Ultrafast Excited-State Intramolecular Proton Transfer of Aloesaponarin I

Time-resolved emission of aloesaponarin I was studied with the fluorescence up-conversion and time-correlated single-photon-counting techniques. The rates of the excited-state intramolecular proton transfer, of the solvent and molecular rearrangements, and of the decay from the excited proton-transferred species were determined and interpreted in the light of time-dependent density functional calculations. These results were discussed in conjunction with UV protection and singlet-oxygen quenching activity of aloe

Pd-Catalyzed Tandem sp²–sp³ Coupling Reactions of Chiral Stannolanes: An Efficient Preparation of Optically Active Tetrahydrobenz[<i>f</i>]isoindoles

A novel double Migita–Kosugi–Stille coupling reaction with dihydrostannolanes, which are readily available from a radical cascade reaction, was achieved with dihalobenzenes in the presence of a palladium catalyst. Use of unsymmetrical 1-bromo-2-iodobenzene derivatives accomplished the double coupling reaction which gave tetrahydrobenz[<i>f</i>]isoindoles in a regioselective manner

Pd-Catalyzed Tandem sp²–sp³ Coupling Reactions of Chiral Stannolanes: An Efficient Preparation of Optically Active Tetrahydrobenz[<i>f</i>]isoindoles

A novel double Migita–Kosugi–Stille coupling reaction with dihydrostannolanes, which are readily available from a radical cascade reaction, was achieved with dihalobenzenes in the presence of a palladium catalyst. Use of unsymmetrical 1-bromo-2-iodobenzene derivatives accomplished the double coupling reaction which gave tetrahydrobenz[<i>f</i>]isoindoles in a regioselective manner

Pd-Catalyzed Tandem sp²–sp³ Coupling Reactions of Chiral Stannolanes: An Efficient Preparation of Optically Active Tetrahydrobenz[<i>f</i>]isoindoles

A novel double Migita–Kosugi–Stille coupling reaction with dihydrostannolanes, which are readily available from a radical cascade reaction, was achieved with dihalobenzenes in the presence of a palladium catalyst. Use of unsymmetrical 1-bromo-2-iodobenzene derivatives accomplished the double coupling reaction which gave tetrahydrobenz[<i>f</i>]isoindoles in a regioselective manner

Syntheses and Molecular Structures of Monomeric and Hydrogen-Bonded Dimeric Dawson-Type Trialuminum-Substituted Polyoxotungstates Derived under Acidic and Basic Conditions

The syntheses and molecular structures of the two types of α-Dawson-type trialuminum-substituted polyoxometalates, [B-α-H₃P₂W₁₅O₅₉{Al­(OH₂)}₃]^6– (<b>1</b>) and [B-α-H₃P₂W₁₅O₅₉{Al­(OH)}₂{Al­(OH₂)}]₂^16– (<b>2</b>), are described herein. The potassium and cesium salts of <b>1</b>, K₆[B-α-H₃P₂W₁₅O₅₉{Al­(OH₂)}₃]·14H₂O (<b>K-1</b>), and Cs₆[B-α-H₃P₂W₁₅O₅₉{Al­(OH₂)}₃]·13H₂O (<b>Cs-1</b>) were formed by a stoichiometric reaction in water of trilacunary α-Dawson polyoxotungstate with aluminum nitrate under acidic conditions (pH ∼3). The potassium/sodium and tetramethylammonium/sodium salts of <b>2</b>, K₁₄Na₂[B-α-H₃P₂W₁₅O₅₉{Al­(OH)}₂{Al­(OH₂)}]₂·30H₂O (<b>KNa-2</b>) and [(CH₃)₄N]₁₄Na₂[B-α-H₃P₂W₁₅O₅₉{Al­(OH)}₂{Al­(OH₂)}]₂·39H₂O (<b>TMANa-2</b>) were obtained under basic conditions (pH ∼9). These compounds were characterized by X-ray structure analyses, elemental analyses, thermogravimetric/differential thermal analyses, Fourier transform infrared, and solution ³¹P, ²⁷Al, and ¹⁸³W NMR spectroscopy. The polyoxoanion <b>1</b> is a monomeric, α-Dawson-type structure, resulting in an overall <i>C</i>_3<i>v</i> symmetry, while the polyoxoanion <b>2</b> is a hydrogen-bonded dimeric structure, resulting in an overall <i>S</i>₃ symmetry in the solid state. The pH dependence of polyoxoanions <b>1</b> and <b>2</b> in aqueous solution was also investigated by ³¹P NMR spectroscopy

Gold(I)-Catalyzed Synthesis of Optically Active 1,4-Oxazepan-7-ones

Optically active seven-membered lactones, dimethyleneoxazepanones, were readily prepared in good yields from chiral β-(<i>N</i>-propargylic)­amino-α-methylene carboxylic acid <i>tert</i>-butyl esters in the presence of catalytic amounts of Ph₃PAuCl and Cu­(OTf)₂. A smooth 7-exo-dig cyclization was observed

Asymmetric Synthesis of Bicyclic Nitrocyclopropanes from Primary Nitro Compounds and Stereoselective Formation of Tetrahydro‑2<i>H</i>‑cyclopenta[<i>b</i>]furans via Ring Expansion/Cyclization Reaction

Optically active bicyclic nitrocyclopropanes are readily prepared from primary chiral nitro compounds, prepared by the conjugate addition of propionaldehyde to a nitro alkene in the presence of proline-derived organocatalysts. The one-step cyclopropanation took place smoothly in a highly stereoselective manner regardless of the stereogenic center adjacent to the allylic unit. Although the allylation reaction catalyzed by BF₃·OEt₂ provides a mixture of two possible diastereomers, subsequent oxidation of the alcoholic carbon after the formation of nitrocyclopropanes gave diastereomerically pure single products. As a result, separation of the diastereomers during the reaction sequence is unnecessary. Baeyer–Villiger oxidation of the bicyclic nitrocyclopropane ketones followed by enolization resulted in stereoselective formation of a novel cyclopenta­[<i>b</i>]­furan ring in good yield via ring expansion followed by transannular nucleophilic cyclization

Sphex sp.

Metalation of 6,13,20,21-tetrakis­(4-methylphenyl)-22<i>H</i>-tribenzo­[14]­triphyrin­(2.1.1) with PtCl₂ gave a platinum­(II) complex having a square-planar coordination structure with two pyrrolic nitrogen atoms and two chloride ions, with a saddle-shaped macrocycle. This platinum­(II) complex was easily oxidized by air to an octahedral platinum­(IV) complex coordinated by three pyrrolic nitrogen atoms as a tridentate monoanionic cyclic ligand and three chloride ions. When platinum­(II) triphyrin was crystallized in air, an oxygen atom was incorporated between two α-carbon atoms of the pyrroles as an oxygen bridge to intercept the 14π aromatic system

4,4′-Diarylsulfanyl-2,2′,5,5′-tetraoxybiaryl Derivatives as a Water-Soluble Fluorescent Dye

4,4′-Disulfanyl-2,2′,5,5′-tetrahydrobiaryl (5,5′-disulfanyl hydroquinone dimer) derivatives were readily synthesized from benzoquinone and thiols via an oxidative coupling reaction. The hydroquinone dimers showed strong fluorescence upon excitation at 330 nm, and it was observed that the presence of the sulfanyl groups at the C4 and C4′ positions is important for achieving strong photoluminescence. The tetrapotassium salts of the hydroquinone dimers also showed good water solubility, but the fluorescence disappeared rapidly on dissolution in water. 2,2′- and 5,5′-protected biaryls were synthesized. The dipotassium salt of the 5,5′-dimethoxy-2,2′-dihydroxy derivative was observed to show good and stable fluorescence in water, while the dipotassium salt of the 2,2′-dimethoxy-5,5′-dihydroxy derivative showed less water solubility. Introduction of propargyl groups was demonstrated to provide a convenient method for installing amino acids derivatives. This derivatization afforded potentially useful compounds for attaching the biologically active fragment to the fluorescent unit

A Radical Cascade Cyclization To Prepare Dihydrothiophenes Induced by Thiyl Radicals as Sulfur Biradical Equivalents

Bicyclic dihydrothiophenes are readily prepared by a radical cascade cyclization reaction triggered by the addition of a thiyl radical under thermal or photoirradiation conditions. The translocated radical attacks the sulfur atom in the initial radical donor unit in an S_Hi manner. Sufficient stereoselectivity is achieved when a large excess of disulfide is used for the reaction under photoirradiation conditions. The reaction in the absence of solvents provides vinylsulfides instead of dihydrothiophenes. Thus, the sulfur atom in the thiyl radical serves as a sulfur biradical synthetic equivalent