Janina Bucher

Bio: Janina Bucher is an academic researcher from Heidelberg University. The author has contributed to research in topics: Alkyne & Allylic rearrangement. The author has an hindex of 10, co-authored 13 publications receiving 401 citations.

Cyclization of gold acetylides: synthesis of vinyl sulfonates via gold vinylidene complexes.

Abstract: Differently substituted terminal alkynes that bear sulfonate leaving groups at an appropriate distance were converted in the presence of a propynyl gold(I) precatalyst After initial formation of a gold acetylide, a cyclization takes place at the β-carbon atom of this species Mechanistic studies support a mechanism that is related to that of dual gold-catalyzed reactions, but for the new substrates, only one gold atom is needed for substrate activation After formation of a gold vinylidene complex, which forms a tight contact ion pair with the sulfonate leaving group, recombination of the two parts delivers vinyl sulfonates, which are valuable targets that can serve as precursors for cross-coupling reactions, for example

On the Gold-Catalyzed Generation of Vinyl Cations from 1,5-Diynes.

Abstract: Conjugated 1,5-diynes bearing two aromatic units at the alkyne termini were converted in the presence of a gold catalyst. Under mild conditions, aryl-substituted dibenzopentalenes were generated. Calculations predict that aurated vinyl cations are key intermediates of the reaction. A bidirectional approach provided selective access to the angular annulated product in high yield, which was explained by calculations.

CO extrusion in homogeneous gold catalysis: reactivity of gold acyl species generated through water addition to gold vinylidenes.

Abstract: Herein, we describe a new gold-catalyzed decarbonylative indene synthesis. Synergistic σ,π-activation of diyne substrates leads to gold vinylidene intermediates, which upon addition of water are transformed into gold acyl species, a type of organogold compound hitherto only scarcely reported. The latter are shown to undergo extrusion of CO, an elementary step completely unknown for homogeneous gold catalysis. By tuning the electronic and steric properties of the starting diyne systems, this new reactivity could be exploited for the synthesis of indene derivatives in high yields.

[3,3]‐Sigmatropic Rearrangement Step in the Gold‐Catalyzed Cyclization of Allyl‐(ortho‐alkinylphenyl)methyl Ethers

Abstract: The gold-catalyzed conversion of allyl-(ortho-alkynylphenyl)methyl ethers was investigated, and allylated isochromenes were obtained. An optimization of the catalysis conditions with respect to different phosphane and carbene ligands on gold, different counterions, and different solvents was conducted. Subsequently, the scope and limitations of this reaction were investigated with 21 substrates. The mechanistic studies show an allylic inversion, as supported by NMR data and an X-ray crystal structure analysis, as well as an intermolecular reaction, as determined by crossover experiments. There is no competition of protodeauration even in the presence of water. All these observations differ from other related conversions and clearly indicate product formation by a [3,3]sigmatropic rearrangement in the step forming the new C-C bond.

Cyclisierung von Goldacetyliden: Synthese von Vinylsulfonaten über Vinylidengold‐Komplexe

Abstract: Verschieden substituierte terminale Alkine mit Sulfonat-Abgangsgruppen in passender Entfernung wurden in Gegenwart von Propinylgold(I)-Prakatalysatoren umgesetzt. Nach der Bildung eines Goldacetylids findet eine Cyclisierung uber das β-Kohlenstoffatom des Goldacetylids statt. Der Mechanismus durfte ahnlich zu dem der dualen Goldkatalyse sein, aber im Fall der neuen Substrate wird nur ein Goldzentrum fur die Aktivierung des Substrates benotigt. Nach Bildung eines Vinylidengold-Komplexes, der ein enges Kontaktionenpaar mit der Sulfonat-Abgangsgruppe bildet, liefert eine Rekombination der beiden Teile Vinylsulfonate, die wertvolle Zielverbindungen sind und z. B. als Vorstufen in Kreuzkupplungen fungieren konnen.

Dual gold catalysis.

Abstract: For more than a decade the innovative field of homogeneous catalysis by gold was dominated by the interaction of the substrate molecule with one gold center, in most cases in mononuclear gold complexes. The initial interaction was typically a π-coordination of a carbon–carbon double bond to the gold, an activation of the unsaturated substrate molecule by a π-acidic metal center. Only recently clear evidence for reactions that involve the activation of organic substrates by two gold centers was obtained. In that new class of gold-catalyzed reactions the two gold centers interact with the substrate in a very different way. One gold complex is σ-bonded to a terminal alkynyl group in the substrate, the other one is π-coordinated. Only in a few cases, a combination π-coordination and σ-coordination to the same alkyne, which is the energetically preferred mode of interaction with two gold centers, initiates the reaction. In most of the cases, the reaction proceeds through an intermediate with one alkyne σ-bonde...

Gold-catalysed reactions of diynes

Abstract: In this critical review the reactivity patterns observed with different types of diyne substrates in gold catalysis are discussed. Apart from the many examples from homogeneous catalysis, the few examples from heterogeneous gold catalysis are also included. With a proper arrangement of the two alkynes unique and exciting reactivity patterns like 1,3-carbonyl transpositions, carbene transfer reactions, cascade annulations, macrocyclisations or the formation of gold vinylidene intermediates are observed. These reactions are of interest for organic synthesis, for pharmaceutical and medicinal chemistry and for material science.

Poly(dimethylsiloxane) Oil Absorbent with a Three-Dimensionally Interconnected Porous Structure and Swellable Skeleton

Abstract: Cleanup of oil spills is a worldwide challenge to prevent serious environmental pollution. A new kind of poly(dimethylsiloxane) (PDMS) oil absorbent with high absorption capacity and excellent reusability was prepared and used for oil/water separation. The preparation process of PDMS oil absorbents involves direct curing of a PDMS prepolymer in a p-xylene solution in the presence of commercial sugar particles, which is simple and economic. PDMS oil absorbents have interconnected pores and a swellable skeleton, combining the advantages of porous materials and gels. Absorption capacities of PDMS oil absorbents are 4–34 g/g for various oils and organic solvents, which are 3 times that reported previously. Owing to their hydrophobicity and oleophilicity, the as-obtained PDMS oil absorbents can selectively collect oils or organic solvents from water. The absorption process can be finished within tens of seconds. Furthermore, the absorbed oils or organic solvents can be recovered by compressing the oil absorben...

Gold-Catalyzed Synthesis of Quinolines from Propargyl Silyl Ethers and Anthranils through the Umpolung of a Gold Carbene Carbon

Abstract: A gold-catalyzed cascade annulation of propargylic silyl ethers with anthranils proceeds through a sequential ring opening/1,2-H-shift/protodeauration/Mukaiyama aldol cyclization. This method offers a regiospecific and modular access to 2-aminoquinolines and other quinoline derivatives under mild conditions and with a broad functional-group tolerance. The conversion is possible on a gram scale, which underlines the synthetic practicability of this methodology. The versatility of the obtained scaffold has been demonstrated by useful postfunctionalization.

Reversal of Regioselectivity in Ynamide Chemistry

Abstract: Ynamides are special alkynes bearing an electron-withdrawing group on the nitrogen atom, and they have been extensively studied over the past decade. However, the addition of functional groups acro...