Novel Nanostructures of Rutile Fabricated by Templating against Yarns of Polystyrene Nanofibrils and Their Catalytic Applications

This Article describes a facile approach to the synthesis of rutile nanostructures in the form of porous fibers or bundles of nanotubes by maneuvering the surface wettability of yarns made of polystyrene nanofibrils. Specifically, hierarchically porous fibers were obtained by hydrolyzing titanium tetraisopropoxide to form TiO₂ nanoparticles in the void spaces among hydrophobic nanofibrils in each yarn. After calcination in air at 800 °C, the resultant fibers were comprised of many interconnected rutile nanoparticles whose diameters were in the range 20–80 nm. After converting the nanofibrils and yarns into hydrophilic surfaces through plasma treatment, however, the TiO₂ formed conformal coatings on the surfaces of nanofibrils in each yarn during hydrolysis instead of just filling the void spaces among the nanofibrils. As a result, bundles of rutile nanotubes were obtained after the sample had been calcined in air at 800 °C. The thermodynamically stable rutile nanostructures were then explored as supports for Pt nanoparticles whose catalytic activity was evaluated using the reduction of <i>p</i>-nitrophenol by NaBH₄. The Pt supported on porous rutile fibers exhibited a better performance than the Pt on rutile nanotubes in terms of both induction time (<i>t</i>_ind) and apparent rate constant (<i>k</i>_app)

Total Synthesis of Maoecrystal V: Early-Stage C–H Functionalization and Lactone Assembly by Radical Cyclization

A total synthesis of the unusual <i>ent</i>-kaurane maoecrystal V is described. The synthesis strategy features a counterintuitive early disconnection of the lactone subunit to a polycyclic enol ether intermediate in order to preserve the central tetrahydrofuran ring until the beginning stages of the synthesis. This strategy enables an application of C–H functionalization at the early phase of the synthesis during the construction of a dihydrobenzofuran intermediate

Three-Component Reaction of Propargyl Amines, Sulfonyl Azides, and Alkynes: One-Pot Synthesis of Tetrasubstituted Imidazoles

An efficient and straightforward strategy for the synthesis of tetrasubstituted imidazoles from propargyl amines, sulfonyl azides, and terminal alkynes is described. <i>N</i>-Sulfonyl ketenimine and aminoallene are believed to be the key intermediates for this two-step one-pot transformation

Divergent Functionalization of Indoles with Acryloyl Silanes via Rhodium-Catalyzed C–H Activation

A protocol enabled by rhodium-catalyzed C–H functionalization of indoles with acryloyl silanes was developed, providing a convenient and highly effective method for the synthesis of functionalized acylsilane derivatives. By tuning the reaction condition, this C–H-activation-initiated reaction proceeds divergently with acryloyl silianes to selectively afford alkylation or alkenylation products via hydroarylation or oxidative cross-coupling, respectively. The mild reaction conditions employed in both cases enable the tolerance of a wide scope of functionalities as well as high reaction efficiency. Furthermore, polycyclic indole derivatives were easily accessed from 2-alkenylation products through a visible-light-induced reaction cascade

Toward the Synthesis of <i>Nuphar</i> Sesquiterpene Thioalkaloids: Stereodivergent Rhodium-Catalyzed Synthesis of the Thiolane Subunit

A stereodivergent approach to the central thiolane subunit of <i>Nuphar</i> sesquiterpene thioalkaloids has been developed. This approach features a rhodium-catalyzed Stevens-type rearrangement in conjunction with an enzyme resolution reaction. Further elaboration into a polycyclic ring system via alcohol oxidation and ring-closing metathesis is also described

A Sinter-Resistant Catalytic System Fabricated by Maneuvering the Selectivity of SiO₂ Deposition onto the TiO₂ Surface versus the Pt Nanoparticle Surface

A triphasic catalytic system (Pt/TiO₂–SiO₂) with an “islands in the sea” configuration was fabricated by controlling the selectivity of SiO₂ deposition onto the surface of TiO₂ versus the surface of Pt nanoparticles. The Pt surface was exposed, while the nanoparticles were supported on TiO₂ and isolated from each other by SiO₂ to achieve both significantly improved sinter resistance up to 700 °C and outstanding activity after high-temperature calcination. This work not only demonstrates the feasibility of using a new triphasic system with uncovered catalyst to maximize the thermal stability and catalytic activity but also offers a general approach to the synthesis of high-performance catalytic systems with tunable compositions

Visible-Light-Mediated Nucleophilic Addition of an α‑Aminoalkyl Radical to Isocyanate or Isothiocyanate

A visible-light photoredox synthesis of α-amino amide or α-amino thioamide from <i>N</i>,<i>N</i>-dimethylaniline derivatives and aryl isocyanate or aryl isothiocyanate was developed. Bis[2-(4,6-difluorophenyl)pyridinato-C²,N](picolinato)iridium(III) (FIrpic) was found to be the effective catalyst among six catalysts screened. The reaction involves generation of α-aminoalkyl radicals from tertiary amines, followed by radical addition to the electron-deficient carbon of isocyanate and isothiocyanate

Copper-Catalyzed Cascade Double C3-Indolations of 3‑Diazoindolin-2-imines with Indoles: Convenient Access to 3,3-Diaryl-2-iminoindoles

Symmetrical 3,3-diaryl-2-iminoindoles were prepared from 3-diazoindolin-2-imines and indoles via a copper-catalyzed cascade arylation/dehydrogenative cross-coupling process. By controlling the molar ratio of reactants and the operation procedure, 3-aryl-2-aminoindoles and asymmetrical 3,3-diaryl-2-iminoindoles could be approached

BF₃‑Promoted Divergent Reactions between Tryptophols and Propargylic Alcohols

Trifluoroboron-promoted cascade reactions between tryptophols and propagylic alcohols furnished three types of skeletons, including carbazoles, cyclopenta­[<i>b</i>]­furo­[2,3-<i>b</i>]­indoles, and allenyl furo­[2,3-<i>b</i>]­indoles, with excellent selectivity based on the substrate structure. Tryptophols without a substituent on the 2-position of the indole ring reacted with 1,1,3-triphenylprop-2-yn-1-ol and 9-(phenylethynyl)-9<i>H</i>-fluoren-9-ol to give carbazoles and cyclopenta­[b]­furo­[2,3-<i>b</i>]­indoles, respectively, while the reaction of 2-substituted tryptophols afforded allenylfuro­[2,3-<i>b</i>]­indoles

Preparation of 3‑Aryl-2-aminoindoles via Rhodium-Catalyzed Coupling Reaction between 2‑Arylpyridines and 3‑Diazoindolin-2-imines

Rhodium-catalyzed coupling reaction of 3-diazo­indolin-2-imines with 2-aryl­pyridines, 2-phenyl­pyrimidines, or 1-phenyl­pyrazoles furnished the corresponding 3-aryl-2-amino­indoles in moderate to excellent yields. A variety of functional groups were tolerant to the reaction conditions