- Aqueous Microdroplets Capture Elusive Carbocations
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Carbocations are short-lived reactive intermediates in many organic and biological reactions that are difficult to observe. This field sprung to life with the discovery by Olah that a superacidic solution allowed the successful capture and nuclear magnetic resonance characterization of transient carbocations. We report here that water microdroplets can directly capture the fleeting carbocation from a reaction aliquot followed by its desorption to the gas phase for mass spectrometric detection. This was accomplished by employing desorption electrospray ionization mass spectrometry to detect a variety of short-lived carbocations (average lifetime ranges from nanoseconds to picoseconds) obtained from different reactions (e.g., elimination, substitution, and oxidation). Solvent-dependent studies revealed that aqueous microdroplets outperform organic microdroplets in the capture of carbocations. We provide a mechanistic insight demonstrating the survival of the reactive carbocation in a positively charged aqueous microdroplet and its subsequent ejection to the gas phase for mass spectrometric analysis.
- Kumar, Anubhav,Mondal, Supratim,Banerjee, Shibdas
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supporting information
p. 2459 - 2463
(2021/02/16)
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- Reactions of Sodium Diisopropylamide: Liquid-Phase and Solid-Liquid Phase-Transfer Catalysis by N, N, N′, N″, N″-Pentamethyldiethylenetriamine
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Sodium diisopropylamide (NaDA) in N,N-dimethylethylamine (DMEA) and DMEA-hydrocarbon mixtures with added N,N,N′,N″,N″-pentamethyldiethylenetriamine (PMDTA) reacts with alkyl halides, epoxides, hydrazones, arenes, alkenes, and allyl ethers. Comparisons of PMDTA with N,N,N′,N′-tetramethylethylenediamine (TMEDA) accompanied by detailed rate and computational studies reveal the importance of the trifunctionality and κ2-κ3 hemilability. Rate studies show exclusively monomer-based reactions of 2-bromooctane, cyclooctene oxide, and dimethylresorcinol. Catalysis with 10 mol % PMDTA shows up to >30-fold accelerations (kcat > 300) with no evidence of inhibition over 10 turnovers. Solid-liquid phase-transfer catalysis (SLPTC) is explored as a means to optimize the catalysis as well as explore the merits of heterogeneous reaction conditions.
- Algera, Russell F.,Collum, David B.,Ma, Yun,Woltornist, Ryan A.
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supporting information
p. 13370 - 13381
(2021/09/03)
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- A mild method for the replacement of a hydroxyl group by halogen: 2. unified procedure and stereochemical studies
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N,N-Dimethyl- and N,N-diisopropyl-1-halo-2-methyl-l-propenylamines are readily available reagents for the mild deoxyhalogenation of alcohols and hydroxyacids. In this study we showed that the reactivity of the reagents can be tuned by varying the size of the alkyl groups on the reagents: the replacement of methyl by isopropyl groups led to a significant increase of reactivity. We then described a unified procedure for all deoxyhalogenations using the readily available α-chloroenamines as reagents with (bromination, iodination) or without (chlorination) an alkaline bromide or iodide. Finally, we showed that deoxyhalogenation reactions of secondary alcohols were highly stereospecific and generally occurred with inversion of configuration.
- Gati, Wafa,Munyemana, Fran?ois,Colens, Alain,Srour, Aladdin,Dufour, Mathilde,Vardhan Reddy, K. Harsha,Téchy, Brigitte,Rosse, Gérard,Schweiger, Ed,Qiao, Qi,Ghosez, Léon
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- Organophotoredox/palladium dual catalytic decarboxylative Csp3-Csp3coupling of carboxylic acids and π-electrophiles
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A dual catalytic decarboxylative allylation and benzylation method for the construction of new C(sp3)-C(sp3) bonds between readily available carboxylic acids and functionally diverse carbonate electrophiles has been developed. The new process is mild, operationally simple, and has greatly improved upon the efficiency and generality of previous methodology. In addition, new insights into the reaction mechanism have been realized and provide further understanding of the harnessed reactivity.
- Cartwright, Kaitie C.,Tunge, Jon A.
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p. 8167 - 8175
(2020/09/09)
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- Selectivity and Mechanism of Iridium-Catalyzed Cyclohexyl Methyl Ether Cleavage
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Cationic bis(phosphine)iridium complexes are found to catalyze the cleavage of cyclohexyl methyl ethers by triethylsilane. Selectivity for C-O cleavage is determined by the relative rates of SN2 demethylation versus SN1 demethoxylation, with the axial or equatorial disposition of the silyloxonium ion intermediate acting as an important contributing factor. Modulation of the electron-donor power of the supporting phosphine ligands enables a switch in selectivity from demethylation of equatorial methyl ethers to 2° demethoxylation. Applications of these accessible catalysts to the selective demethoxylation of the 3α-methoxy group of cholic acid derivatives is demonstrated, including a switch in observed selectivity controlled by 7α-substitution. The resting state of the catalyst has been characterized for two phosphine derivatives, demonstrating that the observed switch in C-O cleavage selectivity likely results from electronic factors rather than from a major perturbation of the catalyst structure.
- Fast, Caleb D.,Jones, Caleb A. H.,Schley, Nathan D.
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p. 6450 - 6456
(2020/07/13)
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- Introduction of Cyclopropyl and Cyclobutyl Ring on Alkyl Iodides through Cobalt-Catalyzed Cross-Coupling
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A cobalt-catalyzed cross-coupling between alkyl iodides and cyclopropyl, cyclobutyl, and alkenyl Grignard reagents is disclosed. The reaction allows the introduction of strained rings on a large panel of primary and secondary alkyl iodides. The catalytic system is simple and nonexpensive, and the reaction is general, chemoselective, and diastereoconvergent. The alkene resulting from the cross-coupling can be transformed to substituted cyclopropanes using a Simmons-Smith reaction. The formation of radical intermediates during the coupling is hypothesized.
- Andersen, Claire,Ferey, Vincent,Daumas, Marc,Bernardelli, Patrick,Guérinot, Amandine,Cossy, Janine
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p. 2285 - 2289
(2019/03/29)
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- Sodium Diisopropylamide in N,N-Dimethylethylamine: Reactivity, Selectivity, and Synthetic Utility
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The reactivities and chemoselectivities of sodium diisopropylamide (NaDA) in N,N-dimethylethylamine (DMEA) are compared with those of lithium diisopropylamide (LDA) in tetrahydrofuran (THF). Metalations of arenes, epoxides, ketones, hydrazones, dienes, and alkyl and vinyl halides are represented. The positive attributes of NaDA-DMEA include high solubility, stability, resistance to solvent decomposition, and ease of preparation. The high reactivities and chemoselectivities often complement those of LDA-THF.
- Ma, Yun,Algera, Russell F.,Collum, David B.
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p. 11312 - 11315
(2016/11/29)
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- Solvent dependent reductive defluorination of aliphatic C-F bonds employing Sm(HMDS)2
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Sm(HMDS)2 in n-hexane mediates fast cleavage of primary, secondary and tertiary alkyl fluorides in good to excellent yields. In n-hexane Sm(HMDS)2 exhibits uniquely enhanced reductive ability towards the C-F bond compared to when using THF as solvent.
- Janjetovic, Mario,Tr?ff, Annika M.,Ankner, Tobias,Wettergren, Jenny,Hilmersson, G?ran
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supporting information
p. 1826 - 1828
(2013/03/29)
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- Tetramethylfluoroformamidinium hexafluorophosphate (TFFH) as a mild deoxofluorination reagent
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The solid, air-stable peptide coupling reagent TFFH (tetramethylfluoroformamidinium hexafluorophosphate) was found to activate a variety of alcohols towards deoxofluorination. These conditions are compatible with carbonyl functional groups thus offering interesting possibilities for the application to sensitive molecules. Georg Thieme Verlag Stuttgart · New York.
- Bellavance, Gabriel,Dubé, Pascal,Nguyen, Bao
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experimental part
p. 569 - 572
(2012/04/17)
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- Efficient oxidation of 1,2-diols into a-hydroxyketones catalyzed by organotin compounds
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Electrochemical oxidation of 1,2-diols with a catalytic amount of an organotin compound and a bromide ion as mediators has been developed. Various cyclic and acyclic 1,2-diols were oxidized into the corresponding α-hydroxyketones in good to excellent yields without C-C bond cleavage. Also, oxidation with the use of chemical oxidants was accomplished in the presence of a catalytic amount of an organotin compound. These reactions could discriminate 1,2-diols from isolated hydoxyl groups or 1,3-diols. In the case of a conformationally restricted cyclic 1,2-diol, the axial hydroxyl group was oxidized exclusively. Mono-, di-, and trialkylated tin compounds were examined as mediators and dialkylated tin compounds showed higher catalytic activity than mono- and trisubstituted ones. Me2SnCl2 was found to be the most suitable mediator for the selective oxidation..
- Maki, Toshihide,Iikawa, Shinya,Mogami, Gen,Harasawa, Hitomi,Matsumura, Yoshihiro,Onomura, Osamu
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experimental part
p. 5364 - 5370
(2009/12/22)
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- Ammonium-directed dihydroxylation of 3-aminocyclohex-1-enes: Development of a metal-free dihydroxylation protocol
-
Treatment of 3-aminocyclohex-1-enes with mCPBA in the presence of trichloroacetic acid gives the corresponding 1,2-anti-2,3-syn-1- trichloroacetoxy-2-hydroxy-3-aminocyclohexane with high levels of diastereoselectivity (90% de). This is consistent with a mechanism of oxidation involving hydrogen-bonded delivery of the oxidant by the allylic ammonium ion formed in situ, followed by highly regioselective ring-opening of the intermediate epoxide by trichloroacetic acid. The effect of conformational constraints upon the oxidation reaction is also examined. The Royal Society of Chemistry 2008.
- Aciro, Caroline,Claridge, Timothy D. W.,Davies, Stephen G.,Roberts, Paul M.,Russell, Angela J.,Thomson, James E.
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supporting information; experimental part
p. 3751 - 3761
(2009/02/04)
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- An efficient method for chlorination of alcohols using PPh3/Cl3CCONH2
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A new and convenient method for the chlorination of alcohols utilizing PPh3/Cl3CCONH2 is addressed. Various alcohols could smoothly be converted into their corresponding alkyl chlorides in high yield under mild conditions with short reaction times. A mechanism is disclosed with the evidence of inversion of configuration of the analogous alkyl chloride derived from R-(-)-2-octanol.
- Pluempanupat, Wanchai,Chavasiri, Warinthorn
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p. 6821 - 6823
(2007/10/03)
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- Reduction of alkyl and vinyl sulfonates using the CuCl2· 2H2O-Li-DTBB(cat.) system
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The reduction of a series of alkyl mesylates, dimesylates and triflates to the corresponding hydrocarbons was efficiently performed using a reducing system composed of CuCl2·2H2O, an excess of lithium sand and a catalytic amount (5 mol%) of 4,4′-di-tert-butylbiphenyl (DTBB), in tetrahydrofuran at room temperature. The process was also applied to enol and dienol triflates affording alkenes and dienes, respectively. The use of the deuterated copper salt CuCl2·2D2O allowed the simple preparation of the corresponding deuterated products.
- Radivoy, Gabriel,Alonso, Francisco,Moglie, Yanina,Vitale, Cristian,Yus, Miguel
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p. 3859 - 3864
(2007/10/03)
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- Michael addition-elimination mechanism for nucleophilic substitution reaction of cycloalkenyl iodonium salts and selectivity of 1,2-hydrogen shift in cycloalkylidene intermediate
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(Chemical Equation Presented) Reactions of cyclohexenyl and cyclopentenyl iodonium salts with cyanide ion in chloroform give cyanide substitution products of allylic and vinylic forms. Deuterium-labeling experiments show that the allylic product is formed via the Michael addition of cyanide to the vinylic iodonium salt, followed by elimination of the iodonio group and 1,2-hydrogen shift in the 2-cyanocycloalkylidene intermediate. The hydrogen shift preferentially occurs from the methylene rather than the methine β-position of the carbene, and the selectivity is rationalized by the DFT calculations. The Michael reaction was also observed in the reaction of cyclopentenyliodonium salt with acetate ion in chloroform. The vinylic substitution products are ascribed to the ligand-coupling (via λ3-iodane) and elimination-addition (via cyclohexyne) pathways.
- Fujita, Morifumi,Wan, Hyeok Kim,Fujiwara, Koji,Okuyama, Tadashi
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p. 480 - 488
(2007/10/03)
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- Fused cycloalkyl amides and acids and their therapeutic applications
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The present invention relates to the use of compounds of formula (I) for the treatment of epilepsy, bipolar disorder, psychiatric disorders, migraine, pain, or movement disorders, and to provide neuroprotection.
- -
-
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- Fused cycloalkyl amides and acids and their therapeutic applications
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The present invention relates to the use of compounds of formula (I) for the treatment of epilepsy, bipolar disorder, psychiatric disorders, migraine, pain, or movement disorders, and to provide neuroprotection.
- -
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-
- Vertical and nonvertical participation by sulfur, selenium, and tellurium
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The mechanism of stabilization of positive charge on carbon by sulfur, selenium, or tellurium at the: β-position has been investigated kinetically, by measurement of rate enhancements, and structurally, by variation of the bond strength to the leaving group. Stabilization can occur either nonvertically with formation of a bridged intermediate or vertically through hyperconjugation within an open carbocation. We observed large rate enhancements (105 for S, 106 for Se) in 97% aqueous trifluoroethanol with trifluoroacetate as the leaving group. These enhancements are consistent with either mechanism. Product structures also are consistent with either mechanism. Nine crystal structures revealed that the bond to the leaving group (C-O) is lengthened by the presence of S or Se at the β-position, in proportion to the basicity of the leaving group. This lengthening is not accompanied by angle distortions expected for the bridging mechanism. The crystallographic data support vertical (hyperconjugative) character along the reaction coordinate, more so for selenium than sulfur.
- White, Jonathan M.,Lambert, Joseph B.,Spiniello, Marisa,Jones, Scott A.,Gable, Robert W.
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p. 2799 - 2811
(2007/10/03)
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- 1,1,2,2-Tetrafluoroethyl-N,N-dimethylamine: A new selective fluorinating agent
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The title compound has been prepared in 96-98% yield by the reaction of tetrafluoroethylene and dimethylamine. 1,1,2,2-Tetrafluoroethyl-N,N-dimethylamine (1) is found to be an effective reagent for the conversion of alcohols into alkyl fluorides. Reaction of 1 and primary alcohols proceeds with high yield formation of the corresponding alkyl fluorides at elevated temperature. However, the reaction of secondary and tertiary alcohols rapidly takes place at 0-10°C, producing corresponding alkyl fluorides as major product along with some olefins.
- Petrov,Swearingen,Hong,Chris Petersen
-
-
- Synthesis of alkenylboronates via palladium-catalyzed borylation of alkenyl triflates (or Iodides) with pinacolborane
-
Various alkenyl iodides and triflates were borylated with pinacolborane in the presence of Et3N and a catalytic amount of PdCl2(dppf) and AsPh3 to afford the corresponding alkenylboronates in good yields.
- Murata, Miki,Oyama, Takashi,Watanabe, Shinji,Masuda, Yuzuru
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p. 778 - 780
(2007/10/03)
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- Reduction of sulfonates and aromatic compounds with the NiCl2 · 2H2O- Li-arene (cat.) combination
-
A series of alkyl mesylates, dimesylates and alkyl or aryl triflates have been reduced to the corresponding hydrocarbons with nickel(II) chloride dihydrate, an excess of lithium powder and a catalytic amount of DTBB (10 mol%) in THF at room temperature. This methodology applied to enol triflates allowed the preparation of olefins or alkanes depending on the amount of the Ni(II) salt used. The reduction of different aromatic or heteroaromatic compounds under the above mentioned conditions leads to the partial or total reduction of the starting materials, the process being a reasonable alternative to the well-known Birch reaction. The use of the deuterium oxide- containing nickel(lI) salt allows the simple preparation of deuterated products.
- Radivoy, Gabriel,Alonso, Francisco,Yus, Miguel
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p. 14479 - 14490
(2007/10/03)
-
- Observations on the generation of organozinc carbenoids from acetals and ketals
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The use of acetals and ketals as direct precursors for organozinc carbenoid chemistry is illustrated by their direct conversion to alkenes in a one pot operation. Aryl acetals can also be used as precursors for the cyclopropanation of cyclohexene.
- Motherwell, William B.,O'Mahony, Donogh J.R.,Popkin, Matthew E.
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p. 5285 - 5288
(2007/10/03)
-
- Interaction of Trimethylsilyl and Trimethylstannyl Substituants with C-O Bonds at the γ Position. Results from X-ray Structural Studies and Solvolysis Studies
-
Accurate X-ray structural studies have been carried on the γ-Me3M (M = Si, Sn)-substituted cyclohexyl esters 21-Ns, 22-Ns, 23-Ns, 21-PNB, and 24-PNB. Analysis of the structural parameters reveals that the C(alkyl)-O(ester) bond distance is lengthened slightly compared to nonmetal- substituted analogues provided that the C-M, C-O, and intervening C-C bonds are in the W arrangement as is the case for 22-Ns, 23-Ns, and 24-Ns. However, the C-O bond distances for 22-PNB and 22-Ns, which do not have the W geometry, are not significantly lengthened. These structural effects are consistent with the presence of a percaudel interaction between the back lobe of the C-M σ bond and the C-O σ* orbital. The γ-Me3Sn cyclohexyl nosylates 21-Ns and 23-Ns undergo unimolecular solvolysis in 97% TFE/H2O with relative rates ca. 1:>10 000.
- Green, Alison J.,Pigdon, Tracey,White, Jonathan M.,Yamen, Joseph
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p. 3943 - 3951
(2007/10/03)
-
- α-Vinylation of 1,3-Dicarbonyl Compounds with Alkenyl(aryl)iodonium Tetrafluoroborates: Effects of Substituents on the Aromatic Ring and of Radical Inhibitors
-
Direct α-vinylations of enolate anions derived from 1,3-dicarbonyl compounds with 4-teri-butyl-1- cyclohexenyl(aryl)iodonium 2 and 1-cyclopentenyl(aryl)iodonium tetrafluoroborates 3 are reported. Frequently, α-phenylations compete with the vinylations in the reaction of 1,3-dicarbonyl compounds with alkenyl(phenyl)iodonium salts 2a and 3a. Use of alkenyl(p-methoxyphenyl)iodonium salts 2b and 3b, however, leads to selective α-vinylation at the expense of the competing arylation of 1,3-dicarbonyl compounds. Use of an efficient aryl radical trap, 1,1-diphenylethylene, inhibits radical-induced decomposition of the alkenyl(aryl)iodonium salts, thereby improving the yields of α-vinylations of enolate anions derived from 1,3-dicarbonyl compounds.
- Ochiai, Masahito,Shu, Toshifusa,Nagaoka, Takema,Kitagawa, Yutaka
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p. 2130 - 2138
(2007/10/03)
-
- On the dihydroxylation of cyclic allylic alcohols
-
The preparation and dihydroxylation (OsO4) of a series of conformationally constrained allylic alcohols is described. By using dichloromethane as solvent, the selectivity that favours the anti triol is substantially reduced by hydrogen-bonding
- Donohoe, Timothy J.,Garg, Rina,Moore, Peter R.
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p. 3407 - 3410
(2007/10/03)
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- Dehydration of secondary alcohols via thermolysis of in situ generated alkyl diphenyl phosphates: An inexpensive and environmentally compatible method for the preparation of alkenes
-
Secondary alcohols are converted into diphenyl phosphate esters by the action of triphenyl phosphate or diphenyl phosphorochloridate in high-boiling, water-miscible solvents in the presence of base. The alkyl diphenyl phosphates undergo thermolysis to afford high yields of alkenes which distill from the reaction mixtures. Purification of the products is achieved by extraction with dilute sulfuric acid which removes traces of solvent and base that may have codistilled. The ratios of 2- (14) and 3-menthene (15), obtained from menthol (13) and neomenthol (16), and the formation of rearranged alkenes by 1,2-shifts from 3, 6, and 3,3-dimethylbutan-2-ol are consistent with ionic intermediates of the elimination reaction. The novel dehydration method offers distinct and important advantages over the existing methods.
- Quast,Dietz
-
p. 1300 - 1304
(2007/10/02)
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- THE REACTION OF PERFLUOROBUTANESULFONYL FLUORIDE WITH ALCOHOLS IN THE PRESENCE OF 4-DIALKYLAMINOPYRIDINES
-
Primary hydroxy groups as in neopentyl alcohol 7 or neopentylglycol 18 react readily with perfluorobutanesulfonyl fluoride 1 in the presence of 2 equiv. of the nucleophilic 4-dialkylaminopyridines 4 to afford high yields of the corresponding N-alkyl-4-dialkylaminopyridinium perfluorobutanesulfonates (nonaflates).Secondary hydroxy groups give rise to a mixture of the corresponding olefins and monofluorides as well as of the corresponding N-alkyl-4-dialkylaminopyridinium nonaflates.
- Bennua-Skalmowski, Baerbel,Krolikiewicz, Konrad,Vorbrueggen, Helmut
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p. 453 - 462
(2007/10/02)
-
- Preparation and reactivity of chiral β-amino-alkylzinc iodides and related configurationally stable zinc organometallics
-
Several zinc organometallics bearing at the β-position a carbamate or an amido function with an acidic N-H group were prepared using the direct insertion of zinc dust into the corresponding alkyl iodides in THF or THF:DMSO mixtures. Most of the starting iodides were obtained from natural α-amino acids and the resulting zinc species afforded after transmetalation with CuCN.2LiCl and reaction with a selection of relatively reactive electrophiles a variety of polyfunctional 1,2-amino alcohol derivatives and carbamates in optically pure form. Several secondary β-amido alkyl iodides were converted to the corresponding chiral zinc reagents and trapped with electrophiles. The configurational stability of chiral secondary organozinc compounds and the stereochemical course of their reactions were examined.
- Duddu,Eckhardt,Furlong,Knoess,Berger,Knochel
-
p. 2415 - 2432
(2007/10/02)
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- Participation of the β Phosphonate Group in Carbocation Formation
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Diethyl (2-(tosyloxy)cyclohexyl)phosphonates have been prepared to test the hypothesis that the strongly electron-withdrawing phosphonate group can stabilize the formation of a β carbocation through hyperconjugation.Systems were constructed with the 180 d
- Lambert, Joseph B.,Emblidge, Robert W.,Zhao, Yan
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p. 5397 - 5403
(2007/10/02)
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- Transition Metal-catalysed Elimination of Unactivated Sulfones
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Lithiated tert-butyl alkyl sulfones undergo an easy elimination in the presence of catalytic amounts of bisacetylacetonatopalladium, thus leading to desulfonylated alkenes.
- Gai, Yonghua,Jin, Liren,Julia, Marc,Verpeaux, Jean-Noel
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p. 1625 - 1626
(2007/10/02)
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- Reaction of thianthrene cation radical with alcohols: Cyclohexanols
-
Cyclohexanol (1), 4-methylcyclohexanol (2), 4-tert-butylcyclohexanol (3), cis-2-methyl- (4) and trans-2-methylcyclohexanol (5) reacted cleanly with thianthrene cation radical perchlorate (Th·+ClO4-) in the presence of 2,6-di-tert-butyl-4-methylpyridine (DTBMP). The alcohols were converted quantitatively into cyclohexenes, while Th·+ was converted quantitatively into thianthrene (Th) and thianthrene 5-oxide (ThO). The oxygen atom of ThO came from the alcohol, as was demonstrated with the use of [18O]cyclohexanol.
- Shine, Henry J.,Yueh, Wang
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p. 6583 - 6586
(2007/10/02)
-
- Hydroboration. 86. Convenient Conversion of Aldehydes and Ketones into the Corresponding Alkenes via Hydroboration of their Enamines. A Remarkably Simple Synthesis of Either (Z)- or (E)-Alkenes
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Aldehydes and ketones are converted into the corresponding alkenes via hydroboration of their enamines.Hydroboration of aldehyde enamines by 9-borabicyclononane (9-BBN), followed by methanolysis, affords the corresponding terminal alkenes in 75-90percent yields.Unsaturated aldehyde enamines produce the corresponding dienes under these conditions.Enamines derived from substituted cyclic ketones and heterocyclic ketones are readily accommodated in this reaction to afford the corresponding alkenes in very good yields.The synthesis of pure (Z)- or (E)-alkenes is readily achieved from the same acyclic ketone enamine by modification of the hydroboration-elimination procedure: (A) hydroboration by 9-BBN followed by methanolysis or (B) hydroboration by borane methyl sulfide (BMS) followed by methanolysis and hydrogen peroxide oxidation.Mechanistic rationale is provided.
- Singaram, Bakthan,Rangaishenvi, Milind V.,Brown, Herbert C.,Goralski, Christian G.,Hasha, Dennis L.
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p. 1543 - 1549
(2007/10/02)
-
- The enigmatic 1J(CH) coupling constants of allyl-type organometallic compounds
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A new attempt has been made to identify the factors responsible for the abnormally small one-bond C, H coupling constants observed for allyl, pentadienyl and heptatrienylmetal compounds.In-plane deformations (widening of the central CCC angle) should have
- Schlosser, Manfred,Lehmann, Ruth,Jenny, Titus
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p. 149 - 157
(2007/10/02)
-
- Dehydration of Alcohols Catalysed by Metallic Sulphates Supported on Silica Gel
-
Many metallic sulphates and hydrogen sulphates supported on silica gel efficiently catalyse dehydration of secondary and tertiary alcohols under mild conditions.The sulphates of CeIV, TiIV, and FeIII were most active.Silica gel was essential for the efficient dehydration in each case.The dehydration catalysed by Fe2(SO4)3, CuSO4, and NaHSO4 on silica gel was studied in detail.The order of the reactivity of alcohols was tertiary > secondary > primary.The dehydration activity of methanesulphonic acid was also enhanced (ca. 14 times at 90 deg C) by the presence of silica gel.Some mechanistic investigations were carried out.
- Nishiguchi, Takeshi,Kamio, Chizuko
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p. 707 - 710
(2007/10/02)
-
- REACTIONS OF o-(N-METHYLCARBAMOYL)PHENYL SULPHOXIDES WITH ELECTROPHILES
-
Reactions of alkyl o-(N-methylcarbamoyl)phenyl sulphoxides 1 with various electrophiles, such as acetic anhydride, acetyl chloride, thionyl chloride and p-toluenesulphonyl chloride, have been carried out.Treatment of 1 with excess acetic anhydride in general leads to the formation of the Pummerer type rearrangement products or related products.In the reactions of 1 with acetyl, thionyl and p-toluenesulphonyl chlorides, 2-methyl-1,2-benzisothiazole-3(2H)-one, 4b, and alkyl chlorides were obtained nearly quantitatively.All these reactions can be rationalized on the basis of the initial O-acylation and subsequent either α-proton removal to result in the Pummerer rearrangement or nucleophilic attack of neighbouring carbamoyl group to afford the five-membered products 4b.
- Uchida, Yuzuru,Oae, Shigeru
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p. 649 - 654
(2007/10/02)
-
- On the Mechanism of Base-Induced Gas-Phase Elimination Reactions of Ethers
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For the base-induced gas-phase elimination reactions of diethyl ether and cis- and trans-1-tert-butyl-4-methoxy-cyclohexane the kinetic isotope and leaving group effects have been determined as functions of the base strength using the method of Fourier transform ion cyclotron resonance mass spectrometry.The results are interpreted in terms of a variable E2 transition-state structure.Increasing the base strength causes the transition state to shift toward the carbanion or E1cb region of the E2 spectrum, which is also a general phenomenon in the condensed phase.Moreover, it appears that the elimination reactions most readily proceed via a transition state in which the β hydrogen and leaving group are periplanar.If the substrate does not easily allow such a relationship, the transition state is found to shift toward the carbenium ion or E1 region of the E2 spectrum where the geometric restrictions of the substrate are less perceptible.The concept of syn/anti dichotomy is used to explain the formation of tree and solvated alkoxide anions in the reactions induced by OH-.Anti elimination is believed to result in the formation of free alkoxide.Syn elimination, which takes advantage of the electrostatic interaction between the base and leaving group, is held responsible for the formation of solvated alkoxide.The importance of base/leaving group association in the transition state of the syn elimination is demonstrated by the low yield of solvated alkoxide in the reaction of OH-, solvated by a dimethylamine molecule, with diethyl ether.Finally, it seems that the selectivity of gas-phase elimination reactions is determined by not only the relative heights of the intrinsic reaction barriers, but also the relative stabilities of the ion/molecule complexes preceding the reaction barriers.
- Koning, Leo J. de,Nibbering, Nico M. M.
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p. 1715 - 1722
(2007/10/02)
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- Solvolysis Reactions and Force Field Calculations with Epimeric Cyclohexane Derivatives
-
Reactions of the epimeric 4-tert-butylcyclohexyl tosylates in hexafluoroisopropyl alcohol (HFIP) (1e, 1a) allow for the first time to observe SN1-type non-stereospecific substitution, whereas conventional solvents including even trifluoroethanol yield SN2-type inversion by solvent assisted pathway (*ks).Large differences are found between the epimers in the solvent participation, measured kinetically by the Schleyer-Bentley equation.This, as well as the even enhanced elimination with the equatorial isomer 1e as compared to 1a (98percent vs. 96percent in HFIP) points to the occurence of non-chair intermediates from 1e-derivatives, and to more E2- than E1-type reactions.Kinetic measurements, including those of cis-3,5-dimethylcyclohexane esters (2a, 2e) and 3α/3β-(tosyloxy)androstanes (3a, 3e) show little differences between the equatorial esters in agreement with MM2 calculations, which establish small strain energy variations between the differently substituted twist-boat intermediates.Large differences, however, of up to 500percent are measured between the axial esters (1a, 2a, 3a), although the alkyl substituents are remote from the leaving group and do not alter the chair geometry.These variations, which demonstrate the severe limitations of the Winstein-Holness equation for solvolysis reactions, are explained by MM2 calculated significant strain differences between the educts and the corresponding substituted cyclohexenes.
- Schneider, Hans-Joerg,Schmidt, Guenter
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- Studies on the Mechanism of Transition-Metal-Assisted Sodium Borohydride and Lithium Aluminium Hydride Reductions
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Studies on the course of transition-metal-assisted NaBH4 and LiAlH4 reductions of (1) nitriles, (2) alkenes, and (3) alkyl halides are described. (1) The kinetics of benzonitrile (PhCN) reduction indicate that at high nitrile:catalyst ratios, the rate of reduction is independent of PhCN concentrations.Furthermore, the rate of PhCN reduction exhibits a first-order dependence on NaBH4 concentration, as measured over a fourfold range of BH4(1-) concentration and several half-lives of PhCN.Moreover, when PhCN was reduced with equimolar mixtures of NaBH4 and NaBD4, a significant primary kinetic isotope effect was observed.Rapid complexation of PhCN to be boride surface apparently activates the nitrile group toward rate-determining hydride addition from dissolved, uncoordinated NaBH4. (2) The selective reduction of alkenes by NaBH4-CoCl2 is attributed to adventitious heterogeneous catalytic hydrogenation. (3) The combination of LiAlH4 with CoCl2 forms a black precipitate of cobalt aluminide (CoAl) which was isolated, analyzed by atomic absorption spectroscopy, and shown to play an essential catalytic role in the reduction of alkyl halides.Labeling experiments demonstrate stereochemical randomization by a heterogeneous process involving solvent as the hydrogen donor and LiAlH4 as a co-reductant.A radical mechanism involving halide atom transfer or oxidative addition to the aluminide is proposed.
- Osby, John O.,Heinzman, Stephen W.,Ganem, Bruce
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- Stereoelectronic Effects in Hydrogen-atom Transfer Reactions of Substituted Cyclohexyl Radicals
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Thermolysis of the peroxyoxalates (1)-(7) and the diacyl peroxides (8)-(11) in cyclohexane at 100 deg C gives cycloalkenes and cycloalkanes by hydrogen-atom transfer reactions of the initially formed conformationally biased 4-t-butyl-, 4-t-butyl-cis,cis-2,6-dimethyl-, 4-t-butyl-cis,trans-2,6-dimethyl-, 4-t-butyl-cis-2-methyl-, 4-t-butyl-trans-2-methyl-, and 5-t-butyl-cis-2-methylcyclohexyl radicals (12)-(17).The composition of the product mixtures indicates that transfer of axial β-hydrogen atoms occurs more rapidly than does transfer of equatorial β-hydrogen atoms.These results support the hypothesis that homolytic fission of a C-H bond is favoured when it lies chlose to the plane of an adjacent semi-occupied orbital.
- Beckwith, Athelstan L. J.,Easton, Christopher J.
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p. 661 - 668
(2007/10/02)
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- Reactions of Cyclohexenyl Halides with Tributylstannane. Stereoelectronic Effects on SH2 Reactions at Halogen
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Allylic halogenation of t-butylcyclohexene (2a) with t-butyl hypochlorite or N-bromosuccinimide affords mixtures containing mainly trans-5-t-butyl-3-chlorocyclohexene (2b) and the corresponding trans bromo compound (2c) respectively.The copper-catalysed r
- Beckwith, Athelstan L. J.,Westwood, Steven W.
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p. 2123 - 2132
(2007/10/02)
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- A New Reducing System: Calcium Metal in Amines. Reduction of Aromatic Hydrocarbons
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A new reducing system consisting of calcium dissolved in a mixture of amines (methylamine-ethylenediamine) is described.Representative aromatic hydrocarbons have been reduced by this new reagent largely to monoalkenes.Hydrocarbons like tetralin, m- and p-xylene, and indan are reduced in excellent yields by the calcium system to a crude product containing 88percent or better of a single alkene.A new technique involving oxymercuration-demercuration is used to purify two of the monoalkene isomer mixtures obtained in these reductions.Unexpectedly, durene is reduced by the calcium reagent to 1,2,4,5-tetramethyl-1,4-cyclohexadiene in excellent yield.Likewise anthracene is reduced in one step to 1,2,3,4,5,6,7,8,9,10-decahydroanthracene.Experiments designed to elucidate why the calcium system does not reduce durene or anthracene to monoalkenes are described.Similarities and differences between the calcium-amine and the lithium-amine reducing systems are discussed.
- Benkeser, Robert A.,Belmonte, Frank G.,Kang, Jahyo
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p. 2796 - 2802
(2007/10/02)
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- Nucleophilic Substitution and Competing Elimination in Cyclohexane and Steroid Reactions. A Comparison of Experiments and Force Field Calculations including the Regioselectivity of Steroid Eliminations
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A number of nucleophilic replacements including hydroxyl group substitutions are reported which show clean inversion with 3β-substituted cholestanes, whereas comparable cyclohexanes yield largely olefinic byproducts.Model calculations with the MM1 molecular mechanics force field demonstrate that twist boot intermediates as proposed in the literature for cyclohexane eliminations will require significantly higher strain energy in the steroid only if the interaction of both leaving group and attacking agent at Cβ-H is included.The predominance of Δ2 over Δ3 products in the steroid eliminations is based less on steric energy differences of these olefins, than on those of the preceding transition states.For the steroid all-chair ground state MM1, MM2 and crystal structure results are found to be in agreement.The calculations show the absence of conformational transmission of the A-ring twist-boat distortions in the C and D rings.
- Gschwendtner, W.,Hoppen, V.,Schneider, H.-J.
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p. 1201 - 1226
(2007/10/02)
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- DIRECT CONVERSION OF OXIRANES TO ALKENES BY CHLOROTRIMETHYLSILANE AND SODIUM IODIDE
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Smooth and quantitative conversion of oxiranes to alkenes is achieved by treatment with in situ generated iodotrimethylsilane.
- Caputo, Romualdo,Mangoni, Lorenzo,Neri, Orsola,Palumbo, Giovanni
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p. 3551 - 3552
(2007/10/02)
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- Asymmetric Induction in Liquid Crystals: Optically Active trans-Cyclooctene from Hofmann Elimination in New Cholesteric Mesophases
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Optically active trans-cyclooctene was obtained by Hofmann elimination of trimethylcyclooctyl ammonium hydroxide in new cholesteric liquid crystals.The extent of asymmetric induction rose 7 percent.Enantiomeric equilibration of racemic trans-cyclooctene in cholesteric medium, at 180 deg C, leads to a 2 percent enantiomeric excess.These asymmetric induction results are interpreted in terms of solute-solvent interactions enhanced by the local ordering of the mesophase.
- Seuron, Patrick,Solladie, Guy
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p. 715 - 719
(2007/10/02)
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- Efficient Coupling of Tertiary Alkyl Halides with Dialkylzinc and Titanium Compounds
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Dialkylzinc compounds react with tertiary halides to afford the corresponding coupling products containing a quaternary carbon atom, thereby making geminal dialkylation of ketones or hydroalkylation of olefins possible.
- Reetz, Manfred T.,Wenderoth, Bernd,Peter, Roland,Steinbach, Rainer,Westermann, Juergen
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p. 1202 - 1204
(2007/10/02)
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- Secondary Deuterium Kinetic Isotope Effects in the Solvolysis of 4-t-Butylcyclohexyl and Bicyclooctan-3-yl Toluene-p-sulphonates. New Results using 50percent Aqueous Ethanol, Acetic Acid, and 97percent Aqueous Hexafluoropropan-2-ol
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Secondary α-deuterium kinetic isotope effects for the solvolysis of cis- and trans-4-t-butylcyclohexyl toluene-p-sulphonates in 50percent aqueous ethanol (1.200 -/+ 0.007 and 1.16 -/+ 0.01 respectively, 44.8 deg), acetic acid (1.172 -/+ 0.004 and 1.13 -/+
- Banks, R. Margaret,Maskill, H.,Natarajan, Rajagopalan,Wilson, Alan A.
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p. 427 - 431
(2007/10/02)
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