- Electrochemical Aziridination of Internal Alkenes with Primary Amines
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An electrochemical approach to prepare aziridines via an oxidative coupling between alkenes and primary alkyl amines was realized. The reaction is carried out in an electrochemical flow reactor, leading to short reaction/residence times (5 min), high yields, and broad scope. At the cathode, hydrogen is generated, which can be used in a second reactor to reduce the aziridine yielding the corresponding hydroaminated product.Aziridines are useful synthetic building blocks, widely employed for the preparation of various nitrogen-containing derivatives. As the current methods require the use of prefunctionalized amines, the development of a synthetic strategy toward aziridines that can establish the union of alkenes and amines would be of great synthetic value. Herein, we report an electrochemical approach, which realizes this concept via an oxidative coupling between alkenes and primary alkylamines. The reaction is carried out in an electrochemical flow reactor leading to short reaction/residence times (5 min), high yields, and broad scope. At the cathode, hydrogen is generated, which can be used in a second reactor to reduce the aziridine, yielding the corresponding hydroaminated product. Mechanistic investigations and DFT calculations revealed that the alkene is first anodically oxidized and subsequently reacted with the amine coupling partner.The central tenet in modern synthetic methodology is to develop new methods only using widely available organic building blocks. As a direct consequence, new activation strategies are required to cajole the coupling partners to react and, subsequently, forge new and useful chemical bonds. Using electrochemical activation, our methodology enables for the first time the direct coupling between olefins and amines to yield aziridines. Aziridines display interesting pharmacological activity and serve as valuable synthetic intermediates to prepare diverse nitrogen-containing derivatives. Interestingly, the sole byproduct generated in this process is hydrogen, which can be subsequently used to reduce the aziridine into the corresponding hydroaminated product. Hence, this electrochemical methodology can be regarded as green and sustainable from the vantage point of upgrading simple and widely available commodity chemicals.
- Bartolomeu, Aloisio de A.,Dyga, Marco,Goo?en, Lukas J.,Laudadio, Gabriele,No?l, Timothy,O?eka, Maksim,de Bruin, Bas,de Oliveira, Kleber T.,van Leest, Nicolaas P.
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supporting information
p. 255 - 266
(2021/01/19)
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- Catalytic Intermolecular C(sp3)-H Amination: Selective Functionalization of Tertiary C-H Bonds vs Activated Benzylic C-H Bonds
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A catalytic intermolecular amination of nonactivated tertiary C(sp3)-H bonds (BDE of 96 kcal·mol-1) is reported for substrates displaying an activated benzylic site (BDE of 85 kcal·mol-1). The tertiary C(sp3)-H bond is selectively functionalized to afford α,α,α-Trisubstituted amides in high yields. This unusual site-selectivity results from the synergistic combination of Rh2(S-Tfpttl)4, a rhodium(II) complex with a well-defined catalytic pocket, with tert-butylphenol sulfamate (TBPhsNH2), which leads to a discriminating rhodium-bound nitrene species under mild oxidative conditions. This catalytic system is very robust, and the reaction was performed on a 50 mmol scale with only 0.01 mol % of catalyst. The TBPhs group can be removed under mild conditions to afford the corresponding NH-free amines.
- Brunard, Erwan,Boquet, Vincent,Van Elslande, Elsa,Saget, Tanguy,Dauban, Philippe
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supporting information
p. 6407 - 6412
(2021/05/29)
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- METHODS OF BORYLATION AND USES THEREOF
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The present invention relates, in general terms, to methods of borylation and uses thereof. In particular, the present invention provides a method of borylating an alkene compound by contacting the compound with a boron compound, a Fe pre-catalyst and a protic additive. The borylation occurs at a vicinal (β) position to an electron donating or electron withdrawing moiety of the compound.
- -
-
Page/Page column 61-62
(2021/04/30)
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- Silver-Catalysed Hydroarylation of Highly Substituted Styrenes
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Hydroarylation is an effective strategy to rapidly increase the complexity of organic structures by transforming flat alkene moieties into three-dimensional frameworks. Many strategies have already been developed to achieve the hydroarylation of styrenes,
- Dalton, Toryn,Gre?ies, Steffen,Das, Mowpriya,Niehues, Maximilian,Schrader, Malte L.,Gutheil, Christian,Ravoo, Bart Jan,Glorius, Frank
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supporting information
p. 8537 - 8541
(2021/03/16)
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- Spiro[1,2]oxaphosphetanes of nonstabilized and semistabilized phosphorus ylide derivatives: Synthesis and kinetic and computational study of their thermolysis
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A series of tri- and tetrasubstituted spiro-oxaphosphetanes stabilized by ortho-benzamide (oBA) and N-methyl ortho-benzamide (MoBA) ligands have been synthesized by the reaction of Cα,Cortho-dilithiated phosphazenes with aldehydes and ketones. They include enantiopure products and the first example of an isolated oxaphosphetane having a phenyl substituent at C3 of the ring. Kinetic studies of their thermal decomposition showed that the process takes place irreversibly through a polar transition state (ρ = -0.22) under the influence of electronic, [1,2], [1,3] steric, and solvent effects, with C3/P-[1,2] interactions as the largest contribution to ΔG of olefination. Inversion of the phosphorus configuration through stereomutation has been observed in a number of cases. DFT calculations showed that oBA derivatives olefinated through the isolated (N, O)(Ph, C6H4, C) oxaphosphetanes (Channel A), whereas MoBA compounds decomposed faster via the isomer (C6H4, O)(C, N, Ph) formed by P-stereomutation involving a MB2 permutational mechanism (Channel B). The energy barrier of P-isomerization is lower than that of olefination. Fragmentation takes place in a concerted asynchronous reaction. The thermal stability of oxaphosphetanes is determined by strong C3/P-[1,2] interactions destabilizing the transition state of olefination. The effect of charge distribution and C3/C4-[1,2] and C4/P-[1,3] steric and solvent interactions on ΔG was also evaluated.
- López, Jesús García,Sansores Peraza, Pablo M.,Iglesias, María José,Roces, Laura,García-Granda, Santiago,Ortiz, Fernando López
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p. 14570 - 14591
(2020/11/20)
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- Iron-Catalyzed Tunable and Site-Selective Olefin Transposition
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The catalytic isomerization of C-C double bonds is an indispensable chemical transformation used to deliver higher-value analogues and has important utility in the chemical industry. Notwithstanding the advances reported in this field, there is compelling demand for a general catalytic solution that enables precise control of the C═C bond migration position, in both cyclic and acyclic systems, to furnish disubstituted and trisubstituted alkenes. Here, we show that catalytic amounts of an appropriate earth-abundant iron-based complex, a base and a boryl compound, promote efficient and controllable alkene transposition. Mechanistic investigations reveal that these processes likely involve in situ formation of an iron-hydride species which promotes olefin isomerization through sequential olefin insertion/β-hydride elimination. Through this strategy, regiodivergent access to different products from one substrate can be facilitated, isomeric olefin mixtures commonly found in petroleum-derived feedstock can be transformed to a single alkene product, and unsaturated moieties embedded within linear and heterocyclic biologically active entities can be obtained.
- Yu, Xiaolong,Zhao, Haonan,Li, Ping,Koh, Ming Joo
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supporting information
p. 18223 - 18230
(2020/12/04)
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- Bioinspired Metal-Free Formal Decarbonylation of α-Branched Aliphatic Aldehydes at Ambient Temperature
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A sequence of a Baeyer–Villiger oxidation and a Lewis acid-promoted reduction of the resulting formate with Et3SiH enabled the metal-free formal decarbonylation of tertiary and secondary aliphatic aldehydes. The new methodology mimics the biosynthetic decarbonylation pathway through oxidative C?C bond cleavage rather than the C(O)?H bond activation known from conventional Tsuji–Wilkinson-type reactions. The substrate scope is complementary to existing transition-metal-catalyzed protocols.
- Richter, Sven C.,Oestreich, Martin
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p. 8508 - 8512
(2019/06/04)
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- Electrochemical Aziridination by Alkene Activation Using a Sulfamate as the Nitrogen Source
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The first direct aziridination of triaryl-substituted alkenes was achieved by means of an electrochemical process that could extend to multisubstituted styrenes. Specifically, hexafluoroisopropanol sulfamate was used as a nucleophilic nitrogen source. Mechanistic experiments suggest that this electrochemical process proceeds by stepwise formation of two C?N bonds through reactions between cationic carbon species and the sulfamate.
- Li, Jin,Huang, Wenhao,Chen, Jingzhi,He, Lingfeng,Cheng, Xu,Li, Guigen
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supporting information
p. 5695 - 5698
(2018/04/30)
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- Enantioselective Oxy-Heck–Matsuda Arylations: Expeditious Synthesis of Dihydrobenzofuran Systems and Total Synthesis of the Neolignan (?)-Conocarpan
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This work discloses the first examples of an effective enantioselective oxy-Heck–Matsuda reaction using a variety of styrenic olefins to generate chiral dihydrobenzofurans. The reaction proceeds in moderate to good yields, with high trans diastereoselectivity (up to 20:1) in enantioselectivities up to 90:10 using the N,N-ligand pyrimidine-bisoxazoline (PyriBox). The oxy-Heck–Matsuda reactions were carried out under mild conditions and rather low catalyst loadings. The feasibility and practicality of the process is demonstrated by a concise total synthesis of the neolignan (?)-conocarpan. X-ray diffraction of an advanced brominated intermediate in the route to (?)-conocarpan has allowed the unequivocal assignment of the absolute stereochemistry of the oxy-Heck–Matsuda aryldihydrobenzofuran products. A rationale for the mechanism operating in these enantioselective oxy-Heck–Matsuda reactions is also presented. (Figure presented.).
- Silva, Allan R.,Polo, Ellen C.,Martins, Nelson C.,Correia, Carlos Roque D.
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p. 346 - 365
(2018/01/26)
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- Cross-coupling synthesis of methylallyl alkenes: Scope extension and mechanistic study
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Cross-coupling reactions between 2-methyl-2-propen-1-ol and various boronic acids are used to obtain aromatic-(2-methylallyl) derivatives. However, deboronation or isomerization side reactions may occur for several boronic acids. We describe herein the synthesis of original alkenes with good yields under mild reaction conditions that decrease these side reactions. The scope of this environmentally benign reaction is thereby extended to a wide variety of boronic acids. A mechanistic study was conducted and suggested a plausible catalytic cycle mechanism, pointing to the importance of the Lewis acidity of the boronic acid used.
- Tabélé, Clémence,Curti, Christophe,Kabri, Youssef,Primas, Nicolas,Vanelle, Patrice
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p. 22890 - 22899
(2016/01/25)
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- Palladium- and nickel-catalyzed kumada cross-coupling reactions of gem -difluoroalkenes and monofluoroalkenes with Grignard reagents
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A novel Kumada-Tamao-Corriu cross-coupling reaction of gem-di- or monofluoroalkenes with Grignard reagents, with or without β-hydrogen atoms, in the presence of a catalytic amount of palladium- or nickel-based catalysts has been developed. The reaction is performed under mild conditions (room temperature or reflux in diethyl ether for 1-2 h) and leads to di-cross- or mono-cross-coupled products in good to high yields.
- Dai, Wenpeng,Xiao, Juan,Jin, Guanyi,Wu, Jingjing,Cao, Song
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p. 10537 - 10546
(2015/02/19)
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- Photochromic performance of 1-thiazolyl-2-vinylcyclopentene derivatives having a phenyl-or 4-methoxyphenyl-substituted olefin
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1-Thiazolyl-2-vinylcyclopentene derivatives, 1-(5-methoxy-2-phenyl-4- thiazolyl)-2-(2-methyl-1-phenyl-1-propenyl) perfluorocyclopentene (1a), 1-[5-methoxy-2-(4-methoxyphenyl)-4-thiazolyl]-2-(2-methyl-1-phenyl-1-propenyl) perfluorocyclopentene (2a), and 1-[5-methoxy-2-(4-methoxyphenyl)-4-thiazolyl]-2- [1-(4-methoxyphenyl)-2-methyl-1-propenyl] perfluorocyclopentene (3a) were synthesized in an attempt to obtain yellow photochromic compounds having low photocycloreversion quantum yields and large absorption coefficients of the closed-ring isomers. Their photochromic performance, thermal stability, and fatigue resistance were compared with 1-[5-methoxy-2-(4-methoxyphenyl)-4- thiazolyl]-2-(1,2-dimethyl-1-propenyl)perfluorocyclopentene (4a) having a methyl-substituted olefin. Upon irradiation with 313 nm light, compounds 1a, 2a, and 3a changed from colorless to various shades of yellow in toluene. The conversions from the open-ring (1a, 2a, and 3a) to the closed-ring (1b, 2b, and 3b) isomers in the photostationary state under irradiation with 313nm light were 93, 95, and 98%, respectively. Among the three derivatives 3b has the largest absorption coefficient (= 18900M-1cm-1) at 428nm and the lowest cycloreversion quantum yield of 1.8 10-3.
- Takami, Shizuka,Shimizu, Ayano,Shimizu, Kazuyuki,Miyoshi, Ryota,Yamaguchi, Tadatsugu,Irie, Masahiro
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p. 1059 - 1064
(2013/10/08)
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- Amido pincer nickel catalyzed kumada cross-coupling of aryl, heteroaryl, and vinyl chlorides
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Amido pincer nickel complexes {Ni(Cl)[2-P(Ph2)C 6H4NC(Ph)=NAr]} (Ar = 4-MeC6H4, 1; Ar = 4-ClC6H4, 2; Ar = 4-MeOC6H4, 3) were shown to efficiently catalyze the cross-coupling of activated, unactivated, and deactivated aryl chlorides, N-heteroaryl chlorides, 1,4-dichlorobenzene, and vinyl chlorides with aryl Grignard reagents. Georg Thieme Verlag Stuttgart, New York.
- Zhang, Xue-Qi,Wang, Zhong-Xia
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supporting information
p. 2081 - 2084
(2013/10/21)
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- Kumada coupling of aryl, heteroaryl, and vinyl chlorides catalyzed by amido pincer nickel complexes
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A series of amido pincer complexes of nickel were examined for their catalysis in the Kumada cross-coupling reaction. The P,N,O-pincer nickel complexes tested are active catalysts for the cross-coupling of aryl, heteroaryl, and vinyl chlorides with aryl Grignard reagents. The reactions can proceed at room temperature and tolerate functional groups in aryl chlorides with the aid of LiCl and ZnCl2 additives (Figure presented).
- Liu, Ning,Wang, Zhong-Xia
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experimental part
p. 10031 - 10038
(2012/02/05)
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- Reaction of secondary and tertiary aliphatic halides with aromatic aldehydes mediated by chromium(II): a selective cross-coupling of alkyl and ketyl radicals
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Takai-Utimoto reactions with secondary and tertiary aliphatic halides usually failed according to previous reports. Now, significant improvements could be achieved, and especially secondary aliphatic halides can be coupled to aromatic aldehydes in yields of up to >95%. A variety of processes are competing with the desired one, and thus conditions must be adapted to the nature of the aldehyde as well as the aliphatic halide used, as the outcome of these reactions is strongly affected by the putative radical intermediates.
- Wessjohann, Ludger A.,Schmidt, Gisela,Schrekker, Henri S.
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p. 2134 - 2142
(2008/09/18)
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- Magnesiation of electron-rich aryl bromides and their use in nickel-catalyzed cross-coupling reactions
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Electron-rich aryl bromides are rapidly converted to the corresponding lithium triarylmagnesiates with (n-Bu)3MgLi, which undergo efficient nickel-catalyzed Kumada-Corriu cross-coupling reactions with a variety of aryl and alkenyl bromides, chlorides, tosylates, and triflates.
- Lau, Stephen Y. W.,Hughes, Greg,O'Shea, Paul D.,Davies, Ian W.
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p. 2239 - 2242
(2008/02/03)
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- A novel redox-sensitive protecting group for boronic acids, MPMP-diol
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A new boronic acid protecting group, 1-(4-methoxyphenyl)-2-methylpropane-1, 2-diol (MPMP-diol), has been developed. Both protection and deprotection can be accomplished under mild conditions with quantitative conversions. The deprotection can be carried out using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ).
- Yan, Jun,Jin, Shan,Wang, Binghe
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p. 8503 - 8505
(2007/10/03)
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- Kumada coupling of aryl and vinyl tosylates under mild conditions
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Aryl and alkenyl tosylates are easily prepared, inexpensive and, thus, attractive for transition-metal-catalyzed couplings, but their reactivity is low. We report examples of mild, palladium-catalyzed coupling of aryl, alkenyl, and alkyl Grignard reagents with aryl and alkenyl tosylates. The resulting biaryls, vinylarenes, and alkylarenes were isolated in good to excellent yield. These couplings were conducted with a nearly equimolar ratio of the two reactants, and many examples were conducted at room temperature.
- Limmert, Michael E.,Roy, Amy H.,Hartwig, John F.
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p. 9364 - 9370
(2007/10/03)
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- Dilithiated phosphazenes: Scaffolds for the synthesis of olefins through a new class of bicyclic 1,2-oxaphosphetanes
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The first examples of the PN-directed dilithiation of (N-methoxycarbonyl)phosphazenes in the Cα and Cortho to the phosphorus, and the use of these dianions in the formation of tri- and tetra-substituted olefins through stereospecific thermolysis of a new type of isolable bicyclic 1,2-oxaphosphetanes are described.
- Garcia-Lopez, Jesus,Peralta-Perez, Emma,Forcen-Acebal, Angela,Garcia-Granda, Santiago,Lopez-Ortiz, Fernando
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p. 856 - 857
(2007/10/03)
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- Synthesis of polysubstituted alkenes by Heck vinylation or Suzuki cross-coupling reactions in the presence of a tetraphosphane-palladium catalyst
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Through the use of [PdCl(C3H5)]2/cis,cis,cis-1,2,3, 4-tetrakis[(diphenylphosphanyl)methyl]cyclopentane as a catalyst, a range of vinyl bromides undergo Suzuki cross-couplings with arylboronic acids in good yields. Furthermore, the catalyst can be used at low loadings, even for reactions of sterically hindered substrates. Mediated by this catalyst, stilbene and 1,1-diphenylethylene undergo Heck reactions with aryl halides to give triarylethylene derivatives. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.
- Berthiol, Florian,Doucet, Henri,Santelli, Maurice
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p. 1091 - 1096
(2007/10/03)
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- Control of regioselectivity by the lone substituent through steric and electronic effects in the nitrosoarene ene reaction of deuterium-labeled trisubstituted alkenes
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For the ene reaction of 4-nitronitrosobenzene (ARNO) with a variety of primary and secondary lone alkyl-substituted substrates, the twix/twin regioselectivity is constant at about 85:15. In contrast, for the lone tert-butyl group and for lone aryl substituents, the twix regioisomer is obtained exclusively. These regioselectivities have been rationalized in terms of steric interactions and coordination between the enophile and the substrates in the transition states of the first reaction step.
- Adam, Waldemar,Krebs, Oliver,Orfanopoulos, Michael,Stratakis, Manolis
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p. 8395 - 8399
(2007/10/03)
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- The first general method for palladium-catalyzed Negishi cross-coupling of aryl and vinyl chlorides: Use of commercially available Pd(P(t-Bu)3)2 as a catalyst
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With a single protocol, commercially available Pd(P(t-Bu)3)2 can effect the Negishi cross-coupling of a wide range of aryl and vinyl chlorides with aryl- and alkylzinc reagents. The process tolerates nitro groups, and it efficiently generates sterically hindered biaryls. In addition, a high turnover number (>3000) can be achieved.
- Dai,Fu
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p. 2719 - 2724
(2007/10/03)
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- Inter- and intramolecular pathways for the formation of tetrahydrofurans from β-(phosphatoxy)alkyl radicals. Evidence for a dissociative mechanism
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β-(Phosphatoxy)alkyl radicals generated by photolysis of Barton PTOC esters in the presence of allyl alcohol and tert-butyl mercaptan undergo nucleophilic substitution followed by 5-exo-trig radical ring closure leading to tetrahydrofurans in good yield and with high trans selectivity. β- (Phosphatoxy)alkyl radicals obtained by intramolecular hydrogen 1,5- abstraction with an alkoxyl radical undergo nucleophilic displacement providing tetrahydrofurans. The ensemble of results, including the effects of leaving groups and substituents, strongly support a dissociative mechanism for these radical nucleophilic displacement reactions.
- Crich, David,Huang, Xianhai,Newcomb, Martin
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p. 523 - 529
(2007/10/03)
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- Spontaneous Hydrolysis Reactions of cis- and trans-β-Methyl-4-methoxystyrene Oxides (Anethole Oxides): Buildup of frans-Anethole Oxide as an Intermediate in the Spontaneous Reaction of cis-Anethole Oxide
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Rates and products of the reactions of trans- and cis-β-methyl-4-methoxystyrene oxides (1 and 2) (anethole oxides) and β,β-dimethyl-4-methoxystyrene oxide (3) in water solutions in the pH range 4-12 have been determined. In the pH range ca. 8-12, each of these epoxides reacts by a spontaneous reaction. The spontaneous reaction of trans-anethole oxide (1) yields ca. 40% of (4-methoxyphenyl)acetone and 60% of 1-(4-methoxyphenyl)-1,2-propanediols (erythro:threo ratio ca. 3:1). The spontaneous reaction of cis-anethole oxide is more complicated. The yields of diol and ketone products vary with pH in the pH range 8-11, even though there is not a corresponding change in rate. These results are interpreted by a mechanism in which 2 undergoes isomerization in part to the more reactive trans-anethole oxide (1), which subsequently reacts by acid-catalyzed and/or spontaneous reactions, depending on the pH, to yield diol and ketone products. The buildup of the intermediate trans-anethole oxide in the spontaneous reaction of cis-anethole oxide was detected by 1H NMR analysis of the reaction mixture. Other primary products of the spontaneous reaction of 2 are (4-methoxyphenyl)acetone (73%) and theo-1-(4-methoxyphenyl)-1,2-propanediol (ca. 3%). The rates and products of the spontaneous reaction of 2 and its β-deuterium-labeled derivative were determined, and the lack of significant kinetic and partitioning deuterium isotope effects indicates that the isomerization of 2 to ketone and to trans-anethole oxide must occur primarily by nonintersecting reaction pathways.
- Mohan, Ram S.,Gavardinas, Kostas,Kyere, Sampson,Whalen, Dale L.
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p. 1407 - 1413
(2007/10/03)
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- Cobalt-catalyzed alkenylation of organomagnesium reagents
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Alkenyl iodides, bromides and chlorides react with organomagnesium reagents in THF, in the presence of Co(acac)2 and NMP (9 to 4 equiv.), to give the cross-coupling products in good yields. The reaction is chemoselective (aryl or alkyl bromides, esters and ketones) and stereoselective (≤ 99.5%).
- Cahiez, Gerard,Avedissian, Hovsep
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p. 6159 - 6162
(2007/10/03)
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- Tandem [2 + 2] cycloaddition-cycloreversion reactions in highly polar media: A convergent one-pot entry to substituted alkenes and dienes
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Reaction at room temperature between acyl chlorides and aromatic or α,β-unsaturated aldehydes in the presence of a tertiary base and in 5M lithium perchlorate-diethyl ether (5M LPDE) as solvent yields substituted alkenes in satisfactory yields. The reaction is formally conceived as a [2 + 2] cycloaddition between the aldehyde and the in situ formed ketene, followed by thermal decarboxylation of the intermediate 2 oxetanone. Ketene itself yields α,β-unsaturated acids under these reaction conditions.
- Arrastia, Iosune,Cossio, Fernando P.
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p. 7143 - 7146
(2007/10/03)
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- Neighbouring group participation in the solvolysis of a class of heterocyclic and acyclic trans-dibromides and bromohydrins
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Solvolysis of heterocyclic trans-dibromides and bromohydrins 1a-e affords the ring contracted aldehydes 10a-c and the benzthiophen derivative 11.The acyclic dibromide 2a similarly provides the expected aldehyde 13.Probable pathways for the formation of the products have been presented.
- Mandal, Asok N,Chatterjee, Amareshwar
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p. 156 - 162
(2007/10/02)
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- Methylation via the Suzuki reaction
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The clean, efficient Pd-catalyzed cross-coupling of vinyl, alkynyl and aryl bromides with the air-stable organoborane, 10-methyl-9-oxa-10-borabicyclo[3.3.2]decane gives excellent yields of the corresponding methylated products.
- Soderquist,Santiago
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p. 5541 - 5542
(2007/10/02)
-
- REACTION OF ORGANIC AZIDES WITH UNSATURATED COMPOUNDS. VIII. REARRANGEMENT OF Δ2-1,2,3-TRIAZOLINES, OBTAINED FROM ARENESULFONYL AZIDES AND β,β-DIMETHYL-4-METHOXYSTYRENE BY AN ARYL SHIFT
-
2-Methyl-2-propanal was found in the products from the reaction of arenesulfonyl azides with β,β-dimethyl-4-methoxystyrene after hydrolysis.This indicates that 1-arylsulfonyl-4,4-dimethyl-5--Δ2-1,2,3-triazolenes rearrange by an aryl and not a hydride shift.
- Semenov, V. P.,Andreeva, T. D.,Ogloblin, K. A.
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p. 195 - 198
(2007/10/02)
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- Cycloadditions of 1-(4-Methoxyphenyl)-2,2-dimethylvinyl Cation to Olefins
-
1-Bromo-1-(4-methoxyphenyl)-2-methyl-1-propene (1) reacts with cyclohexene, cycloheptene, (Z)-cyclooctene and the silver salts AgBF4, AgSbF6 via the vinyl cation 2 by cycloaddition to form the cyclobutenes 7b - d.Cyclobutene 8 is obtained from (Z)- and (E
- Harder, Ingo,Hanack, Michael
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p. 2974 - 2992
(2007/10/02)
-
- Photochemistry of Vinyl Halides. Heterocycles from Reaction of Photogenerated Vinyl Cations with Azide Anion
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Irradiation of 1,2,2-tris(p-methoxyphenyl)vinyl bromide (1a-Br) and tetrabutylammonium azide in acetonitrile afforded 1,1,3,4,6,6-hexakis(p-methoxyphenyl)-2,5-diaza-1,3,5-hexatriene (2a).Formation of 2a suggests the presence of azirine 3a as a reactive intermediate and a route to synthesis of heterocycles in combination with azirine photochemistry.Irradiation of α-arylvinyl halides 1 and tetrabutylammonium azide in acetonitrile in the presence of dimethyl fumarate gave 1-pyrrolidine derivatives 5.When the irradiation was performed in acetone, oxazoline derivatives 6 were obtained.The reaction of vinyl halides 1 with azide anion took place succesfully even in a two phase system, i.e., water-methylene chloride-tetrabutylammonium halide as a phase-transfer catalyst.In addition, photolysis of 2,2-bis(p-methoxyphenyl)-1-phenylvinyl bromide (1f-Br) in a two-phase system led to the formation of the β-aryl rearranged pyrrolines 5f.This results indicates strong evidence for the intervention of vinyl cations in the photochemical reaction of the vinyl halide 1 and azide anion.The mechanistic points on the photochemical substitution and the scope and limitation of the reaction are discussed.
- Kitamura, Tsugio,Kobayashi, Shinjiro,Taniguchi, Hiroshi
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p. 4755 - 4760
(2007/10/02)
-
- Thermolabile Hydrocarbons, XVIII. 1-Substituted Neopentyl radicals and their Dimers
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Five 3,4-diaryl-2,2,5,5-tetramethylhexanes 1a - e were prepared as pure meso- and DL-isomers.According to the NMR spectra, x-ray analyses for meso- and DL-1e (with an (FB)2E conformation as energy minimum for DL-1e), and force field calculations the diastereomers have distinctly different minimum energy conformations, rotational potentials, and strain enthalpies.Also the activation parameters for the thermal dissociation into 1-arylneopentyl radicals 2 are typically differing.From an entropy discussion it is concluded that sandwich-like diastereomeric radical complexes are formed in these reactions as first intermediates.Their tightness influences ΔS%.The recombinations of the radicals 2 likewise take place stereoselectively.Their substituent effects on the selectivity can also be understood by primary formation of diastereomeric complexes of radical pairs.
- Eichin, Karl-Heinz,Beckhaus, Hans-Dieter,Hellmann, Siegried,Fritz, Hans,Peters, Eva-Maria,et al.
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p. 1787 - 1821
(2007/10/02)
-
- Structural Effects on Twisted Olefin Triplet Lifetimes. Styrene Derivatives
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The triplet lifetimes in methanol of a series of anisylalkenes and anisylcycloalkenes, including several phenyl analogues, have been determined by nanosecond flash kinetic absorption spectrophotometry with nitrogen laser excitation.Electron-transfer scavenging by paraquat dication, PQ2+, (methyl viologen) afforded the readily detectable reduced species PQ+*.Both triplet lifetimes and rate constants for electron transfer from triplet to PQ2+ were determined.The results indicate that acyclic styrene triplets prefer the twisted, "1,2-biradical" structure.Lifetimes are increased by vinyl deuteration, by increasing alkylation, and by constraint within a small ring; in the absence of geometric constraints, the dominant influence on the triplet lifetimes is the extent of substitution at the double bond.Mechanisms for intersystem crossing are discussed, and the tentative conclusion is reached that nuclear motions are important.
- Caldwell, R. A.,Cao, C. V.
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p. 6174 - 6180
(2007/10/02)
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- The Anomalous Reaction of p-Methoxy-β,β-dimethylstyrene with Mercury(II) Acetate in Methanol
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The methoxymercurations of β,β-dimethylstyrene (7) and its p-nitro (12) and p-methoxy (13) derivatives with mercury(II) acetate in methanol are regiospecific and give methoxymercuration products in which the methoxy group is on the β-carbon.Demercuration of the adducts from (12) and (13) with alkaline borohydride proceeds normally, but the demercuration of the adduct from (7) gives considerable formation of the diastereoisomeric dimeric products (9a,b).The methoxymercuration product from (13) is surprisingly reactive and gives mercury(I) acetate and the vicinal diether 1,2-dimethoxy-1-(p-methoxyphenyl)-2-methylpropane (17)
- Norris, Robert K.,Wright, Timothy A.
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p. 2161 - 2167
(2007/10/02)
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- Thermal fragmentation of 3-alkyl-2-phenyloxetanes, 3,3-dimethyl-2-aryloxetanes, and related compounds. A case study of 2-aryl-substituted oxetanes
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Thermolyses of epimeric 3-alkyl-2-phenyloxetanes (1c, 1t, 2c, 2t, 3c, and 3t), 3,3-dimethyl-2-aryloxetanes (4, 5, 6, 7, and 8), 3,3,4,4-tetramethyl-2,2-diphenyloxetane (9), and 3,3-dimethyl-2,2-diphenyloxetane (10) were studied in degassed N,N,N',N'-tetramethylethylenediamine at 270-350 deg C.Although the fragmentation of 9 and 10 can be understandable on the basis of a diradical mechanism, there were several observations, in the reaction of certain other oxetanes, which could hardly be explained simply in terms of such a mechanism.Namely, (1) less strained 1t reacted faster than more strained 1c; (2) a major mode of the fragmentation for 1c, 2c, and 3c was "B" (forming an alkene and benzaldehyde), whereas that for 1t, 2t, and 3t was "A" (forming an alkenylbenzene and formaldehyde); (3) the apparent energy of activation for the "B" process seemed to be larger than that for the "A"; (4) a dramatic change of the major fragmentation mode from "B" to "A" was brought about by a substituent on the phenyl group, as was observed in 4-8.These results may be explained reasonably by assuming that the fragmentation proceeds, at least, in dual reaction courses.In competition with an anticipated diradical pathway, there will be another process, which is energetically little more favorable than the diradical fragmentation, rather specific to the "A" mode fragmentation, and important particularly in the reaction of the trans isomers.Probable candidates for the second process are discussed.
- Imai, Toshiro,Nishida, Shinya
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p. 2503 - 2509
(2007/10/02)
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- CONCERTED FRAGMENTATION CONCURRENT WITH A STEPWISE-DIRADICAL FISSION IN THE OXETANE THERMOANALYSIS; IMPORTANCE OF STERIC STRAIN
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Thermolytic behavior of 3-alkyl-2-phenyloxetanes, in particular that of trans isomers, is best explained by concurrent concerted fragmentation and stepwise diradical fission.Proportion of the concerted process should be small in the cis isomers because of destabilization of the transition state by steric strain.The argument is supported by the thermal behavior of 3-alkyl-4-phenyl-oxetanones.
- Imai, Toshiro,Nishida, Shinya
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