- Absence of Intermediates in the BINOL-Derived Mg(II)/Phosphate-Catalyzed Desymmetrizative Ring Expansion of 1-Vinylcyclobutanols
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The catalyzed desymmetrizative ring expansion of alkenylcyclobutanols promoted by halofunctionalization of the alkene moiety with N-bromosuccinimide has been experimentally and computationally studied. The reaction yields highly enantioenriched cyclopenta
- Capel, Estefania,Rodríguez-Rodríguez, Marta,Uria, Uxue,Pedron, Manuel,Tejero, Tomas,Vicario, Jose L.,Merino, Pedro
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supporting information
p. 693 - 707
(2022/01/04)
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- Synthesis of Unsymmetrical 1,4-Dicarbonyl Compounds by Photocatalytic Oxidative Radical Additions
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Herein we report a photocatalytic oxidative radical addition reaction for the synthesis of unsymmetrical 1,4-dicarbonyl compounds. This reaction utilizes a desulfurization process to generate electrophilic radicals, which add to α-halogenated alkenes and undergo further oxidation to deliver 1,4-dicarbonyl compounds. This mild and highly efficient method provides a valuable alternative to known strategies.
- Dong, Ya,Li, Ruining,Zhou, Junliang,Sun, Zhankui
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supporting information
p. 6387 - 6390
(2021/08/23)
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- Catalytic Asymmetric Halogenation/Semipinacol Rearrangement of 3-Hydroxyl-3-vinyl Oxindoles: A Stereodivergent Kinetic Resolution Process
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A highly enantioselective halogenation/semipinacol rearrangement of isatin-derived allylic alcohols has been developed with a chiral N,N′-dioxide/ScIII complex as catalyst. This strategy involved a pivotal stereodivergent kinetic resolution process and provided a facile and efficient entry to optically active halo-substituted quinolone derivatives and quinoline alkaloids with a quaternary stereocenter simultaneously under mild reaction conditions. Based on the control experiments together with kinetic studies and DFT calculations, a possible catalytic cycle was proposed to illustrate the reaction process and enantiocontrol.
- Cao, Weidi,Dai, Li,Feng, Xiaoming,Hu, Xinyue,Liu, Wen,Zeng, Zi,Zhou, Yuqiao
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supporting information
p. 26599 - 26603
(2021/11/16)
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- The intramolecular reaction of acetophenoneN-tosylhydrazone and vinyl: Br?nsted acid-promoted cationic cyclization toward polysubstituted indenes
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In the presence of TsNHNH2, a Br?nsted acid-promoted intramolecular cyclization ofo-(1-arylvinyl) acetophenone derivatives was developed, leading to polysubstituted indenes with complexity and diversity in moderate to excellent yields. In sharp contrast with either the radical or carbene involved cyclization of aldehydicN-tosylhydrazone with vinyl, a cationic cyclization pathway was involved, whereN-tosylhydrazone served as an electrophile and alkylation reagent during this transformation.
- Wang, Zhixin,Li, Yang,Chen, Fan,Qian, Peng-Cheng,Cheng, Jiang
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supporting information
p. 1810 - 1813
(2021/02/27)
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- Electrochemical Semipinacol Rearrangements of Allylic Alcohols: Construction of All-Carbon Quaternary Stereocenters
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The first examples of electrochemical trifluoromethylation and sulfonylation/semipinacol rearrangements of allylic alcohols were developed using cheap and stable RSO2Na (R = CF3, Ph) as reagents. Various β-trifluoromethyl and sulfonated ketones were obtained in moderate to excellent yields. This strategy provides a facile, direct, and complementary approach to construct all-carbon quaternary stereocenters. In addition, the reaction has the advantages of being chemical oxidant-free and metal-free and has safe and mild reaction conditions.
- Kang, Jun-Chen,Tu, Yong-Qiang,Dong, Jia-Wei,Chen, Chao,Zhou, Jia,Ding, Tong-Mei,Zai, Jian-Tao,Chen, Zhi-Min,Zhang, Shu-Yu
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supporting information
p. 2536 - 2540
(2019/04/30)
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- Selective Aerobic Oxygenation of Tertiary Allylic Alcohols with Molecular Oxygen
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Aerobic epoxidation of tertiary allylic alcohols remains a significant challenge. Reported here is an efficient and highly chemoselective copper-catalyzed epoxidation and semipinacol rearrangement reaction of tertiary allylic alcohols with molecular oxygen. The solvent 1,4-dioxane activates dioxygen, thereby precluding the addition of a sacrificial reductant.
- Zhu, Bencong,Shen, Tao,Huang, Xiaoqiang,Zhu, Yuchao,Song, Song,Jiao, Ning
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supporting information
p. 11028 - 11032
(2019/07/08)
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- Why is cis/trans stereoinversion with Li+(THF)4 migration across the phenyl ring of α-lithiostyrene accelerated by two ortho-methyl groups?
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Common wisdom might anticipate that two methyl groups placed on a molecular migration route should act as an impediment. However, the “conducted tour” migration of Li+(THF)4 across the aryl ring (“π-route”) during the cis/trans stereoinversion of α-arylvinyllithiums had been found to occur with practically equal velocities in the presence of either one or two ortho-alkyl substituents. We now report that the omission of both ortho-methyl groups retards the stereoinversion process. In order to arrive at an answer to the title question, we investigate the aggregation equilibria and microsolvation states of ortho, ortho′-unsubstituted α-lithiostyrenes by means of approved secondary NMR criteria. Beyond such necessary knowledge about the ground-state properties, we provide kinetic evidence showing that the retarded cis/trans stereoinversion of α-lithiostyrene proceeds by the pseudomonomolecular, ionic mechanism with Li+(THF)4 migration.
- Knorr, Rudolf,Lattke, Ernst,Ruhdorfer, Jakob,Ferchland, Kathrin,von Roman, Ulrich
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p. 1621 - 1631
(2018/02/28)
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- Electrophilic Trifluoromethylthiolation/Semipinacol Rearrangement: Preparation of β-SCF3 Carbonyl Compounds with α-Quaternary Carbon Center
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A new and modular electrophilic trifluoromethylthiolation/semipinacol rearrangement of allylic silyl ethers has been developed under mild conditions. This approach allows the formation of a number of β-SCF3 carbonyl compounds with a cyclic and all-carbon quaternary center framework in moderate to good yields. It should be noted that this achievement is a metal-free process and just requires the use of simple acetyl chloride as an acidic promoter. Additionally, an interesting H-migration in competition with aryl-migration process was revealed.
- Xi, Chao-Chao,Chen, Zhi-Min,Zhang, Shu-Yu,Tu, Yong-Qiang
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supporting information
p. 4227 - 4230
(2018/07/29)
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- Cyclic Hypervalent Iodine Reagents for Azidation: Safer Reagents and Photoredox-Catalyzed Ring Expansion
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Azides are building blocks of increasing importance in synthetic chemistry, chemical biology, and materials science. Azidobenziodoxolone (ABX, Zhdankin reagent) is a valuable azide source, but its safety profile has not been thoroughly established. Herein, we report a safety study of ABX, which shows its hazardous nature. We introduce two derivatives, tBu-ABX and ABZ (azidobenziodazolone), with a better safety profile, and use them in established photoredox- and metal-mediated azidations, and in a new ring-expansion of silylated cyclobutanols to give azidated cyclopentanones.
- Alazet, Sebastien,Preindl, Johannes,Simonet-Davin, Raphael,Nicolai, Stefano,Nanchen, Annik,Meyer, Thierry,Waser, Jerome
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supporting information
p. 12334 - 12356
(2018/09/27)
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- Intermolecular Carboamination of Unactivated Alkenes
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Herein, we report the first example of group transfer radical addition of O-vinylhydroxylamine derivatives onto unactivated alkenes. By utilizing O-vinylhydroxylamine derivatives as both the N- and C-donors, this reaction enables intermolecular carboamination of unactivated alkenes in an atom economical fashion. As the process is initiated through N-radical addition followed by C-transfer, linear carboamination products are afforded. This differs from canonical radical carbofunctionalization of olefins, which typically favors branched product owing to initiation by C-radical addition.
- Zhang, Yu,Liu, Haidong,Tang, Luning,Tang, Hai-Jun,Wang, Lu,Zhu, Chuan,Feng, Chao
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p. 10695 - 10699
(2018/09/06)
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- Cyrene as a Bio-Based Solvent for the Suzuki-Miyaura Cross-Coupling
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The Suzuki-Miyaura (SM) cross-coupling is the most broadly utilized Pd-catalyzed C-C bond-forming reaction in the chemical industry. A large proportion of SM couplings employ dipolar aprotic solvents; however, current sustainability initiatives and increasingly stringent regulations advocate the use of alternatives that exhibit more desirable properties. Here we describe the scope and utility of the bio-derived solvent Cyrene in SM cross-couplings and evaluate its suitability as a reaction medium for this benchmark transformation from discovery to gram scale.
- Wilson, Kirsty L.,Murray, Jane,Jamieson, Craig,Watson, Allan J. B.
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p. 650 - 654
(2017/12/26)
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- Regioselective Synthesis of Vinyl Halides, Vinyl Sulfones, and Alkynes: A Tandem Intermolecular Nucleophilic and Electrophilic Vinylation of Tosylhydrazones
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A diazo species is trapped in an intermolecular fashion by two independent ion species in tandem at the carbene center to install an electrophile and a nucleophile on the same carbon. This metal-free concept, which is unprecedented, has been illustrated by regioselective synthesis of a variety of vinyl halides, vinyl sulfones, and alkyne derivatives. (Chemical Equation Presented).
- Ojha, Devi Prasan,Prabhu, Kandikere Ramaiah
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- Green and Efficient: Iron-Catalyzed Selective Oxidation of Olefins to Carbonyls with O2
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A mild and operationally simple iron-catalyzed protocol for the selective aerobic oxidation of aromatic olefins to carbonyl compounds is described. Catalyzed by a Fe(III) species bearing a pyridine bisimidazoline ligand at 1 atm of O2, α- and β-substituted styrenes were cleaved to afford benzaldehydes and aromatic ketones generally in high yields with excellent chemoselectivity and very good functional group tolerance, including those containing radical-sensitive groups. With α-halo-substituted styrenes, the oxidation took place with concomitant halide migration to afford α-halo acetophenones. Various observations have been made, pointing to a mechanism in which both molecular oxygen and the olefinic substrate coordinate to the iron center, leading to the formation of a dioxetane intermediate, which collapses to give the carbonyl product. (Chemical Equation).
- Gonzalez-De-Castro, Angela,Xiao, Jianliang
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p. 8206 - 8218
(2015/07/15)
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- Metal-free regioselective hydrobromination of alkynes through CH/CBr activation
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A metal-free regioselective hydrobromination of alkynes has been developed to provide the Markovnikov-type vinyl bromides in good yields using dibromomethane/N,N-dimethylaniline as in-situ 'HBr' source. This protocol also represents an elegant example of the activation of sp2 CH and CBr bonds in one pot, in which 'HBr' is generated and transferred under mild metal-free conditions. D-incorporated experiments were employed to investigate the reaction mechanism and a plausible reaction path was proposed.
- Chen, Xiuling,Chen, Tieqiao,Xiang, Yuqiang,Zhou, Yongbo,Han, Daoqing,Han, Li-Biao,Yin, Shuang-Feng
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supporting information
p. 4572 - 4575
(2014/12/10)
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- The concerted addition of HBr to aryl alkynes; orthogonal pi bond selectivity
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In a weakly acidic solution, the addition of HBr to 1-phenylprop-1-yne produces predominantly the anti-Markovnikov product. In this paper, we consider five possible explanations for this behavior and conclude that the concerted addition is occurring on the acetylenic π bond orthogonal to the extended aromatic π system. The electronic effect of the distal methyl group and the steric hindrance of the coplanar phenyl ring combine to promote bromide attack at the β carbon. Attack on this π bond is insensitive to the electronic effect of meta and para substituents on the ring but is very (sterically) sensitive toward all ortho substituents.
- Weiss, Hilton M.,Touchette, Kim M.,Angell, Sarah,Khan, Jihan
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p. 2152 - 2156
(2007/10/03)
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- Use of kinetic isotope effects in mechanism studies. Isotope effects and element effects associated with Hydron-Transfer steps during alkoxide-promoted dehydrohalogenations
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The Arrhenius behavior of the primary kinetic isotope effect, (k(H)/k(D))(Obs) and (k(H)/k(T))(Obs), associated with the methanolic sodium methoxide-promoted dehydrohalogenations of m-ClC6H4C(i)HClCH2Cl (I), m-CF3C6H4C(i)-HClCH2Cl (II) and p-CF3C6H4C(i)HClCH2F (III) has been used to calculate the internal-return parameters, a = k(-1)/K(Elim)(X), in a two-step mechanism featuring a hydrogen-bonded carbanion. This carbanion partitions between returning the hydron to carbon, k(-1), and the loss of halide, K(Elm)(X). Isotope effects at 25°C for I, (k(H)/k(D))(Obs) = 3.40 and (k(H)/ k(T))(Obs) = 6.20, and II, (k(H)/k(D))(Obs) = 3.49 and (k(H)/k(T))(Obs) = 6.55, result in similar values for a: a(H) = 0.59, a(D) = 0.13-0.14 and a(T) = 0.07. Smaller values of (k(H)/k(D))(Obs) = 2.19 and (k(H)/k(T))(Obs) = 3.56 for III are due to more internal return [a(H) = 1.9, a(D) = 0.50, and a(T) = 0.28] associated with the dehydrofluorination reaction. Calculation of k1 ( k(Obs) [a + 1]) results in similar isotope effects for hydron transfer in these reactions: k1(H)/k1(D) = 4.74 and k1(H)/K1(T) = 9.20; II, k1(H)/k1(D) = 4.91 and k1(H)/k1(T) = 9.75; III, k1(H)/k1(D) = 4.75 and k1(H)/k1(T) = 9.17. Reactions of m-ClC6H4C(i)HBrCH2Br and m-ClC6H4C(i)HClCH2Br have very small amounts of internal return, a(H) = 0.05 and a(D) = 0.01, and (k(H)/k(D))(Obs) = 4.95 results in k1(H)/k1(D) = 5.11 The measured isotope effects are therefore due to differences in the amount of internal return and not in the symmetry of transition state structures for the hydron transfer, and the element effect, (k(HBr)/ k(HCl)) = 29, for m-ClC6H4CHClCH2X is mainly due to the hydron-transfer step, k1(HBr)/k1(HCl) = 19, and not the breaking of the C-X bend. The kinetic solvent isotope effects, k(MeOD)/k(MeOH) ~ 2.5, are consistent with three methanols of solvation lost prior to the hydron-transfer step. The energetics associated with desolvation of methoxide ion are part of the measured reaction energetics of these systems.
- Koch, Heinz F.,Lodder, Gerrit,Koch, Judith G.,Bogdan, David J.,Brown, Geoffrey H.,Carlson, Carrie A.,Dean, Amy B.,Hage, Ronald,Han, Patrick,Hopman, Johan C. P.,James, Lisa A.,Knape, Petra M.,Roos, Eric C.,Sardina, Melissa L.,Sawyer, Rachael A.,Scott, Barbara O.,Testa III, Charles A.,Wickham, Steven D.
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p. 9965 - 9974
(2007/10/03)
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- Effect of the α-Trifluoromethyl Moiety on the Solvolysis of Allylic Sulfonates
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A series of allylic sulfonates bearing aryl substituents on the 2-position and/or trifluoromethyl groups on the 1- and/or 3-positions has been studied under solvolytic conditions in 2,2,2-trifluoroethanol.Nonarylated 1,3-di(trifluoromethyl)-substituted allylic sulfonates did not solvolyze in a conventional manner but instead gave products diagnostic of a complex isomerization-cleavage process.Mono(trifluoromethyl)-substituted allylic sulfonates solvolyzed by normal paths to give kH/kCF3 ratios of 2E6 and 4E4 for the substitution at the 1- and 3-positions, respectively.No evidence for 1,3-? interactions was discerned.
- Gassman, Paul G.,Harrington, Clinton K.
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p. 2258 - 2273
(2007/10/02)
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