- Directed Regioselective Carbometallation of 1,2-Dialkyl-Substituted Cyclopropenes
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A regio- and diastereoselective copper-catalyzed carbomagnesiation of 1,2-dialkylated cyclopropenes is reported. The regioselectivity is controlled by a subtle tethered Lewis basic moiety. The chelating moieties allow the differentiation between two electronically tantamount organometallic intermediates. Further functionalization grants access to polysubstituted stereodefined cyclopropanes bearing up to five alkyl groups.
- Cohen, Yair,Marek, Ilan
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supporting information
p. 26368 - 26372
(2021/11/10)
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- Activation and Functionalization of C-C σ Bonds of Alkylidene Cyclopropanes at Main Group Centers
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Aluminum(I) and magnesium(I) compounds are reported for the C-C σ-bond activation of strained alkylidene cyclopropanes. These reactions result in the formal addition of the C-C σ bond to the main group center either at a single site (Al) or across a metal-metal bond (Mg-Mg). Mechanistic studies suggest that rather than occurring by a concerted oxidative addition, these reactions involve stepwise processes in which substrate binding to the main group metal acts as a precursor to α- or β-alkyl migration steps that break the C-C σ bond. This mechanistic understanding is used to develop the magnesium-catalyzed hydrosilylation of the C-C σ bonds of alkylidene cyclopropanes.
- Crimmin, Mark R.,Kong, Richard Y.
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p. 11967 - 11971
(2020/08/06)
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- Boron Complexes With Gradual 1- Methylcyclopropene Releasing Capability
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Compounds having one of the following formulae: wherein R1 and R2 are alkyl or aryl and R1 and R2 may be the same or different, wherein R1 is alkyl o aryl, or wherein alkyl is a liner or branched, saturated or unsaturated alkyl having C1-20 and wherein aryl is an aromatic ring having C1-15. Also methods of using the compounds, including method of inhibiting and ethylene response in a plant.
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Paragraph 0052
(2016/03/09)
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- Systematic repression of β-silyl carboeation stabilization
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Solvolysis of 1-(trimethylsilylmethyl)cyclopropyl mesylate in CD 3CO2D gives ring-opened products as well as methylenecyclopropane. The rate enhancement due to the β-trimethylsilyl group is a factor of about 106. The large
- Creary, Xavier,Kochly, Elizabeth D.
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experimental part
p. 2134 - 2144
(2009/08/07)
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- Highly efficient synthesis of methylenecyclopropane
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An efficient procedure for the preparation of methylenecyclopropane (3), a valuable starting material in organic synthesis, has been developed from methallyl chloride (1) and alkali metal [bis(trimethylsilyl)]amide [M(BTMSA) (M = Na, K), 2b,c]. The advantages of this new method are the higher yield of methylenecyclopropane up to 79% and a homogenous reaction mixture, i.e. both substrates are soluble in organic solvents such as toluene and dibutyl ether.
- Binger, Paul,Brinkmann, Axel,Wedemann, Petra
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p. 1344 - 1346
(2007/10/03)
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- Products from photochemical reactions and electrochemical oxidation of methylenecyclopropane
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The reactivity of methylenecyclopropane (MCP, 1) and its radical cation (1+.) have been studied in the presence and absence of a nucleophile (methanol). Photochemical reactions of 1 in the presence of an electron-acceptor (1,4-dicyanobenzene, 6) and a codonor (biphenyl, 7) in acetonitrile (with and without methanol present) or chloroform lead to cycloadditions (ortho, meta, and para; products 12-17) rather than products from photoinduced electron transfer (PET). Based on the measured (cyclic voltammetry, CV) oxidation potential, using the Weller equation, electron transfer (ET) was predicted to occur. It was shown that the measured oxidation potential of 1 represents the adiabatic ionization potential. For PET processes the value for the vertical ionization potential must be used. Electrochemical (EC) generation of 1+. without a nucleophile present results in the formation of one major product: tert-butyl acetamide (25). A series of rearrangements leading to the tert-butyl cation is proposed. Addition of a nucleophile (methanol) to the mixture leads to the formation of 3-methoxy-2-(methoxymethyl)-1-propene (26). This product may arise from trapping of the initially formed ring-opened (trimethylenemethane) radical cation (1a+.), which undergoes a second oxidation and nucleophilic addition (ECE).
- De Lijser,Cameron, T. Stanley,Arnold, Donald R.
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p. 1795 - 1809
(2007/10/03)
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- Laser-Powered Decomposition of Spiroalkanes (n = 2-5)
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The laser heating of spiroalkanes (n=2-5) and of their 1,1,2,2-tetradeuterated isotopomers reveals dissimilar modes of their thermal decomposition.Spiropentane decomposes into ethene and propadiene via two competing routes: the direct cleavage and the more important cleavage via intermediary methylenecyclobutane.Spirohexane decomposes through two important concurrent pathways which are the expulsions of ethene from the three-membered ring and a more feasible expulsion of ethene from the four-membered ring.Spiroheptane and spirooctane decompose by a radical-chain mechanism and afford complex mixtures of products; upon addition of propene both compounds rearrange into two cycloalkanes wherein the larger ring of the spiroalkane is preserved and substituted with ethylidene and a vinyl group.
- Fajgar, Radek,Pola, Josef
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p. 7709 - 7717
(2007/10/02)
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- The isomerization of 1-methylcyclopropene: A multichannel unimolecular reaction induced by overtone excitation
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The distribution of products resulting from the isomerization of gas phase 1-methylcyclopropene (1) induced by C-H stretch overtone excitation has been studied in a search for mode specific effects.Quantum yields for the disappearance of 1 have been determined as a function of the total pressure of a mixture of 1 and methylenecyclopropane and of the added bath gases SF6 and Ar using a combination of intracavity dye laser photolysis and end product analysis by gas chromatography.These data, together with the ratios of the yields of the major isomerization products, are adequately reproduced by RRKM theory and a weak collisional energy transfer model: no evidence for mode specifity is obtained.The experimental data demonstrate the importance of inefficient collisional energy transfer but allow some conclusions to be drawn concerning the applicability of RRKM theory which are not strongly dependent upon the details of the energy transfer model.
- Baggott, J. E.,Law, D. W.
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p. 900 - 906
(2007/10/02)
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- 13C MAGNETIC RESONANCE STUDIES. 129. HOMOENOLIZATION IN THE CAMPHENILONE SYSTEM. EXAMINATION OF SOME 7-SUBSTITUTED DERIVATIVES
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The behavior of the 7,7-dimethyl, 7-spirocyclopropyl, and 7-isopropylidene derivatives of champhenilone under strongly basic conditions (t-BuO-/t-BuOH/185 deg C) has been investigated to examine substituent effects on β-enolization in the system.In each case, an equilibrium mixture of the initial ketone and its corresponding 5-substituted isomer was obtained, with the latter increasingly favored through the series.In each case the 1H/2H exchange processes were examined by experiments utilizing t-BuO-/t-BuOD to establish the individual sites of deuterium incorporation in these ketones with 2H and 13C magnetic resonance.These data provide the stereoselectivities and relative rates of the exchange processes.The 2H-induced effects in the 13C spectra are discussed.
- Peiris, Sriyawathie,Ragauskas, Arthur J.,Stothers, J. B.
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p. 789 - 797
(2007/10/02)
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- 1,2-DIMETHYLSPIROHEX-1-ENE BY ADDITION OF CYCLOBUTYLIDENE TO 2-BUTYNE
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The first addition of a cyclobutylidene (carbenoid) to an alkyne is reported.By C4+C2-coupling the spirohex-1-ene system 8 is constructed.Furthermore, cyclobutylidene adds to methylenecyclopropane, its intramolecular reaction product, to give the novel dispirooctane 11.
- Brinker, Udo H.,Weber, Juergen
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p. 5371 - 5374
(2007/10/02)
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- Deamination Reactions, 44. Decomposition of 1-Alkylcyclopropanediazonium Ions
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1-Methyl- (17), 1,2-dimethyl- (41, 44), 1-propyl- (64), 1-(1-methylethyl)cyclopropanediazonium ions (80), and -1-diazonium ions (93) have been generated by alkaline cleavage of the analogous nitrosocarbamates in methanol.Cyclopropyl-allyl transformation and nucleophilic displacement were the only reactions of 17, 41, 44, and 93 while elimination and 1,2-shifts of an α-hydrogen compete increasingly with 64 and 80.The stereochemistry of ring cleavage and nucleophilic displacement has been explored, using 2-D labels in the case of 17 and 93.Cyclopropanediazonium ions (1) and 41 react stereospecifically, 17 and 44 are moderately stereoselective (ca. 85:15), and 93 is entirely unselective.The data indicate a gradual changeover from concerted to stepwise mechanisms.Appreciable stabilization of the positive charge is required to reach the SN1 extreme.
- Kirmse, Wolfgang,Rode, Jutta,Rode, Klaus
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p. 3672 - 3693
(2007/10/02)
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- 185-nm Photochemistry of Cyclobutene and Bicyclobutane
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The high quantum yield of the direct 185-nm photolysis of cyclobutene (φs=0.71) leading to 1,3-butadiene is in accord with symmetry-allowed electrocyclic ring opening of a ?,?*-excited singlet state of cyclobutene.The formation of ethene, acetylene, and methylenecyclopropane as minor products presumably involves cyclopropylmethylene and cyclobutylidene as carbene intermediates, formed on (?,3s)-Rydberg excitation of cyclobutene.The 185-nm photolysis of bicyclobutane resembles that of the homologous bicycloalkanes.As main products cyclobutene (φp=0.30) and 1,3-butadiene (φp=0.29) are formed.On the other hand, the transformations of methylenecyclopropane on 185-nm irradiation, leading to ethene, acetylene, and 1,3-butadiene, are akin to radiolysis and gas-phase photolysis results of this substrate.
- Adam, Waldemar,Oppenlaender, Thomas,Zang, Gerald
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p. 3921 - 3924
(2007/10/02)
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- Thermal Rearrangements, part XIV. Gas Phase Kinetics of Pyrolysis of 1-Methyl-1-cyclopropene
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The title study has been carried out in the temperature range 210-250 deg C.The isomerisation products are butyne (91-94percent), 1,3-butadiene (5-8percent), and 1,2-butadiene (1-2percent).No other products were detected and material recovery was complete within experimental error (+/- 5percent).The reaction obeyed first-order kinetics, with the products formed by parallel pathways, and appeared to both unimolecular and homogeneous although some surface sensitivity was detected in packed vessels.Studies of pressure dependence showed characteristic rate constant "fall-off" below 20 Torr (SF6) and 100 Torr (N2).Within at least 2percent of the high pressure limit, the following Arrhenius equation for overall decomposition was found: log(k/s-1) = (12.91 +/- 0.15) - (160 +/- 1.5 kJ mol-1)/RTln 10.Arrhenius equations were similarly found for the individual pathways.The figures are discussed in the light of Transition State Theory and represent a significant improvement over a previous study.It is argued that all products arise via 1,2 shifts in a diradical-like intermediate and the propensities for different H shifts are discussed.A 1-methyl substituent, rather surprisingly, deactivates cyclopropene in its isomerisation reactions.
- Hopf, Henning,Wachholz, Gerhard,Walsh, Robin
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p. 3579 - 3587
(2007/10/02)
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- Cyclobutylidenes from Geminal Dihalogenocyclobutanes
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Cyclobutylidene, or a related carbenoid, can be generated by reaction of geminal dibromocyclobutane with methyl-lithium at temperatures as low as -78 deg C to yield methylenecyclopropane and cyclobutene nearly quantitatively.
- Brinker, Udo H.,Schenker, Gilbert
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p. 679 - 681
(2007/10/02)
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- Reactions retrodieniques. XII. Cycloreversions et rearrangements d'ethano-9,10 dihydro-9-10 anthracenes cyclopropaniques
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Five Diels-Alder adducts of anthracene, containing respectively the spiro cyclopropane (3), vinylcyclopropane (4), allenylcyclopropane (5) and methylenecyclopropane systems (6 and 7) have been synthesized and their flash thermolytic behaviour investigated.Whereas the adduct 3 undergoes exclusively a retro-Diels-Alder cleavage leading to methylenecyclopropane, two types of rearrangements are observed, owing to their structure, as predominant reaction paths with compound 4-7 : the adducts 4 and 5, possessing a vinylcyclopropane unit, almost only rearrange into the corresponding cyclopentene 14 and methylenecyclopentene 15, respectively; on the other hand, the methylenecyclopropene adducts 6 and 7 undergo a more unexpected rearrangement of the anthracenic framework leading to the polycyclic methylenecyclobutanes 19 and 20.The structure proposed for 19 follows unambiguously from its spectral properties and is confirmed by its ozonolysis yielding the cyclobutanone 21.In the same way, the retro-Diels-Alder cleavage of the adducts 4-7, also observed as a minor reaction path (10-40percent), is followed by the isomerization of the firstly obtained cyclopropanic cumulenes, leading to 1,4-hexadiyne (from 5), dimethylenecyclopropane (from 6), or 1-hexen-4-yne and ethylidenemethylenecyclopropane (from 7).
- Lasne, Marie-Claire,Ripoll, Jean-Louis
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p. 340 - 344
(2007/10/02)
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- Secondary deuterium isotope effects on both rate and product determining steps in the thermolysis of 4-methylene-1-pyrazoline
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The secondary deuterium kinetic isotope effect in the thermolysis of 4-methylene-1-pyrazoline and four of its deuterated isomers has been studied.The value of δΔG*/n is 142 cal mol-1 if it is a single C-N cleavage process or 71 cal mol-1 if it is a concerted rupture of two C-N bonds.The product distributions can only be rationalized in terms of a mechanism involving a rate determining C-N bond rupture to form a diazenyl diradical intermediate which then can close to methylenecyclopropanes by three possible modes.This requires a secondary isotope effect in the product determining step of 1.33 +/- 0.05, for the rotation of CH2 (CD2) out of the plane of the allylic radical in the intermediate.
- Chang, Moon Ho,Crawford, Robert J.
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p. 2556 - 2568
(2007/10/02)
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