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411.
Prof. Kazutaka Shibatomi 《Chemical record (New York, N.Y.)》2023,23(7):e202300061
This account summarizes our recent efforts in the enantioselective organocatalytic synthesis of chiral halogenated compounds. The enantioselective α-halogenation of aldehydes, decarboxylative chlorination of β-keto acids, and enantioselective C−C bond formation at the trifluoromethylated prochiral carbon to yield the corresponding organohalides with chlorinated, fluorinated, or trifluoromethylated chiral stereogenic centers are discussed. We applied common organocatalysts, such as Jørgensen-Hayashi catalyst and cinchona alkaloid-derivatived catalyst, and developed novel chiral amine catalysts for these reactions. This account also discusses stereospecific derivatizations of the resulting chiral halogenated compounds via nucleophilic substitution. Thus, we synthesized many novel chiral compounds that have not been reported, even as racemates. 相似文献
412.
Manuel Weh Dr. Asja A. Kroeger Dr. Kazutaka Shoyama Dr. Matthias Grüne Prof. Amir Karton Prof. Dr. Frank Würthner 《Angewandte Chemie (International ed. in English)》2023,62(19):e202301301
Enzymes actuate catalysis through a combination of transition state stabilization and ground state destabilization, inducing enantioselectivity through chiral binding sites. Here, we present a supramolecular model system which employs these basic principles to catalyze the enantiomerization of [5]helicene. Catalysis is hereby mediated not through a network of functional groups but through π-π catalysis exerted from the curved aromatic framework of a chiral perylene bisimide (PBI) cyclophane offering a binding pocket that is intricately complementary with the enantiomerization transition structure. Although transition state stabilization originates simply from dispersion and electrostatic interactions, enantiomerization kinetics are accelerated by a factor of ca. 700 at 295 K. Comparison with the meso-congener of the catalytically active cyclophane shows that upon configurational inversion in only one PBI moiety the catalytic effect is lost, highlighting the importance of precise transition structure recognition in supramolecular enzyme mimics. 相似文献
413.
Acridone units were incorporated into the arylene–ethynylene structure as polar arene units. Cyclic trimers consisting of three acridone-2,7-diyl units and three 1,3-phenylene units were synthesized by Sonogashira couplings via stepwise or direct route. X-ray analysis revealed that the trimer had a nearly planar macrocyclic framework with a cavity surrounded by three carbonyl groups. In contrast, the corresponding tetramer had a nonplanar macrocyclic framework. 1H NMR measurements showed that the trimer formed a 1 : 1 complex as a macrocyclic host with dihydric phenol guests, and the association constants were determined to be ca. 1.0×103 L mol−1 for hydroquinone or resorcinol guests in CDCl3 at 298 K. The calculated structures of these complexes by the DFT method supported the presence of two sets of OH⋅⋅⋅O=C hydrogen bonds between the host and guest molecules. The spectroscopic data of the cyclic trimers and tetramers are compared with those of reference acridone compounds. 相似文献
414.
The title organoboron complex undergoes dissociation of the intramolecular B–S coordination bond much faster than the corresponding mono ethylthiomethyl complex as revealed by the dynamic NMR study. The facile dissociation is attributable to an SN2-type mechanism, where the uncoordinated ligand assists the dissociation of the coordinated ligand in the transition state. This mechanism is supported by the initio calculations of a model reaction system. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:241–245, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20005 相似文献
415.