- Mechanistic Studies on the Base-Promoted Conversion of Alkoxy-Substituted, Ring-Fused gem-Dihalocyclopropanes into Furans: Evidence for a Process Involving Electrocyclic Ring Closure of a Carbonyl Ylide Intermediate
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The mechanism associated with the base-promoted conversion of alkoxy-substituted and ring-fused gem-dihalocyclopropanes such as 40 into annulated furans has been explored. Treatment of compound 40 with potassium tert-butoxide affords a mixture of furans 23/27 and 41, an outcome that suggests the intermediacy of the slowly interconverting carbonyl ylides 42 and 43 that undergo rapid [1,5]-electrocyclizations and subsequent dehydrohalogenation to afford the observed products. This proposal is supported by ab initio MO and DFT calculations that also suggest a vinylcarbene insertion pathway is less likely to be operative.
- Sharp, Phillip P.,Mikusek, Jiri,Ho, Junming,Krenske, Elizabeth H.,Banwell, Martin G.,Coote, Michelle L.,Ward, Jas S.,Willis, Anthony C.
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- Kinetics and mechanisms of the unimolecular elimination of 2,2-diethoxypropane and 1,1-diethoxycyclohexane in the gas phase: Experimental and theoretical study
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The gas-phase thermal elimination of 2,2-diethoxypropane was found to give ethanol, acetone, and ethylene, while 1,1-diethoxycyclohexane yielded 1-ethoxycyclohexene and ethanol. The kinetics determinations were carried out, with the reaction vessels deactivated with allyl bromide, and the presence of the free radical suppressor cyclohexene and toluene. Temperature and pressure ranges were 240.1-358.3 °C and 38-102 Torr. The elimination reactions are homogeneous, unimolecular, and follow a first-order rate law. The rate coefficients are given by the following Arrhenius equations: for 2,2-diethoxypropane, log k1 (s-1) = (13.04 ± 0.07) - (186.6 ± 0.8) kJ mol-1 (2.303RT)-1; for the intermediate 2-ethoxypropene, log k1 (s-1) = (13.36 ± 0.33) - (188.8 ± 3.4) kJ mol-1 (2.303RT) -1; and for 1,1-diethoxycyclohexane, log k = (14.02 ± 0.11) - (176.6 ± 1.1) kJ mol-1 (2.303RT)-1. Theoretical calculations of these reactions using DFT methods B3LYP, MPW1PW91, and PBEPBE, with 6-31G(d,p) and 6-31++G(d,p) basis set, demonstrated that the elimination of 2,2-diethoxypropane and 1,1-diethoxycyclohexane proceeds through a concerted nonsynchronous four-membered cyclic transition state type of mechanism. The rate-determining factor in these reactions is the elongation of the C-O bond. The intermediate product of 2,2-diethoxypropane elimination, that is, 2-ethoxypropene, further decomposes through a concerted cyclic six-membered cyclic transition state mechanism.
- Rosas, Felix,Maldonado, Alexis,Lezama, Jesus,Domínguez, Rosa M.,Mora, José R.,Cordova, Tania,Chuchani, Gabriel
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- Catalytic behavior of melamine glyoxal resin towards consecutive oxidation and oxy-Michael addition
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Synthesis of melamine glyoxal resin involves a catalyst-free, one pot reaction between melamine and glyoxal in DMF. The synthesized resins have a similar morphological arrangement to that of layered materials as depicted by their XRD pattern and Raman spectra. The catalytic behavior of melamine glyoxal resin (MGR) have been studied in allylic oxidation of cyclohexene and simultaneous Michael addition. The MGR/solvent/O2 oxidant system can be regarded as a metalfree, additive-free, cost-effective and environmentally benign catalytic system. The oxidative behavior of MGR is attributed to its ability to generate in situ organic peroxide species during the course of reaction. Generation of peroxide species is confirmed by the KI/starch test and further confirmed by the complete suppression effect of TEMPO (2,2,6,6- tetramethylpiperidine-1-oxyl) over oxidation. The activity for Michael addition can be attributed to the presence of a higher content of nitrogen atoms, which serves as the active site. In oxidation, 28.1% conversion of cyclohexene with 37.19 and 62.81% selectivities for cyclohexenol and cyclohexenone were observed, respectively. In consecutive oxidation and oxy-Michael addition, 31.5% conversion of cyclohexene was observed with selectivities of 61.6% for cyclohexenone and 38.4% for alkoxy product. Springer Science+Business Media B.V. 2010.
- Ansari, Mohd Bismillah,Prasetyanto, Eko Adi,Lee, Jun,Park, Sang-Eon
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- A Lamellar Coordination Polymer with Remarkable Catalytic Activity
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A positively charged lamellar coordination polymer based on a flexible triphosphonic acid linker is reported. [Gd(H4nmp)(H2O)2]Cl?2 H2O (1) [H6nmp=nitrilotris(methylenephosphonic acid)] was obtained by a one-pot approach by using water as a green solvent and by forcing the inclusion of additional acid sites by employing HCl in the synthesis. Compound 1 acts as a versatile heterogeneous acid catalyst with outstanding activity in organic reactions such as alcoholysis of styrene oxide, acetalization of benzaldehyde and cyclohexanaldehyde and ketalization of cyclohexanone. For all reaction systems, very high conversions were reached (92–97 %) in only 15–30 min under mild conditions (35 °C, atmospheric pressure). The coordination polymer exhibits a protonic conductivity of 1.23×10?5S cm?1at 98 % relative humidity and 40 °C.
- Mendes, Ricardo F.,Antunes, Margarida M.,Silva, Patrícia,Barbosa, Paula,Figueiredo, Filipe,Linden, Anthony,Rocha, Jo?o,Valente, Anabela A.,Almeida Paz, Filipe A.
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- Merging Halogen-Atom Transfer (XAT) and Cobalt Catalysis to Override E2-Selectivity in the Elimination of Alkyl Halides: A Mild Route towardcontra-Thermodynamic Olefins
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We report here a mechanistically distinct tactic to carry E2-type eliminations on alkyl halides. This strategy exploits the interplay of α-aminoalkyl radical-mediated halogen-atom transfer (XAT) with desaturative cobalt catalysis. The methodology is high-yielding, tolerates many functionalities, and was used to access industrially relevant materials. In contrast to thermal E2 eliminations where unsymmetrical substrates give regioisomeric mixtures, this approach enables, by fine-tuning of the electronic and steric properties of the cobalt catalyst, to obtain high olefin positional selectivity. This unprecedented mechanistic feature has allowed access tocontra-thermodynamic olefins, elusive by E2 eliminations.
- Zhao, Huaibo,McMillan, Alastair J.,Constantin, Timothée,Mykura, Rory C.,Juliá, Fabio,Leonori, Daniele
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supporting information
p. 14806 - 14813
(2021/09/18)
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- Copper catalyzed β-difluoroacetylation of dihydropyrans and glycals by means of direct C-H functionalization
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A copper catalyzed direct functionalization of dihydropyrans and glycals has been developed. This method affords a new and straightforward access to C-2-CF2 dihydropyrans and glycosides in a single step starting from readily available starting
- Belhomme, Marie-Charlotte,Poisson, Thomas,Pannecoucke, Xavier
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supporting information
p. 3428 - 3431
(2013/07/26)
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- Enantioselective cyanocarbonation of ketones with chiral base
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A highly enantioselective cyanocarbonation of dialkyl ketones catalyzed by commercially available and easily recyclable cinchona alkaloid derivatives has been developed. The reaction provides a useful approach for the enantioselective construction of tetrasubstituted carbon stereocenters. Mechanistic studies have been carried out to shed light on the origin of the catalytic activity of the cinchona alkaloid and the asymmetric induction step.
- Tian, Shi-Kai,Deng, Li
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p. 11320 - 11330
(2007/10/03)
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- 2-Aminoethanols in Transacetalization Reactions
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Symmetric and mixed nitrogen-containing acetals and enol ethers were synthesized in an overall yield of 46-63% by reactions of N,N- dialkylaminoethanols with diethyl acetals derived from cyclohexanone, cyclopentanone, and acetophenone.
- Kukharev,Stankevich,Kukhareva
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p. 622 - 624
(2007/10/03)
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- Composition of Mixtures of Hydrocarbons after BIRCH-Reduction of Substituted Benzenes and Acid Catalyzed Addition of Alcohols to Alkylsubstituted Cyclohexenes and Carbohexa-1,4-dienes
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10 different benzene hydrocarbons 1, indane, tetraline, anisol and phenol are reduced by sodium in liquid ammonia in the presence of methanol to the BIRCH products 2.The product mixture compositions are determined through capillary GLC.On storage at +6 deg C some rearomatization of the 1,4-cyclohexadienes 2 occurs.Data of the 1H- and 13C-.n.m.r. spectra and also mass spectra of the BIRCH 1,4-dienes 2 are given.For comparison 4-alkoxycyclohexenes 4 and 1-alkoxy-1-methylcyclohexanes 8 are prepared and spectroscopically characterized.Acid-catalyzed addition of alcohols to the 1,4-cyclohexadienes systems is a slow process and gives the 4-alkoxy-4-alkylcyclohex-1-enes (4) only in moderate yields up to 30percent.Most of the products are dimers 5 and also oligomers 6 of the parent hydrocarbons 2.
- Beger, J.,Thomas, B.,Vogel, T.,Kirmse, K.,Lang, R.
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p. 481 - 488
(2007/10/02)
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- REACTION OF ORGANIC AZIDES WITH UNSATURATED COMPOUNDS. X. N-ARYLSULFONYLCARBOXIMIDIC ESTERS
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N-Arylsulfonylcarboximidic esters were obtained in the reaction of arenesulfonyl azides with 1-methoxypropene, 2-methyl-1-methoxypropene, 1-alkoxycyclohexenes, and 3,3,5,5-tetramethyl-1-ethoxycyclohexene.Hydrolysis of the imidic esters gave N-arylsulfonyl
- Semenov, V. P.,Ogloblin, K. A.
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p. 2154 - 2161
(2007/10/02)
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