Hydrogen‐Bonding Catalysis of Alkyl‐Onium Salts

The synthetic utility of alkyl‐onium salt compounds is widely recognized in the field of organic chemistry. Among the wide variety of onium salts, quaternary ammonium, phosphonium, and tertiary sulfonium salts have been the most useful compounds in organic syntheses. These compounds have been very useful reagents in the construction of organic building blocks. In addition, onium salts are known as reliable catalysts, which are used to promote important organic transformations by serving as phase‐transfer and ion‐pair catalysts through the activation of nucleophiles. Although phase‐transfer catalysis is a major direction for onium salt catalysis, hydrogen‐bonding catalysis of alkyl‐onium salts, which is promoted via the activation of electrophiles, has recently become a relevant topic in the field of onium salt chemistry. This Minireview introduces new possibilities and future directions for alkyl‐onium salt chemistry based on its use in hydrogen‐bonding catalysis and on its overall utility.     

New lanostane triterpene lactones from the Vietnamese mushroom Ganoderma colossum (FR.) C. F. BAKER

Four new lanostane triterpene lactones (colossolactone I, colossolactone II, colossolactone III and colossolactone IV) were isolated from the Vietnamese mushroom Ganoderma colossum (FR.) C. F. BAKER along with five known compounds. The structures of the new compounds were determined on the basis of MS, NMR and circular dichroism.     

Bay-area selective thermal [4+2] and [4+4] cycloaddition reactions of triply linked ZnII diporphyrin with o-xylylene

A triply linked ZnII diporphyrin underwent site-selective cycloaddition reactions with thermally generated o-xylylene to provide a triply linked porphyrin-chlorin hybrid and a triply linked chlorin dimer in moderate yields. The former product is a symmetry-allowed [4+2] cycloadduct, while the latter is a symmetry-forbidden [4+4] cycloadduct. Oxidation of the latter product with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) provided a triply linked diporphyrin fused with a benzocyclooctatriene segment. This oxidized product and above [4+2] cycloadduct were structurally characterized by single crystal X-ray diffraction analysis. The observed site-selectivity is considered to arise from the large MO coefficients at the bay-area in the LUMO of the triply linked diporphyrin. The anomalous thermal [4+4] cycloaddition may be ascribed to the highly conjugated and quite perturbed electronic properties of triply linked ZnII diporphyrin.     

Magnetite 3D colloidal crystals formed in the early solar system 4.6 billion years ago

Three-dimensional colloidal crystals made of ferromagnetic particles, such as magnetite (Fe(3)O(4)), cannot be synthesized in principle because of the strong attractive magnetic interaction. However, we discovered colloidal crystals composed of polyhedral magnetite nanocrystallites of uniform size in the range of a few hundred nanometers in the Tagish Lake meteorite. Those colloidal crystals were formed 4.6 billion years ago and thus are much older than natural colloidal crystals on earth, such as opals, which formed about 100 million years ago. We found that the size of each individual magnetite particle determines its morphology, which in turn plays an important role in deciding the packing structure of the colloidal crystals. We also hypothesize that each particle has a flux-closed magnetic domain structure, which reduces the interparticle magnetic force significantly.     

Carbon‐bridged Oligo(phenylenevinylene)s as Light‐harvesting Antenna for Porphyrins

The efficacy of carbon‐bridged oligo(phenylenevinylenes)s (COPVs) as light‐harvesting antenna for porphyrins is demonstrated using a series of 5,15‐di‐COPVn‐substituted free‐base and zinc porphyrins, COPVn‐MP‐COPVn (n=1–3, M=H₂, Zn). These molecules were synthesized by Suzuki–Miyaura cross‐coupling reactions of COPVn‐Bpin and Br‐H₂P‐Br . The absorption spectra of these compounds in solution show a significant expansion of the Soret band region together with a bathochromic shift of the Q band, suggesting a significant interaction between these chromophores in the ground state. The photoluminescence quantum yield of the porphyrin‐COPV conjugates is enhanced up to four times relative to the parent porphyrins. Theoretical calculations also indicated interactions between these chromophores in the HOMO, which suggests that the light‐harvesting ability stems from the expansion of the π‐electron‐conjugation system.     

Stereoselective Preparation of 1-[5-O-(tert-Butyldimethylsilyl)-2,3-dideoxy-3-iodo-β-D-threo-pentofuranosyl]thymine from Thymidine: An Efficient Entry to 3′,4′-Unsaturated Nucleoside

The title compound (13) has been synthesized from 5′-O-TBS-thymidine (8) through a highly stereoselective iodination of the 3′-hydroxyl group utilizing I₂/PPh₃/imidazole. This method provides an efficient entry to the 3′,4′-unsaturated derivative (7).     

1‐Aryl‐4‐Silylmethyl[60]fullerenes: Synthesis,Properties, and Photovoltaic Performance

The efficient nucleophilic addition of aryl Grignard reagents (aryl=4‐MeOC₆H₄, 4‐Me₂NC₆H₄, Ph, 4‐CF₃C₆H₄, and thienyl) to C₆₀ in the presence of DMSO produced 1,2‐arylhydro[60]fullerenes after acid treatment. The reactions of the anions of these arylhydro[60]fullerenes with either dimethylphenylsilylmethyl iodide or dimethyl(2‐isopropoxyphenyl)silylmethyl iodide yielded the target compounds, 1‐aryl‐4‐silylmethyl[60]fullerenes. The properties and structures of these 1‐aryl‐4‐silylmethyl[60]fullerenes (aryl=4‐MeOC₆H₄, thienyl) were examined by electrochemical studies, X‐ray crystallography, flash‐photolysis time‐resolved microwave‐conductivity (FP‐TRMC) measurements, and electron‐mobility measurements by using a space‐charge‐limited current (SCLC) model. Organic photovoltaic devices with a polymer‐based bulk heterojunction structure and small‐molecule‐based p–n and p–i–n heterojunction configurations were fabricated by using 1‐aryl‐4‐silylmethyl[60]fullerenes as an electron acceptor. The most efficient device exhibited a power‐conversion efficiency of 3.4 % (short‐circuit current density: 8.1 mA/ cm², open‐circuit voltage: 0.69 V, fill factor: 0.59).     

Studies on the Thioglycosides of N-Acetylneuraminic Acid 1: Synthesis of Alkyl α-Glycosides of 2-Thio-N-Acetylneuraminic Acid

Methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-2-S-acetyl-3,5-di-deoxy-2-thio-D-glycero-α-D-galacto-2-nonulopyranosonate (2) was prepared via methyl 5-acetamTdo-4,7,8,9-tetra-O-acetyl-2-chloro-2,3,5-trideoxy-D-glycero-α-D-galacto-2-nonulopyranosonate (1) and was converted into the sodium salt (3). Condensation of 3 with n-alkyl bromides gave the corresponding methyl (alkyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-α-D-galacto-2-nonulo-pyranosid)onates, which were converted, via O-deacetylation and hydrolysis of the methyl ester group, into the title compounds.