Theoretical Study of the Cycloaddition Reaction of a Tungsten‐Containing Carbonyl Ylide

The [3+2] cycloaddition reaction of a tungsten‐containing carbonyl ylide with methyl vinyl ether and the insertion reactions of the nonstabilized carbene complex intermediates produced have been investigated through the use of B3LYP density functional theory. The [3+2] cycloaddition reaction of the tungsten‐containing carbonyl ylide has been proven to proceed concertedly, reversibly, and with high endo selectivity. The intermolecular Si? H insertion reactions of the carbene complex intermediates have been proven to be favored over the intramolecular C? H insertion, in good agreement with experimental results. Moreover, the kinetic endo/exo ratio of the [3+2] cycloaddition reaction has been shown to determine the endo/exo selectivity of the Si? H insertion products. In addition, secondary orbital interactions involving the benzene ring and the carbonyl ligand on the metal center have turned out to strongly influence the high endo selectivity of the [3+2] cycloaddition reaction with methyl vinyl ether.     

Studies on new platelet aggregation inhibitors 1. Synthesis of 7-nitro-3,4-dihydroquinoline-2(1H)-one derivatives.

A series of 6-cyclic aliphatic amino-7-nitro-3,4-dihydroquinoline-2(1H)-ones were prepared and tested for platelet aggregation inhibitory effect, cardiotonic activity and chronotropic activity. These compounds appeared to show selective inhibitory activity against platelet aggregation. Among them, 6-(4-ethoxycarbonylpiperidino)-7-nitro-3,4-dihydroquinoline-2(1H)-one (22f) showed the most potent inhibitory activity and high selectivity. A divergent synthetic route to 6-cyclic aliphatic amino-7-nitro-3,4-dihydroquinoline-2(1H)-one derivatives has also been investigated.     

Effect of amount of monomer on radiation-induced polymerization of styrene adsorbed on silica gel

The effect of amount of monomer on radiation-induced polymerization of styrene adsorbed on silica gel was investigated with the monomer amounting from less than monolayer adsorption to more than the equilibrium adsorption. The rate of graft polymerization and the molecular weight of the polymer changed with the amount of monomer adsorbed on silica gel. Maximum grafting efficiency was obtained at monolayer adsorption. The molecular weight of graft polymer was higher than that of homopolymer in both radical and cationic polymerizations, and the ratio in molecular weight of graft polymer to that of homopolymer tends to be unity with increasing amount of adsorbed monomer. These results can mainly be explained in terms of the number of initiating species (radical and cation) that change in relation to the amount of adsorbed monomer. Propagation and termination change with amount of adsorbed monomer in relation to the molecular mobility of adsorbed monomer. A very high-molecular-weight graft polymer is formed only with a small amount of adsorbed monomer in the initial stage. The grafting percent with a large amount of adsorbed monomer increased after most of the monomer has been polymerized. Secondary effect of radiation on the graft and homopolymers due to energy transfer from silica gel is suggested from the complicated phenomena in the later stage of the reaction.     

Synthesis and antitumor activity of lipid A analogs having a phosphonooxyethyl group with alpha- or beta-configuration at position 1

Three novel lipid A analogs, which have an alpha- or beta-glycosidically bound phosphonooxyethyl group instead of the alpha-glycosyl phosphate group of natural lipid A, were synthesized. The first analog (2) had an alpha-phosphonooxyethyl group on the identical acylated disaccharide 4'-phosphate structure found in natural lipid A (from Escherichia coli) and hence differed from the latter only in the nature of the acidic group at position 1. The second one (3) had tetradecanoyl groups in place of the two (R)-3-hydroxytetradecanoyl groups bound to the 2- and 3-hydroxyl function of 2, retaining the alpha-phosphonooxyethyl group. The structure of the third analog (4) was the same as that of 3 except that the phosphonooxyethyl group of the former was beta-oriented. Compounds 2 and 3 exhibited potent activity against Meth A at the same level as natural lipid A, whereas 4 showed less activity. This fact revealed that the glycosidic phosphate is not a prerequisite for the antitumor activity of lipopolysaccharide. It can be replaced with a phosphonooxyethyl group without any loss of activity provided that the alpha-anomeric configuration at C-1 is retained. The replacement of the hydroxytetradecanoyl groups with tetradecanoyl groups does not change the activity either.     

Synthesis of isochromene esters utilizing 1,6-addition of nucleophiles to benzopyranylidenetungsten(0) complexes

[reaction: see text] A concise method for the preparation of isochromene carboxylates has been developed by the regioselective 1,6-addition of various nucleophiles such as Grignard reagents, alkoxide, and cyanide onto benzopyranylidenetungsten(0) complexes, followed by iodine oxidation of the addition intermediates.     

Efficient Generation and Synthetic Applications of Alkyl-Substituted Siloxycarbenes: Suppression of Norrish-Type Fragmentations of Alkanoylsilanes by Triplet Energy Transfer

Acylsilanes have been known to undergo isomerization to siloxycarbenes under photoirradiation and the thus generated carbenes can be utilized for various synthetic reactions. But this carbene formation is not necessarily efficient with some alkanoylsilanes because Norrish-type fragmentations compete, which limit the synthetic utility of alkanoylsilanes as carbene precursors. In this study, generation of siloxycarbenes from alkanoylsilanes by visible-light-induced energy transfer was examined by using an Ir complex, [Ir{dF(CF₃)ppy}₂(dtbpy)]PF₆, and was successfully applied to the C−C coupling reactions with boronic esters or aldehydes. This methodology efficiently suppressed undesired Norrish-type reactions and broadened synthetic utility of alkanoylsilanes.     

Influence of pyrimidine additives in electrolytic solution on dye-sensitized solar cell performance

The influence of pyrimidine additives on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) dye-sensitized TiO₂ solar cell with an I⁻/I₃⁻ redox electrolyte in acetonitrile was studied. The current–voltage characteristics were measured for more than 10 different pyrimidine derivatives under AM 1.5 (100 mW/cm²). The pyrimidine additives tested had varying effects on the performance of the cell. The additives drastically enhanced the open-circuit photovoltage (V_oc) and the solar energy conversion efficiency (η), but usually reduced the short circuit photocurrent density (J_sc) of the solar cell. Physical and chemical properties of the pyrimidines were computationally calculated in order to determine the reasons for the additive effects on cell performance. Consequently, the greater the calculated partial charge of the nitrogen atoms in the pyrimidine groups, the larger the V_oc but the smaller the J_sc values. The V_oc of the cell also increased as the ionization energy of the pyrimidine molecules decreased. Moreover, as the calculated dipole moment of the pyrimidine derivatives increased, the J_sc value was reduced, but the V_oc value was enhanced. These results suggest that the electron donicity of pyrimidine additives influenced the interaction with TiO₂ electrode and I⁻/I₃⁻ electrolyte, which lead to the changes in dye-sensitized solar cell performance.