- α-Silicon- and α-alkynyl-substituted vinyl cations
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The solvolytic reactivity of a number of silicon- and alkynyl-substituted vinyl triflates was investigated in aqueous ethanol.Activation parameters and solvent m values were determined for all subtrates.Relative rate data show that the Me3Si group is accelerating and hence stabilizing relative to hydrogen but destabilizing relative to a t-Bu group.The α-ethynyl substituent causes a rate decrease compared to a methyl group despite its ?-donating resonance ability.These results are discussed.
- Schiavelli, Melvyn D.,Jung, Dorothy M.,Vaden, Anne Keller,Stang, Peter J.,Fisk, Thomas E.,Morrison, David S.
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Read Online
- Ynonylation of Acyl Radicals by Electroinduced Homolysis of 4-Acyl-1,4-dihydropyridines
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Herein we report the conversion of 4-Acyl-1,4-dihydropyridines (DHPs) into ynones under electrochemical conditions. The reaction proceeds via the homolysis of acyl-DHP under electron activation. The resulting acyl radicals react with hypervalent iodine(III) reagents to form the target ynones or ynamides in acceptable yields. This mild reaction condition allows wider functionality tolerance that includes halides, carboxylates, or alkenes. The synthetic utility of this methodology is further demonstrated by the late-stage modification of complex molecules.
- Luo, Xiaosheng,Wang, Ping
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supporting information
p. 4960 - 4965
(2021/07/20)
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- γ-Carboline synthesis enabled by Rh(iii)-catalysed regioselective C-H annulation
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A redox-neutral Rh(iii)-catalyzed C-H annulation of indolyl oximes was developed. Relying on the use of various alkynyl silanes as the terminal alkyne surrogates, the reaction exhibited a reverse regioselectivity, thus giving an exclusive and easy way for the synthesis of a wide range of substituent free γ-carbolines at C3 position with high efficiency. Deuterium-labelling experiments and kinetic analysis have preliminarily shed light on the working mode of this catalytic system. This journal is
- Jiang, Bo,Jia, Jingwen,Sun, Yufei,Wang, Yichun,Zeng, Jing,Bu, Xiubin,Shi, Liangliang,Sun, Xiaoying,Yang, Xiaobo
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supporting information
p. 13389 - 13392
(2020/11/10)
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- “Doubly Orthogonal” Labeling of Peptides and Proteins
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Herein, we report a cysteine bioconjugation methodology for the introduction of hypervalent iodine compounds onto biomolecules. Ethynylbenziodoxolones (EBXs) engage thiols in small organic molecules and cysteine-containing peptides and proteins in a fast and selective addition onto the alkynyl triple bond, resulting in stable vinylbenziodoxolone hypervalent iodine conjugates. The conjugation occurs at room temperature in an open flask under physiological conditions. The use of an azide-bearing EBX reagent enables a “doubly orthogonal” functionalization of the bioconjugate via strain-release-driven cycloaddition and Suzuki-Miyaura cross-coupling of the vinyl hypervalent iodine bond. We successfully applied the methodology on relevant and complex biomolecules, such as histone proteins. Through single-molecule experiments, we illustrated the potential of this doubly reactive bioconjugate by introducing a triplet-state quencher close to a fluorophore, which extended its lifetime by suppressing photobleaching. This work is therefore expected to find broad applications for peptide and protein functionalization. Understanding the molecular basis of life is essential in the search for new medicines. Chemical biology develops molecular tools for studying biological processes, setting the basis for new diagnostics and therapeutics, and relies heavily on the ability to selectively modify biomolecules. Two approaches have been especially fruitful: (1) selective modification of natural biomolecules and (2) selective reaction between non-natural functionalities in the presence of biomolecules (the so-called orthogonal bioconjugation). In our work, we contribute to both by transferring highly reactive hypervalent iodine reagents to cysteine residues in proteins and peptides. The obtained bioconjugates retain the reactive hypervalent bonds, which can be selectively functionalized via a metal-mediated reaction. Combined with a traditional azide tag, our approach allows a doubly orthogonal functionalization of biomolecules and is hence expected to be highly useful in chemical biology. Chemical biology develops molecular tools for studying biological processes, setting the basis for new diagnostics and therapeutics, and relies heavily on the ability to modify selectively biomolecules. In our work, we introduce hypervalent iodine bonds into peptides and proteins, via functionalization of cysteine, by using unique cyclic reagents developed in our group. The hypervalent bond can then be selectively modified in the presence of both natural and synthetic functional groups, opening new opportunities for applications in chemical biology.
- Tessier, Romain,Ceballos, Javier,Guidotti, Nora,Simonet-Davin, Raphael,Fierz, Beat,Waser, Jerome
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supporting information
p. 2243 - 2263
(2019/08/08)
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- One-pot, three-component arylalkynyl sulfone synthesis
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A one-pot three-component protocol for the preparation of arylsulfonyl alkynes through the reaction of ethynyl-benziodoxolone (EBX) reagents, DABSO (DABCO?·SO2), and either organomagnesium reagents or aryl iodides with a palladium catalyst is r
- Chen, C. Chun,Waser, Jerome
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supporting information
p. 736 - 739
(2015/03/05)
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- Ethynyl benziodoxolones for the direct alkynylation of heterocycles: Structural requirement, improved procedure for pyrroles, and insights into the mechanism
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This report describes a full study of the gold-catalyzed direct alkynylation of indoles, pyrroles, and thiophenes using alkynyl hypervalent iodine reagents, especially the study of the structural requirements of alkynyl benziodoxolones for an efficient acetylene transfer to heterocycles. An improved procedure for the alkynylation of pyrroles using pyridine as additive is also reported. Nineteen alkynyl benziodoxol(on)es were synthesized and evaluated in the direct alkynylation of indoles and/or thiophenes. Bulky silyl groups as acetylene substituents were optimal. Nevertheless, transfer of aromatic acetylenes to thiophene was achieved for the first time. An accelerating effect of a methyl substituent in both the 3-and 6-position of triisopropylsilylethynyl-1,2-benziodoxol-3(1H)-one (TIPS-EBX) on the reaction rate was observed. Competitive experiments between substrates of different nucleophilicity, deuterium labeling experiments, as well as the regioselectivity observed are all in agreement with electrophilic aromatic substitution. Gold(III) 2-pyridinecarboxylate dichloride was also an efficient catalyst for the reaction. Investigations indicated that gold(III) could be eventually reduced to gold(I) during the process. As a result of these investigations, a π activation or an oxidative mechanism are most probable for the alkynylation reaction.
- Brand, Jonathan P.,Chevalley, Clara,Scopelliti, Rosario,Waser, Jerome
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supporting information; experimental part
p. 5655 - 5666
(2012/06/01)
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- Unique σ-bond metathesis of silylalkynes promoted by an ansa-dimethylsilyl and oxo-bridged uranium metallocene
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The tetrachloride salt of uranium reacts with 1 equiv of the lithium ligand Li2[(C5Me4)2SiMe2] in DME to form the complex [η5-(C5Me4)2SiMe2]UCl2·2LiCl·2DME (1), which undergoes a rapid hydrolysis in toluene to yield the dimeric bridged monochloride, monooxide complex [{[η5-(C5Me4)2SiMe2]UCl}2(μ-O)(μ-Cl)?Li?1/2DME]2 (2). Metathesis of 2 with BuLi in DME gives the mono-bridged dibutyl complex {[η5-(C5Me4)2SiMe2]UBu}2(μ-O) (3). Complex 2 was characterized by solid-state X-ray analysis. Complex 3 was found to be an active catalyst for the disproportionation metathesis of TMSC≡CH (TMS = SiMe3) and the cross-metathesis of TMSC≡CH or TMSC≡CTMS with various terminal alkynes. The metathesis of TMSC≡CH gives TMSC≡CTMS and HC≡CH, whereas the cross-metathesis of TMSC≡CH or TMSC≡CTMS with terminal alkynes (RC≡CH) yields TMSC≡CTMS, TMSC≡CR, and HC≡CH. In addition, TMSC≡CCH3 also was found to react with tBuC≡CH, yielding TMSC≡CBut and CH3C≡CH. A plausible mechanism for the catalytic process is presented. Copyright
- Wang, Jiaxi,Gurevich, Ylia,Botoshansky, Mark,Eisen, Moris S.
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p. 9350 - 9351
(2007/10/03)
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- Exploring skeletal diversity via ring contraction of glycal-derived scaffolds
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(Chemical Equation Presented) Aryl ether C-glycoside scaffolds have been prepared from tri-O-acetyl-D-glucal by C-glycosylation followed by allylic substitution with phenols mediated by Pd(0). The aryl ethers were subjected to either [3,3]-sigmatropic rea
- Yeager, Adam R.,Min, Geanna K.,Porco Jr., John A.,Schaus, Scott E.
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p. 5065 - 5068
(2007/10/03)
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- A simple synthesis of B-2-(1-trimethylsilyl-1-alkyl)-1,3,2-dioxaborinanes. Isolation and selective oxidation to 1-trimethylsilyl-1-alkanols
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(Z)-1-Trimethylsilyl-1-alkenes easily prepared by the hydroboration of the corresponding 1-trimethylsilyl-1-alkynes followed by protonolysis with acetic acid, readily react with dibromoborane-methyl sulfide complex in dichloromethane for 6 h. The resulting solution is then treated with 1, 3-propane diol in a 1:1 mixture of dichloromethane and n-pentane at 0°C for half an hour to provide the corresponding gem-dimetalloalkanes containing boron and silicon. These alpha-trimethylsilylalkylboronate esters are purified by vacuum distillation in high yields (72-84%) and the structures of these novel intermediates are further confirmed by selective oxidation with alkaline hydrogen peroxide to provide the corresponding alcohols containing trimethylsilyl group.
- Bhat, Narayan G.,Garza, Amanda
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p. 6833 - 6835
(2007/10/03)
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- Synthesis of internal acetylenes from vinylic tellurides
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Vinylic tellurides were prepared by carbotelluration of acetylenes under light. The subsequent oxidation with sodium hypochlorite followed by pyrolysis gave internal acetylenes in good yields. Combination of these reactions provides a useful method for introduction of alkyl groups to terminal acetylenes.
- Terao, Jun,Kambe, Nobuaki,Sonoda, Noboru
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p. 5511 - 5512
(2007/10/03)
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- Small Rings, 78. - Tri-tert-butyl(trimethylsilyl)cyclobutadiene and Tri-tert-butyl(trimethylsilyl)tetrahedrane
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The chemistry of diazo(1,2,3-tri-tert-butylcyclopropenyl)(trimethylsilyl)methane (6) is unexpectedly diverse.Upon irradiation it fragments exclusively into the acetylenes 7 and 8.Flash thermolysis, on the other hand, gives - aside from the two acetylenes - tri-tert-butylazete (10) and trimethylsilyl cyanide (11).Upon heating 6 presumbaly isomerizes via betaine 17 to Dewar-diazabenzene 13 - which is split into 10 and 11 - and diazabenzvalene 18.This reaction course is supported by the isolation of the carbonyliron complexes 15 and 16. - The CuCl-catalyzed thermal decomposition again follows a different route.Under these conditions tri-tert-butyl(trimethylsilyl)cyclobutadiene (5) is formed, probably as a weak CuCl complex.Only after addition of ethylenebis(diphenylphosphane) free cyclobutadiene 5 can be isolated.Upon irradiation of 5 a quantitative isomerization to tri-tert-butyl(trimethylsilyl)tetrahedrane (29) occurs.This second, spectroscopically unequivocally confirmed tetrahedrane melts at 179 deg C.In solution the isomerization to cyclobutadiene 5 starts at about 160 deg C.That means, it is thermally even more stable than tetra-tert-butyltetrahedrane. - Key Words: Diazo compounds / Transition-metal complexes / Photoisomerization / Homocyclopropenylium ions
- Maier, Guenther,Born, Dieter,Bauer, Ines,Wolf, Reinhard,Boese, Roland,Cremer, Dieter
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p. 173 - 190
(2007/10/02)
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- Acylsilenes (3-Oxo-1-sila-1-propenes) from Acyl(disilanyl)carbenes
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UV photolysis of diazo(disilanyl)methyl ketones 2 in benzene generates acyl(disilanyl)carbenes 3, which rearrange to 3-oxo-1-sila-1-propenes 4.The latter compounds are reactive intermediates which either cyclize to 1-oxa-2-sila-3-cyclobutenes 5 or form th
- Schneider, Klaus,Daucher, Birgit,Fronda, Antonio,Maas, Gerhard
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p. 589 - 594
(2007/10/02)
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- Cyclic Isomers and Cyclodimers of 3-Oxo-1-silaprop-1-enes
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3-Oxo-1-silaprop-1-enes, when generated by photochemical decomposition of α-diazo-α-silyl carbonyl compounds, cyclize to 1-oxa-2-silacyclobut-3-enes provided that the substituent at C-3 is sterically demanding; otherwise, the head-to-tail cyclodimers (1,5,dioxa-2,6-disilacyclo-octa-3,7-dienes) are obtained.
- Maas, Gerhard,Schneider, Klaus,Ando, Wataru
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- SYNTHESIS OF TERTIARY ALKYL-SUBSTITUTED ACETYLENES BY ELECTROPHILIC ADDITION TO SILYLACETYLENES
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The reaction of silylacetylenes 6-8 with tertiary alkyl halides 11-13 under Lewis acid catalysis affords tertiary alkyl-substituted acetylenes 1-5.The reaction occurs under mild conditions (from -78 to -17 deg C) and requires fairly short times (1-6 h).Se
- Capozzi, Giuseppe,Ottana, Rosaria,Romeo, Giovanni,Marcuzzi, Franco
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p. 311 - 314
(2007/10/02)
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- Sulfone reagents in organic synthesis. VI. Sulfonyl- and silyl-substituted hydrocarbons as versatile carbanion precursors in organic synthesis
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The basic organometallic chemistry of β-silyl-substituted acetylenic, vinylic and alkyl sulfones has been investigated, with attention being given to metallation, carbometallation and the chemical reduction of carbon-carbon unsaturation. 2-Trimethylsilylvinyl and 2-trimethylsilylalkyl sulfones underwent smooth and stereoselective lithiation with RLi on the carbon α to the sulfonyl group. Carbometallation of vinyl sulfones could be achieved with RMgX or LiCuR2, but acetylenic sulfones carbometallated smoothly only with LiCuR2; with RMgX or RLi, these acetylenes underwent alkyldesulfonylation. The utility in synthesis of these metallo derivatives of sulfonyl-silyl-hydrocarbons is discussed and their value in elaborating carbon skeletons is illustrated for the preparation of alkenes, allenes, carbocycles and stereo-defined vinyl sulfones.
- Eisch, John J.,Behrooz, Mohammad,Dua, Suresh K.
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p. 121 - 136
(2007/10/02)
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- Preparation of Cumulenes by Lithium Metal Addition to 1,3-Diynes. X-Ray Structure of 2, a 1,4-Dilithiobutatriene Dimer
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Addition of lithium metal to 2,2,7,7-tetramethyl-3,5-octadiyne (9) in tetrahydrofuran (THF) gave 3,6-dilithio-2,2,7,7-tetramethyl-3,4,5-octatriene (10), as a crystalline bis-THF addukt.X-ray analysis revealed the dilithiobutatriene 10 to have a dimeric cis-structure with two different kinds of lithium atoms and a true butatriene geometry (19).Model MNDO calculations (both with and without solvation) agree remarkably well with experiment and help reveal why the observed structure is preferred over alternative geometrical arrangements.
- Neugebauer, Wolfgang,Geiger, Gottfried A. P.,Kos, Alexander J.,Stezowski, John J.,Schleyer, Paul von Rague
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p. 1504 - 1516
(2007/10/02)
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- HOCHSUBSTITUIERTE TRICYCLOPENTANONE UND CYCLOPROPENYLDIAZOMETHANE - VORSTUFEN FUER TETRAHEDRANE?
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Reaction of tri-tert-butylcyclopropenylium tetrafluoroborate 7 with the Li-salt of tert-butyldiazomethane leads to the astonishingly stable diazo compound 6.The trimethylsilyl derivative 8 can be prepared via the same route.On photolysis or pyrolysis both
- Maier, Guenter,Reuter, Karl Arnold,Reisenauer, Hans Peter
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p. 1845 - 1848
(2007/10/02)
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- THE ELECTRON SPIN RESONANCE SPECTRA OF THE ANNULENE (CYCLOBUTADIENE) RADICAL CATIONS, R4C4+.
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A series of simple (R=R') and mixed (RR') cyclobutadiene radical cations, R2R'2C4+., have been prepared by photolysis of the alkynes, RCCR' or of mixtures of the alkynes RCCR and R'CCR', in dichloromethane in the presence of aluminium chloride, and the e.s.r. spectra have been recorded.The magnitude of the 13C hyperfine coupling in Et4C4+. confirms that it is a ?-radical, with no evidence for out-of-plane or in-plane (Jahn-Teller) distortion.The values of a(Hβ) for the radicals (RCH2)4C4+. and (RCH2)2R'2C4+. indicate that, as the bulk of the alkyl substituents increases, the group R is pushed out of the plane of the ring.Some unusual temperature effects on a(Hβ) are ascribed to interaction of the radical cation with the solvent or with the counterion.As the bulk of the alkyl groups increases, the g-value decreases from 2.0030 to about 2.0022. cis- and trans-Isomers of the radicals Me2tBu2C4+., Et2tBu2C4+., iBu2tBu2C4+., and propably Me2Et2C4+. have been identified, and the spectra of cis- and trans-Me2tBu2C+. are analysed in terms of breaking of the degeneracy of the molecular orbitals of the cyclobutadiene system by differential electron release by the alkyl groups (tBu > Me).
- Courtneidge, John L.,Davies, Alwyn G.,Lusztyk, Ewa,Lusztyk, Janusz
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p. 155 - 164
(2007/10/02)
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- Action du chlorure de fer(III) sur des acetyleniques substitues par des elements de la colonne IVB. Formation de diynes
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We have studied the behaviour of mono- and diheterosubstituted acetylenies (1,2,3) in the presence of iron(III) chloride in a carbon tetrachloride-toluene medium at 25 deg C. 1: ; 2: ; 3: .The reaction always takes place in heterogeneous phase, the reaction medium being carefully kept free from air and humidity. Compounds of type 1. The reaction rate increases from the carbon compound to the stannyl compound. The germyl and stannyl acetylenics give 2,4-hexadiyne with good yields, respectively 62 and 84percent . Compounds of types 2 and 3. The influence of heterosubstituents on the reaction rate is the same as for compounds 1.For the mixed compound 3b, only one hexadiyne can be obtained with a yield of 90percent, gis(trimethylsilyl)buta-1,3-diyne.In the course of all these reactions, iron(III) is reduced into iron(II). The influence of the metal and its substituents as well as the action of iron chloride on the various conjugated diynes are discussed.A mechanism based on the respective reaction rates is suggested.
- Braun, Jacques,Trung, Bui Khac
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- Vinyl Cations, 35. Mechanisms of Formation of Vinyl Triflates on Treatment of Ketones with Trifluoromethanesulfonic Anhydride
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Alkynones (5) are treated with trifluoromethanesulfonic anhydride in the presence of various bases to give 1-(1-alkynyl)vinyl triflates (6).The mechanisms of formation of vinyl triflates are discussed in detail.
- Hanack, Michael,Hassdenteufel, Juergen R.
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p. 764 - 771
(2007/10/02)
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