- 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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- Cyclopropanation of alkenes with CH2I2/Et3Al by the phase-vanishing method based on fluorous phase screen
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Phase-vanishing (PV) method using perfluorohexanes as a screen phase was applied to cyclopropanation reactions with CH2I2/Et2Zn and CH2I2/Et3Al. When Et3Al was used as a carbenoid generator, the reaction proceeded smoothly and desired cyclopropane derivatives were obtained in high yield. The PV cyclopropanation took 2 or 3 days to complete, however, reduction of reaction time by a factor of 2-3 was also achieved by vigorous stirring after the bottom CH2I2 layer disappeared.
- Matsubara, Hiroshi,Tsukida, Masaaki,Yasuda, Shinji,Ryu, Ilhyong
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scheme or table
p. 951 - 954
(2009/04/04)
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- Lanthanum metal-assisted cyclopropanation of alkenes with gem-dihaloalkanes
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It was confirmed that lanthanum metal was an efficient reagent for the reductive dehalogenation of gem-dihaloalkanes. When gem-dihaloalkanes were allowed to react with lanthanum metal in the presence of alkenes, cyclopropanation of the alkenes occurred under mild conditions giving the corresponding cyclopropanes in moderate to good yields.
- Nishiyama, Yutaka,Tanimizu, Hana,Tomita, Tsuyoshi
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p. 6405 - 6407
(2008/02/12)
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- Processing of cyclopropylarenes by toluene dioxygenase: Isolation and absolute configuration of metabolites
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Several arenes possessing a cyclopropyl substituent were subjected to enzymatic oxidation with toluene dioxygenase. The absolute configuration of metabolites was established by chemical means.
- Finn, Kevin J.,Rochon, Lena,Hudlicky, Tomas
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p. 3606 - 3613
(2007/10/03)
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- Highly diastereoselective hydrostannylation of allyl and homoallyl alcohols with dibutyl(trifluoromethanesulfoxy)stannane
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Dibutyl(trifluoromethanesulfoxy)stannane (Bu2Sn(OTf)H, 1a) was found to be very valuable for highly diastereoselective homolytic hydrostannylation of allyl and homoallyl alcohols. α,β-Disubstituted allyl alcohols and α,γ-disubstituted homoallyl alcohols were converted into γ- and δ-stannylated alcohols with high 1,2-syn and 1,3-syn diastereoselectivity, respectively. The origin of the stereochemical outcomes can be rationalized by conformational fixation of the intermediary β-stannylalkyl radical by coordination of the hydroxy group to the Lewis acidic tin center. Copyright
- Miura, Katsukiyo,Wang, Di,Hosomi, Akira
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p. 9366 - 9367
(2007/10/03)
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- A Novel Class of Tunable Zinc Reagents (RXZnCH2Y) for Efficient Cyclopropanation of Olefins
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A class of zinc reagents (RXZnCH2Y) generated with an appropriate organozinc is very effective for the cyclopropanation of olefins. The reactivity and selectivity of these reagents can be regulated by tuning the electronic and steric nature of the RX group on Zn. A reasonable level of enantioselectivity was obtained for the cyclopropanation of unfunctionalized olefins when a chiral (iodomethyl)zinc species was used, providing a valuable approach for the asymmetric cyclopropanation of unfunctionalized olefins.
- Lorenz, Jon C.,Long, Jiang,Yang, Zhiqiang,Xue, Song,Xie, Yinong,Shi, Yian
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p. 327 - 334
(2007/10/03)
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- A one-pot access to cyclopropanes from allylic ethers via hydrozirconation-deoxygenative ring formation
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A synthetic method for the direct transformation of allylic ethers into mono-, di- and trisubstituted cyclopropanes is presented.
- Gandon, Vincent,Szymoniak, Jan
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p. 1308 - 1309
(2007/10/03)
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- Oxidation of aryl- and diarylcyclopropanes in a pentasil zeolite: Ring opening with deprotonation or net hydrogen migration
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Incorporation of trans-1,2-diphenylcyclopropane (1) and its 3,3-D2- isotopomer into the channels of a redox-active pentasil zeolite (Na-ZSM-5) resulted in the formation of exo,exo-1,3-diphenylallyl radical (2.) and its 2-D1 isotopomer, respectively. This conversion requires oxidation, ring opening, and deprotonation, in an unspecified sequence. The allyl radical 2. is also formed upon incorporation of trans-1,3-diphenylpropene (3). A comparison with the solution photochemistry, in the presence or absence of added base, shows the conversion of 1 into 2. to be a zeolite-specific reaction. Incorporation of arylcyclopropanes 9 (R = H, OCH3) into ZSM-5 generated trans-propenylbenzene radical cations 10.+ (R = H, OCH3); the 2,2-D2 isotopomer of 9 (R = OCH3) gave rise to three different isotopomers of 10.+) (R = OCH3).
- Herbertz, Torsten,Lakkaraju, Prasad Sreeramachandra,Blume, Florian,Blume, Matthias,Roth, Heinz Dieter
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p. 467 - 472
(2007/10/03)
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- Exploring new reactive species for cyclopropanation
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An organozinc species RXZnCH2I generated by reacting Zn(CH2I)2 with RXH was found to be an efficient reagent for the cyclopropanation of olefins at room temperature. A 50.7% ee was obtained for the cyclopropanation of trans-β-methylstyrene when a chiral alcohol was used.
- Yang, Zhiqiang,Lorenz, Jon C.,Shi, Yian
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p. 8621 - 8624
(2007/10/03)
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- Conversion of non-activated alkenes into cyclopropanes with lithiated sulfones under nickel catalysis
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Summary -Lithiated alkyl ierf-butyl sulfones convert alkenes into cyclopropane derivatives under nickel catalysis. The new reaction appears to differ from the known cyclopropanation reactions from both the stereochemical and the electronic points of view. Elsevier.
- Gai, Yonghua,Julia, Marc,Verpeaux, Jean-Noel
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p. 817 - 829
(2007/10/03)
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- Picosecond radical kinetics. Ring openings of phenyl substituted cyclopropylcarbinyl radicals
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Rate constants for ring openings of the trans-(2-phenylcyclopropyl)carbinyl radical (1a), the cis-(2-phenylcyclopropyl)carbinyl radical (1b), and the (2,2-diphenylcyclopropyl)carbinyl radical (1c) were studied by competition kinetics using PTOC esters as radical precursors and hydrogen atom transfer trapping from benzeneselenol as the basis reaction. Radical la was studied in two solvents, toluene and THF; the experimental Arrhenius function for ring opening of 1a was log (kr·s) = 13.9 - 33/2.3RT (R in kcal/mol). It is possible that the immediate precursor to 1a, acyloxy radical 3a, suffers a concomitant decarboxylation-ring opening process that competes with simple decarboxylation leading to 1a. The experimental rate constant for ring opening of la at 25°C is 3 × 1011 s-1. Preliminary kinetic studies of radicals 1b and 1c gave Arrhenius functions of log (kr·s) = 13.9 - 3.1/2.3RT and log (kr·s) = 13.1 - 2.0/2.3RT, respectively, and the respective rate constants for ring openings at 25°C are 4 and 5 × 1011 s-1. Rate constants for ring openings of substituted cyclopropylcarbinyl radicals were estimated by Marcus theory using the known rate constants and equilibrium constant for the parent system and expected ΔG° values for the substituted systems. From these results, the estimated rate constants at 25°C for ring opening of 1a and 1b were 1 × 1011 s-1 and that for le was 4 × 1011 s-1. Precursors to radicals 1, such as the corresponding hydrocarbons, represent hypersensitive radical probes that, in principle, can provide unequivocal conclusions regarding the intermediacy of a radical in a reaction.
- Newcomb, Martin,Johnson, Cathy C.,Manek, M. Beata,Varick, Thomas R.
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p. 10915 - 10921
(2007/10/02)
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- Substituent Effects in the Solvolysis of p-(2-Substituted Cyclopropyl)-α-Methylbenzyl Chlorides
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The solvolysis rates of p-(cis- or trans-2-substituted cyclopropyl)-α-methylbenzyl chlorides including electron-donating and electron-attracting substituents relative to a hydrogen substituent were measured in 80percent aqueous acetone.The trans isomers w
- Kusuyama, Yoshiaki,Kubo, Takako,Iyo, Masami,Kagosaku, Tamami,Tokami, Kenjiro
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p. 2954 - 2960
(2007/10/02)
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- A Comparison of (Chloromethyl)- and (Iodomethyl)zinc Cyclopropanation Reagents
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A study comparing the rate of cyclopropanation of a range of olefins using (chloromethyl)- and (iodomethyl)zinc reagents is described.The (chloromethyl)zinc reagent derived from diethylzinc and chloroiodomethane is generally more reactive than the (iodomethyl)zinc analogue.The use of 1,2-dichloroethane as the solvent for these reactions was shown to be a crucial factor necessary to achieve clean, rapid, high-yielding cyclopropanations.The well-known directing effect of proximal oxygen substituents on the stereochemical outcome of "Simmons-Smith" cyclopropanations was shown to hold for the (chloromethyl)zinc reagent as well.The diethylzinc/chloroiodomethane reagent system in 1,2-dichloroethane should prove to be a valuable alternative to traditional (iodomethyl)zinc-based cyclopropanation reagents.
- Denmark, Scott E.,Edwards, James P.
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p. 6974 - 6981
(2007/10/02)
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- Synthesis and spectral characterization of a series of iron and ruthenium benzylidene complexes, Cp(CO)(L)M=CH(C6H4R)+ (M = Fe, Ru; L = CO, PPh3; R = p-H, p-F, p-CH3, p-OCH3). Barriers to a
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The α-ether complexes Cp(CO)2Fe-CH(OCH3)C6H4R (7a, R = H; 7b, R = p-F; 7c, R = p-CH3; 7d, R = p-OCH3; 7e, R = m-OCH3; 7f, R = p-CF3), Cp(CO)2Ru-CH(OCH3
- Brookhart,Studabaker, William B.,Humphrey, M. Beth,Husk, G. Ronald
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p. 132 - 140
(2008/10/08)
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- VIBRATIONAL CIRCULAR DICHROISM OF OPTICALLY ACTIVE CYCLOPROPANES. 3. TRANS-2-PHENYLCYCLOPROPANECARBOXYLIC ACID DERIVATIVES AND RELATED COMPOUNDS
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Vibrational circular dichroism (VCD) data are presented for a series of (1R,2R)-trans-2-phenyl-1-(R-substituted)cyclopropanes where R=COOCH3, COOCD3, COOH, CONH2, COCl, CN, CH2OH, CD2OD, CH3, CD3, and NH2 (1S,2R).In addition, VCD for (1S,2S)-1-phenylpropylene oxide is presented for comparison.These data can be correlated to show certain characteristic, structure-indicating transitions common to all of the molecules.This is particularly true in the cyclopropane C-H stretching bands in the near-IR and less so of CH2 deformations and ring modes in the mid-IR.To elucidate these comparisons it is necessary to interpret the frerquency shifts of the characteristic bands as the substituent is varied.The range of compounds studied permits such an analysis for certain characteristic modes.The results for monocarbonyl and-cyano substitution further explain the presence and absence, respectively, of coupled oscillator VCD in the corresponding symmetrically disubstituted cyclopropyl compounds.
- Yasui, Sritana C.,Keiderling, Timothy A.
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p. 2311 - 2320
(2007/10/02)
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- DIRECT CONVERSION OF ALKENES INTO METHYL-SUBSTITUTED CYCLOPROPANES USING AN ORGANOIRON ETHYLIDENE TRANSFER REAGENT
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(η5-C5H5)(CO)2FeCH(CH3)SPh (8) serves as a quite useful reagent for the transfer of ethylidene groups to alkenes to give methyl-substituted cyclopropanes in good yields.The reaction is accomplished by allowing 8 to react with an alkylating agent such as trimethyloxonium tetrafluoroborate or methyl fluorosulfonate in the presence of the alkene substrate.The active ethylidene transfer reagent is apparently a sulfonium salt which is too reactive to be isolated under normal conditions.In all csases, cyclopropanes are obtained stereospecifically with respect to the configuration of the starting alkenes, and with certain classes of substrates such as cis-disubstituted alkenes, the reaction also occurs with very high syn-stereoselectivity.
- Kremer, Kenneth A. M.,Helquist, Paul
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p. 231 - 252
(2007/10/02)
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