Convergent synthesis of polycyclic ethers via the intramolecular allylation of alpha-acetoxy ethers and subsequent ring-closing metathesis

The Lewis acid mediated reaction of alpha-acetoxy ethers 15-22 gave the corresponding cyclized products 23, 25, 27, 29, 31, 32, 34, and 36 in good yields with high stereoselectivities. Those cyclized products were subjected to ring-closing metathesis to afford the polycyclic ethers 38-42, 44, and 45 in good yields. The usefulness of the present methodology was demonstrated by the convergent synthesis of the CDEF ring system of brevetoxin B (1) and the CDEFG ring system of gambierol (2).     

Polycyclic pyridazines. II [3]. Synthesis of pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyrid-azine derivatives from dimethyl pyrazolo[3,4-d]pyrid-azine-5,6-dicarboxylates as the key intermediates

The synthesis of the novel pyrazolo[4′,3′:5,6]pyrido[2,3-d]pyridazine ring system and some of its derivatives has been accomplished such as 4-amino-1-phenyl-5,8-dioxo-, 4-amino-5,8-dioxo-, 1-phenyl-5,8-dioxo-, 5,8-dioxo-, 5,8-dichloro-1-phenyl-, 5-ethoxy-1-phenyl- and 8-ethoxy-1-phenylpyrazolo[4′,3′:5,6]pyrido[2,3-d]pyrid-azines.     

Effect of encaged aromatic guests on the shape and connectivity of molecular cavity in crystalline polystyrene evaluated by molecular simulations

The delta form of crystalline syndiotactic polystyrene is a clathrate molecular compound in which various aromatic molecules are encaged. We have investigated the size, shape, and connectivity of the molecular cavity in the crystal using a molecular dynamics simulation. The effects of the guest species on the cavity structure were investigated in detail. In order to systematically vary the guest structure, various aromatic guests, e.g., benzene, toluene, p-xylene, m-xylene, o and mesitylene were examined. The interstitial spaces between the guests and the polymer chains were analyzed by cluster analysis of the free volumes. The individual cavity volumes into which the guests are clathrated were also evaluated. It was found that the guest molecules can greatly affect not only the cavity size and shape but also the connectivity of the cavities. The transport of small molecules in the crystal is discussed in connection with the cavity structure.     

AuBr(3)-catalyzed [4 + 2] benzannulation between an enynal unit and enol

The reaction of enynals 1, including o-alkynylbenzaldehydes, and carbonyl compounds 2 in the presence of a catalytic amount of AuBr3 in 1,4-dioxane at 100 degrees C gave the functionalized aromatic compounds 3 in high yields. The AuBr3-catalyzed formal [4 + 2] benzannulation proceeds most probably through the coordination of the triple bond of 1 to AuBr3, the formation of a pyrylium auric ate complex via the nucleophilic addition of the carbonyl oxygen atom, the reverse electron demand-type Diels-Alder addition of the enols, derived from 2, to the auric ate complex, and subsequent dehydration and bond rearrangement. Similarly, the AuBr3-catalyzed reactions of 1 with acetal compounds afforded the corresponding aromatic compounds in good yields.     

Dicopper-dioxygen complex supported by asymmetric pentapyridine dinucleating ligand

A dicopper(I) complex supported by a novel asymmetric pentapyridine dinucleating ligand, consisting of tetradentate and tridentate metal-binding sites, has been synthesized and characterized. The dicopper(I) complex reacted with molecular oxygen at a low temperature to give an unprecedented mu-peroxo dicopper(II) complex presumably having a mu-eta1:eta2 binding mode, the spectroscopic features and the reactivity of which have been explored in detail.     

New sesquiterpenoids from the New Zealand liverwort Chiloscyphus subporosus

A new aromadendrane-type sesquiterpenoid, 4(15)-aromadendren-12,5alpha-olide and an aromadendrane-guaianolide dimer have been isolated from the New Zealand liverwort Chiloscyphus subporosus. Their structures were established by extensive NMR techniques and X-ray crystallographic analysis.     

Cu-mediated chemoselective trifluoromethylation of benzyl bromides using shelf-stable electrophilic trifluoromethylating reagents

Copper-mediated chemoselective trifluoromethylation at the benzylic position by the use of shelf-stable electrophilic trifluoromethylating reagents 3 in good to high yields under mild conditions is described for the first time. The generality of this trifluoromethylation for a wide variety of benzyl bromides facilitates the rapid creation of structural diversity of medicinal candidates in drug discovery.     

High-pressure hydrothermal crystal growth and multiferroic properties of a perovskite YMnO3

Orthorhombic perovskites RMnO(3) are representative of spin-driven ferroelectrics. When the radius of the rare-earth ion R is smaller than that of Dy, for instance in YMnO(3), the orthorhombic phase becomes metastable at ambient pressure, which impedes the crystal growth; thus, the detailed magnetic and multiferroic properties of the metastable phase have not been characterized. In this work, we successfully obtained single crystals of orthorhombic YMnO(3) using quasi-hydrothermal conditions under a high pressure of 5.5 GPa. Magnetic and dielectric measurements under magnetic fields revealed that the magnetic ground state is the commensurate E-type antiferromagnetic, while a cycloidal spin phase likely coexists in the intermediate temperature range, which enhances the magnetoelectric response to external fields.