10 research outputs found

    Pd(II)/Brønsted Acid Catalyzed Enantioselective Allylic C–H Activation for the Synthesis of Spirocyclic Rings

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    A Pd­(II)/Brønsted acid catalyzed migratory ring expansion for the synthesis of indene derivatives possessing a stereogenic spirocyclic carbon center was developed. This transformation is believed to mechanistically proceed via enantioselective allylic C–H activation with concomitant semipinacol ring expansion to the nascent π-allylpalladium species. Enantioselectivities as high as 98% ee were attainable

    Phosphine Catalyst-Controlled Cycloaddition or Dienylation Reactions of Trifluoromethyl Aryl Ketones with Bis-Substituted Allenoates

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    A chemoselective phosphine-catalyzed cycloaddition or dienylation reaction between trifluoromethyl-substituted ketones and bis-substituted allenoates was described. Under the catalysis of triarylphosphine, the reaction gave a range of trifluoromethylated tetrahydrofurans with broad substrate tolerance and good to excellent stereoselectivity, while the use of trialkylphosphine switched the reaction pathway to furnish CF<sub>3</sub>-substituted dienyl tertiary alcohols chemoselectively. Moreover, a preliminary study on the asymmetric version of the reaction was also performed, which represents the first example of a phosphine-catalyzed asymmetric reaction between allenoates and carbonyl compounds

    FeCl<sub>3</sub>‑Promoted [3 + 2] Annulations of γ‑Butyrolactone Fused Cyclopropanes with Heterocumulenes

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    The [3 + 2] annulations of γ-butyrolactone fused donor–acceptor (D–A) cyclopropanes with aromatic isothiocyanates and dialkyl carbodiimides promoted by FeCl<sub>3</sub> is reported. A series of bicyclic/polycyclic γ-butyrolactone fused thioimidates and γ-butyrolactone fused amidines containing four contiguous stereogenic centers were obtained in excellent yields as single stereoisomers

    Lewis Acid-Catalyzed Annulations of Geminally Disubstituted Cyclopropanes with Aldehydes or 1,3,5-Triazinanes

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    Under the catalysis of simple Lewis acid catalysts, 2-(1-aroylcyclopropyl)malonates demonstrated unique reactivities in annulation reactions with aryl/alkyl aldehydes, paraformaldehyde, and 1,3,5-triazinanes. Three types of structurally diverse cyclic products that are otherwise not easy to obtain were generated in moderate to good yields and excellent diastereoselectivities. Possible reaction pathways leading to these products were proposed on the basis of the results of control experiments

    <i>cis</i>-2,3-Disubstituted Cyclopropane 1,1-Diesters in [3 + 2] Annulations with Aldehydes: Highly Diastereoselective Construction of Densely Substituted Tetrahydrofurans

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    A series of <i>cis</i>-2,3-disubstituted cyclopropane 1,1-diesters were examined in the AlCl<sub>3</sub>-promoted [3 + 2]-annulations with aldehydes. In this reaction, these <i>cis</i>-cyclopropanes displayed reactivities starkly different from their <i>trans</i> counterparts in terms of the high chemical yields (up to 98%) and provided the desired annulation products with excellent diastereomeric purity. This protocol provides a facile and highly stereoselective way to construct synthetically useful pentasubstituted tetrahydrofurans not easily accessible using other methods

    <i>cis</i>-2,3-Disubstituted Cyclopropane 1,1-Diesters in [3 + 2] Annulations with Aldehydes: Highly Diastereoselective Construction of Densely Substituted Tetrahydrofurans

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    A series of <i>cis</i>-2,3-disubstituted cyclopropane 1,1-diesters were examined in the AlCl<sub>3</sub>-promoted [3 + 2]-annulations with aldehydes. In this reaction, these <i>cis</i>-cyclopropanes displayed reactivities starkly different from their <i>trans</i> counterparts in terms of the high chemical yields (up to 98%) and provided the desired annulation products with excellent diastereomeric purity. This protocol provides a facile and highly stereoselective way to construct synthetically useful pentasubstituted tetrahydrofurans not easily accessible using other methods

    A Novel Lewis Acid Catalyzed [3 + 3]-Annulation Strategy for the Syntheses of Tetrahydro-β-Carbolines and Tetrahydroisoquinolines

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    A novel Lewis acid catalyzed [3 + 3]-annulation process for the efficient syntheses of both tetrahydro-β-carbolines and tetrahydroisoquinolines from readily available benzylic alcohols and aziridines was developed, which would be a highly valuable complement to the widely used Pictet–Spengler reaction. A probable mechanism was proposed based on the isolation and characterization of two key intermediates. This strategy enables facile access to important alkaloid frameworks not easily available with other known methods

    Lewis Acid Catalyzed Cascade Reaction to Carbazoles and Naphthalenes via Dehydrative [3 + 3]-Annulation

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    A novel Lewis acid catalyzed dehydrative [3 + 3]-annulation of readily available benzylic alcohols and propargylic alcohols was developed to give polysubstituted carbazoles and naphthalenes in moderate to good yields with water as the only byproduct. The reaction was presumed to proceed via a cascade process involving Friedel–Crafts-type allenylation, 1,5-hydride shift, 6π-eletrocyclization, and Wagner–Meerwein rearrangement

    Copper(I)-Catalyzed Kinetic Resolution of <i>N</i>‑Sulfonylaziridines with Indoles: Efficient Construction of Pyrroloindolines

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    The first Lewis acid catalyzed [3 + 2] annulation of indoles and 2-aryl-<i>N</i>-tosylaziridines was realized by using copper­(I)/chiral diphosphine complexes as a catalyst. With this method, a variety of uniquely substituted chiral pyrroloindolines bearing multiple contiguous stereogenic centers were facilely accessed in a straightforward, high-yielding, and highly stereoselective way under mild conditions

    Indolyl-based Copper(I) Complex-Catalyzed Intermolecular Trifluoromethylazolation of Alkenes via Radical Process

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    Herein, we synthesized and characterized a binuclear copper(I) complex supported by the indolyl-based ligand. Employing this complex as catalyst, we have developed a three-component intermolecular trifluoromethylazolation of alkenes to deliver various trifluoromethylated azole derivatives. The method features exclusive chemo- and regioselectivity, a broad scope of alkenes and oxazoles, thiazoles, and good tolerance of functional groups under mild conditions. Preliminary mechanistic studies support a radical process for the transformation
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