- ELECTRON-TRANSFER INDUCED CONVERSION OF ENOL-ETHERS INTO KETONES
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Alkoxy (aryl)-methylidene adamantanes react with catalytic amounts of tris p-bromophenylammoniumyl hexachloroantimonate in CH2Cl2 under argon atmosphere, yielding adamantyl-arylketones together with the corresponding alcohols.The reaction most likely proc
- Lopez, Luigi,Troisi, Luigino
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- Synergistic Activation of Amides and Hydrocarbons for Direct C(sp3)–H Acylation Enabled by Metallaphotoredox Catalysis
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The utilizations of omnipresent, thermodynamically stable amides and aliphatic C(sp3)?H bonds for various functionalizations are ongoing challenges in catalysis. In particular, the direct coupling between the two functional groups has not been realized. Here, we report the synergistic activation of the two challenging bonds, the amide C?N and unactivated aliphatic C(sp3)?H, via metallaphotoredox catalysis to directly acylate aliphatic C?H bonds utilizing amides as stable and readily accessible acyl surrogates. N-acylsuccinimides served as efficient acyl reagents for the streamlined synthesis of synthetically useful ketones from simple C(sp3)?H substrates. Detailed mechanistic investigations using both computational and experimental mechanistic studies were performed to construct a detailed and complete catalytic cycle. The origin of the superior reactivity of the N-acylsuccinimides over other more reactive acyl sources such as acyl chlorides was found to be an uncommon reaction pathway which commences with C?H activation prior to oxidative addition of the acyl substrate.
- Baik, Mu-Hyun,Choi, Seulhui,Hong, Soon Hyeok,Lee, Geun Seok,Won, Joonghee
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p. 16933 - 16942
(2020/08/03)
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- Enhanced enantio- and diastereoselectivity via confinement and cation binding: Yang photocyclization of 2-benzoyladamantane derivatives within zeolites
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Irradiation of 2-benzoyladamantane derivatives in zeolites yields the endo-cyclobutanols as the only photoproduct via a γ-hydrogen abstraction process. The cyclobutanols readily undergo retroaldol reaction to give δ-ketoesters. The enantiomeric excess (ee) in the endo-cyclobutanols is measured by monitoring the ee in the ketoesters. Whereas in solution the ee in the product ketoester is zero, within achiral NaY zeolite, in the presence of a chiral inductor such as pseudoephedrine, ee's up to 28% have been obtained. The influence of zeolite on several chiral esters of 2-benzoyladamantane-2-carboxylic acids has also been examined. Whereas in solution the diastereomeric excess is 15%, in zeolite the δ-ketoesters are obtained in 79% de (best examples). Ab initio computations suggest that enhancement of chiral induction within zeolites is likely to be due to cation complexation with the reactant ketone. Alkali ion-organic interaction, a powerful tool, is waiting to be fully exploited in photochemical and thermal reactions. In this context zeolites could be a useful medium as one could view them as a reservoir of "naked" alkali ions that are only partially coordinated to the zeolite walls.
- Natarajan, Arunkumar,Joy, Abraham,Kaanumalle, Lakshmi S.,Scheffer, John R.,Ramamurthy
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p. 8339 - 8350
(2007/10/03)
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- McMurry intermolecular cross-coupling between an ester and a ketone: Scope and limitations
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In the course of our studies towards the synthesis of a dioxetane bearing chemiluminescent probe for the detection of thiols, we were faced with the synthesis of sterically hindered benzylic enol ethers. This issue was solved via the use of an intermolecular McMurry cross-coupling between an ester and a ketone. In this article, together with the synthesis of the chemiluminescent probe, the scope and limitations of this low valent titanium based carbon-carbon double bond formation are discussed.
- Sabelle, Stéphane,Hydrio, Jér?me,Leclerc, Eric,Mioskowski, Charles,Renard, Pierre-Yves
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p. 3645 - 3648
(2007/10/03)
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- Three-Component Coupling of Acylphosphonates and Two Carbonyl Compounds Promoted by Low-Valent Samariums: One-Pot Synthesis of β-Hydroxyphosphonates
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Three-component coupling of acylphosphonates and two carbonyl compounds leading to β-hydroxyphosphonates has been achieved with low-valent samariums. Thus, acylphosphonates reacted with aldehydes in the presence of semicatalytic amounts of samarium metal or SmI2 to give acyloxyphosphonates in good yields. The second coupling reaction of the acyloxyphosphonates with aldehydes or ketones promoted by SmI2 afforded β-hydroxyphosphonates instead of olefins. Moreover, these two reactions could be carried out in one pot.
- Takaki, Ken,Itono, Yuichiro,Nagafuji, Akihiro,Naito, Yoji,Shishido, Tetsuya,Takehira, Katsuomi,Makioka, Yoshikazu,Taniguchi, Yuki,Fujiwara, Yuzo
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p. 475 - 481
(2007/10/03)
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- An investigation of the Yang photocyclization reaction in the solid state: Asymmetric induction studies and crystal structure-reactivity relationships
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The Norrish/Yang type II photochemistry of 16 ketones having the basic cis-4-tert-butyl-1-benzoylcyclohexane or 2-benzoyladamantane structure has been investigated in the solid state and solution. In both media, ketones bearing methyl substituents α to th
- Leibovitch, Mordechai,Olovsson, Gunnar,Scheffer, John R.,Trotter, James
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p. 12755 - 12769
(2007/10/03)
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- Electron-Transfer Reactions On Enol-Ethers Induced By Aminium Salts Syntheses of 1,2-Dioxetanes And/Or Ketones
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Thermally stable 4-alkoxy-4-(aryl)spiro 2a-e have been synthesized by reaction of oxygen-saturated methylene chloride solutions of alkoxy(aryl) methylidene adamantanes 1a-e with catalytic amounts of one electron oxidizing agents as tris-p-bromophenyl ammoniumyl and/or tris-o,p-dibromophenyl ammoniumyl hexachloroantimonates (reagents A,B).Similar reactions carried out on 1a-d, under argon-atmosphere, yield adamantyl-arylketones 5a-c together with the corresponding alcohols 6a-b.Both processes most likely involve the formation of radical cation intermediates (1+.), leading to the reaction products through chain electron-transfer mechanisms.
- Lopez, Luigi,Troisi, Luigino
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p. 7321 - 7330
(2007/10/02)
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- Competing, kc, Borderline, ks, and Carbonyl Addition Processes in Solvolyses of α-Keto Mesylates and Triflates. α-Keto Cations. 5
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Solvolysis studies on tertiary α-keto mesylates show quite varying responses in rate to solvent ionizing power.The m values are 1.01 for 2-benzoyl-2-adamantyl mesylate (12), 0.66 for the mesylate derivative of 2-hydroxy-2,4,4-trimethyl-3-pentanone (4), and 0.63 for the mesylate derivative of 2-hydroxy-2-methylpropiophenone (3).The mesylate derivative of methyl α-hydroxyisobutyrate (5) does not correlate well with YOTs values, but instead it gives behavior that parallels that of isopropyl tosylate.Mesylates 3-5 solvolyze giving varying ratios of elimination and substitution products at rates comparable to that of isopropyl mesylate. β-d6 isotope effects for 3 and 4 range from 1.69 to 2.08 and are consistent with the intermediacy of α-keto cations. β-Deuterium isotope effects for 5 are quite variable (1.40-2.52) and parallel the amount of elimination product formed (22-94percent).This is consistent with the intermediacy of a reversibly formed ion-pair intermediate which can suffer proton loss.However, the SN2 (intermediate) mechanism remains a possibility in solvolyses of 5.Mesylate 3 solvolyzed in trifluoroethanol with added triethylamine to give an alkoxyoxirane.With small amounts of added 2,6-lutidine the 1,2-elimination product was major , while with added methanesulfonic acid the rearranged trifluoroethyl ester of dimethylphenyl acetic acid was major.These variable products were interpreted in terms of competing carbonyl addition processes and processes involving the α-keto cation.Secondary triflates derived from α-hydroxypropiophenone, 2,2-dimethyl-4-hydroxy-3-pentanone, and ethyl lactate solvolyzed giving the simple substitution product.Rates parallel solvent nucleophilicity and suggest a ks process involving negligible cationic character at the carbon α to the carbonyl group. kΔ processes are also not involved in solvolyses of these secondary triflates.
- Creary, Xavier
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p. 5568 - 5577
(2007/10/02)
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