| 1. |
- Henry, Jeffrey L., et al.
(author)
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Highly Selective Olefin-Assisted Pd-II-Catalyzed Oxidative Alkynylation of Enallenes
- 2017
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In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 23:33, s. 7896-7899
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Journal article (peer-reviewed)abstract
- An olefin-assisted, palladium-catalyzed oxidative alkynylation of enallenes for regio- and stereoselective synthesis of substituted trienynes has been developed. The reaction shows a broad substrate scope and good tolerance for various functional groups on the allene moiety, including carboxylic acid esters, free hydroxyls, imides, and alkyl groups. Also, a wide range of terminal alkynes with electron-donating and electron-withdrawing aryls, heteroaryls, alkyls, trimethylsilyl, and free hydroxyl groups are tolerated.
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| 2. |
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| 3. |
- Li, Man-Bo, et al.
(author)
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Diastereoselective Cyclobutenol Synthesis : A Heterogeneous Palladium-Catalyzed Oxidative Carbocyclization-Borylation of Enallenols
- 2019
-
In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 25:1, s. 210-215
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Journal article (peer-reviewed)abstract
- A highly selective and efficient oxidative carbocyclization/borylation of enallenols catalyzed by palladium immobilized on amino-functionalized siliceous mesocellular foam (Pd-AmP-MCF) was developed for diastereoselective cyclobutenol synthesis. The heterogeneous palladium catalyst can be recovered and recycled without any observed loss of activity or selectivity. The high diastereoselectivity of the reaction is proposed to originate from a directing effect of the enallenol hydroxyl group. Optically pure cyclobutenol synthesis was achieved by the heterogeneous strategy by using chiral enallenol obtained from kinetic resolution.
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| 4. |
- Posevins, Daniels, et al.
(author)
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Highly Diastereoselective Palladium-Catalyzed Oxidative Carbocyclization of Enallenes Assisted by a Weakly Coordinating Hydroxyl Group
- 2018
-
In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 140:9, s. 3210-3214
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Journal article (peer-reviewed)abstract
- A highly diastereoselective palladium-catalyzed oxidative carbocyclization-borylation of enallenes assisted by a weakly coordinating hydroxyl group was developed. The reaction afforded functionalized cyclo-hexenol derivatives, in which the 1,3-relative stereo chemistry is controlled (d.r. > 50:1). Other weakly coordinating oxygen-containing groups (ketone, alkoxide, acetate) also assisted the carbocyclization toward cyclo-hexenes. The reaction proceeds via a ligand exchange on Pd of the weakly coordinating group with a distant olefin group. The high diastereoselectivity of the hydroxyl directed reaction could be rationalized by a face-selective coordination of the distant olefin. It was demonstrated that the primary coordination of the close-by oxygen containing functionality was necessary for the reaction to occur and removal of this functionality shut down the reaction.
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| 5. |
- Posevins, Daniels, et al.
(author)
-
Highly Diastereoselective Palladium-Catalyzed Oxidative Cascade Carbonylative Carbocyclization of Enallenols
- 2020
-
In: Organic Letters. - : American Chemical Society (ACS). - 1523-7060 .- 1523-7052. ; 22:2, s. 417-421
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Journal article (peer-reviewed)abstract
- A palladium-catalyzed oxidative cascade carbonylative carbocyclization of enallenols was developed. Under mild reaction conditions, a range of cis-fused [5,5] bicyclic gamma-lactones and gamma-lactams with a 1,3-diene motif were obtained in good yields with high diastereoselectivity. The obtained lactone/lactam products are viable substrates for a stereoselective Diels-Alder reaction with N-phenylmaleimide, providing polycyclic compounds with increased molecular complexity.
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| 6. |
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| 7. |
- Qiu, Youai, et al.
(author)
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Highly selective olefin-assisted palladium-catalyzed oxidative carbocyclization via remote olefin insertion
- 2017
-
In: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 8:1, s. 616-620
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Journal article (peer-reviewed)abstract
- A highly selective olefin-assisted palladium-catalyzed oxidative carbocyclization via remote olefin insertion to afford cyclohexenes has been developed. It was shown that the assisting olefin moiety was indispensable for the formation of the cyclohexene product. Furthermore, preliminary studies on chiral anion-induced asymmetrical carbocyclization-borylation of enallenes have been carried out.
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| 8. |
- Qiu, Youai, et al.
(author)
-
Mechanistic Insight into Enantioselective Palladium-Catalyzed Oxidative Carbocyclization-Borylation of Enallenes
- 2018
-
In: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 24:10, s. 2433-2439
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Journal article (peer-reviewed)abstract
- The asymmetric palladium-catalyzed oxidative carbocyclization-borylation of enallenes, employing a chiral phosphoric acid as co-catalyst, constitutes an efficient and convenient entry into functionalized building blocks with cyclopentene scaffolds in high enantiopurity. Up till now there has been a lack of knowledge concerning the origin of enantioselectivity of this reaction as well as the absolute configuration of the product. Herein, we report the crystal structure of one of the compounds generated via this carbocyclization, providing the link between the configuration of the products and the configuration of the chiral phosphoric acid used in the reaction. Furthermore, the origin of the enantioselectivity is thoroughly investigated with density functional theory (DFT) calculations. By careful examination of different possible coordination modes, it is shown that the chiral phosphoric acid and the corresponding phosphate anion serve as ligands for palladium during the key stereoselectivity-determining cyclization step. In addition, we examine reactions wherein an extra chiral reagent, a p-benzoquinone containing a chiral sulfoxide, is used. The combined experimental and theoretical studies provide insight into the details of complexation of palladium with various species present in the reaction mixture, furnishing a general understanding of the factors governing the stereoselectivity of this and related catalytic reactions.
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| 9. |
- Qiu, Youai, et al.
(author)
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Palladium-Catalyzed Oxidative Carbocyclization–Borylation of Enallenes to Cyclobutenes
- 2016
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In: Angewandte Chemie International Edition. - : Wiley-VCH Verlagsgesellschaft. - 1433-7851 .- 1521-3773. ; 55:22, s. 6520-6524
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Journal article (peer-reviewed)abstract
- A highly efficient palladium-catalyzed oxidative borylation of enallenes was developed for the selective formation of cyclobutene derivatives and fully-substituted alkenylboron compounds. Cyclobutenes are formed as the exclusive products in MeOH in the presence of H2O and Et3N, whereas the use of AcOH leads to alkenylboron compounds. Both reactions showed a broad substrate scope and good tolerance for various functional groups, including carboxylic acid ester, free hydroxy, imide, and alkyl groups. Furthermore, transformations of the borylated products were conducted to show their potential applications.
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| 10. |
- Qiu, Youai, et al.
(author)
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Palladium-Catalyzed Oxidative Cascade Carbonylative Spirolactonization of Enallenols
- 2017
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In: Angewandte Chemie International Edition. - : Wiley-VCH Verlagsgesellschaft. - 1433-7851 .- 1521-3773. ; 56:12, s. 3221-3225
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Journal article (peer-reviewed)abstract
- A highly selective palladium-catalyzed oxidative carbonylation/carbocyclization/alkoxycarbonylation of enallenols to afford spirolactones bearing an all-carbon quaternary center was developed. This transformation involves the overall formation of three C-C bonds and one C-O bond through a cascade insertion of carbon monoxide (CO), an olefin, and CO. Preliminary experiments on chiral anion-induced enantioselective carbonylation/carbocyclization of enallenols afforded spirolactones with moderate enantioselectivity.
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| 11. |
- Qiu, Youai, et al.
(author)
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Selective Palladium-Catalyzed Allenic C-H Bond Oxidation for the Synthesis of [3]Dendralenes
- 2017
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In: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 56:42, s. 13112-13116
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Journal article (peer-reviewed)abstract
- A highly selective palladium-catalyzed allenic C-H bond oxidation was developed, and it provides a novel and straightforward synthesis of [3]dendralene derivatives. A variety of [3]dendralenes with diverse substitution patterns are accessible with good efficiency and high stereoselectivity. The reaction tolerates a broad substrate scope containing various functional groups on the allene moiety, including ketone, aldehyde, ester, and phenyl groups. Also, a wide range of olefins with both electron-donating and electron-withdrawing aryls, acrylate, sulfone, and phosphonate groups are tolerated.
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| 12. |
- Yang, Bin, et al.
(author)
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Control of Selectivity in Palladium(II)-Catalyzed Oxidative Transformations of Allenes
- 2018
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In: Accounts of Chemical Research. - : American Chemical Society (ACS). - 0001-4842 .- 1520-4898. ; 51:6, s. 1520-1531
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Research review (peer-reviewed)abstract
- Oxidation reactions play a central role in organic synthesis, and it is highly desirable that these reactions are mild and occur under catalytic conditions. In Nature, oxidation reactions occur under mild conditions via cascade processes, and furthermore, they often occur in an enantioselective manner with many of them involving molecular oxygen or hydrogen peroxide as the terminal oxidant. Inspired by the reactions in Nature, we have developed a number of Pd(II)-catalyzed cascade reactions under mild oxidative conditions. These reactions have an intrinsic advantage of step economy and rely on selectivity control in each step. In this Account, we will discuss the control of chemo-, regio-, and diastereoselectivity in Pd(II)-catalyzed dehydrogenative cascade coupling reactions. The enantioselective version of this methodology has also been addressed, and new chiral centers have been introduced using a catalytic amount of a chiral phosphoric acid (CPA). Research on this topic has provided access to important compounds attractive for synthetic and pharmaceutical chemists. These compounds include carbocyclic, heterocyclic, and polycyclic systems, as well as polyunsaturated open-chain structures. Reactions leading to these compounds are initiated by coordination of an allene and an unsaturated pi-bond moiety, such as olefin, alkyne, or another allene, to the Pd(II) center, followed by allene attack involving a C(sp(3))-H cleavage under mild reaction conditions. Recent progress within our research group has shown that weakly coordinating groups (e.g., hydroxyl, alkoxide, or ketone) could also initiate the allene attack on Pd(II), which is essential for the oxidative carbocyclization. Furthermore, a highly selective palladium-catalyzed allenic C(sp(3))-H bond oxidation of allenes in the absence of an assisting group was developed, which provides a novel and straightforward synthesis of [3]dendralene derivatives. For the oxidative systems, benzoquinone (BQ) and its derivatives are commonly used as oxidants or catalytic co-oxidants (electron transfer mediators, ETMs) together with molecular oxygen. A variety of transformations including carbocyclization, acetoxylation, arylation, carbonylation, borylation, beta-hydride elimination, alkynylation, alkoxylation, and olefination have been demonstrated to be compatible with this Pd(II)-based catalytic oxidative system. Recently, several challenging synthetic targets, such as cyclobutenes, seven-membered ring carbocycles, spirocyclic derivatives, functional cyclohexenes, and chiral cyclopentenone derivatives were obtained with high selectivity using these methods. The mechanisms of the reactions were mainly studied by kinetic isotope effects (KIEs) or DFT computations, which showed that in most cases the C(sp(3))-H cleavage is the rate-determining step (RDS) or partially RDS. This Account will describe our efforts toward the development of highly selective and atom-economic palladium(II)-catalyzed oxidative transformation of allenes (including enallenes, dienallenes, bisallenes, allenynes, simple allenes, and allenols) with a focus on overcoming the selectivity problem during the reactions.
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| 13. |
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| 14. |
- Yang, Bin, et al.
(author)
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Enzyme- and Ruthenium-Catalyzed Enantioselective Transformation of alpha-Allenic Alcohols into 2,3-Dihydrofurans
- 2016
-
In: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 55:18, s. 5568-5572
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Journal article (peer-reviewed)abstract
- An efficient one-pot method for the enzyme- and ruthenium-catalyzed enantioselective transformation of alpha-allenic alcohols into 2,3-dihydrofurans has been developed. The method involves an enzymatic kinetic resolution and a subsequent ruthenium-catalyzed cycloisomerization, which provides 2,3-dihydrofurans with excellent enantioselectivity (up to >99%ee). A ruthenium carbene species was proposed as a key intermediate in the cycloisomerization.
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| 15. |
- Zhu, Can, et al.
(author)
-
Highly Selective Construction of Seven-Membered Carbocycles by Olefin-Assisted Palladium-Catalyzed Oxidative Carbocyclization-Alkoxycarbonylation of Bisallenes
- 2016
-
In: Angewandte Chemie International Edition. - : Wiley-VCH Verlagsgesellschaft. - 1433-7851 .- 1521-3773. ; 55:46, s. 14405-14408
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Journal article (peer-reviewed)abstract
- An olefin-assisted palladium-catalyzed oxidative carbocyclization-alkoxycarbonylation of bisallenes to afford seven-membered carbocycles has been established. This dehydrogenative coupling reaction showed excellent substrate scope and functional group compatibility. The reaction exhibited high chemo-and regioselectivity, and ester 3 was the only product obtained. The olefin unit has been proven to be indispensable during the reaction. Moreover, intramolecular oxidative coupling suggests that the reaction proceeds via a (pallyl)palladium intermediate.
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| 16. |
- Zhu, Can, et al.
(author)
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Highly Selective Palladium-Catalyzed Hydroborylative Carbocyclization of Bisallenes to Seven-Membered Rings
- 2018
-
In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 140:43, s. 14324-14333
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Journal article (peer-reviewed)abstract
- A highly selective palladium-catalyzed hydroborylative carbocyclization of bisallenes to afford seven-membered rings has been established. This ring-closing coupling reaction showed good functional group compatibility with high chemo- and regioselectivity, as seven-membered ring 3 was the only product obtained. The extensive use of different linkers, including nitrogen, oxygen, malononitrile, and malonate, showed a broad substrate scope for this approach. A one-pot cascade reaction was realized by trapping the primary allylboron compound with an aldehyde, affording a diastereomerically pure alcohol and a quaternary carbon center by formation of a new C-C bond. A comprehensive mechanistic DFT investigation is also presented. The calculations suggest that the reaction proceeds via a concerted hydropalladation pathway from a Pd(0)-olefin complex rather than via a pathway involving a defined palladium hydride species. The reaction was significantly accelerated by the coordination of the pendant olefin, as well as the introduction of suitable substituents in the bridge, due to the Thorpe-Ingold effect.
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| 17. |
- Zhu, Can, et al.
(author)
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Olefin-Directed Palladium-Catalyzed Regio- and Stereoselective Hydroboration of Allenes
- 2016
-
In: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 22:9, s. 2939-2943
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Journal article (peer-reviewed)abstract
- An olefin-directed palladium-catalyzed regio- and stereoselective hydroboration of allenes has been developed to afford fully substituted alkenylboron compounds. The reaction showed a broad substrate scope: a number of functionalized allenes, including 2,3-dienoate, 3,4-dienoate, 3,4-dienol, 1,2-allenylphosphonate, and alkyl-substituted allenes, could be used in this olefin-directed allene hydroboration. The olefin unit was proven to be an indispensable element for this transformation.
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