- From Esters to Ketones via a Photoredox-Assisted Reductive Acyl Cross-Coupling Strategy
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A method was developed for ketone synthesis via a photoredox-assisted reductive acyl cross-coupling (PARAC) using a nickel/photoredox dual-catalyzed cross-electrophile coupling of two different carboxylic acid esters. A variety of aryl, 1°, 2°, 3°-alkyl 2-pyridyl esters can act as acyl electrophiles while N-(acyloxy)phthalimides (NHPI esters) act as 1°, 2°, 3°-radical precursors. Our PARAC strategy provides an alternative and reliable way to synthesize various sterically congested 3°-3°, 3°-2°, and aryl-3° ketones under mild and highly unified conditions, which have been otherwise difficult to access. The combined experimental and computational studies identified a Ni0/NiI/NiIII pathway for ketone formation.
- Chen, Yukun,Li, Weirong,Luo, Yixin,Qi, Xiaotian,Xi, Xiaoxiang,Xu, Minghao,Yuan, Weiming,Zhao, Hongping,Zheng, Songlin
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supporting information
(2021/12/06)
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- Arylketones as Aryl Donors in Palladium-Catalyzed Suzuki-Miyaura Couplings
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Herein, we report the arylation, alkylation, and alkenylation of aryl ketones via a palladium-catalyzed Suzuki-Miyaura cross-coupling reaction. The use of the pyridine-oxazoline ligand is the key to the cleavage of the unstrained C-C bond. The late-stage arylation of aryl ketones derived from drugs and natural products demonstrated the synthetic utility of this protocol.
- Wang, Zhen-Yu,Ma, Biao,Xu, Hui,Wang, Xing,Zhang, Xu,Dai, Hui-Xiong
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p. 8291 - 8295
(2021/11/13)
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- Chromium-Catalyzed Borylative Coupling of Aliphatic Bromides with Pinacolborane by Hydrogen Evolution
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The chromium-catalyzed borylative coupling between aliphatic bromides and pinacolborane (HBpin) is described. This reaction was promoted by low-cost and bench-stable CrCl3as a precatalyst combined with 4,4′-di-tert-butyl-2,2′-dipyridyl and aluminum, presenting a rare example of using HBpin as a borane reagent by coupling with alkyl bromides in forming borylated alkanes. Mechanistic studies indicate that aluminum plays important roles in the formation of reactive Cr species and aliphatic radicals, which lead to (alkyl)Cr by reaction with HBpin to give the products.
- Fu, Aiping,Li, Chao,Luo, Meiming,Zeng, Xiaoming,Zhao, Lixing
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p. 2204 - 2208
(2021/06/28)
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- "bulky-Yet-Flexible" α-Diimine Palladium-Catalyzed Reductive Heck Cross-Coupling: Highly Anti-Markovnikov-Selective Hydroarylation of Alkene in Air
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To pursue a highly regioselective and efficient reductive Heck reaction, a series of moisture-and air-stable α-diimine palladium precatalysts were rationally designed, readily synthesized, and fully characterized. The relationship between the structures of the palladium complexes and the catalytic properties was investigated. It was revealed that the"bulky-yet-flexible"palladium complexes allowed highly anti-Markovnikov-selective hydroarylation of alkenes with (hetero)aryl bromides under aerobic conditions. Further synthetic application of the present protocol could provide rapid and straightforward access to functional and biologically active molecules.
- Yang, Xu-Wen,Li, Dong-Hui,Song, A-Xiang,Liu, Feng-Shou
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p. 11750 - 11765
(2020/10/23)
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- Combined Photoredox/Enzymatic C?H Benzylic Hydroxylations
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Chemical transformations that install heteroatoms into C?H bonds are of significant interest because they streamline the construction of value-added small molecules. Direct C?H oxyfunctionalization, or the one step conversion of a C?H bond to a C?O bond, could be a highly enabling transformation due to the prevalence of the resulting enantioenriched alcohols in pharmaceuticals and natural products,. Here we report a single-flask photoredox/enzymatic process for direct C?H hydroxylation that proceeds with broad reactivity, chemoselectivity and enantioselectivity. This unified strategy advances general photoredox and enzymatic catalysis synergy and enables chemoenzymatic processes for powerful and selective oxidative transformations.
- Betori, Rick C.,May, Catherine M.,Scheidt, Karl A.
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supporting information
p. 16490 - 16494
(2019/11/03)
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- Switchable Selectivity in the Pd-Catalyzed Alkylative Cross-Coupling of Esters
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The Pd-catalyzed cross-coupling of phenyl esters and alkyl boranes is disclosed. Two reaction modes are rendered accessible in a selective fashion by interchange of the catalyst. With a Pd-NHC system, alkyl ketones can be prepared in good yields via a Suzuki-Miyaura reaction proceeding by activation of the C(acyl)-O bond. Use of a Pd-dcype catalyst enables alkylated arenes to be synthesized by a modified pathway with extrusion of CO. Applications of this divergent coupling strategy and the origin of the switchable selectivity are discussed.
- Masson-Makdissi, Jeanne,Vandavasi, Jaya Kishore,Newman, Stephen G.
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supporting information
p. 4094 - 4098
(2018/07/15)
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- Nickel-catalyzed alkylative cross-coupling of anisoles with grignard reagents via C-O bond activation
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We report nickel-catalyzed cross-coupling of methoxyarenes with alkylmagnesium halides, in which a methoxy group is eliminated. A wide range of alkyl groups, including those bearing β-hydrogens, can be introduced directly at the ipso position of anisole derivatives. We demonstrate that the robustness of a methoxy group allows this alkylation protocol to be used to synthesize elaborate molecules by combining it with traditional cross-coupling reactions or oxidative transformation. The success of this method is dependent on the use of alkylmagnesium iodides, but not chlorides or bromides, which highlights the importance of the halide used in developing catalytic reactions using Grignard reagents.
- Tobisu, Mamoru,Takahira, Tsuyoshi,Morioka, Toshifumi,Chatani, Naoto
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supporting information
p. 6711 - 6714
(2016/06/14)
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- Lewis Acid Assisted Nickel-Catalyzed Cross-Coupling of Aryl Methyl Ethers by C-O Bond-Cleaving Alkylation: Prevention of Undesired β-Hydride Elimination
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In the presence of trialkylaluminum reagents, diverse aryl methyl ethers can be transformed into valuable products by C-O bond-cleaving alkylation, for the first time without the limiting β-hydride elimination. This new nickel-catalyzed dealkoxylative alkylation method enables powerful orthogonal synthetic strategies for the transformation of a variety of naturally occurring and easily accessible anisole derivatives. The directing and/or activating properties of aromatic methoxy groups are utilized first, before they are replaced by alkyl chains in a subsequent coupling process.
- Liu, Xiangqian,Hsiao, Chien-Chi,Kalvet, Indrek,Leiendecker, Matthias,Guo, Lin,Schoenebeck, Franziska,Rueping, Magnus
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supporting information
p. 6093 - 6098
(2016/05/19)
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- Direct arylation/alkylation/magnesiation of benzyl alcohols in the presence of grignard reagents via Ni-, Fe-, or Co-catalyzed sp3 C-O Bond activation
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Direct application of benzyl alcohols (or their magnesium salts) as electrophiles in various reactions with Grignard reagents has been developed via transition metal-catalyzed sp3 C-O bond activation. Ni complex was found to be an efficient catalyst for the first direct cross coupling of benzyl alcohols with aryl/alkyl Grignard reagents, while Fe, Co, or Ni catalysts could promote the unprecedented conversion of benzyl alcohols to benzyl Grignard reagents in the presence of nhexylMgCl. These methods offer straightforward pathways to transform benzyl alcohols into a variety of functionalities.
- Yu, Da-Gang,Wang, Xin,Zhu, Ru-Yi,Luo, Shuang,Zhang, Xiao-Bo,Wang, Bi-Qin,Wang, Lei,Shi, Zhang-Jie
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p. 14638 - 14641
(2012/11/07)
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- Photoextrusion of SO2 from Arylmethyl Sulfones: Exploration of the Mechanism by Chemical Trapping, Chiral, and CIDNP Probes
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The photochemistry of eight benzylic sulfones, all of which efficiently extrude sulfur dioxide, was studied by a variety of methods.Optically active sulfones (S)-(-)-8, (S)-(-)-11, (S)-(-)-12, (S)-(+)-13, and (R)-(+)-14 were employed to measure the extent of the "hidden" return of the initial photogenerated intermediates by the stereoequilibration of the chiral center.By comparison of the regioisomeric methyl sulfones 11 vs. 13 and 12 vs. 14, preferential C-S bond fragmentation on the naphthyl side was established for the singlet excited sulfones.Added nucleophilic and proton trapping agents had no effect on the course of the reaction, ruling out ionic intermediates.The three hydrocarbon products of photodesulfonation from the unsymmetrical sulfones 8-14 provided a measure of the cage effects, which were highly structure and multiplicity dependent.Rate constants for reaction, and fluorescence, as well as the energy transfer rates from benzophenone were determined.The reaction rate constant for singlet reactivity from the 1-naphthyl sulfones was about three times greater than that for the 2-naphthyl derivatives.CIDNP studies showed a strong product signal for the 1-naphthyl sulfones from desulfonation of a triplet caged radical pair.Naphthaldehyde formation, a very minor, triplet process, was also detected by the CIDNP study of sulfones 9-12.
- Givens, Richard S.,Hrinczenko, Borys,Liu, Jerry H.-S.,Matuszewski, Bogdan,Tholen-Collison, Joan
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p. 1779 - 1789
(2007/10/02)
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- MECHANISTIC STUDIES OF THE PHOTODECOMPOSITION OF ARYLMETHYL SULFONES IN HOMOGENEOUS AND MICELLAR SOLUTIONS.
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The mechanism of photodecomposition of aryl sulfones has been investigated by using both steady-state and time-resolved techniques. Direct evidence for radical and triplet-state intermediates is provided. A correlation is found between the dynamics of reaction of the intermediate triplet states with the stabilities of the intermediate radicals.
- Gould,Tung,Turro,Givens,Matuszewski
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p. 1789 - 1793
(2007/10/02)
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