- Experimental and Computational Studies of Palladium-Catalyzed Spirocyclization via a Narasaka-Heck/C(sp3or sp2)-H Activation Cascade Reaction
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The first synthesis of highly strained spirocyclobutane-pyrrolines via a palladium-catalyzed tandem Narasaka-Heck/C(sp3 or sp2)-H activation reaction is reported here. The key step in this transformation is the activation of a δ-C-H bond via an in situ generated σ-alkyl-Pd(II) species to form a five-membered spiro-palladacycle intermediate. The concerted metalation-deprotonation (CMD) process, rate-determining step, and energy barrier of the entire reaction were explored by density functional theory (DFT) calculations. Moreover, a series of control experiments was conducted to probe the rate-determining step and reversibility of the C(sp3)-H activation step.
- Wei, Wan-Xu,Li, Yuke,Wen, Ya-Ting,Li, Ming,Li, Xue-Song,Wang, Cui-Tian,Liu, Hong-Chao,Xia, Yu,Zhang, Bo-Sheng,Jiao, Rui-Qiang,Liang, Yong-Min
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supporting information
p. 7868 - 7875
(2021/05/27)
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- Organic base-catalysed solvent-tuned chemoselective carbotrifluoromethylation and oxytrifluoromethylation of unactivated alkenes
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An unprecedented and efficient organic base-catalysed highly chemoselective carbo- and oxytrifluoromethylation of unactivated alkenes with Togni's reagent was developed. The switchable chemoselectivity was tuned by simply changing the organic base catalyst and solvent. Mechanistic studies indicated that a radical cyclization pathway for carbotrifluoromethylation in DMSO and a carbocation pathway for oxytrifluoromethylation in DCE were probably involved.
- Yang, Ning-Yuan,Li, Zhong-Liang,Ye, Liu,Tan, Bin,Liu, Xin-Yuan
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supporting information
p. 9052 - 9055
(2016/07/21)
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- Asymmetric Copper-Catalyzed Carbozincation of Cyclopropenes en Route to the Formation of Diastereo- and Enantiomerically Enriched Polysubstituted Cyclopropanes
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The enantioselective synthesis of cyclopropylzinc reagents has been achieved via a copper-catalyzed carbozincation of 3,3-disubstituted cyclopropenes with diorganozinc reagents. The obtained organozinc compounds can be easily functionalized with a broad range of electrophiles, including palladium-catalyzed cross-couplings, affording highly substituted cyclopropanes. The operationally simple procedure using very low quantities of a commercially available and inexpensive copper catalyst provides a new tool for the synthesis of highly enantioenriched cyclopropanes as single diastereoisomers.
- Müller, Daniel S.,Marek, Ilan
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supporting information
p. 15414 - 15417
(2015/12/26)
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- The methylation of alkenes to triptyls with dimethyl carbonate
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A series of methylating reagents: methanol, dimethylether and dimethylcarbonate, have been evaluated for their ability to methylate 2,3-dimethylbut-2-ene to yield triptyls (a mixture of triptane and triptene). The results presented highlight that dimethylcarbonate is a far superior methylating agent compared to methanol or dimethylether, providing a higher yield of triptyls.
- Armitage, Gareth G.,Bonati, Matteo L. M.,Guo, Neng,Gaemers, Sander,Shabaker, John W.
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p. 370 - 374
(2013/05/21)
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- Process for the production of hydrocarbons
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A process for the production of a hydrocarbon comprises reacting methanol, dimethyl ether, methyl acetate or mixtures thereof, with an olefin in the presence of methyl halide and/or hydrogen halide and at least one compound selected from the group consisting of ruthenium carbonyl halides, osmium carbonyl halides and mixtures thereof.
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Page/Page column 4-6
(2008/06/13)
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- PROCESS FOR THE PRODUCTION OF A HYDROCARBON
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A process for the production of a hydrocarbon which comprises contacting, in a reactor, methanol and/or dimethyl ether with a catalyst comprising a metal halide, such as a zinc halide, in which the methanol and/or dimethyl ether is contacted with the catalyst in the presence of at least one phosphorus compound having at least one P-H bond.
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Page/Page column 19-20; 25-26
(2008/06/13)
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- On the mechanism of the conversion of methanol to 2,2,3-trimethylbutane (triptane) over zinc iodide
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Methanol is converted to a mixture of hydrocarbons by reaction with zinc iodide at 200 °C with one highly branched alkane, 2,2,3-trimethylbutane (triptane), being obtained in surprisingly high selectivity. Mechanistic studies implicate a two-stage process, the first involving heterogeneously catalyzed formation of a carbon-carbon-bonded species, probably ethylene, that undergoes homogeneously catalyzed sequential cationic methylation to higher hydrocarbons. The first stage can be bypassed by addition of olefins, higher alcohols, or arenes, which act as initiators. Rationales for the particular activity of zinc iodide and for the selectivity to triptane are proposed.
- Bercaw, John E.,Diaconescu, Paula L.,Grubbs, Robert H.,Kay, Richard D.,Kitching, Sarah,Labinger, Jay A.,Li, Xingwei,Mehrkhodavandi, Parisa,Morris, George E.,Sunley, Glenn J.,Vagner, Patrick
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p. 8907 - 8917
(2007/10/03)
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- PYRIDOPYRAZINES FOR COMBATTING PHYTOPATHOGENIC FUNGI
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The compounds of the general formula (I) wherein R, R1, R2, R8, and R9 are defined as set forth in the specification.
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Page/Page column 11-12
(2008/06/13)
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- Novel, Very Strong, Uncharged Auxiliary Bases; Design and Synthesis of Monomeric and Polmer-Bound Triaminoiminophosphorane Bases of Broadly Varied Steric Demand
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The synthesis and properties of a number of very strong iminophosphorane bases up to an extremely high level of steric hindrance are described.They cover a range of ca. 4 pK units in basicity and a range of more than 11 orders of magnitude in their rates of methylation with methyl iodide.Most of the systems are readily prepared in up to molar quantities, conveniently recovered from their salts and are of high chemical and thermal stability.Crystal structures were determined in order to parametrize a force field, which is utilized in molecular modeling studies offering a rationalization of the observed differences in steric hindrance and basicity.Depending on the degree of steric protection of the basic center, these novel bases are proposed as unprecedented, versatile auxiliary bases in E2 eliminations and in reactions involving deprotonation in the presence of more or less strong electrophiles. - Key Words: Uncharged auxiliary bases / Triaminoiminophosphorane bases / Deprotonation / Hindered bases / Polymeric bases
- Schwesinger, Reinhard,Willaredt, Juergen,Schlemper, Helmut,Keller, Manfred,Schmitt, Dieter,Fritz, Hans
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p. 2435 - 2454
(2007/10/02)
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- Synthesis, structure, and reactions of heterobinuclear μ-methylene complexes
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Sources of the reactive fragment Cp2Ti==CH2 react with a variety of late-transition-metal complexes containing μ-halides [Cl-MLn]2 to yield early-late binuclear complexes containing μ-CH2, and μ-Cl ligands. Complexes containing Rh, Ir, Pt, Pd, and Au have been prepared and characterized. The X-ray structure of the complex Cp2Ti-CH2-RhCl(COD) (COD = 1,5-cyclooctadiene) prepared from Cp2Ti-CH2C-(CH3)2-CH2 and [Cl-Rh(COD)]2 has been determined. Crystallographic data: space group Pbcm; Z = 4; a = 8.268 (2) A?, b = 16.409 (4) A?, c = 12.604 (3) A?; V = 1710 (1) A?3. The structure was refined to a final R of 0.069 and R3σ of 0.048 for the 1061 reflections that had Fo > 3σ(Fo).
- Mackenzie, Peter B.,Coots, Robert J.,Grubbs, Robert H.
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- Synthesis of group 4 metallocene-substituted ylides and their reactions with ketones
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A new method has been developed to synthezise group 4 metallocene ylides.Ph3P=CH2 reacts with in situ generated (η2-ethene)MCp2 (M = Zr, Hf), (η2-aryne)MCp2 (M = Ti, Zr), or with (η4-conjugated diene)MCp2 (M = Zr, Hf) via intramolecular hydrogen transfer to form metallocene ylides Cp2M(R)CH=PPh3.In some cases competitive methylene transfer occurs leading to four-membered metallacycles.The metallocene ylides all exhibit a substantial metal to carbon ?-interaction, increasing in strength on going from hafnium to titanium as the central metal atom.Ylide reactivity is greatly reduced.With a non-enolizable ketone, Cp2Zr(CH2CH=CHCH3)CH=PPh3 reacts via the reverse of metallocene ylide forming reaction.With enolizable ketones, zirconocene or hafnocene ylides serve as bases and form metal enolates.The resulting enolate (E)/(Z) ratio strongly depends on the group R of the metallocene ylide base Cp2Zr(R)CH=PPh3.
- Erker, Gerhard,Czisch, Peter,Mynott, Richard
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- Electrophilic Cleavage of Cyclopropanes. Acetolysis of Alkylcyclopropanes
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The solvent kinetic hydrogen isotope effect showed that proton transfer is at least partially rate determining for the acetolysis of cyclopropanes which span a range of 1010 in reactivity.The energies and structures of protonated cyclobutanes were calculated and provide an explanation for the large difference in reactivity between cyclopropanes and cyclobutanes despite their similarity in enthalpies of reaction.The rates and products of acetolysis of a series of alkyl-substituted cyclopropanes were examined.The data, along with the results of ab initio calculations, indicate that for alkyl-substituted cyclopropanes, the protonated species is highly unsymmetrical.Cleavage of the cyclopropane ring always occurs so that the nucleophile becomes attached to the most substituted carbon, but the proton may attack either of the remaining carbons.Proton attack may lead to either retention or inversion of configuration depending on the orientation of the attacking proton with respect to the ring.
- Wiberg, Kenneth B.,Kass, Steven R.
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p. 988 - 995
(2007/10/02)
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- Perhydroazulenes. 4. The 6-tert-Butyl-4-oxoperhydroazulene System
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The four diastereoisomeric 6-tert-butyl-4-oxoperhydroazulenes (3-6) have been prepared and characterized.Molecular mechanics calculations suggest that each of these ketones will exist as one or both of a pair of closely related conformers as follows: 3, C-3 or TC-7; 4, TC-1 or TC-2; 5, B-3 or TB-4; 6, TC-4 or TC-5.A combination of 1H NMR data and X-ray crystallographic data support the correctness of these predictions.
- House, Herbert O.,Gaa, Peter, C.,Lee, Joseph H. C.,VanDerveer, Don
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p. 1670 - 1678
(2007/10/02)
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- Thermolytic Reactions of Esters. Part 12. Steric versus Polar Effects in Pyrolytic β-Elimination of Acetic Acid from (Tertiary) Alkyl Acetates
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The vapour-phase pyrolysis of the crowded tertiary alkyl acetates AcOCMe2But (II) and AcOCMePri2 (III) to give acetic acid and the appropriate alkene(s) has been studied.Rates of formation of alk-1-ene and of isobutene from t-butyl acetate were compared.On this basis steric acceleration in pyrolysis of AcOR, employing known steric parameters Es' from groups R, is quantitatively analysed.Altough the steric effect can be quite substantial, the remarkable rate increase in the series AcOEt-AcOPri-AcOBut is largely due to a polar effect.A rationale is presented for the apparent inconsistency : the rate effect of α-alkylation in R is even larger than in SN1-type solvolysis of RBr, suggesting a large charge separation AcO-, R+ in the transition state for concerted β-elimination, whereas the Hammett ρ value observed for pyrolysis of e.g.AcOCH(Me)C6H4Z is only a few percent of that associated with formation of benzylic carbenium ions.
- Louw, Robert,Vermeeren, Hans P.W.,Vogelzang, Martijn W.
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p. 1875 - 1880
(2007/10/02)
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- Addition of 2,2,3-Trimethylbutane to Slowly Reacting Mixtures of Hydrogen and Oxygen at 480 deg C
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The oxidation of 2,2,3-trimethylbutane(TRIMB) has been studied by adding traces of the alkane to slowly reacting mixtures of H2+O2 in aged boric-acid-coated vessels at 480 deg C.Rate constants for H and OH attack on TRIMB have been obtained and, by use of an additivity principle, Arrhenius parameters of log10(A/dm3mol-1s-1)=9.32+/-0.13 and E=460+/-950 J mol-1 are suggested for OH attack at a tertiary C-H bond in alkanes from a combination of the present results with studies at lower temperatures.Propene, isobutene, and 2,2,3-trimethylbut-1-ene (TRIMB-1) are the major initial products, the yield of the latter increasing markedly at high O2 pressures.The proportions of the three species of trimethylbutyl radicals formed in each mixture have been estimated.Two of the species of trimethylbutyl radicals react almost completely by homolysis of the strained central C-C bond to give propene and isobutene as products.The tird radical (CH3)3CC(CH3)2 is removed by either reaction (1C) or (2C), and it is suggested that (1C) occurs by a concerted mechanism: (CH3)3CC(CH3)2 i-C4H8 + i-C3H7 (1C) (CH3)3CC(CH3)2 + O2 (CH3)3CC(CH3)=CH2 + HO2. (2C) Rate constants have been obtained for a number of the homolysis reactions of the trimethylbutyl radicals, for which there is a good correlation between log k and ΔU, the internal energy change.
- Baldwin, Roy R.,Walker, Raymond W.,Walker, Robert W.
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p. 2157 - 2174
(2007/10/02)
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- Decomposition of 2,2,3-Trimethylbutane in the Presence of Oxygene
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The decomposition of 2,2,3-trimethylbutane in the presence of O2 in KCl-cloated vessels has been studied at 480 deg C and 550 deg C over the pressure range 60-500 Torr.At low alkane pressures, where the chain contribution is small, the results are consistent with a simple mechanism comprising reactions (10), (11), (2) and (3). (CH3)3CCH(CH3)2 -> t-C4H9 + i-C3H7 (10), i-C3H7 + O2 -> C3H6 + HO2 (11), t-C4H9 + O2 -> i-C4H8 + HO2 (2), HO2 -> 1/2 H2O + 3/4 O2 (3).From measurements of the i-butene yields, accurate rate constants may be obtained for reaction (10) wich, when combined with Tsangs results, give log10(A10/s-1) = 16.46 +/- 0.12 and E10 = 305.0 +/- 1.5 kJmol-1 over the temperature range 480-925 deg C.Following a discussion of the thermochemistry of reaction (10) and the value of k-10, values of ΔfHo298(t-Bu) = 37.6 +/- 2.0 and ΔfHo298(i-Pr) = 80.8 +/- 4.0 kJmol-1 are recommended, wich correspond to Do298(t-Bu) = 390.2 +/- 2.0 and Do298(i=Pr) = 402.5 +/- 4.0 kJmol-1, respectively.Two of three species of radicals formed by radial attack on 2,2,3-trimethylbutane appear to react solely by C-C homolysis of the central C-C bond.The third radical, (CH3)3CC(CH3)2, reacts mainly by homolysis, but also forms the minor initial products 2,3,3-trimethylbut-1-ene, acetone and 2,3-dimethylbut-2-ene.A value of k17 = 1.4 * 103s-1 at 480 deg C has been obtained. (CH3)3CC(CH3)2 -> (CH3)2=C(CH3)2 + CH3 (17).
- Baldwin, Roy R.,Walker, Raymond W.,Walker, Robert W.
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p. 825 - 837
(2007/10/02)
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- Cyclopropanimines, V. - Ring-substituted Cyclopropanimines from α-Bromoketimines
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Good yields of N-alkyl- and N-arylcyclopropanimines 9 are obtained from the α-bromoketimines 8 in a 1,3-elimination of hydrogen bromide by means of an excess of potassium tert-butoxide in tetrahydrofuran.The α-bromoimine 14 forms the imine 15 derived from bicyclohexane.In part, the limitations of this 1,3-elimination can be traced back to an unsufficient acidity of the α'-protons of the α-bromoimines.All isolated cyclopropanimines are colorless, in vacuo distillable oils or low-melting crystals.Their stability parallels the size of the nitrogen subtituent.As shown by their 1H- and 13C-NMR spectra as well as the measurement of the ASIS and the temperature dependence of the 1H-NMR spectra the cyclopropanimines 9 exist as mixtures of (E,Z)-diastereomers.The (E)/(Z) ratio of the diastereomers increases with increasing size of the nitrogen substituent.According to its 13C-NMR spectrum, the bicyclohexanimine 15 prefers the boat conformation.The IR, UV, 1H-, and 13C-NMR spectra of the cyclopropanimines are compared to those of other heteromethylenecyclopropanes and of acyclic compounds.The main fragmentation paths in the mass spectrometer do not correspond to the thermal decomposition of the cyclopropanimines into isocyanides and alkenes.
- Quast, Helmut,Frank, Rolf,Heublein, Alfred,Schmitt, Edeltraud
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p. 1814 - 1835
(2007/10/02)
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- Gas-Phase Pyrolysis Kinetics of 2-Substituted-2-Propyl Acetates. Effect of Substituents on the α-Carbon of Tertiary Acetates
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Three 2-substituted-2-propyl acetates undergo a homogeneous, first-order, unimolecular elimination in the gas phase at temperatures from 230 to 340 deg C and pressures from 56 to 210 mmHg.The rate constants are expressible by the Arrhenius equation: for 2,3,3-trimethyl-2-butyl acetate, log k (s-1) = (14.40 +/- 0.49) - (171.5 +/- 4.6) kJ mol-1 (2.303RT)-1; for α-acetoxyisobutyronitrile, log k (s-1) = (14.45 +/- 0.82) - (198.7 +/- 8.8) kJ mol-1 (2.303RT)-1; for methyl α-acetoxyisobutyrate, log k (s-1) = (12.53 +/- 0.32) - (176.1 +/- 3.6) kJ mol-1 (2.303RT)-1.The Taft correlation for the pyrolyses of tertiary esters with substituents on the α-carbon is projected and discussed.Many of these substituents enhance the elimination by steric accelaration.
- Martin, Ignacio,Chuchani, Gabriel,Avila, Irama,Rotinov, Alexandra,Olmos, Rolando
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