-Xin,Loh, Teck-Peng,Jiang, Yaojia
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supporting information
p. 5978 - 5983
(2020/08/05)
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- Synthesis of Functionalized α-Vinyl Aldehydes from Enaminones
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An efficient RhII-catalyzed synthesis of functionalized α-vinyl aldehydes with high E/Z stereoselectivity was developed. The reaction mediates the cyclopropanation of enaminones with vinyl carbenoids that are generated from cyclopropenes in situ to give the aminocyclopropane intermediates. Selective C?C bond cleavage of the cyclopropane intermediates leads to formation of α-vinyl aldehyde derivatives with high E/Z selectivity. This method proceeds at room temperature under very mild reaction conditions and works with a broad substrate scope.
- Chen, Jie,Guo, Pan,Zhang, Jianguo,Rong, Jiaxin,Sun, Wangbin,Jiang, Yaojia,Loh, Teck-Peng
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supporting information
p. 12674 - 12679
(2019/08/07)
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- Mild Ring-Opening 1,3-Hydroborations of Non-Activated Cyclopropanes
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The Brown hydroboration reaction, first reported in 1957, is the addition of B?H across an olefin in an anti-Markovnikov fashion. Here, we solved a long-standing problem on mild 1,3-hydroborations of non-activated cyclopropanes. A three-component system including cyclopropanes, boron halides, and hydrosilanes has been developed for borylative ring-opening of cyclopropanes following the anti-Markovnikov rule, under mild reaction conditions. Density functional theory (M06-2X) calculations show that the preferred pathway involves a cationic boron intermediate which is quenched by hydride transfer from the silane.
- Wang, Di,Xue, Xiao-Song,Houk, Kendall N.,Shi, Zhuangzhi
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supporting information
p. 16861 - 16865
(2018/11/27)
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- Mechanism-based design and optimization of a catalytic electrophilic cyclopropanation without diazomethane
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Iodomethylboron compounds, either the trifluoroborate or a boronic ester, cyclopropanate electron-rich olefins and unprotected allylic alcohols with Pd catalysts according to a novel, designed catalytic cycle. Proposed intermediates in a "diverted Heck" mechanism are observed by means of spectroscopic studies and by isolation and X-ray crystallographic characterization, which together with reaction kinetics point to a separation of rate-determining and product-determining steps, and a mechanism-based optimization of the yield, selectivity, and scope of the catalytic electrophilic cyclopropanation. The reaction with crystalline, air-stable, nonhygroscopic, and nontoxic reagents provides an alternative to Simmons-Smith-type reactions, as well as cyclopropanation procedures that require the use of diazomethane.
- Tchawou, Augustin A. S. W.,Raducan, Mihai,Chen, Peter
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supporting information
p. 180 - 191
(2017/11/27)
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- B(C6F5)3-Catalyzed Ring Opening and Isomerization of Unactivated Cyclopropanes
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Catalytic amounts of B(C6F5)3 promote the ring opening and subsequent isomerization of a series of unactivated cyclopropanes to afford terminal olefins in good yields when a hydrosilane and 2,6-dibromopyridine are employed as additives.
- Zhang, Zi-Yu,Liu, Zhi-Yun,Guo, Rui-Ting,Zhao, Yu-Quan,Li, Xiang,Wang, Xiao-Chen
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supporting information
p. 4028 - 4032
(2017/03/27)
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- Rh(II)-Catalyzed [2,3]-Sigmatropic Rearrangement of Sulfur Ylides Derived from Cyclopropenes and Sulfides
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(Chemical Equation Presented) A new type of Rh2(OAc)4-catalyzed [2,3]-sigmatropic rearrangement of sulfur ylides is reported. A series of cyclopropenes were successfully employed for [2,3]-sigmatropic rearrangement by a reaction with either allylic or propargylic sulfides. Under the optimized conditions, the reaction afforded the products in moderate to excellent yields. In these transformations, the vinyl metal carbenes generated in situ from the cyclopropenes were effectively trapped by sulfides, resulting in the formation of corresponding products upon [2,3]-sigmatropic rearrangements.
- Zhang, Hang,Wang, Bo,Yi, Heng,Zhang, Yan,Wang, Jianbo
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supporting information
p. 3322 - 3325
(2015/07/15)
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- Copper-carbene complexes as catalysts in the synthesis of functionalized styrenes and aliphatic alkenes
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(NHC)-Cu (NHC = N-heterocyclic carbene) complexes efficiently catalyzed the methylenation of a variety of aliphatic and aromatic aldehydes and ketones in the presence of trimethylsilyldiazomethane, triphenylphosphine, and 2-propanol. The copper catalysts are not only inexpensive compared to rhodium complexes, but they also exhibit better functional group compatibility with aromatic aldehydes and ketones. Indeed very high yields were obtained for the formation of styrenes containing nitro, trifluoromethyl, amino, and ester groups, as well as for pyridine-, pyrrole-, and indole-substituted alkenes.
- Lebel, Helene,Davi, Michael,Diez-Gonzalez, Silvia,Nolan, Steven P.
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p. 144 - 149
(2007/10/03)
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- Wittig type methylenation of ketones with bis(iodozincio)methane and ionic liquid
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Ketones were transformed into alkenes via methylenation with bis(iodozincio)methane and ionic liquid, 1-butyl-3-methyl-imidazolium hexafluorophosphate ([bmim][PF6]) in the absence of additional metal salt such as titanium chlorides.
- Yoshino, Hideaki,Kobata, Masami,Yamamoto, Yuhei,Oshima, Koichiro,Matsubara, Seijiro
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p. 1224 - 1224
(2007/10/03)
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- Reaction of arylsulfonylhydrazones of aldehydes with α-magnesio sulfones. A novel olefin synthesis
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Reactions of representative tosylhydrazones of aldehydes and ketones with α-metalated sulfones were examined in order to develop a practical olefination method. Treatment of aldehyde tosylhydrazone 2 with an excess of α-lithiated methyl phenyl or dimethyl sulfones yielded 3a. The reaction of 2 with sterically unhindered lithiated alkyl sulfones gave mixtures of the respective olefination products 3b-d along with the Shapiro fragmentation product 4. Sterically hindered lithiated sulfones afforded Shapiro products exclusively. In contrast, aldehyde tosylhydrazones 2 or 6 in reactions with a variety of α-magnesio primary or secondary alkyl sulfones gave olefination products 3a-j and 7a-c in high yields (Tables 1 and 2). β-Branched alkyl sulfones afforded predominantly (E)-alkenes, whereas unhindered primary sulfones gave mixtures of (E)- and (Z)- alkenes with low selectivity. Reaction of the 2,4,6-triisopropylbenzenesulfonylhydrazone (trisylhydrazone) of cyclodecanone 11c with α-magnesio methyl phenyl sulfone afforded the methylidene derivative 12a contaminated with the Shapiro product 13. Tosylhydrazone 2 resisted reaction with i-PrMgCl and gave only a small amount of the addition product in reaction with Bu2Mg. Some mechanistic aspects of the reaction of tosylhydrazones with organomagnesium compounds are discussed.
- Kurek-Tyrlik,Marczak,Michalak,Wicha,Zarecki
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p. 6994 - 7001
(2007/10/03)
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- Selective Deprotection of Acetals with Me3SiCH2MgCl. Peterson-Type Olefination of Acetals
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By employing the chelation strategy, treatment of an acetal of a contiguous diol with Me3SiCH2-MgCl liberates the corresponding diol regioselectively. In addition, acetals of different structural variety are transformed upon treatment with Me3SiCH2MgCl and ZnI2 into the corresponding olefination products in good yield.
- Chiang, Chao-Cheng,Chen, Yu-Huei,Hsieh, Yu-Tsai,Luh, Tien-Yau
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p. 4694 - 4697
(2007/10/03)
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- Samarium(II) triflate as a new reagent for the grignard-type carbonyl addition reaction
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On treatment of a THF solution of Sm(OTf)3 with 1 equiv of an organolithium or organomagnesium reagent at ambient temperature, the purple or deep green solution of the divalent samarium triflate [Sm(OTf)2] was readily obtained. For this preparation, s-BuLi was the most effective as was evidenced by the reduction of 2-phenylethyl iodide in the presence of HMPA. The Sm(OTf)2 reagent mediated the Grignard-type reaction effectively in THF/HMPA; alkylation and allylation of ketones or aldehydes with alkyl, allyl, or benzyl halides proceeded via organosamarium intermediates. Diastereoselectivity of the samarium-Grignard reaction was examined using 2-methylcyclohexanone, 4-tert-butylcyclohexanone, and 2-phenylpropanal and was found to be higher in each case than that with SmI2. With 2-methylcyclohexanone, for example, Sm(OTf)2 gave the greatest ratio of axial alcohol:equatorial alcohol = 99:1, and SmI2 gave a ratio of 91:9. Halides containing an ester or a silyl group were reactive in the Reformatsky- or Peterson-type reaction, respectively, using the Sm(OTf)2 reagent.
- Fukuzawa, Shin-Ichi,Mutoh, Keisuke,Tsuchimoto, Teruhisa,Hiyama, Tamejiro
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p. 5400 - 5405
(2007/10/03)
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- METHYLENECYCLOALKANES. STRAIN AND PROPERTIES
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The synthesis of methylenecycloalkanes and of epoxides based on them was studied.The role of angular strain in the electron density distribution and the reactivity of the alkenes was investigated by quantum-chemical calculation by the LCAO-MO SCF method in the MINDO/3 valence approximation.The data from the calculation are compared with the spectral and kinetic parameters of the epoxidation of methylene-cycloalkanes by peracetic acid in ethyl acetate.
- Kas'yan, L. I.,Seferova, M. F.,Gorb, L. G.,Kozina, M. P.,Dryuk, V. G.
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p. 1019 - 1025
(2007/10/02)
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- Dehydration of Alcohols Catalysed by Metallic Sulphates Supported on Silica Gel
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Many metallic sulphates and hydrogen sulphates supported on silica gel efficiently catalyse dehydration of secondary and tertiary alcohols under mild conditions.The sulphates of CeIV, TiIV, and FeIII were most active.Silica gel was essential for the efficient dehydration in each case.The dehydration catalysed by Fe2(SO4)3, CuSO4, and NaHSO4 on silica gel was studied in detail.The order of the reactivity of alcohols was tertiary > secondary > primary.The dehydration activity of methanesulphonic acid was also enhanced (ca. 14 times at 90 deg C) by the presence of silica gel.Some mechanistic investigations were carried out.
- Nishiguchi, Takeshi,Kamio, Chizuko
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p. 707 - 710
(2007/10/02)
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- Reaction of Raney Nickel with Alcohols
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The reaction of Raney nickel with a variety of functional groups was studied.Ethers, esters, and alkyl chlorides were found to be stable to Raney nickel in refluxing toluene; however, alcohols were found to be reactive.Primary alcohols were oxidized to aldehydes and the subsequently decarbonylated, secondary alcohols were oxidized to the corresponding ketone, and tertiary alcohols were deoxygenated.
- Krafft, Marie E.,Crooks, William J.,Zorc, Branka,Milczanowski, Stephen E.
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p. 3158 - 3163
(2007/10/02)
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- A CONVENIENT AND EFFICIENT METALLATION OF METHYLSILANE. CARBONYL METHYLENATIONS USING METALLATED (2-AMINOALKOXY)TRIMETHYLSILANE
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When (2-aminoalkoxy)trimethylsilane is activated by two intramolecular heteroatoms (oxygen and nitrogen), it undergoes metallation efficiently with t-butyllithium to yield α-silyl carbanion.This process is applicable to carbonyl methylenations.Keywords-lithiated methylsilane; α-silyl carbanion; (2-aminoalkoxy)trimethylsilane; Peterson reaction; alkene synthesis
- Hosomi, Akira,Kohra, Shinya,Tominaga, Yoshinori,Shoji, Masataka,Sakurai, Hideki
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p. 1663 - 1665
(2007/10/02)
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- SmI2-Induced Deoxygenation of Epoxides and Its Application to Carbonyl Methylenation in Combination with Iodomethylation
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Deoxygenation of epoxides to olefins was effected by an efficient electron transfer system of SmI2-THF-HMPA in the presence of N,N-dimethylaminoethanol (DMAE) or glutaric anhydride.This procedure, in combination with the SmI2-induced iodomethylation, afforded a new, rapid and mild one-pot carbonyl methylenation method.
- Matsukawa, Mihaya,Tabuchi, Takanori,Inanaga, Junji,Yamaguchi, Masaru
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p. 2101 - 2102
(2007/10/02)
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- DEHYDRATION OF ALCOHOLS CATALYZED BY COPPER(II) SULFATE ADSORBED ON SILICA GEL.
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Copper(II) sulfate adsorbed on silica gel efficiently dehydrated secondary and tertiary alcohols under mild conditions to give olefins.The rate of dehydration of tertiary alcohols is much faster than that of secondary alcohols.
- Nishiguchi, Takeshi,Machida, Nakahira,Yamamoto, Etsuko
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p. 4565 - 4568
(2007/10/02)
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- CARBONYL METHYLENATION OF EASILY ENOLIZABLE KETONES
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An organometallic reagent prepared from CH2I2, Zn, and TiCl4 is effective for methylenation of the title ketones.
- Hibino, Jun-ichi,Okazoe, Takashi,Takai, Kazuhiko,Nozaki, Hitosi
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p. 5579 - 5580
(2007/10/02)
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- Wittig-type Reaction of Dimetallated Carbodianion Species as Produced by Zinc Reduction of gem-Polyhalogen Compounds in the Presence of Levis Acids
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Treatment of R1COR2 with a suspension prepared from diiodomethane, trimethylaluminium and excess zinc in tetrahydrofuran at room temperature affords olefins R1R2C=CH2 in fair (R1,R2=alkyl) to good (R1=alkyl, R2=H) yields.The ketone methylenation is better carried with another system consisting of CH2Br2-Zn-TiCl4.Ketones and aldehydes are transformed into α-chloro α,β-unsaturated esters or α,β-unsaturated esters in good yields on treatment with methyl trichloroacetate or t-butyl dichloroacetate (ethyl dibromoacetate) in the presence of diethylaluminium chloride and zinc.
- Takai, Kazuhiko,Hotta, Yuji,Oshima, Koichiro,Nozaki, Hitosi
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p. 1698 - 1702
(2007/10/02)
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- (TRIMETHYLSILYLMETHYL)TRIBUTYLTIN: A CONVENIENT IN SITU PRECURSOR OF TRIMETHYLSILYLMETHYLLITHIUM
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The transmetalation reaction between (trimethylsilylmethyl)tributyltin and n-butyllithium proceeds in quantitative yield at 0 deg C in a mixture of tetrahydrofuran and hexane to afford trimethylsilylmethyllithium and tetrabutyltin.The methylenation of aldehydes and ketones utilizing this in situ procedure is demonstrated.
- Seitz, David E.,Zapata, Antonio
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p. 3451 - 3454
(2007/10/02)
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