- Triphosgene and DMAP as Mild Reagents for Chemoselective Dehydration of Tertiary Alcohols
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The utility of triphosgene and DMAP as mild reagents for chemoselective dehydration of tertiary alcohols is reported. Performed in dichloromethane at room temperature, this reaction is readily tolerated by a broad scope of substrates, yielding alkenes preferentially with the (E)-geometry. While formation of the Hofmann products is generally favored, a dramatic change in alkene selectivity toward the Zaitzev products is observed when the reaction is carried out in dichloroethane at reflux.
- Ganiu, Moshood O.,Cleveland, Alexander H.,Paul, Jarrod L.,Kartika, Rendy
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p. 5611 - 5615
(2019/08/01)
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- Cobalt co-catalysis for cross-electrophile coupling: Diarylmethanes from benzyl mesylates and aryl halides
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The nickel-catalyzed cross-coupling of aryl halides with alkyl radicals derived from alkyl halides has recently been extended to couplings with carbon radicals generated by a co-catalyst. In this study, a new co-catalyst, cobalt phthalocyanine (Co(Pc)), is introduced and demonstrated to be effective for coupling substrates not prone to homolysis. This is because Co(Pc) reacts with electrophiles by an SN2 mechanism instead of by the electron-transfer or halogen abstraction mechanisms previously explored. Studies demonstrating the orthogonal reactivity of (bpy)Ni and Co(Pc), applying this selectivity to the coupling of benzyl mesylates with aryl halides, and the adaptation of these conditions to the less reactive benzyl phosphate ester and an enantioconvergent reaction are presented.
- Ackerman, Laura K. G.,Anka-Lufford, Lukiana L.,Naodovic, Marina,Weix, Daniel J.
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p. 1115 - 1119
(2015/02/05)
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- Nickel-Catalyzed Cross-Coupling of Anisoles with Alkyl Grignard Reagents via C-O Bond Cleavage
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Nickel-catalyzed cross-coupling of methoxyarenes with alkyl Grignard reagents, which involves the cleavage of the C(aryl)-OMe bond, has been developed. The use of 1,3-dicyclohexylimidazol-2-ylidene as a ligand allows the introduction of a variety of alkyl groups, including Me, Me3SiCH2, ArCH2, adamantyl, and cyclopropyl. The method can also be used for the alkylative elaboration of complex molecules bearing a C(aryl)-OMe bond.
- Tobisu, Mamoru,Takahira, Tsuyoshi,Chatani, Naoto
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supporting information
p. 4352 - 4355
(2015/09/15)
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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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- Modern Friedel-Crafts chemistry. Part-271. Alkylation of benzene with 1-benzyl- and 1-phenylcyclohexanols in the presence of H 2SO4 and AlCl3/CH3NO2 catalysts
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The alkylation of benzyene with 1-benzylcyclohexanol (3) gave a mixture of 2,3-benzobicyclo[3.3.1]nona-2-ene (8, 79%) and cyclohexyldiphenylmethane (10, 21%) with AlCl3/CH3NO2 catalyst and a mixture of 1-benzylcyclohexene 5 (47.5%), 8 (8%), 10 (21.5%), 1-cyclopentyl-1,2- diphenylethane (12, 18%) and 1-benzyl-1-phenylcyclohexene (13, 4%) with H 2SO4 catalyst. Treatment of 3 with AlCl 3/CH3NO2 in petroleum ether gave a mixture of 5 (26%) and 8 (62%). Attempted alkylation of benzene with 1-phenylcyclohexanol (4) in the presence of either AlCl3/CH3NO2 or H2SO4 catalyst gave 1-(1-phenylcyclohexyl)-2- phenylcyclohexene (17) as sole product. Mechanistic interpretation of the results in terms of carbocation behaviour is offered.
- Khalaf, Ali A.,Awad, Ibrahim M.,El-Emary, Talaat I.,Abd El-Aal, Hassan A. K.
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p. 1018 - 1022
(2007/10/03)
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- Disproportionation of diarylmethanol derivatives by using supercritical water
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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
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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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- New efficient nickel- and palladium-catalyzed cross-coupling reactions mediated by tetrabutylammonium iodide
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(formula presented) The addition of Bu4NI has been found to accelerate the palladium(0)-catalyzed cross-coupling between benzylic zinc bromides and aryl or alkenyl triflates. Remarkably, it further allows a new nickel(0)-catalyzed cross-coupling between functionalized benzylic zinc reagents and primary alkyl iodides leading to polyfunctional products in good yields under mild reaction conditions (0-20 °C, 4-16 h).
- Piber, Michael,Jensen, Anne Eeg,Rottlaender, Mario,Knochel, Paul
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p. 1323 - 1326
(2008/02/09)
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- Integrated chemical process. Construction of highly substituted allylic moieties from allylic sulfones in one-pot
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According to 'integrated chemical process', a novel one-pot process for construction of highly substituted allylic moieties has been achieved. A series of alkylation of allylic sulfones and palladium-catalyzed reductive desulfonylation by use of LiBHEt3 is integrated. The double alkylation furnishes more substituted olefins. Use of arylzinc compounds in place of the hydride enables electrophilic alkylation/nucleophilic arylation in one-pot. The integrated process provides higher overall yields than the corresponding stepwise process.
- Orita, Akihiro,Watanabe, Akihiro,Tsuchiya, Hiroshi,Otera, Junzo
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p. 2889 - 2898
(2007/10/03)
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- Free radical chemistry of β-lactones. Arrhenius parameters for the decarboxylative cleavage and ring expansion of 2-oxetanon-4-ylcarbinyl radicals. Facilitation of chain propagation by catalytic benzeneselenol
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2-Oxetanon-4-ylcarbinyl radicals undergo facile ring opening with cleavage of the C-O bond to give 3-butenoxyl radicals which in turn suffer loss of carbon dioxide to provide allyl radicals. When the initial radical is generated from a bromolactone with Bu3SnH and AIBN, chain propagation is poor owing to the relatively slow abstraction of hydrogen from the stannane by the allyl radical. The inclusion of catalytic Ph2Se2, reduced in situ to PhSeH, provides for much smoother cleaner reactions because of the better hydrogen donating capacity of the selenol. The oxetanon-4-ylcarbinyl radical derived from 6-benzyl-1-(bromomethyl)-8-oxa-7-oxobicyclo[4.2.0]octane is anomalous and undergoes a radical ring expansion in competition with the fragmentation process. Possible reasons for this anomaly are presented as are Arrhenius functions for the fragmentation and rearrangement. The Arrhenius function for the fragmentation of a simple 2-oxetanon-4-yl radical is also presented. Conditions are described under which the fragmentation of 2- oxetanon-4-yl radicals may be suppressed.
- Crich, David,Mo, Xue-Sheng
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p. 8298 - 8304
(2007/10/03)
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- Rh(I)-katalysierte Cycloaromatisierung acyclischer 3-En-1,5-diine
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Keywords: Cycloaromatisierungen; Endiine; Katalyse; Rhodiumverbindungen
- Ohe, Kouichi,Kojima, Masa-aki,Yonehara, Koji,Uemura, Sakae
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p. 1959 - 1962
(2007/10/03)
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- Ruthenium complex-catalyzed novel transformation of alkyl formates
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The following ruthenium-catalyzed novel transformations of alkyl formates have been developed: (1) selective decarbonylation of alkyl formates to the corresponding alcohols; (2) alkylation of arenes and alkenes using alkyl formates as an alkylating reagent via decarboxylation.Also the ruthenium-catalyzed addition of alcohols to alkenes has been developed as an appendant reaction, providing an effective method for the protection of alcohols.Keywords: Ruthenium; Catalysis; Alkyl; Arene; Alkene; Alcohol
- Kondo, Teruyuki,Kajiya, Satoshi,Tantayanon, Supawan,Watanabe, Yoshihisa
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- Homolytic addition of bromine-containing addends to cyclohexene
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The addition of XBr (X = CCl3, CHBr2, CH2CO2Me, or PhCH2) to cyclohexene in the presence of benzoyl peroxide (BP) or Fe(CO)5 + DMF was studied.In the presence of BP, a product of the addition of the Br and PhCO2 radicals is formed along with the expected adduct.The content of the former increases as the efficiency of XBr as the carrier of the chain reaction decreases. - Key words: radicals; addition; cyclohexene; bromotrichloromethane; bromoform; methyl bromoacetate; benzyl bromide; metallocomplex initiation.
- Vasil'eva, T. T.,Mysov, E. I.,Terent'ev, A. B.
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p. 2062 - 2064
(2007/10/02)
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- Radical ions in photochemistry. 21. The photosensitized (electron transfer) tautomerization of alkenes; the phenyl alkene system
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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.
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p. 689 - 698
(2007/10/02)
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- Palladium-Catalyzed Regio- and Stereoselective Reduction of Allylic Compounds with LiHBEt3. Application to the Synthesis of Co-enzyme Q10
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Regio- and stereoselective desulfonylation of allylic sulfones with LiHBEt3 in the presence of a catalytic amount of was succesfully applied to the synthesis of co-enzyme Q10.It was found that this reduction system was applicable to a wide variety of allylic functional groups.
- Mohri, Mitsunobu,Kinoshita, Hideki,Inomata, Katsuhiko,Kotake, Hiroshi,Takagaki, Hidetsugu,Yamazaki, Keiji
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p. 1177 - 1180
(2007/10/02)
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- Stereochemical Evidence for Aryl Participation in the Ring Opening of Oxiranes. Ring-Opening Reactions of 1-Benzyl-1,2-epoxycyclohexane under Acidic Conditions
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The reactions of 1-benzyl-1,2-epoxycyclohexane (1) have been investigated and compared with the ones of the corresponding methyl-substituted oxirane (3) in order to evaluate the possibility that an aryl group not directly linked to the oxirane ring can participate in the ring-opening processes.The acid-catalyzed ring-opening reactions of 1 are not completly anti stereoselective and give mixtures of syn and anti addition products accompanied by rearrangement compounds.The stereoselectivity and the amounts of rearrangement products vary noticeably with the reactionconditions.The results obtained and in particular the presence of substantial amounts of syn products observed in the ring-opening reactions of 1, markedly higher than those from epoxide 3, strongly suggest the incursion of aryl participation and have been rationalized through a mechanism implying the intermediacy of a phenonium-type ion.
- Costantino, Paolo,Crotti, Paolo,Ferretti, Maria,Macchia, Franco
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p. 2917 - 2923
(2007/10/02)
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- Synthesis of Olefins from α-Chlorocarbonyl Compounds
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Olefins or diolefins with the double bonds in predetermined positions are obtained in moderate to good yields by treatment of α-chlorocarbonyl compounds with Grignard reagents and lithium in a single process.
- Barluenga, Jose,Yus, Miguel,Concellon, Jose M.,Bernad, Pablo
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p. 677 - 692
(2007/10/02)
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