- Cobalt-Catalyzed Kumada Coupling Forming Sterically Encumbered C-C Bonds
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A Co(acac)3/PN precatalyst was developed and optimized for catalytic Kumada coupling of aryl Grignard reagents to sterically encumbered alkyl halides. The substrate scope demonstrates excellent yields for primary alkyl chlorides and bromides, including good performance using neopentyl chloride and neophyl chloride. Secondary alkyl halides were also successfully arylated in good yields, and the presence of β-hydrogen atoms in a substrate did not inhibit product formation. An intermolecular functional group tolerance screen was conducted which indicates that ester and amide functionality are well tolerated by the reaction conditions. Electrophiles containing ester, pyridine, and nitrile functionality were all coupled with 2-mesitylmagnesium bromide in good yields, supporting tolerance screen results. The intermolecular screen also showed that functional groups which are typically reactive with Grignard reagents such as alcohols and terminal alkynes were not well-tolerated by the reaction.
- Brennan, Marshall R.,Darrow, William T.,Fout, Alison R.,Killion, Jack A.,Leahy, Clare A.
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- Teaching an old carbocation new tricks: Intermolecular C-H insertion reactions of vinyl cations
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Vinyl carbocations have been the subject of extensive experimental and theoretical studies over the past five decades. Despite this long history in chemistry, the utility of vinyl cations in chemical synthesis has been limited, with most reactivity studies focusing on solvolysis reactions or intramolecular processes. Here we report synthetic and mechanistic studies of vinyl cations generated through silylium-weakly coordinating anion catalysis. We find that these reactive intermediates undergo mild intermolecular carbon-carbon bond-forming reactions, including carbon-hydrogen (C-H) insertion into unactivated sp3 C-H bonds and reductive Friedel-Crafts reactions with arenes. Moreover, we conducted computational studies of these alkane C-H functionalization reactions and discovered that they proceed through nonclassical, ambimodal transition structures. This reaction manifold provides a framework for the catalytic functionalization of hydrocarbons using simple ketone derivatives.
- Popov, Stasik,Shao, Brian,Bagdasarian, Alex L.,Benton, Tyler R.,Zou, Luyi,Yang, Zhongyue,Houk,Nelson, Hosea M.
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p. 381 - 387
(2018/08/07)
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- Sterically congested phosphonium borate acids as effective Br?nsted acid catalysts
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Phosphonium borate acids [HPPh2(C6F5)][B(C6F5)4] (2), [HPMes2(C6F5)][B(C6F5)4] (3) and [HPMes(C6F5)2][B(C6F5)4] (4) were synthesized via heterolytic dihydrogen cleavage in the presence of triisopropylsilylium and characterized by spectroscopic and crystallographic methods. Br?nsted acid catalysis using compounds 2–4 proved to be efficient for a number of challenging reactions (namely ionic hydrogenation, hydroamination and hydroarylation), owing to the restrained nucleophilicity of the sterically hindered conjugate bases. Reactivity of compounds 2–4 suggests that their pKavalues are similar to that of diethyl oxonium acid.
- Sinha, Arup,Jaiswal, Amit K.,Young, Rowan D.
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- Disambiguation of metal and Bronsted acid catalyzed pathways for hydroarylation with platinum(II) catalysts
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The hydroarylation of unactivated olefins effected by Pt(II) precatalysts was found to proceed through the in situ production of protic acid followed by a Friedel-Crafts mechanism. The reaction was investigated using the hindered base 2,6-di-tert-butyl-4-methylpyridine and a variety of substrates.
- Bowring, Miriam A.,Bergman, Robert G.,Tilley, T. Don
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scheme or table
p. 1295 - 1298
(2011/04/22)
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- Microporous acidic cesium salt of 12-tungstosilicic acid Cs 3HSiW12O40 as a size-selective solid acid catalyst
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An acidic Cs salt of H4SiW12O4O 40 (Cs3HSiW12O40), which was prepared by titrating an aqueous solution of H4SiW12O 40 with an aqueous solution of Cs2CO3, possessed only micropores and exhibited size-selective catalysis for acid-catalyzed reactions in liquid phase.
- Kamiya, Yuichi,Sano, Shogo,Miura, Yu-Ki,Uchida, Yohei,Ogawa, Yuki,Iwase, Yukari,Okuhara, Toshio,Degnan Jr.
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supporting information; scheme or table
p. 881 - 883
(2011/01/08)
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- C-F Activation of hydrofluorocarbons (HFCs) mediated by aluminum reagents
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In the presence of various aluminum reagents, the difluoromethylene group (CF2) in selected hydrofluorocarbons (HFCs) undergoes a Friedel-Crafts type reaction with aromatic compounds in satisfactory yields.
- Ali, Majeid,Liu, Le-Ping,Hammond, Gerald B.,Xu, Bo
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body text
p. 4078 - 4080
(2009/10/11)
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- Nitrosonium salts, NO+X- (X = B(3,5-diCF 3Ph)4- or PW12O40 3-), as electrophilic catalysts for alkene activation in arene alkylation and dimerization reactions
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It has been found that in apolar reaction media the nitrosonium cation (NO+) activated alkenes under mild conditions toward electrophilic substitution of arene substrates to yield the alkylated arene with Markovnikov orientation. In the absence of arenes the alkenes react with themselves to yield a mixture of dimeric alkenes. The nitrosonium cation can be dissolved in the reaction medium by using the tetrakis-(bis-(3,5-trifluromethyl)phenyl) borate anion, where upon the reactions occur effectively at 30 °C. Alternatively an insoluble, heterogeneous catalyst was prepared so as to yield a NO+ cation with a polyoxometalate (PW12O403-) anion. This catalyst was generally more effective and selective toward a broader range of substrates at 70 °C. Copyright
- Khenkin, Alexander M.,Neumann, Ronny
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supporting information; scheme or table
p. 11876 - 11877
(2009/02/05)
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- Perfect switching of photoreactivity by acid: Photochemical decarboxylation versus transesterification of mesityl cyclohexanecarboxylate
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(matrix presented) Mesityl cyclohexanecarboxylate has been photodecarboxylated upon excitation at 254 nm to form cyclohexylmesitylene in good yield in neutral acetonitrile solutions. In the presence of a catalytic amount of the acid and ethanol as a nucleophile, however, the same compound undergoes facile transesterification upon irradiation, affording its ethyl ester in almost quantitative yield.
- Mori, Tadashi,Wada, Takehiko,Inoue, Yoshihisa
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p. 3401 - 3404
(2007/10/03)
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- A new convenient Friedel-Crafts alkylation of aromatic compounds with secondary alcohol methanesulfonates in the presence of scandium(III) trifluoromethanesulfonate or trifluoromethanesulfonic acid as the catalyst
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Scandium(III) triflate and triflic acid were both found to be efficient catalysts for the Friedel-Crafts alkylation of aromatic compounds using methanesulfonates derived from secondary alcohols as alkylating agents.
- Kotsuki, Hiyoshizo,Ohishi, Takeshi,Inoue, Motoshi,Kojima, Tomoyuki
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p. 603 - 606
(2007/10/03)
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- Scandium(III) trifluoromethanesulfonate-catalyzed Friedel-Crafts alkylation of aromatic compounds with secondary alcohol methanesulfonates
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Scandium(III) inflate was found to be an efficient catalyst for the Friedel-Crafts alkylation of aromatic compounds with methanesulfonates derived from secondary alcohols; the catalyst can be reused without a significant loss of activity.
- Kotsuki, Hiyoshizo,Oshisi, Takeshi,Inoue, Motoshi
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p. 255 - 256
(2007/10/03)
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- Friedel-Crafts Cyclohexylation of Arenes with 1,3-Dicyclohexylcarbodiimide (DCC)
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The reaction of arenes with 1,3-dicyclohexylcarbodiimide in the presence of concentrated sulfuric acid or anhydrous aluminum chloride gave the corresponding cyclohexylated arenes in good yields.
- Kim, Jae Nyoung,Chung, Kun Hoe,Ryu, Eung K.
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p. 903 - 904
(2007/10/02)
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- High Catalytic Activities of Pseudoliquid Phase of Dodecatungstophosphoric Acid for Reactions of Polar Molecules
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A solid H3PW12O40 exhibited very high catalytic activities for the reations of polar molecules in the liqiud phase, while it was much less active for the reactions of nonpolar molecules.It was confirmed that the pseudoliquid phase behavior of H3PW12O40 is responsible for the high activities.
- Nishimura, Toru,Okuhara, Toshio,Misono, Makoto
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p. 1695 - 1698
(2007/10/02)
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