- Easy-handling and low-leaching heterogeneous palladium and platinum catalysts via coating with a silicone elastomer
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We have developed a practical protocol for coating of commercial Pd/Al2O3 and Pt/Al2O3 catalysts in micro-powders with a silicone elastomer. Compared to original catalysts, the treated catalysts are easier to weight and transfer, and they are easier to recover by simple filtration. More importantly, the metal leaching of treated catalysts was significantly reduced. The treated catalysts worked very well in diverse hydrogenation reactions.
- Zhou, Mi,Li, Tingting,Xu, Bo
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supporting information
p. 948 - 952
(2019/03/08)
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- Influence of norbornanone substituents on both the Wagner-Meerwein skeletal rearrangements under sulfonation conditions and the diastereoselectivity of the corresponding N,N′-bis-fumaroyl sultams in uncatalyzed Diels-Alder cycloadditions to cyclopenta-1,3-diene
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The Wagner-Meerwein domino rearrangement of norbornanone skeletons, under sulfonation conditions, is strongly influenced by the absence of a gem-dimethyl moiety at C(7). As a result, sulfonation at C(10) is less efficient due to a divergent pathway in the intermediate double bond formation and/or isomerization. Furthermore, the absence of such a gem-dimethyl moiety in the corresponding norbornane[10,2]sultam derivatives, sterically influences the orientation of the SO(1) and SO(2) substituents, hence on the π-facial steric shielding of the thermodynamically more stable anti-s-cis N-alkenoyl dienophiles. As a consequence, their diastereoselective [4+2] cycloadditions to cyclopenta-1,3-diene, under nonchelating conditions, are not as efficient due to a less pseudo axial SO(1) and the consequent loss of pseudo C 2-symmetry.
- Pia?tek, Anna,Chapuis, Christian
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p. 4247 - 4249
(2013/07/26)
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- A practical synthesis of optically active (R)-2-propyloctanoic acid: Therapeutic agent for Alzheimer's disease
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(R)-2-Propyloctanoic acid has been developed as a novel therapeutic agent for Alzheimer's disease. A large-scale synthesis of this candidate was achieved by using Oppolzer's camphorsultam as a chiral auxiliary under improved conditions. It was essential for the successful synthesis of this compound to utilize a new removal method for the chiral source with a combination of tetrabutylammonium hydroxide and hydrogen peroxide. The present process afforded the desired product in high yield with high optical purity.
- Hasegawa, Tomoyuki,Yamamoto, Hisashi
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p. 423 - 428
(2007/10/03)
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- Novel application of chiral micellar media to the Diels-Alder reaction
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A novel chiral surfactant has been used in the first reported aqueous chiral micellar catalysis of a Diels-Alder reaction and enantioselectivities have been observed.
- Diego-Castro, Michael J.,Hailes, Helen C.
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p. 1549 - 1550
(2007/10/03)
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- Application of the sulfonamide functional groups as an anchor for solid phase organic synthesis (SPOS)
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Sulfonyl chlorides have been found to readily couple to an amino functionalized resin. The resulting sulfonamide anchoring group is stable to a variety of reactions commonly used in SPOS. Acid induced cleavage is facile, affording functionalized sulfonamides in high yields.
- Beaver,Siegmund,Spear
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p. 1145 - 1148
(2007/10/03)
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- Methylenecyclopropanes, XI. - Asymmetric Nickel(0)-Catalyzed Cycloadditions of Methylenecyclopropanes with Chiral Derivatives of Acrylic Acid
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The nickel(0)-catalyzed codimerisation of methylenecyclopropane 1a or 2,2-dimethylmethylenecyclopropane (1b) with the chiral derivatives of acrylic acid 2a-2f leads to the optically active 3-methylenecyclopentanecarboxylic esters 3a, 3c-3f, 4a, and 4c, or amides 3b and 4b in good yields.The diastereomeric excess accesible depends on the steric demand of the chiral auxiliaries, de values up to 98percent can be achieved.Some improvements of the preparation of optically pure auxiliaries are also described.
- Binger, Paul,Brinkmann, Axel,Roefke, Petra,Schaefer, Bernd
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p. 739 - 750
(2007/10/02)
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- Camphor-Derived N-Acryloyl and N-Crotonoyl Sultams: Practical Activated Dienophiles in Asymmetric Diels-Alder Reactions
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Starting from (+)-camphor-10-sulfonyl chloride (5), the crystalline sultam 8 was easily prepared.Lewis-acid-promoted Diels-Alder additions of the crystalline N-acryloyl and N-crotonoyl derivatives 9 and 10, respectively, to cyclopentadiene and 1,3-butadiene at -130 to -78 grad furnished adducts 11, 12 and 17 with high chiral efficiency.Crystallization of the adducts and nondestructive removal of 8 gave either alcohols 13, 14 and 18 or acid 19 in 99percent enantiomeric purity.The sense of induction was reversed on using the enantiomer of 8 as the auxiliary.The structure of 10 was established by X-ray diffraction analysis
- Oppolzer, Wolfgang,Chapuis, Christian,Bernardinelli, Gerald
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p. 1397 - 1401
(2007/10/02)
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- Chemistry of Oxaziridines. 3. Asymmetric Oxidation of Organosulfur Compounds Using Chiral 2-Sulfonyloxaziridines
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Chiral 2-sulfonyloxaziridines, 9-12, afford the best enantioselectivity of any chiral oxidizing reagent for the asymmetric oxidation of sulfides and disulfides to sulfoxides and thiosulfinates, respectively, 5-8 times better than chiral peracids.For asymmetric oxidations using 9-12, the configuration of the oxaziridine three-membered ring was shown to control the configuration of the product, which could be predicted using a chiral recognition mechanism (Figure 2).The increased asymmetric bias exhibited by chiral 2-sulfonyloxaziridines was attrbuted to the fact that the active-site oxygen was incorporated into a rigid chiral environment.The group size difference (GSD) effect in both the oxaziridine and substrate play important roles in determining the absolute configuration of the product and the magnitude of the asymmetric bias.As the GSD increases the enantioselectivity increases.
- Davis, Franklin A.,Jenkins, Robert H.,Awad, Sami B.,Stringer, Orum D.,Watson, William H.,Galloy, Jean
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p. 5412 - 5418
(2007/10/02)
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