The electrochemical behavior of Os(II) complexes with α,α′-bipyridine and o-phenanthroline in non-aqueous solvents

The electrode reactions of Os(II) complexes with α,α′-bipyridine and o-phenanthroline have been studied in non aqueous solvents. Tris bipyridine and tris phenanthroline complexes of Os(II) give one-step oxidation waves and three-step reduction waves, while bis bipyridine complexes of Os(II) containing py₂, en, CN₂, Cl₂ and Br₂ as mixed ligands give one-step oxidation waves and two-step reduction waves. Most of these waves correspond to reversible single electron transfers. It is noticed that the half-wave potentials or the peak potentials of bis bipyridine complexes are shifted to more negative direction than those of the tris complex in both oxidation and reduction processes. This is attributable to less electron with drawing nature of substituted ligands than bipyridine. These potential data, the shifts of E_1/2 or E_p from those of tris complexes, and δE*, the potential difference between two consecutive single electron waves, are discussed in terms of molecular orbital scheme.     

Hypotensive effects on spontaneously hypertensive rats and antifungal activity on various species of Fusarium oxysporum of diethylstilbestrol-related compounds

The diethylstilbestrol-related compounds 3,3'-dihydroxy-alpha, beta-diethyldiphenylethane (I), diethylstilbestrol (II) and hexestrol (III) showed hypotensive effects on spontaneously hypertensive rats (SHR) and antifungal activities against all Fusarium oxysporum sp. tested. As previously reported, I had strong hypotensive action on normotensive rats at the dose of 10 mg/kg, while II and III showed weak hypotensive effects on these rats at the same dose. In this work, all three compounds also had hypotensive actions on SHR at the same dose. I showed the strongest hypotensive effect (-80.0 +/- 5.0 mmHg, 10 mg/kg, i.v.) on both SHR and normotensive rats. The three compounds also had antifungal activities against five kinds of Fusarium oxysporum sp. tested. Especially, II strongly inhibited the growth of Fusarium oxysporum f. sp. raphani IFO-9972 (minimum inhibitory concentration (MIC): 1.0 micrograms/ml).     

Lewis Acid-Catalyzed Hydrostannation of Acetylenes. Regio- and Stereoselective Trans-Addition of Tributyltin Hydride and Dibutyltin Dihydride

Lewis acids such as ZrCl(4) or HfCl(4) catalyze the hydrostannation of acetylenes 1 by tributyltin hydride to produce the cis vinylstannanes 2 by regio- and stereoselective anti-hydrostannation. The hydrostannation of acetylenes using dibutyltin dihydride was also catalyzed by ZrCl(4) to give the stereodefined Z-Z divinyltin derivatives 4 by an anti-hydrostannation pathway. The use of nonpolar solvents such as toluene or hexane was essential for obtaining high stereoselectivity and chemical yield. Since ZrCl(4) and HfCl(4) are not soluble in such solvents, the hydrostannations were carried out in a heterogeneous system. The reactions of internal acetylenes with Bu(3)SnH proceeded smoothly, although the use of stoichiometric amounts of ZrCl(4) gave better results. The ZrCl(4)-catalyzed hydrostannation at 0 degrees C gave better yields and stereoselectivities than the reaction at room temperature. To help clalify the reason, the reaction of Bu(3)SnH with ZrCl(4) was monitored by (1)H and (119)Sn NMR spectroscopy, and it was found that Bu(3)SnH reacted with ZrCl(4) at room temperature to afford a mixture of tributyltin hydride, dibutyltin dihydride, and tetrabutyltin.     

One- or two-dimensional organometallic arrays containing PdIr2(μ3-S)2 mixed-metal sulfido cluster units connected via the nicotinamide or isonicotinamide ligands on their Pd sites through hydrogen-bonding interactions

Mixed-metal sulfido cluster [(PdCl₂)(Cp*Ir)₂(μ₃-S)₂] (Cp*=η⁵-C₅Me₅) dissolved in CH₂Cl₂ reacted with two equivalent of L (L=nicotinamide, isonicotinamide, or N-methylnicotinamide) in the presence of AgBF₄ to give the cationic clusters [(PdL₂)(Cp*Ir)₂(μ₃-S)₂][BF₄]₂. The single-crystal X-ray diffraction studies of these products have disclosed that in the solid state the PdIr₂S₂ cores are self-assembled to form one-dimensional chains through the intermolecular hydrogen-bonding between the amide groups for L=nicotinamide or two-dimensional sheets via the hydrogen-bonding between the amide groups and the BF₄ anions for L=isonicotinamide, whereas no organization of the cluster cores is observed for L=N-methylnicotinamide.     

An effective method to use ionic liquids as reaction media for asymmetric reduction by Geotrichum candidum

An effective method was developed to use an enzyme in ionic liquids; the asymmetric reduction of ketones by Geotrichum candidum in ionic liquids proceeded smoothly with excellent enantioselectivity when the cell was immobilized on water-absorbing polymer containing water, while the reaction without the polymer did not proceed.     

Concise synthesis of anti-HIV-1 active (+)-inophyllum B and (+)-calanolide A by application of (-)-quinine-catalyzed intramolecular oxo-Michael addition

(-)-Quinine-catalyzed intramolecular oxo-Michael addition (IMA) of 7-hydroxy-5-methoxy-8-tigloylcoumarins was developed for the enantioselective construction of 2,3-dimethyl-4-chromanone systems in the context of the asymmetric synthesis of anti-HIV-1 active Calophyllum coumarins. Combination of the IMA and MgI(2)-assisted demethylation of the 5-methoxy group along with isomerization of the formed chromanone systems as key steps successfully led to the concise synthesis of (+)-inophyllum B and (+)-calanolide A, possible candidates for AIDS drugs. Further examination of the asymmetric IMA with cinchona alkaloids lacking a methoxy group on the quinoline skeleton suggested the influence of the methoxy substituent on stereoselectivity at the stereogenic centers of the chromanone systems.