- A donor-acceptor complex enables the synthesis of: E -olefins from alcohols, amines and carboxylic acids
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Olefins are prevalent substrates and functionalities. The synthesis of olefins from readily available starting materials such as alcohols, amines and carboxylic acids is of great significance to address the sustainability concerns in organic synthesis. Metallaphotoredox-catalyzed defunctionalizations were reported to achieve such transformations under mild conditions. However, all these valuable strategies require a transition metal catalyst, a ligand or an expensive photocatalyst, with the challenges of controlling the region- and stereoselectivities remaining. Herein, we present a fundamentally distinct strategy enabled by electron donor-acceptor (EDA) complexes, for the selective synthesis of olefins from these simple and easily available starting materials. The conversions took place via photoactivation of the EDA complexes of the activated substrates with alkali salts, followed by hydrogen atom elimination from in situ generated alkyl radicals. This method is operationally simple and straightforward and free of photocatalysts and transition-metals, and shows high regio- and stereoselectivities.
- Chen, Kun-Quan,Shen, Jie,Wang, Zhi-Xiang,Chen, Xiang-Yu
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p. 6684 - 6690
(2021/05/31)
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- Harnessing Applied Potential: Selective β-Hydrocarboxylation of Substituted Olefins
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The construction of carboxylic acid compounds in a selective fashion from low value materials such as alkenes remains a long-standing challenge to synthetic chemists. In particular, β-addition to styrenes is underdeveloped. Herein we report a new electrosynthetic approach to the selective hydrocarboxylation of alkenes that overcomes the limitations of current transition metal and photochemical approaches. The reported method allows unprecedented direct access to carboxylic acids derived from β,β-trisubstituted alkenes, in a highly regioselective manner.
- Alkayal, Anas,Buckley, Benjamin R.,Malkov, Andrei V.,Montanaro, Stephanie,Tabas, Volodymyr,Wright, Iain A.
-
supporting information
(2020/02/13)
-
- Synthesis of α-Arylated Cycloalkanones from Congested Trisubstituted Spiro-epoxides: Application of the House-Meinwald Rearrangement for Ring Expansion
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A three-step sequence for the synthesis of α-arylated cyclohexanones and the most challenging cycloheptanones is reported. First, an efficient one-pot synthesis of β,β'-disubstituted benzylidene cycloalkanes (styrenes) using the palladium-catalyzed Barluenga reaction from readily available feedstock chemicals is described. Furthermore, an epoxidation followed by the House-Meinwald rearrangement (HMR) of spiro-epoxides is reported to produce a number of α-arylated cycloalkanones upon ring expansion. Reactions catalyzed by bismuth triflate underwent quasi-exclusively ring expansion for all substrates (electronically poor and rich), with yields ranging from 15% to 95%, thus demonstrating the difficulty of achieving ring enlargement for electron-deficient spiro-epoxides. On the other hand, by means of catalysis with aluminum trichloride, the rearrangement of spiro-epoxides proceeded typically in high yields and with remarkable regioselectivity on a broader substrate scope. In this case, a switch of regioselectivity was achieved for spiro-epoxides with electron-withdrawing substituents which enable the method to be successfully extended to some chemospecific arene shifts and the synthesis of aldehydes bearing a α-quaternary carbon. While the HMR has been extensively studied for smaller ring enlargement, we are pleased to report herein that larger cyclohexanones and cycloheptanones can be obtained efficiently from more sterically demanding trisubstituted spiro-epoxides bearing electron-releasing and electron-neutral arene substituents.
- Jeedimalla, Nagalakshmi,Jacquet, Camille,Bahneva, Diana,Youte Tendoung, Jean-Jacques,Roche, Stéphane P.
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p. 12357 - 12373
(2018/09/06)
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- Olefination with Sulfonyl Halides and Esters: E-Selective Synthesis of Alkenes from Semistabilized Carbanion Precursors
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Carbanions of sulfonyl halides and activated sulfonates add to carbonyl compounds, and so-formed aldol-type adducts spontaneously fragment into olefins. This transformation mimics the one-pot Julia olefination with (hetero)aryl sulfones, but the mechanism of fragmentation involves a four-membered intermediate, typical for reactivity of phosphorus reagents. Moreover, in contrast to the reactions of sulfones, sulfonates of fluorinated alcohols (TFE and HFI) produce byproducts that are easily removed during workup. In our report, we focus on reactions of unstabilized and semistabilized carbanion precursors: alkylsulfonates, and allyl- and benzylsulfonates, respectively. In particular for semistabilized systems, olefins were synthesized as predominant E isomers in good yields. The presented studies reveal that optimal reaction conditions, including the type of base and alcohol groups of the sulfonates, are different depending on stabilization of the carbanion precursors and structure of the carbonyl substrates. The practical synthetic guide is supplemented with a discussion of the mechanism, based on reactivity studies of intermediates and identification of side-products.
- Górski, Bartosz,Basiak, Dariusz,Talko, Alicja,Basak, Tymoteusz,Mazurek, Tomasz,Barbasiewicz, Micha?
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p. 1774 - 1784
(2018/04/27)
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- Switchable Synthetic Strategy toward Trisubstituted and Tetrasubstituted Exocyclic Alkenes
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An efficient and facile method for the construction of tri- or tetrasubstituted exocyclic alkenes is achieved via a Cu(I)-catalytic system. This protocol exhibits mild conditions, low-cost catalyst, good functional group tolerance, and good yields. The selectivity toward tri- or tetrasubstituted alkenes can be delicately controlled by adjustment of base and solvent. A preliminary mechanism study manifested that the reaction undergoes a radical process, where B2pin2 plays an indispensable role.
- Zhou, Sen,Yuan, Fangyuan,Guo, Minjie,Wang, Guangwei,Tang, Xiangyang,Zhao, Wentao
-
supporting information
p. 6710 - 6714
(2018/11/21)
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- Consecutive visible-light photoredox decarboxylative couplings of adipic acid active esters with alkynyl sulfones leading to cyclic compounds
-
Novel and efficient consecutive photoredox decarboxylative couplings of adipic acid active esters (bis(1,3-dioxoisoindolin-2-yl)-substituted hexanedioates) with substituted 1-(2-arylethynylsulfonyl)benzenes have been developed under visible-light photocatalysis. The successive photoredox decarboxylative C-C bond formation at room temperature afforded the corresponding cyclic compounds in good yields with tolerance of some functional groups.
- Li, Jingjing,Tian, Hua,Jiang, Min,Yang, Haijun,Zhao, Yufen,Fu, Hua
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p. 8862 - 8864
(2016/07/22)
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- Copper-catalyzed alkene arylation with diaryliodonium salts
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Alkenes and arenes represent two classes of feedstock compounds whose union has fundamental importance to synthetic organic chemistry. We report a new approach to alkene arylation using diaryliodonium salts and Cu catalysis. Using a range of simple alkenes, we have shown that the product outcomes differ significantly from those commonly obtained by the Heck reaction. We have used these insights to develop a number of new tandem and cascade reactions that transform readily available alkenes into complex arylated products that may have broad applications in chemical synthesis.
- Phipps, Robert J.,McMurray, Lindsay,Ritter, Stefanie,Duong, Hung A.,Gaunt, Matthew J.
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supporting information; experimental part
p. 10773 - 10776
(2012/08/07)
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- Cross-coupling of aryllithiums with aryl and vinyl halides in flow microreactors
-
The use of Pd catalysts that contained a carbene ligand, such as PEPPSI-SIPr, speeded up the Murahashi coupling of ArLi with ArBr, by enabling its integration with the Br/Li exchange of ArBr with BuLi in flow. Space integration realized the rapid cross-coupling of two different ArBr substrates. However, the cross-coupling reaction with vinyl halides could not be achieved under similar conditions. Pd(OAc)2 was an effective catalyst, and the space integration of the Br/Li exchange of ArBr with BuLi and the Murahashi coupling with vinyl halides was successfully achieved.
- Nagaki, Aiichiro,Moriwaki, Yuya,Haraki, Suguru,Kenmoku, Akira,Takabayashi, Naofumi,Hayashi, Atsushi,Yoshida, Jun-Ichi
-
supporting information; experimental part
p. 1061 - 1068
(2012/07/31)
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- Fluoride-promoted cross-coupling of chloro(mono-, di-, or triphenyl)germanes with aryl halides in "moist" toluene. Multiple transfer of the phenyl group from organogermane substrates and comparison of the coupling efficiencies of chloro(phenyl)germanes with their corresponding stannane and silane counterparts
-
The trichlorophenyl-, dichlorodiphenyl-, and chlorotriphenylgermanes undergo Pd-catalyzed cross-couplings with aryl bromides and iodides in the presence of tetrabutylammonium fluoride in toluene with addition of the measured amount of water. One chloride ligand on the Ge center allows efficient activation by fluoride to promote transfer of one, two, or three phenyl groups from the organogermanes. The corresponding chlorophenylstannanes were found to be more reactive than chlorophenylsilanes, which in turn were more effective than chlorophenylgermanes. One chloride ligand on the Ge or Si center allows efficient activation by fluoride to promote transfer of up to three aryl groups from germane or silicon. However, no haloligand was necessary to be present on the Sn center, since tetraphenyltin efficiently transferred up to four phenyl groups during fluoride-promoted couplings with aryl halides. 19F NMR studies suggested formation of the fluorophenylgermanes and the hypervalent germanate species as possible intermediates.
- Pitteloud, Jean-Philippe,Zhang, Zun-Ting,Liang, Yong,Cabrera, Laura,Wnuk, Stanislaw F.
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supporting information; experimental part
p. 8199 - 8212
(2011/03/18)
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- Microwave-assisted, aqueous wittig reactions: Organic-solvent- And protecting-group-free chemoselective synthesis of functionalized alkenes
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(Chemical Equation Presented) Free from protection! A general, chemoselective, protecting-group- and organic-solvent-free route to stilbenes and heterostilbenes involving the direct synthesis of triethyl benzylic and allylic phosphonium salts from the corresponding alcohols and their microwave-assisted, aqueous Wittig reactions is described.
- McNulty, James,Das, Priyabrata,McLeod, David
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supporting information; experimental part
p. 6756 - 6760
(2010/08/06)
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- Conformational and structural analysis of exocyclic olefins and ketimines by multinuclear magnetic resonance
-
The 1H, 13C, and 15N NMR spectra of 5 exocyclic alkenes and 15 different ketimines obtained from cyclohexanone and derivatives using benzyl bromide and primary amines - are analyzed. Relative stereochemical and preferentia
- Montalvo-Gonzalez, Ruben,Montalvo-Gonzalez, J. Ascencion,Ariza-Castolo, Armando
-
experimental part
p. 907 - 912
(2009/05/09)
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- Vinyl tris(trimethylsilyl)silanes: substrates for Hiyama coupling
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The oxidative treatment of vinyl tris(trimethylsilyl)silanes with hydrogen peroxide in aqueous sodium hydroxide in tetrahydrofuran generates reactive silanol or siloxane species that undergo Pd-catalyzed cross-couplings with aryl, heterocyclic, and alkenyl halides in the presence of Pd(PPh3)4 and tetrabutylammonium fluoride. Hydrogen peroxide and base are necessary for the coupling to occur while activation of the silanes with fluoride is not required. The conjugated and unconjugated tris(trimethylsilyl)silanes serve as good cross-coupling substrates. The (E)-silanes undergo coupling with retention of stereochemistry while coupling of (Z)-silanes occurred with lower stereoselectivity to produce an E/Z mixture of products.
- Wang, Zhizhong,Pitteloud, Jean-Philippe,Montes, Lucresia,Rapp, Magdalena,Derane, Djenny,Wnuk, Stanislaw F.
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p. 5322 - 5327
(2008/09/21)
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- Catalytic reduction of phenyl-conjugated acetylenic halides by nickel(I) salen: Cyclization versus coupling
-
Cyclic voltammetry and controlled-potential electrolysis were employed to study the catalytic reduction of five phenyl-conjugated haloalkynes by nickel(I) salen electro-generated at carbon cathodes in dimethylformamide containing tetramethylammonium tetrafluoroborate. Electrocatalytic reduction of 7-bromo- and 7-iodo-1-phenyl-1-heptyne affords the carbocyclic product, benzylidenecyclohexane, in up to 41 % yield, whereas under similar conditions reduction of 5-halo-1-phenyl-1-pentyne and 8-bromo-1-phenyl-1-octyne gives benzylidenecyclobutane and benzylidenecycloheptane, respectively, in very low yield (≤1 %). Dimers, alkynes, and alkenynes are other products formed from the phenyl-conjugated haloalkynes. Dimers (diphenylalkadiynes) derived from 5-halo-1-phenyl-1-pentyne and 8-bromo-1-phenyl-1-octyne are obtained in yields ranging from 85 to 93 %, whereas 1,14-diphenyltetradeca-1,13-diyne (the dimer produced from 7-halo-1-phenyl-1-heptyne) is found in yields of 45-51 %. To account for the formation of the various products, a mechanistic scheme that involves phenyl-conjugated alkynyl radicals arising from nickel(I) salen catalyzed cleavage of the carbon-halogen bond of each substrate was formulated. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Mubarak, Mohammad S.,Jennermann, Theodore B.,Ischay, Michael A.,Peters, Dennis G.
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p. 5346 - 5352
(2008/03/14)
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- Disproportionation of diarylmethanol derivatives by using supercritical water
-
Non-catalytic disproportionation of diarylmethanol derivatives was found to proceed efficiently in supercritical water. This method was also applied to various diarylmethylamine derivatives to give the disproportionation products in good yields.
- Hatano, Bunpei,Kadokawa, Jun-Ichi,Tagaya, Hideyuki
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p. 5859 - 5861
(2007/10/03)
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- Enantioselective protonation of samarium enolates derived from α- heterosubstituted ketones and lactone by SmI2-mediated reduction
-
SmI2-mediated reductive cleavage of α-heterosubstituents of α-alkyl or α-aryl ketones and lactone gave the corresponding 'thermodynamic samarium enolates'. Enantioselective protonation of the samarium enolates with C2- symmetric chiral diols afforded the corresponding ketones and lactone in moderate to high enantioselectivities.
- Nakamura, Yutaka,Takeuchi, Seiji,Ohgo, Yoshiaki,Yamaoka, Makoto,Yoshida, Akihiro,Mikami, Koichi
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p. 4595 - 4620
(2007/10/03)
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- Synthesis of dialkenyl dichalcogenides via alkenechalcogenolate ions generated by treating ketone p-Toluenesulfonylhydrazones with a base and elemental chalcogen
-
Alkeneselenolate and alkenetellurolate ions were generated by treating ketone p-toluenesulfonylhydrazones possessing an α-methylene or an α-methine group with t-BuOK and elemental selenium or tellurium, respectively, at 110-150°C, and were converted into dialkenyl dichalcogenides by aerobic oxidation.
- Shimada, Kazuaki,Asahida, Mitsuharu,Takahashi, Ken,Sato, Yoshitaka,Aoyagi, Shigenobu,Takikawa, Yuji,Kabuto, Chizuko
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p. 513 - 514
(2007/10/03)
-
- Reaction of trithiazyl trichloride with active methylene compounds
-
Activated allylic compounds react with trithiazyl trichloride, (NSCl)3, to give 1,2,5-thiadiazoles 1 and isothiazoles 2. An allylic 2-substituent normally prevents formation of an aromatic 1,2,5-thiadiazole, and isothiazole formation becomes the major pathway. Simple allylic compounds are not very reactive towards (NSCl)3 but a terminal electron withdrawing group (CO2Et) enhances the reactivity. With unsymmetrical allylic compounds, isothiazole formation is regiospecific placing the more electron withdrawing group adjacent to the ring sulfur. 1,3-Diketones give 3-acyl-1,2,5-thiadiazoles; unsymmetrical 1,3-diketones give these thiadiazoles regiospecifically, explicable by cyclisation of an intermediate onto the more reactive carbonyl group. 1,4-Diketones give 3,4-diacyl-1,2,5-thiadiazoles; thus 1,2-dibenzoyl-ethane,-echene and -ethyne all give 3,4-dibenzoylthiadiazole (40-44%). Many of these trithiazyl trichloride reactions provide attractive one-step routes to 1,2,5-thiadiazoles and isothiazoles.
- Duan, Xiao-Guang,Duan, Xiao-Lan,Rees, Charles W.
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p. 2831 - 2836
(2007/10/03)
-
- Cyclohexynes as intermediates in a novel endo-cyclization of alkynylzincates derived from 5-hexynyl tosylates
-
The n-type endo-cyclization of metal acetylides to form cyclohexynes was observed for the first time in the reaction of alkynylzincates derived from 5-hexynyl tosylates. The endo-cyclization took place in competition with erocyclization, leading to the formation of 1-(cyclopentylidene)alkylzincs.
- Harada, Toshiro,Otani, Takeshi,Oku, Akira
-
p. 2855 - 2858
(2007/10/03)
-
- Cyclizations during the Grignard Reactions of ω-Bromoalkynes
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The Grignard reactions of a number of ω-bromoalkynes have been shown to undergo regioselective cyclizations in certain instances to give the smaller possible carbocycle. These cyclizations are shown to result from two competing processes, whose relative efficiencies depend upon the chain length and the remote substitutent on the acetylene. These are interpreted as a radical cyclization which occurs only during the time the Grignard is being formed from the bromide and an organometallic reaction which slowly transforms the Grignard reagent into its cyclic isomer. The mechanistic details of these transformations are discussed.
- Crandall, Jack K.,Michaely, William J.,Collonges, Francois,Nelson, Deanna J.,Ayers, Timothy A.,Gajewski, Joseph J.
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p. 1473 - 1490
(2007/10/03)
-
- A modified Clemmensen reduction procedure for conversion of aryl ketones into aryl alkenes
-
Aryl alkenes can be prepared from aryl ketones through reduction by refluxing with amalgamated zinc in a mixture of formic acid and ethanol.
- Hiegel, Gene A.,Carney, John R.
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p. 2625 - 2631
(2007/10/03)
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- Conversion of ketone trimethylsilylcyanohydrins to several types of compounds
-
Cyclic ketone O-trimethylsilylcyanohydrins (2) were prepared and converted to various compounds: α-hydroxyketones (3), dehydroxylated ketones (4), α,β-unsaturated ketones (9), tricyclic ketones (10), 1-ethoxycarbonyl-4- phenyl-1,2,4a,5,6,7,8,8a-octahydro-2-naphthalenone (13), 1- phenylperhydroisocoumarin (18) and 1,2,3,4,4a,10,11,11a-octahydro-5h- benzo[a,d]cyclohepten-10-one (20).
- Ohta,Yamashita,Arita,Kajiura,Kawasaki,Noda,Izumi
-
p. 1294 - 1301
(2007/10/02)
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- Cyclization of α,ω-diborylalkanes via double Suzuki-Miyaura coupling
-
Both carbo- and heterocyclic six-membered ring systems (3) containing an exocyclic carbon-carbon double bond have been prepared (25-76%) from α,ω-dienes (1) through the cross coupling of their dihydroboration products (2) with either aromatic or aliphatic vinylidene dibromides (4) in a one-pot Pd-catalyzed sequence.
- Soderquist, John A.,Leon, Gisela,Colberg, Juan C.,Martinez, Isamir
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p. 3119 - 3122
(2007/10/02)
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- Stereochemistry of direct olefin formation from carbonyl compounds and lithiated heterocyclic sulfones
-
The conditions for the title reaction were studied for the 2-benzothiazole and 2-pyridine series and for some examples in the 2-pyrimidine series.The olefin preparations were generally observed to be more efficient for 2-BT-sulfone systems.From the data of the hundred cases studied, it can be concluded that (E)-olefins are obtained: (i) from saturated BT-sulfones and aromatic aldehydes; and (ii) from benzylic BT-sulfones and branched saturated aldehydes (isobutyraldehyde, pivalaldehyde) or α,β-ethylenic or aromatic aldehydes. (Z)-olefins arise: (i) fom propargylic BT-sulfones and saturated or aromatic aldehydes; and (ii) from allylic or benzylic Pyr-sulfones and saturated aldehydes.Possible mechanisms for this new olefination procedure were examined. - heteroaromatic sulfones, organolithium derivatives, intramolecular ipso reactions, stereochemistry, elimination, olefination.
- Baudin, J. B.,Hareau, G.,Julia, S. A.,Lorne, R.,Ruel, O.
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p. 856 - 878
(2007/10/02)
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- Alkene Formation through Condensation of Phenylmethanesulphonyl Fluoride with Carbonyl Compounds
-
Arylmethanesulphonyl fluorides condense with aromatic, aliphatic and conjugated aldehydes and ketones in the presence of potassium carbonate and a crown ether to give aryl-substituted alkenes in satisfactory to modest yields.
- Kagabu, Shinzo,Hara, Kenji,Takahashi, Junko
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p. 408 - 410
(2007/10/02)
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- A direct synthesis of olefins by reaction of carbonyl compounds with lithio derivatives of 2-[alkyl- or (2'-alkenyl)- or benzyl-sulfonyl]-benzothiazoles
-
During the title reaction, the lithium alkoxides formed as intermediates undergo an intramolecular addition to the neighboring C = N group followed an S to O benzothiazole transfer and simultaneous extrusion of sulfur dioxide and ejection of 2(3H)-benzothiazolone anion.
- Baudin,Hareau,Julia,Ruel
-
p. 1175 - 1178
(2007/10/02)
-
- Photolyses of 1,4-Bis(1,1-diarylhept-2-ynyl)benzenes and 1,4-Bis(1,1-diarylalkyl)benzenes
-
Photolyses of 1,4-bis(1,1-diarylhept-2-ynyl)benzenes or 1,4-bis(1,1-diarylalkyl)benzenes 2 in a tetrahydrofuran-methanol mixture gave 1-biphenyl-4-yl-1,1-diarylhept-2-ynes or 1-biphenyl-4-yl-1,1-diarylalkanes 3 as major products and biaryls 1 as minor products.The products 3 were obtained with quantum yields of 0.010-0.020, respectively.
- Shi, Min,Okamoto, Yoshiki,Takamuku, Setsuo
-
p. 2391 - 2393
(2007/10/02)
-
- Photolysis of 1,1,1-Triarylalkane. A New Photochemical Carbene Generation Process
-
Upon UV irradiation in methanol some 1,1,1-triarylalkanes underwent an α,α-elimination of two aryl groups to give biaryls and the corresponding carbene intermediates, which inserted into the OH bond of the methanol to afford methyl ethers and/or underwent a 1,2-H shift to afford olefins.Furthermore, the efficieny of this elimination was highly dependent upon the bulkiness of the alkyl groups.
- Shi, Min,Okamoto, Yoshiki,Takamuku, Setsuo
-
p. 3821 - 3824
(2007/10/02)
-
- REACTION OF LITHIUM DERIVATIVE OF DIETHYL PHENYLMETHANE-PHOSPHONATE WITH KETONES
-
The reaction of the lithium derivative of diethyl ester of phenylmethanephosphonic acid (1-Li) with alkanones, cycloalkanones, alkylaryl and diarylketones 2a-h is studied at -70 deg C in THF.The corresponding adducts - diethyl esters of 1-phenyl-2,2-dialkyl(phenyl)-2-hydroxyethanephosphonic acids 3a-h are isolated, their yields being usually higher at short reaction time.The olefination of 3-Li as well as of 3 (both by thermolysis or in acidic media) proceeds in low degree, while in the case of 3-Na the yields of alkene 4 are good.The relative configuration of 3b, 3f and 3g are determined by IR and NMR-spectra, as well as by their stereospecific olefination. "Threo"-stereoselectivity of the addition stage of the reaction of 1-Li with 2b, 2f and 2g is observed, the "threo"/"erythro" ratio remaining independent on the reaction time.
- Petrova, Jordanka,Vassilev, Nikolai G.,Kirilov, Marko
-
p. 457 - 463
(2007/10/02)
-
- INTRAMOLECULAR ADDITION OF ALKYLLITHIUMS TO ACETYLENES: REGIOSPECIFIC 4-, 5-, and 6-EXO-DIG CYCLIZATIONS
-
Primary acetylenic alkyllithiums bearing a phenyl substituent on the triple bond, which may be prepared in virtually quantitative yield by low-temperature lithium-iodine interchange, undergo regiospecific exo-dig cyclization via stereoselective syn-additi
- Bailey, William F.,Ovaska, Timo V.
-
p. 627 - 630
(2007/10/02)
-
- Radical ions in photochemistry. 21. The photosensitized (electron transfer) tautomerization of alkenes; the phenyl alkene system
-
Alkenes, conjugated with a phenyl group, can be converted to nonconjugated tautomers by sensitized (electron transfer) irradiation.For example, irradiation of an acetonitrile solution of the conjugated alkene 1-phenylpropene, the electron accepting photosensitizer 1,4-dicyanobenzene, the cosensitizer biphenyl, and the base 2,4,6-trimethylpiridine gave the nonconjugated tautomer 3-phenylpropene in good yield.Similarly, 2-methyl-1-phenylpropene gave 2-methyl-3-phenylpropene, and 1-phenyl-1-butene gave E- and Z-1-phenyl-2-butene.The reaction also works well with cyclic alkenes.For example, 1-phenylcyclohexene gave 3-phenylcyclohexene, and 1-(phenylmethylene)cyclohexane gave 1-(phenylmethyl)cyclohexene.The proposed mechanism involves the initial formation of the alkene radical cation and the sensitizer radical anion, induced by irradiation of the sensitizer and mediated by the cosensitizer.Deprotonation of the radical cation assisted by the base gives the ambident radical, which is then reduced to the anion by the sensitizer radical anion.Protonation of the ambident anion at the benzylic position completes the sequence.Reprotonation at the original position is an energy wasting step.Tautomerization is driven toward the isomer with the higher oxidation potential, which is, in the cases studied, the less thermodinamically stable isomer.The tautomerization of 2-methyl-1-phenylbutene gave both 2-phenylmethyl-1-butene and 2-methyl-1-phenyl-2-butene (E and Z isomers), while 2,3-dimethyl-1-phenylbutene gave only 3-methyl-2-phenylmethyl-1-butene.In the latter case, steric interaction of the methyls on the isopropyl group prevents effective overlap of the tertiary carbon-hydrogen bond with the singly occupied molecular orbital, thus inhibiting deprotonation from this site.Key words: photosensitized, electron transfer, alkene, tautomerization, radical cation.
- Arnold, Donald R.,Mines, Shelley A.
-
p. 689 - 698
(2007/10/02)
-
- Photolysis of 1,1,1-triphenylalkanes
-
Photolysis of 1,1,1-triphenylalkane in methanol gave biphenyl, 1-methoxy-1-phenylalkane, and 1-phenylalkene. The generation of the carbene intermediate by photo α,α-elimination of two phenyl groups was presumed.
- Shi,Okamoto,Takamuku
-
p. 6709 - 6712
(2007/10/02)
-
- OLEFIN SYNTHESIS VIA THE LITHIUM DERIVATIVE OF THE N,N,N',N'-TETRAMETHYLDIAMIDES OF ARYLMETHANEPHOSPHONIC ACIDS. 3. SYNTHESYS OF SOME β-DISUBSTITUTED STYRENES
-
The reaction of Li-derivatives of N,N,N',N'-tetramethyldiamides of arylmethanephosphonic acids (1-Li) with alkanones, cycloalkanones, alkylaryl- and diarylketones 2a-h is studied.It is found that in THF at -70 deg C adducts 3-Li and 4-Li are formed, the corresponding hydroxyl compounds 3 and 4 being isolated in 36-81percent yields, while by elevated temperatures the reaction is completely shifted to the starting 1-Li and 2.By thermolysis of 3 and 4 in neutral medium olefins 5 and 6 are obtained even from readily enolysable ketones.The stereochemistry of the addition reaction with nonsymmetrical ketones as well as the influence of the substituents at the carbonyl groups on the conformation and adsorption properties of the adducts are discussed.
- Momchilova, Snejana,Petrova, Jordanka,Kirilov, Marko
-
p. 319 - 328
(2007/10/02)
-
- A SELF-IMMOLATIVE STRATEGY FOR 1,2-ELIMINATION OF HOMOALLYL SULFONES TO 1,3-DIENES
-
Treatment of homoallyl sulfones with t-butyl lithium at low temperature affords ortho-lithio sulfones which undergo intramolecular deprotonation to produce 1,3-dienes.
- Radisson, X.,Kwiatkowski, P. L.,Fuchs, P. L.
-
-
- Fluoride Ion-Induced Horner-Emmons Reaction of α-Silylalkylphosphonic Derivatives with Carbonyl Compounds
-
Dimethyl α-trimethylsilylbenzylphosphonate was allowed to react with carbonyl compounds in the presence of fluoride ion to give the corresponding olefins in fairly good yields.Use of CsF in tetrahydrofuran gave the best result.On the other hand, dimethyl trimethylsilylmethylphosphonate was allowed to react similarly with benzophenone to afford 1,1-diphenylethylene, dimethyl methylphosphonate, and dimethyl 2,2-diphenylethenylphosphonate.A similar result was obtained by using O,O-diethyl trimethylsilylmethylphophonothioate.But, reaction of trimethylsilylmethylphosphonic bis(diethylamide) afforded only the protodesilylation product.
- Kawashima, Takayuki,Ishii, Takafumi,Inamoto, Naoki
-
p. 1831 - 1838
(2007/10/02)
-
- Synthesis of Alkenes via Peterson Reaction
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The α-phenylthiosilanes (2) have been used to prepare the α-silyl anions (1) by reaction with lithium naphthalenide; subsequent condensation with a carbonyl compound gave the alkene (8) via the Peterson reaction.The α-phenylthiosilanes (2) were prepared from n,n-bis(phenylthio)acetals (4) by reaction with lithium naphthalenide and chlorotrimethylsilane.The n,n-bis(phenylthio)acetals (4) were obtained, in turn, from 1,1-bis(phenylthio)acetals (5) by anion formation with butyl-lithium-N,N,N',N'-tetramethylethylenediamine complex in hexane followed by reaction with an alkyl halide.The Peterson reaction was also used to prepare vinyl sulphides (9) and vinyl sulphones (13).
- Ager, David J.
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p. 183 - 194
(2007/10/02)
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- AZO ANIONS IN SYNTHESIS. USE OF TRITYL- AND DIPHENYL-4-PYRIDYLMETHYLHYDRAZONES FOR REDUCTIVE C-C BOND FORMATION.
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The lithium salts of trityl- and diphenyl-4-pyridylmethyl-hydrazones of both aldehydes and ketones react with electrophiles (alkyl halides, aldehydes, ketones, crotonates) at low temperature to form C-trapped azo compounds; these intermediates decompose homolytically with loss of nitrogen below room temperature and can be diverted in a synthetically useful way to alkanes, alkenes, alcohols or saturated esters.
- Baldwin, Jack E.,Adlington, Robert M.,Bottaro, Jeffrey C.,Kolhe, Jayant N.,Newington, Ian M.,Perry, Matthew W. D.
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p. 4235 - 4246
(2007/10/02)
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- Cyclizations of ω-Alkynyl Halides by Cr(II) Reduction
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Reduction of halides of the types RCC(CH2)nX with Cr(II) in aqueous DMF containing ethylenediamine proceeds by way of the intermediate radicals which cyclize regioselectively in the n=4 and n=5 cases to give substituted methylenecycloalkanes.Experimental conditions which favor longer lifetimes for the intermediate radicals (low concentrations, slow addition times, and an inverse-addition mode) result in increased cyclization.The iodides curiously give more cyclic product than the corresponding bromides.These results are discussed.
- Crandall, Jack. K.,Michaely, W. J.
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p. 4244 - 4248
(2007/10/02)
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- Azo Anions in Synthesis. Use of Trityl- and Diphenyl-4-pyridylmethyl-hydrazones for Reductive C-C Bond Formation from Aldehydes and Ketones
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The lithium salts for trityl- and diphenyl-4-pyridylmethyl-hydrazones of both aldehydes and ketones react with electrophiles (alkyl halides, aldehydes, and ketones) at low temperature to form C-trapped azo compounds; these intermediates decompose homolytically with loss of nitrogen below room temperature and can be diverted in a synthetically useful way to alkanes, or alkenes, or alcohols.
- Baldwin, Jack E.,Bottaro, Jeffrey C.,Kolhe, Jayant N.,Adlington, Robert M.
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- OLEFIN SYNTHESIS VIA FRAGMENTATION OF HINDERED ESTER HALIDES
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Hindered methyl esters possessing allylic or benzylic bromine substituents undergo smooth dealkylative decarboxylation to afford olefinic derivatives.
- Belletire, J. L.,Walley, D. R.
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p. 1475 - 1476
(2007/10/02)
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- FLUORIDE ION INDUCED HORNER-EMMONS REACTION OF α-SILYLALKYLPHOSPHONATES WITH CARBONYL COMPOUNDS
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α-Trimethylsilylalkylphosphonates react with carbonyl compounds to give the corresponding olefins in the presence of fluoride ion.Use of CsF gave the best result.
- Kawashima, Takayuki,Ishii, Takafumi,Inamoto, Naoki
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p. 739 - 742
(2007/10/02)
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- Synthesis and Addition Reactions of 2-Phenyl-1-cyclopropene-1-carboxylates
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From the olefins 1, 2, and 4 - 7 the 1-chloro-1-cyclopropanecarboxylic acids 15 - 20 are prepareded via the dichlorocyclopropanes 8, 9, and 11 - 14.The trans-isomers 15a - 20a were readily separated.Spiropentane 10 undergoes anionic ring cleavage with BuLi to give finally the ester 33.The tert-butyl esters 21 - 26 yield with KOtBu the cyclopropene esters 27 - 32.The trans-esters 21a - 26a react much faster than the cis-esters b.At C-3 unsubstituted chlorocyclopropane esters, e.g. 34, do not give stable cyclopropene esters even with lithium dialkylamides.Diazomethane adds to the esters 27 - 32 to give the pyrazolines 38 - 43, their isomers a and b being separable.With traces of base the bicyclic pyrazolines are cleaved to 1,4-dihydropyridazines 44 - 46.Cyclopropenes 27 - 30 react with thiophenolate to form the isomeric products 47 - 50; malonate adds to 28 and 31 to give 51, 52.With malononitrile via subsequent reactions the cyclopentadienes 55 - 57 are obtained.
- Norden, Wolfgang,Sander, Volker,Weyerstahl, Peter
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p. 3097 - 3111
(2007/10/02)
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- Anwendungen der Phasentransfer-Katalyse 17. Wittig-Reaktionen in verschiedenen Zweiphasen-Systemen
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EINE vergleichende Untersuchung von Wittig-Reaktionen unter Phasentransfer-Katalyse (PTC) bei verschiedenen Bedingungen wurde durchgefuehrt.Es erwies sich als unnoetig, ausser den Phosphoniumsalzen einen PTC-Katalysator zu verwenden.Mechanistische Konsequenzen dieses Befundes werden diskutiert.Als ein besonders geeignetes Basensystem stellte sich Kalium-tert-butoxid in Benzol heraus.Erstmals gelang die Umzetzung von Ketonen und aliphatischen Aldehyden.Einige sehr hohe Literaturausbeuten von PTC-Wittig-Reaktionen konnten unter praeparativen Bedingungen nicht reproduziert werden.
- Dehmlow, Eckehard V.,Barahona-Naranjo, Simon
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p. 1748 - 1762
(2007/10/02)
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- Anwendungen der Phasentransfer-Katalyse 18. Horner-Emmons Reaktionen
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Optimale Bedingungen fuer die Darstellung von Olefinen aus den relativ wenig aktivierten Benzyl-, Cinnamyl- und Crotonylphosphonestern wurden aufgesucht.Als Carbonylkomponenten koennen aromatische Aldehyde und (mit verminderten Ausbeuten) auch aliphatische Aldehyde und Ketone eingesetzt werden.Die beste Basen-Loesungsmittel-Katalysator-Kombination ist Benzol/gepulvertes KOH/18-Krone-6.Im Gegensatz zur phasentransfer-Katalytischen Wittig-Reaktion wird die Ausbeute bei der Horner-Reaktion durch die Gegenwart des Kronenethers verbessert.Mechanistische Schlussfolgerungen aus diesem Befund werden diskutiert.
- Dehmlow, Eckehard V.,Barahona-Naranjo, Simon
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p. 1763 - 1771
(2007/10/02)
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