- Direct Synthesis of Enones by Visible-Light-Promoted Oxygenation of Trisubstituted Olefins Using Molecular Oxygen
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A one-step synthesis of enones from olefins is described. The reaction was performed under visible-light irradiation in the presence of molecular oxygen and a photocatalyst. The reaction proceeded with various types of trisubstituted olefins to give enones in good yields with high regioselectivity. In particular, oxygen- and nitrogen-containing functional groups, heteroaromatic rings, and cyclopropanes were tolerated. Mechanistic studies and previous reports indicated that the active oxygen species generated in the reaction system is singlet oxygen.
- Harada, Shinji,Matsuda, Daiki,Morikawa, Takahiro,Nishida, Atsushi
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supporting information
p. 1372 - 1377
(2020/10/02)
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- Enantioselective Copper(I)/Chiral Phosphoric Acid Catalyzed Intramolecular Amination of Allylic and Benzylic C?H Bonds
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Radical-involved enantioselective oxidative C?H bond functionalization by a hydrogen-atom transfer (HAT) process has emerged as a promising method for accessing functionally diverse enantioenriched products, while asymmetric C(sp3)?H bond amination remains a formidable challenge. To address this problem, described herein is a dual CuI/chiral phosphoric acid (CPA) catalytic system for radical-involved enantioselective intramolecular C(sp3)?H amination of not only allylic positions but also benzylic positions with broad substrate scope. The use of 4-methoxy-NHPI (NHPI=N-hydroxyphthalimide) as a stable and chemoselective HAT mediator precursor is crucial for the fulfillment of this transformation. Preliminary mechanistic studies indicate that a crucial allylic or benzylic radical intermediate resulting from a HAT process is involved.
- Ye, Liu,Tian, Yu,Meng, Xiang,Gu, Qiang-Shuai,Liu, Xin-Yuan
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supporting information
p. 1129 - 1133
(2019/12/12)
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- Enantioselective Bromolactonization of Trisubstituted Olefinic Acids Catalyzed by Chiral Pyridyl Phosphoramides
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Enantioselective bromolactonization of trisubstituted olefinic acids producing synthetically useful chiral lactones with two contiguous asymmetric centers has remained mainly unexplored except for the 6-exo cyclization mode. In this work, the 5-exo- and 6
- Nishikawa, Yasuhiro,Hamamoto, Yuhta,Satoh, Rika,Akada, Naho,Kajita, Shuhei,Nomoto, Marina,Miyata, Megumi,Nakamura, Madoka,Matsubara, Chinatsu,Hara, Osamu
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supporting information
p. 18880 - 18885
(2018/12/04)
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- Br?nsted Acid-Catalyzed Carbonyl-Olefin Metathesis inside a Self-Assembled Supramolecular Host
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Carbonyl–olefin metathesis represents a powerful yet underdeveloped method for the formation of carbon–carbon bonds. So far, no Br?nsted acid based method for the catalytic carbonyl–olefin metathesis has been described. Herein, a cocatalytic system based on a simple Br?nsted acid (HCl) and a self-assembled supramolecular host is presented. The developed system compares well with the current benchmark catalyst for carbonyl–olefin metathesis in terms of substrate scope and yield of isolated product. Control experiments provide strong evidence that the reaction proceeds inside the cavity of the supramolecular host. A mechanistic probe indicates that a stepwise reaction mechanism is likely.
- Catti, Lorenzo,Tiefenbacher, Konrad
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supporting information
p. 14589 - 14592
(2018/01/27)
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- Chiral Selenide-Catalyzed Enantioselective Allylic Reaction and Intermolecular Difunctionalization of Alkenes: Efficient Construction of C-SCF3 Stereogenic Molecules
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New approaches for the synthesis of enantiopure trifluoromethylthiolated molecules by chiral selenide-catalyzed allylic trifluoromethylthiolation and intermolecular difunctionalization of unactivated alkenes are disclosed. In these transformations, functi
- Liu, Xiang,Liang, Yaoyu,Ji, Jieying,Luo, Jie,Zhao, Xiaodan
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supporting information
p. 4782 - 4786
(2018/04/17)
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- Catalytic olefin hydroamination with aminium radical cations: A photoredox method for direct C-N bond formation
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While olefin amination with aminium radical cations is a classical method for C-N bond formation, catalytic variants that utilize simple 2° amine precursors remain largely undeveloped. Herein we report a new visible-light photoredox protocol for the intramolecular anti-Markovnikov hydroamination of aryl olefins that proceeds through catalytically generated aminium radical intermediates. Mechanistic studies are consistent with a process involving amine oxidation via electron transfer, turnover-limiting C-N bond formation, and a second electron transfer step to reduce a carbon-centered radical, rendering the overall process redox-neutral. A range of structurally diverse N-aryl heterocycles can be prepared in good to excellent yields under conditions significantly milder than those required by conventional aminium-based protocols.
- Musacchio, Andrew J.,Nguyen, Lucas Q.,Beard, G. Hudson,Knowles, Robert R.
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supporting information
p. 12217 - 12220
(2014/12/09)
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- Controlling 6-endo-selectivity in oxidation/bromocyclization cascades for synthesis of aplysiapyranoids and other 2,2,6,6-substituted tetrahydropyrans
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A cascade, composed of (i) oxovanadium(V)-catalyzed oxidation of bromide by tert-butyl hydroperoxide and (ii) stereoselective 6-endo-bromocyclization, affords 3-bromo-2-aryl-2,6,6-trimethyltetrahydropyrans from styrene-type tertiary alkenols in synthetically useful yields. (E)-Alkenols add the bromo- and the alkoxy substituent anti-selectively across the double bond, indicating a bromonium ion-mechanism for the ring closure. 6-endo-control of the alkenol cyclization thereby arises from the polar effect of the aryl substituent. Two methyl substituents bound to the alkene terminus are not similarly able to favor 6-endo-cyclization, because strain arising from methyl group repulsion, as the bromonium-activated π-bond and the hydroxyl oxygen approach, directs bromocyclization of tertiary prenyl-type substrates toward tetrahydrofuran formation. A hexasubstituted bromotetrahydropyran prepared from the oxidation/bromocyclization cascade served as starting material for synthesis of racemic aplysiapyranoid A, in a sequence of free radical and polar functional group interconversion.
- Brücher, Oliver,Bergstr??er, Uwe,Kelm, Harald,Hartung, Jens,Greb, Marco,Svoboda, Ingrid,Fuess, Hartmut
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supporting information; experimental part
p. 6968 - 6980
(2012/09/07)
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- Selenium-catalyzed regioselective cyclization of unsaturated carboxylic acids using hypervalent iodine oxidants
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A new and convenient selenium-catalyzed regioselective cyclization of γ, δ-unsaturated carboxylic acids to the corresponding 3, 6-dihydro-2Hpyran- 2-ones is described. The cyclization products have been obtained in good to excellent yields using diphenyl diselenide as a catalyst and [bis(trifluoroacetoxy)iodo]benzene as a stoichiometric oxidant 2011 American Chemical Society.
- Singh, Fateh V.,Wirth, Thomas
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supporting information; experimental part
p. 6504 - 6507
(2012/02/02)
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- A convenient one-pot synthesis of homoallylic halides and 1,3-butadienes
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An efficient one-pot synthetic pathway for the preparation of homoallylic halides by in situ generated MgBrCl-promoted ring opening of cyclopropylcarbinyl acetates has been established. An easily accessible one-pot synthetic protocol of 1,3-butadienes by the elimination of hydrogen halides from the resulting homoallylic halides in the presence of an excess amount of strong base has also been developed.
- Wong, Ken-Tsung,Hung, Ying-Yueh
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p. 8033 - 8036
(2007/10/03)
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- Hydrogen atom transfer reactions of transition-metal hydrides. Kinetics and mechanism of the hydrogenation of α-cyclopropylstyrene by metal carbonyl hydrides
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The hydrogenation of α-cyclopropylstyrene (CPS) by a series of metal carbonyl hydrides (MH) gives a mixture of the unrearranged hydrogenation product Ph(CH3)(c-C3H5)CH (UN) and the rearranged hydrogenation product (E)-Ph(CH 3)C=CHCH2CH3 (RE). With the exception of HCr(CO)3Cp, second-order kinetics are found, conforming to the rate law -d[CPS]/dt = k[CPS][MH]. The proposed mechanism involves hydrogenation by sequential hydrogen atom transfers from the metal hydride to the organic substrate. The rate-determining step is the first hydrogen atom transfer in which a carbon-centered radical and a metal-centered radical are formed. In the case of HCr(CO)3Cp at 22 °C, the equilibrium constant for this step is K ~ 10-12. The effect of the significant amount of 17-electron *Cr(CO)3Cp radical formed in the hydrogenation of CPS by HCr(CO)3Cp is accommodated by the kinetic analysis. Since the initially formed carbon-centered radical undergoes first-order ring-opening rearrangement in competition with second-order trapping by MH, analysis of the product ratio as a function of [MH] concentration provides relative rates of hydrogen atom transfer from metal hydrides to a carbon-centered radical. Relative rates of hydrogen atom transfer at 60 °C from MH to 1 are as follows: krel = 1 for HMn(CO)4PPh3, krel = 4 for HMo(CO)3(C5Me5), krel = 93 for HMo(CO)3Cp, krel = 94 for HFe(CO)2(C5Me5). Comparison of the hydrogenation of CPS by HW(CO)3Cp and DW(CO)3Cp indicates that the kinetic isotope effect is inverse (kHW/kDW = 0.55) for the first hydrogen atom transfer but normal (kHW/kDW = 1.8-2.2) for the second hydrogen atom transfer. The first hydrogen atom transfer is endothermic, and its rate is largely influenced by the strength of the M-H bond. Steric effects appear to exert a dominant influence on the rate of the second hydrogen atom transfer, which is exothermic. Kinetic and mechanistic experiments indicate that hydrogenation of 2-cyclopropylpropene by HCr(CO)3Cp also occurs by a radical pathway.
- Morris Bullock,Samsel, Edward G.
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p. 6886 - 6898
(2007/10/02)
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