- Metal-Free Transfer Hydrobromination of C-C Triple Bonds
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A transfer hydrobromination of C-C triple bonds inititated by Br?nsted acids is reported. Hydrogen bromide is released stepwise from a bench-stable cyclohexa-1,4-diene-based surrogate, generating biphenyl and ethylene as waste. A range of vinyl bromides was prepared from terminal and internal, mainly acceptor-substituted alkynes with good functional-group tolerance.
- Chen, Weiqiang,Oestreich, Martin
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supporting information
p. 4531 - 4534
(2019/06/27)
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- Stereoselective Alkyne Hydrohalogenation by Trapping of Transfer Hydrogenation Intermediates
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A catalytically generated vinylcopper complex, the reactive intermediate of a copper(I)-catalyzed alkyne transfer hydrogenation, can be trapped by commercially available halogen electrophiles. In this manner, internal alkynes can stereoselectively be hydrohalogenated to the corresponding vinyl chlorides, bromides, and iodides.
- Das, Manas,Kaicharla, Trinadh,Teichert, Johannes F.
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supporting information
p. 4926 - 4929
(2018/08/24)
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- Catalytic anti-Markovnikov hydrobromination of alkynes
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We have developed the first catalytic method for anti-Markovnikov hydrobromination of alkynes. The reaction affords terminal E-alkenyl bromides in high yield and with excellent regio- and diastereoselectivity. Both aryl- and alkyl-substituted terminal alkynes can be used as substrates. Furthermore, the reaction conditions are compatible with a wide range of functional groups, including esters, nitriles, epoxides, aryl boronic esters, terminal alkenes, silyl ethers, aryl halides, and alkyl halides. A preliminary study of the reaction mechanism suggests that the hydrobromination reaction involves hydrocupration of an alkyne, followed by the bromination of the alkenyl copper intermediate. This study also suggests that 2-tert-butyl potassium phenoxide functions as a mild catalyst turnover reagent and provides a better understanding of the unique effectiveness of (BrCl2C)2 among brominating reagents.
- Uehling, Mycah R.,Rucker, Richard P.,Lalic, Gojko
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supporting information
p. 8799 - 8803
(2014/07/07)
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- Titanium tetraiodide-promoted tandem prins reaction of alkynes with acetals: Synthesis of (Z,Z)-1,5-Diiodo-1,3,5-triarylpenta-1,4-dienes
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In the presence of titanium tetraiodide, a tandem Prins reaction of alkynes proceeded with acetals to give (Z,Z)-1,5diiodo-1,3,5-triarylpenta-1,4-dienes in good yields, where an intriguing reversal of the stereoselectivity was observed among titanium tetr
- Shimizu, Makoto,Okura, Kanako,Arai, Takuya,Hachiya, Iwao
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scheme or table
p. 1052 - 1054
(2011/01/10)
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- Regiochemical variation in the electrophilic addition of HBr to 1-phenylprop-1-yne
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The reaction of aryl alkynes with dilute methylene chloride solutions of quaternary ammonium bromide and 20% trifluoroacetic acid produces primarily the syn Markovnikov adducts of hydrogen bromide. At moderate concentrations of the bromide, the principal
- Weiss, Hilton M.,Touchette, Kim M.,Andersen, Frantz,Iskhakov, David
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p. 2148 - 2151
(2007/10/03)
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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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- Surface-Mediated Reactions. 4. Hydrohalogenation of Alkynes
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The use of appropriately prepared silica gel and alumina has been found to mediate the addition of hydrogen halides to alkynes.The technique has been rendered even more convenient by the use of various organic and inorganic acid halides that react in the presence of silica gel or alumina to generate hydrogen halides in situ.Treatment in this fashion of 1-propynylbenzene (1), which underwent no reaction in CH2Cl2 solution saturated with HCl, readily afforded the syn addition product, alkenyl chloride (E)-4a.On extended treatment (E)-4a underwent subsequent iaomerization to the thermodynamically more stable Z isomer.Thus either isomer of 4a could be obtained in good yield depending on the reaction conditions.In a similar way bromides (E)- and (Z)-4b were obtained without competing formation of the radical products (E)- and (Z)-5, which occurred in solution.In contrast with solution-phase hydroiodination of alkyne 1, which slowly afforded iodide (E)-4c, surface-mediated addition readily afforded (E)-4c, followed by isomerization to the Z isomer.E ->/- Z equilibration of the alkenyl halides 4 was shown to involve, at last in part, addition-elimination via the gem-dihalides 13.Analogous behavior was exhibited by the phenylalkynes 2 and 3 on surface-mediated hydrohalogenation.Surface-mediated addition of HBr and HI to the internal alkylalkyne 14 afforded principally the anti addition products (Z)-15b,c.Treatment of the terminal alkynes 17 and 22 with (COBr)2 over alumina gave the dibromides 20 and 24/25, respectively, whereas use of acetyl bromide as the HBr precursor afforded the alkenyl bromides 18b and 23.
- Kropp, Paul J.,Crawford, Scott D.
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p. 3102 - 3112
(2007/10/02)
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- MASS SPECTROMETRY OF 1-PHENYL-1,2-DIBROMOPROPYLPHOSPHONIC ACID AND ITS METHYL ESTERS
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erythro-1-Phenyl-1,2-dibromopropylphosphonic acid is known to decompose rapidly into the monomeric metaphosphate anion(PO3(1-)), 1-phenyl-1-bromopropene, and bromide ion in protic or aprotic solvents in the presence of a hindered tertiary amine.The present study compares the behavior of this phosphonic acid in solution and in the gas phase.The gas-phase thermolysis of the acid involves mainly the loss of bromine and of the phosphoryl group, -P(O)(OR)(OR') (R=R'=H).The same type of pathway is followed in the ionization/excitation processes ("cationic reactions") that follow from electron impact in mass spectrometry.The thermal and cationic reactions of the monomethyl and dimethyl esters of the phosphoric acids (R=H, R'=CH3 and R=R'=CH3, respectively, in -P(O)(OR)(OR')) are entirely analogous to those of the free dibasic acid.
- Meyerson, Seymour,Kuhn, Eugene S.,Ramirez, Fausto,Yemul, Shrishailam S.,Marecek, James F.
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p. 2633 - 2642
(2007/10/02)
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