- A new approach to promoting sluggish Diels-Alder reactions: Dihapto-coordination of the diene
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The cycloaddition between 1,3-cyclohexadiene and various enones and enals (methyl vinyl ketone, ethyl vinyl ketone, methacrolien) is accomplished at room temperature in yields ranging from 51 to 68% without the use of Lewis acids, high pressures, or microwave reactors. This normally sluggish cyclization is accomplished by precoordination of the diene to a π-basic molybdenum complex. The η2-bound metal is thought to promote a Michael reaction between the uncoordinated portion of the diene and the enone, and the resulting enolate then closes to form the cycloalkene product. The organic cycloadduct is removed by oxidation with air or with silver triflate in nearly quantitative yield. For more sterically hindered enones (e.g., mesityl oxide) and for methyl acrylate, the desired outcome requires the use of BF3·OEt2, and yields are significantly lower (15-35%) Copyright
- Liu, Weijun,You, Fei,Mocella, Christopher J.,Harman, W. Dean
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- A Bidentate Iodine(III)-Based Halogen-Bond Donor as a Powerful Organocatalyst**
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In contrast to iodine(I)-based halogen bond donors, iodine(III)-derived ones have only been used as Lewis acidic organocatalysts in a handful of examples, and in all cases they acted in a monodentate fashion. Herein, we report the first application of a bidentate bis(iodolium) salt as organocatalyst in a Michael and a nitro-Michael addition reaction as well as in a Diels–Alder reaction that had not been activated by noncovalent organocatalysts before. In all cases, the performance of this bidentate XB donor distinctly surpassed the one of arguably the currently strongest iodine(I)-based organocatalyst. Bidentate coordination to the substrate was corroborated by a structural analysis and by DFT calculations of the transition states. Overall, the catalytic activity of the bis(iodolium) system approaches that of strong Lewis acids like BF3.
- Heinen, Flemming,Reinhard, Dominik L.,Engelage, Elric,Huber, Stefan M.
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- An FT-IR study on Diels-Alder reactions catalysed by heteropoly acid containing sol-gel silica
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Following the general trend of using heterogeneous catalysts whenever possible, the replacement of traditional homogeneous Lewis acid catalysts for the Diels-Alder reaction is currently considered in the literature. In this contribution, we report the suc
- Kukovecz,Kónya,Kiricsi
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- N-Heterocyclic Iod(az)olium Salts – Potent Halogen-Bond Donors in Organocatalysis
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This article describes the application of N-heterocyclic iod(az)olium salts (NHISs) as highly reactive organocatalysts. A variety of mono- and dicationic NHISs are described and utilized as potent XB-donors in halogen-bond catalysis. They were benchmarked in seven diverse test reactions in which the activation of carbon- and metal-chloride bonds as well as carbonyl and nitro groups was achieved. N-methylated dicationic NHISs rendered the highest reactivity in all investigated catalytic applications with reactivities even higher than all previously described monodentate XB-donors based on iodine(I) and (III) and the strong Lewis acid BF3.
- Boelke, Andreas,Kuczmera, Thomas J.,Lork, Enno,Nachtsheim, Boris J.
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supporting information
p. 13128 - 13134
(2021/08/09)
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- BTK INHIBITORS
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Provided are Bruton's Tyrosine Kinase (Btk) inhibitor compounds according to Formula I, or pharmaceutically acceptable salts thereof, or pharmaceutical compositions comprising these compounds and their use in therapy. In particular, provided is the use of Btk inhibitor compounds of Formula I in the treatment of Btk mediated disorders.
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Page/Page column 143; 144
(2016/07/27)
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- COMPOUNDS USEFUL AS MODULATORS OF TRPM8
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The present invention includes compounds useful as modulators of TRPM8, such as compounds of Formulae (Ia), (Ib) and (Ic), and the subgenus and species thereof; personal products containing those compounds; and the use of those compounds and the personal products, particularly the use of increasing or inducing chemesthetic sensations, such as cooling or cold sensations.
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Paragraph 0578
(2016/03/29)
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- Intramolecularly Sulfur-Stabilized Silicon Cations with Chiral Binaphthyl Backbones: Synthesis of Three Different Motifs and Their Application in Enantioselective Diels-Alder Reactions
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The formation and 29Si NMR spectroscopic characterization of silicon cations that are intramolecularly stabilized by a dialkyl thioether are described. The chemical stability of the silicon-sulfur Lewis pair and, hence, the viability of the approach, were probed with a 2-[(alkylthio)methyl]phenyl-substituted hydrosilane as a proxy before three different motifs with chiral binaphthyl backbones were prepared in multistep sequences. The degree of shielding of the silicon atom in these cations was found to depend on the substitution pattern at the silicon atom and the ring size generated by the silicon-sulfur interaction. These sulfur-stabilized silicon cations are sufficiently reactive to promote Diels-Alder reactions of cyclohexa-1,3-diene with various dienophiles; the same set of reactions with cyclopentadiene is also reported. One of the three chiral Lewis acids induces low, but promising, enantioselectivity, and 24% ee is the highest value so far obtained with a cationic tetracoordinate silicon catalyst.
- Rohde, Volker H. G.,Müller, Maria F.,Oestreich, Martin
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p. 3358 - 3373
(2016/01/15)
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- Monomeric metal aqua complexes in the interlayer space of montmorillonites as strong Lewis acid catalysts for heterogeneous carbon-carbon bond-forming reactions
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Montmorillonite-enwrapped copper and scandium catalysts (Cu2-- and Sc3+-monts) were easily prepared by treating Na--mont with the aqueous solution of the copper nitrate and scandium triflate, respectively. The resulting Cu2+- and Sc3+-monts showed outstanding catalytic activities for a variety of carbon-carbon bond-forming reactions, such as the Michael reaction, the Sakurai-Hosomi allylation, and the Diels-Alder reaction, under solvent-free or aqueous conditions. The remarkable activity of the mont catalysts is attributable to the negatively charged silicate layers that are capable of stabilizing metal cations. Furthermore, these catalysts were reusable without any appreciable loss in activity and selectivity. The Cu2+-mont-catalyzed Michael reaction proceeds via a ternary complex in which both the 1,3-dicarbonyl compound and the enone are coordinated to a Lewis acid Cu2+ center.
- Kawabata, Tomonori,Kato, Masaki,Mizugaki, Tomoo,Ebitani, Kohki,Kaneda, Kiyotomi
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p. 288 - 297
(2007/10/03)
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- Homogeneous catalysis. Transition metal based lewis acid catalysts
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Transition metal based Lewis acids provide catalysts for the Diels-Alder and Mukaiyama reactions. These catalysts must possess an electron deficient axophilic metal center and a labile coordination position. Unlike traditional Lewis acids, those derived from transition metals can function in the presence of water and have well defined structures. It is shown how a normally electron rich ruthenium atom can be converted to a Lewis acid by incorporation of electron withdrawing ligands and ligands with hard donor atoms. This ruthenium complex, [Ru(salen)(NO)(H2O)]+, is an efficient catalyst for the Diels-Alder reaction, but in the Mukaiyama reaction, it tends to be reduced and thereby deactivated by the silyl enol ether. It is shown that the complex [TiCp*2(H2O)2]2+ (Cp* is pentamethylcyclopentadienyl) is an efficient catalyst for the Diels-Alder reaction even when water is present. Similarly, the triflato complexes [TiCp2(CF3 SO3)2] and [ZrCp2(CF3SO3)2] (Cp is cyclopentadienyl) are efficient catalysts for both the Diels-Alder and Mukaiyama reactions. All of these catalysts are effective at very low loadings of ≈ 1 mol%. Catalysis has been shown to occur via substrate-catalyst adducts and moreover these adducts are formed rapidly and reversibly as required for efficient catalysis.
- Hollis, T. Keith,Odenkirk, William,Robinson,Whelan, John,Bosnich
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p. 5415 - 5430
(2007/10/02)
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- On Baldwin's Kinetic Barrier Against 5-(Enol-endo)-exo-trigonal Closures: a Comparison of Ionic and Analogous Radical Reactions, and a New Synthesis of Cyclopentanones
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The kinetic barrier that impedes ionic 5-(enol-endo)-exo-trigonal closures does not play such a dominant role in the case of α-oxo radicals (17); these radicals cyclize directly to cyclopentanones in a process that constitutes a synthetic method for conve
- Clive, Derrick L. J.,Cheshire, David R.
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p. 1520 - 1523
(2007/10/02)
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