Synthesis and structural properties of para-diselenopyrazines.

Recently, dithienopyrazines have emerged as promising building blocks in the field of materials science, showcasing their potential as hole-transport materials in organic electronic devices. Herein, we report the synthesis of its heavier analogues, the diselenopyrazines, along with an analysis of their optoelectronic and structural properties. In the acquired crystal structures, interesting molecular packing motifs suitable for potential device fabrication were observed. Additionally, short contact interactions are present in one of the investigated molecules.

Gold-Catalyzed Formal [4+2] Cycloaddition as Access to Antitumor-Active Spirocyclic Oxindoles from Alkynes and Isatin-Derived Ketimines.

Due to its excellent bioactivity profile, which is increasingly utilized in pharmaceutical and synthetic chemistry, spirooxindole is an important core scaffold. We herein describe an efficient method for the construction of highly functionalized new spirooxindolocarbamates via a gold-catalyzed cycloaddition reaction of terminal alkynes or ynamides with isatin-derived ketimines. This protocol has a good functional group compatibility, uses readily available starting materials, mild reaction conditions, low catalyst loadings and no additives. It enables the transformation of various functionalized alkyne groups into cyclic carbamates. Gram-scale synthesis was achieved and DFT calculations verify the feasibility of the mechanistic proposal. Some of the target products exhibit good to excellent antiproliferative activity on human tumor cell lines. In addition, one of the most active compounds displayed a remarkable selectivity towards tumor cells over normal ones.

Synthesis of Amide Enol 2-Iodobenzoates by the Regio- and Stereoselective Gold-Catalyzed Acyloxyalkynylation of Ynamides with Hypervalent Iodine Reagents.

Multisubstituted alkenes are accessible by a gold-catalyzed acyloxyalkynylation of ynamides with ethynylbenziodoxolones (EBXs) with perfect atom-economy. The EBX reagents transfer both the carboxylate as well as the alkynyl entity. Overall, this cascade comprises the in situ generation of an alkynyl gold(III) species, a stereoselective C(sp)-C(sp2) bond formation, and a C-O coupling at the alkynyl position of the ynamides. This reaction proceeds under mild conditions and accepts a wide range of substrates. A number of tetrasubstituted amide enol 2-iodobenzoates bearing different functional groups were obtained in good to excellent yields. DFT calculations explain the observed regioselectivity. The synthetic potential of the reaction was further demonstrated by a number of selected follow-up transformations.

Synthesis of α-Ketoamides via Gold(I) Carbene Intermediates.

α-Ketoamides have been found to be an important functional group in a broad spectrum of inhibitors such as the Corona virus and other viruses. Here we report an unprecedented gold-catalyzed 2-fold reaction of a bromoalkyne with anthranils. Hydrolysis of the initial product then directly leads to α-ketoamides. Water addition to the intermediate α-iminoimidoyl halides delivered α-ketoamides from a broad range of bromoalkynes.

Modular Two-Step Access to π-Extended Naphthyridine Systems-Potent Building Blocks for Organic Electronics.

Efficient synthetic approaches for the incorporation of nitrogen into polyaromatic compounds (PACs) in different patterns as stabilising moiety for π-extended systems and modification tool for optoelectronic properties remain a challenge until today. Herein, we developed a new versatile pathway to napthyridine-based PACs as non-symmetric and regioisomeric pendant to pyrazine-based PACs. A combination of a gold-catalysed synthesis of 2-aminoquinolines and the development of an in situ desulfonation and condensation of these precursors are the key steps of the protocol. The shape and type of attached functional groups of the PACs can be designed in a late stage of the overall synthetic procedure by the chosen anthranile and backbone of the ynamide introduced in the gold-catalysed step. Single-crystal X-ray diffraction and the investigation of electronic properties of the compounds show the influence of the attached substituents. All naphthyridine-based PACs show halochromic behaviour implying their use as highly sensitive proton sensor in non-protic solvents.

Au-Ag Bimetallic Catalysis: 3-Alkynyl Benzofurans from Phenols via Tandem C-H Alkynylation/Oxy-Alkynylation.

The development of new methodologies enabling a facile access to valuable heterocyclic frameworks still is an important subject of research. In this context, we describe a dual catalytic cycle merging C-H alkynylation of phenols and oxy-alkynylation of the newly introduced triple bond by using a unique redox property and the carbophilic π acidity of gold. Mechanistic studies support the participation of a bimetallic gold-silver species. The one-pot protocol offers a direct, simple, and regio-specific approach to 3-alkynyl benzofurans from readily available phenols. A broad range of substrates, including heterocycles, is transferred with excellent functional group tolerance. Thus, this methodology can be used for the late-stage incorporation of benzofurans.

Intermolecular Desymmetrizing Gold-Catalyzed Yne-Yne Reaction of Push-Pull Diarylalkynes.

Push-pull diaryl alkynes are dimerized in the presence of a cationic gold catalyst. The polarized structure of the applied starting materials enables the generation of a highly reactive vinyl cation intermediate in an intermolecular reaction. Trapping of the vinyl cation by a nucleophilic attack of the electron-poor aryl unit then leads to the selective formation of highly substituted naphthalenes in a single step and in complete atom economy.