11 research outputs found

    The Role of Gold Acetylides as a Selectivity Trigger and the Importance of <i>gem</i>-Diaurated Species in the Gold-Catalyzed Hydroarylating-Aromatization of Arene-Diynes

    No full text
    Terminal 1,2-dialkynylarenes undergo an unexpected cyclization hydroarylation reaction toward naphthalene derivatives in benzene as the solvent. The regioselectivity of the reaction can be controlled by careful catalyst tuning. Also, the preparation of a bench-stable cationic amine complex or simple heterogenization of the catalyst on neutral aluminum oxide, which enables efficient catalyst recycling, was possible. Intensive mechanistic investigations were undertaken, giving new insights into the so-far underestimated role of acetylides in gold chemistry. The gold plays a fascinating dual role serving to both catalyze the reaction and activate the substrate by Au–C-σ bond formation. Evidence of <i>gem</i>-diaurated compounds playing an important part for gold catalysis is also reported

    Gold-Catalyzed [3,3]-Sigmatropic Rearrangement of <i>ortho</i>-Alkynyl‑<i>S</i>,<i>S</i>‑diarylsulfilimines

    No full text
    Highly functionalized 5H-pyrrolo[2,3-b]pyrazine cores, carrying a diaryl sulfide moiety at the C-7 position, were obtained from a gold-catalyzed reaction using easily accessible ortho-alkynyl-substituted S,S-diarylsulfilimines as intramolecular nitrene transfer reagents for the first time. The reaction proceeds under mild conditions, providing excellent yields while tolerating a large variety of different substitution patterns. We provide experimental evidence for an intramolecular reaction mechanism, likely including an unprecedented gold-catalyzed amino sulfonium [3,3]-sigmatropic rearrangement

    A Highly Diastereoselective Recognition Process as the Basis for the Resolution of Palladatricyclo[4.1.0.0<sup>2,4</sup>]heptanes

    No full text
    The synthesis of palladatricyclo­[4.1.0.0<sup>2,4</sup>]­heptane diastereomers by positional selective transesterification with (1<i>R</i>,2<i>S</i>,5<i>R</i>)-(−)-menthol is used for the resolution of these chiral organometallic compounds. The separation process of the two diastereomers is simplified by an unprecedented aggregation phenomenon. In a molecular recognition process the highly diastereoselective formation of dimers of strongly differing stability allows an efficient separation by normal column chromatography. The stereoselective dimerization was proven by IR and mass spectroscopic studies as well as <sup>1</sup>H NMR techniques and X-ray crystal structure analysis

    A Highly Diastereoselective Recognition Process as the Basis for the Resolution of Palladatricyclo[4.1.0.0<sup>2,4</sup>]heptanes

    No full text
    The synthesis of palladatricyclo­[4.1.0.0<sup>2,4</sup>]­heptane diastereomers by positional selective transesterification with (1<i>R</i>,2<i>S</i>,5<i>R</i>)-(−)-menthol is used for the resolution of these chiral organometallic compounds. The separation process of the two diastereomers is simplified by an unprecedented aggregation phenomenon. In a molecular recognition process the highly diastereoselective formation of dimers of strongly differing stability allows an efficient separation by normal column chromatography. The stereoselective dimerization was proven by IR and mass spectroscopic studies as well as <sup>1</sup>H NMR techniques and X-ray crystal structure analysis

    1,6-Carbene Transfer: Gold-Catalyzed Oxidative Diyne Cyclizations

    No full text
    In the presence of a gold catalyst an unprecedented oxidative cyclization of diynes takes place. The reaction cascade is initiated by an oxygen transfer from a <i>N</i>-oxide onto a gold-activated alkyne. The formed α-oxo carbene is transferred across the second alkyne yielding a stabilized vinyl carbene/cation. Alkyl migration or sp<sup>3</sup>-CH insertion then terminates the catalytic cycle by formation of highly substituted functionalized indenones. A 1,6-carbene shift could be supported by the oxidation of the vinyl carbene. This protocol represents an attractive alternative to procedures which are based on the metal-catalyzed decomposition of hazardous, not easily accessible, diazo compounds

    Dual Gold Catalysis: A Novel Synthesis of Bicyclic and Tricyclic Pyrroles from <i>N</i>‑Propargyl Ynamides

    No full text
    Various <i>N</i>-propargyl ynamides were converted to bicylic and tricyclic pyrroles by the use of a cationic dual-activation gold catalyst. This reaction starts with the nucleophilic addition of a gold acetylide onto an ynamide triple bond at the β-position of the nitrogen atom. Thus, gold vinylidene is formed, and then a second cyclization takes place. The formation of the gold vinylidene is indicated by the evidence that not only aryl ynamides but also alkyl ynamides undergo C–H activation in these reactions

    α‑Imino Gold Carbenes from 1,2,4-Oxadiazoles: Atom-Economical Access to Fully Substituted 4‑Aminoimidazoles

    No full text
    A novel and atom-economical synthesis of fully substituted 4-aminoimidazoles via gold-catalyzed selective [3 + 2] annulation of 1,2,4-oxadiazoles with ynamides is reported. This protocol represents a new strategy to access α-imino gold carbenes, which corresponds to an unprecedented intermolecular transfer of <i>N</i>-acylimino nitrenes to ynamides. Moreover, the reaction proceeds with 100% atom economy, exhibits good functional group tolerance, and can be conducted in gram scale

    Cyclopropanation/Carboboration Reactions of Enynes with B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>

    No full text
    Stoichiometric reaction of B­(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> with 1,6-enynes is shown to proceed via initial cyclopropanation and formal 1,1-carboboration. Depending on the substitution on the alkene moiety, subsequent ring-opening of the cyclopropane affords either cyclopentane or cyclohexane derivatives in which the C<sub>6</sub>F<sub>5</sub> and B­(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> adopt a 1,4-positioning. Mechanistically, this transformation involves π-activation of the alkyne moiety, which triggers cyclopropanation, followed by carboboration. Both the cyclopropanation and subsequent ring-opening are shown to be stereospecific. Both cyclopropanation and 1,4-carboborated products were employed as Lewis acid components in frustrated Lewis pair activation of H<sub>2</sub> and CO<sub>2</sub>

    Cyclopropanation/Carboboration Reactions of Enynes with B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>

    No full text
    Stoichiometric reaction of B­(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> with 1,6-enynes is shown to proceed via initial cyclopropanation and formal 1,1-carboboration. Depending on the substitution on the alkene moiety, subsequent ring-opening of the cyclopropane affords either cyclopentane or cyclohexane derivatives in which the C<sub>6</sub>F<sub>5</sub> and B­(C<sub>6</sub>F<sub>5</sub>)<sub>2</sub> adopt a 1,4-positioning. Mechanistically, this transformation involves π-activation of the alkyne moiety, which triggers cyclopropanation, followed by carboboration. Both the cyclopropanation and subsequent ring-opening are shown to be stereospecific. Both cyclopropanation and 1,4-carboborated products were employed as Lewis acid components in frustrated Lewis pair activation of H<sub>2</sub> and CO<sub>2</sub>
    corecore