10 research outputs found

    Highly Enantioselective Synthesis of 3,4-Dihydropyrans through a Phosphine-Catalyzed [4+2] Annulation of Allenones and β,γ-Unsaturated α‑Keto Esters

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    A phosphine-catalyzed novel [4+2] annulation process was devised employing allene ketones as C<sub>2</sub> synthons and β,γ-unsaturated α-keto esters as C<sub>4</sub> synthons. In the presence of an l-threonine-derived bifunctional phosphine, 3,4-dihydro­pyrans were obtained in high yields and with virtually perfect enantio­selectivities. The synthetic value of the dihydro­pyran motif was demonstrated by a concise preparation of an anti-hyper­cholesterol­emic agent

    Bifuctional Amino-Squaramides Catalyzed Asymmetric Spiroannulation Cascades with Aliphatic β,γ-Unsaturated α-Keto Esters: Controlling an Aldehyde Enolate

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    A quinidine-derived squaramide <b>Ib</b> catalyzed cyclization reaction of β-oxo aldehydes <b>1</b> and aliphatic or aromatic β,γ-unsaturated α-keto ester <b>2</b> is described. Using cyclic aldehyde substrates, this procedure provided a promising approach to a variety of spiro-3,4-dihydropyrans bearing three continuous quaternary and tertiary stereocenters in moderate to good yield with high stereoselectivities. Substituents on the nitrogen atoms of the squaramide moiety of the catalyst proved crucial to the reaction outcome. The stereochemistry of the three newly formed chiral centers (<i>trans</i>-selective) of the major product indicates a Micheal addition/hemiacetalization domino sequence for the present annulations

    Phosphine-Catalyzed Enantioselective [4 + 2] Annulation of <i>o</i>‑Quinone Methides with Allene Ketones

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    A phosphine-catalyzed highly enantioselective [4 + 2] annulation between <i>ortho</i>-quinone methides and allene ketones has been developed. The reported method led to the formation of chromane derivatives in high yields and excellent enantioselectivity. This is the first time that <i>ortho</i>-quinone methides are employed in phosphine-mediated cyclization reactions

    Chiral Spirooxindole–Butenolide Synthesis through Asymmetric N‑Heterocyclic Carbene-Catalyzed Formal (3 + 2) Annulation of 3‑Bromoenals and Isatins

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    By using an N-heterocyclic carbene catalyst bearing a hydroxyl moiety, the asymmetric formal (3 + 2) cyclization of aryl 3-bromoenals and isatins was achieved to produce a series of chiral spirooxindole–butenolides including an alkenyl-substituted compound, which underwent benzannulations with benzynes to form intriguing spirocyclic scaffolds

    NHC-Catalyzed <i>O</i>‑Selective Addition of Nitrosoarenes with Aldehydes

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    An NHC-catalyzed <i>O</i>-selective addition of nitrosoarenes with aldehydes probably upon a dual-activation mode was developed, generating a variety of <i>O</i>-acyl hydroxylamines without any detectable competing amidation byproducts

    Three-Component Assembly of Conjugated Enyne Scaffolds via <i>E</i>-Selective Olefination of Ynals

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    Benefited by the accessible ynamido–lithium intermediates <b>Ib</b> from a Cu-catalyzed azide–alkyne cycloaddition in the presence of stoichiometric amounts of LiOH, a mild and flexible three-component route to conjugated enyne scaffolds was successfully achieved via a formal <i>E</i>-selective olefination strategy

    Divergent NHC-Catalyzed Oxidative Transformations of 3‑Bromoenal: Selective Synthesis of 2<i>H</i>‑Pyran-2-ones and Chiral Dihydropyranones

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    A selective synthesis of either 2<i>H</i>-pyran-2-ones (<b>4</b>) or chiral dihydropyranones (<b>6</b>) from the same substrates of 3-bromoenals and 1,3-dicarbonyl compounds upon oxidative <i>N</i>-heterocyclic carbene catalysis is presented. It is shown that the oxidative transformation of 3-bromoenals under NHC catalyst can be well controlled to proceed through two pathways, i.e., elimination of reducible β-bromide or by an external oxidant <b>3</b>, allowing the selective generation two sorts of unsaturated acyl azoliums, respectively

    Enantioselective [4 + 2]-Annulation of Oxadienes and Allenones Catalyzed by an Amino Acid Derived Phosphine: Synthesis of Functionalized Dihydropyrans

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    An enantioselective [4 + 2]-annulation process between cyano-activated oxadienes and allenones is developed. An l-valine-derived phosphine was efficient in catalyzing the reaction, and a wide range of highly functionalized dihydropyrans were prepared in high yields and with excellent enantioselectivities

    A Facile Approach for the Asymmetric Synthesis of Oxindoles with a 3‑Sulfenyl-Substituted Quaternary Stereocenter

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    With the employment of a threonine-incorporating multifunctional catalyst <b>9</b>, Michael addition of 3-sulfenyloxindoles to nitroolefins proceeded stereoselectively, leading to the formation of oxindoles with a 3-sulfenyl-substituted quaternary center in excellent yields, and with high diastereoselectivities and excellent enantioselectivities

    Construction of Enantioenriched Quaternary C–Cl Oxindoles through Palladium-Catalyzed Asymmetric Allylic Substitution with Chloroenolates

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    A palladium-catalyzed asymmetric chloroenolate allylation with vinyl benzoxazinanones under mild reaction conditions has been developed, affording a series of optically active 3,3-disubstituted oxindoles exhibiting a chloro-group and a linear aryl amino side chain in good yields with up to 96% ee. Versatile functional group tolerance on the benzene ring has been demonstrated, and the utility of this method was probed by a scale-up synthesis and highlighted by product derivatizations
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