TEMPO/NaIO4-SiO2: a catalytic oxidative rearrangement of tertiary allylic alcohols to beta-substituted alpha,beta-unsaturated ketones

The novel catalytic method for the oxidative rearrangement of tertiary allylic alcohols to beta-substituted alpha,beta-unsaturated ketones is described. TEMPO/NaIO4-SiO2 causes facile and efficient oxidative rearrangement of various acyclic substrates as well as medium-sized and macrocyclic substrates.     

Isomerization dynamics of the 2-phenylazo-1,3-dimethylimidazolium cation photoexcited to the S2 (π, π*) state as studied by transient absorption spectroscopy in the time domain of 10(-13) to 10(3) seconds

Photoinduced isomerization of a novel photochromic cation, [2PA-Mmim](+) (2-phenylazo-1,3-dimethylimidazolium cation), was studied by optical spectroscopic methods. The UV-Vis absorption spectra of the [2PA-Mmim](+) cation show two prominent bands starting around 410 and 520 nm, corresponding to the S(0)-S(2) (π, π*) and S(0)-S(1) (n, π*) transitions, respectively. The photoisomerization mechanism is studied by femtosecond time-resolved transient absorption experiments performed after S(0)-S(2) (π, π*) excitation in several solvents with different viscosity, including ionic liquids. The transient absorption signals at two representative wavelengths were fitted by bi-exponential functions, which yield four decay components. The photoisomerization mechanism is discussed in light of the relaxation schemes available for azobenzene. Only one of the components depends on the solvent viscosity and it changes from 1.2 ps (dichloromethane, 0.4 cP) to 5.6 ps ([Bmim][BF(4)], 93 cP). This component is assigned to a molecule at the S(1) state, which is responsible for the "rotational" isomerization. The weak dependence on the solvent viscosity of this component is explained in terms of local change in the viscosity as a result of local heating due to excess energy released at S(2)-S(1) internal conversion. The other three components of ～0.4, 1.0 and 10 ps are attributed to relaxation processes of the molecule at S(2), S(1) and S(0) states, respectively. The quantum yields for the forward E-Z photoisomerization are ～0.15 after S(2) excitation. The backward Z-E isomerization is slow with a lifetime of 1 hour and an activation energy of 91 kJ mol(-1) through an "inversion" mechanism.     

Classical Valence Similarity in Fullerene Derivatives

Summary.  The generalized Pauling bond order was enumerated in the C₆₀ fullerene cage molecule (truncated icosahedral symmetry). This index measures chemical similarity in fullerene derivatives such as dihydrofullerene (C₆₀H₂), anionized monohydrofullerene (C₆₀H⁻), N-substituted monohydrofullerene (C₅₉NH), the fullerene dimer ((C₆₀)₂), and the dianionic fullerene dimer ((C₆₀)₂ ²⁻). It is also useful in judging the chemical stability of isomers. Received October 9, 2001. Accepted November 9, 2001     

Nucleic acid related compounds. 116. Nonaqueous diazotization of aminopurine nucleosides. Mechanistic considerations and efficient procedures with tert-butyl nitrite or sodium nitrite

Nonaqueous diazotization-dediazoniation of two types of aminopurine nucleoside derivatives has been investigated. Treatment of 9-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl)-2-amino-6-chloropurine (1) with SbCl(3)/CH(2)Cl(2) was examined with benzyltriethylammonium (BTEA) chloride as a soluble halide source and tert-butyl nitrite (TBN) or sodium nitrite as the diazotization reagent. Optimized yields (>80%) of the 2,6-dichloropurine derivative were obtained with SbCl(3). Combinations with SbBr(3)/CH(2)Br(2) gave the 2-bromo-6-chloropurine product (>60%), and SbI(3)/CH(2)I(2)/THF gave the 2-iodo-6-chloropurine derivative (>45%). Antimony trihalide catalysis was highly beneficial. Mixed combinations (SbX(3)/CH(2)X'(2); X/X' = Br/Cl) gave mixtures of 2-(bromo, chloro, and hydro)-6-chloropurine derivatives that were dependent on reaction conditions. Addition of iodoacetic acid (IAA) resulted in diversion of purine radical species into a 2-iodo-6-chloropurine derivative with commensurate loss of other radical-derived products. This allowed evaluation of the efficiency of SbX(3)-promoted cation-derived dediazoniations relative to radical-derived reactions. Efficient conversions of adenosine, 2'-deoxyadenosine, and related adenine nucleosides into 6-halopurine derivatives of current interest were developed with analogous combinations.     

Ruthenium‐Catalyzed Transfer‐Hydrogenative Cyclization of 1,6‐Diynes with Hantzsch 1,4‐Dihydropyridine as a H2 Surrogate

The transfer‐hydrogenative cyclization of 1,6‐diynes with Hantzsch 1,4‐dihydropyridine as a H₂ surrogate was performed in the presence of a cationic ruthenium catalyst of the type [Cp′Ru(MeCN)₃PF₆]. Exocyclic 1,3‐dienes or their 1,4‐hydrogenation products, cycloalkenes, were selectively obtained, depending on the substrate structure and the reaction conditions.     

Infrared spectroscopy of ozone-water complex in a neon matrix

Matrix isolation infrared spectroscopy has been applied to study an ozone-water complex of atmospheric interest. The complex was identified in the spectral region of three normal modes of ozone and water. Ab initio calculation at MP4(SDQ), QCISD, and CCSD(T) levels indicates the existence of only one stable conformer, which accords with the present experimental result. This conformer belongs to the Cs symmetry group where two molecular planes of ozone and water are perpendicular to the Cs symmetry plane. The binding energy was calculated to be 1.89 kcal/mol at the CCSD(T)/6-311++G(3df,3pd)//CCSD(T)/6-311++G(d,p) level of theory. The formation constant and atmospheric abundance of the ozone-water complex are estimated using the thermodynamic and spectroscopic data obtained.     

Transformation of Cinchona alkaloids into 1-N-oxide derivatives by endophytic Xylaria sp isolated from Cinchona pubescens

The microbial transformation of four Cinchona alkaloids (quinine, quinidine, cinchonidine, and cinchonine) by endophytic fungi isolated from Cinchona pubescens was investigated. The endophytic filamentous fungus Xylaria sp. was found to transform the Cinchona alkaloids into their 1-N-oxide derivatives.     

Biooxidation of (+)-catechin and (-)-epicatechin into 3,4-dihydroxyflavan derivatives by the endophytic fungus Diaporthe sp. isolated from a tea plant

The microbial transformation of (+)-catechin (1) and (-)-epicatechin (2) by endophytic fungi isolated from a tea plant was investigated. It was found that the endophytic filamentous fungus Diaporthe sp. transformed them (1, 2) into the 3,4-cis-dihydroxyflavan derivatives, (+)-(2R,3S,4S)-3,4,5,7,3',4'-hexahydroxyflavan (3) and (-)-(2R,3R,4R)-3,4,5,7,3',4'-hexahydroxyflavan (7), respectively, whereas (-)-catechin (ent-1) and (+)-epicatechin (ent-2) with a 2S-phenyl group resisted the biooxidation.     

One-dimensional beam ordering of protons in a storage ring

The ordering of protons has been observed at a new storage ring, S-LSR, at Kyoto University. Abrupt jumps in the momentum spread and the Schottky noise power were observed for protons for the first time at a particle number of approximately 2000, upon applying electron cooling with electron currents of 25, 50, and 100 mA. The transition temperature was 0.17 and 1 meV in the longitudinal and transverse directions, respectively. The transverse temperature of the proton beam was much below that of electrons at the transition, which played an essential role in the ordering of protons.     

Effect of charge transfer state on the exchange interaction of radical-triplet encounter pairs

Chemically induced dynamic electron polarization (CIDEP) of galvinoxyl was measured in various excited molecule-galvinoxyl systems prepared by laser photolysis. Most of the systems examined showed net emission CIDEP, which is well explained by the quartet precursor radical-triplet pair mechanism with exchange interaction,J, of negative sign (quartet is higher than doublet). Several systems with molecules such as naphthalene, quinoxaline, biphenyl and triphenylene, however, showed net absorption CIDEP. Time profiles of CIDEP and kinetic analysis of quenching suggest that net absorption CIDEP is generated during the triplet quenching process by the galvinoxyl radical. We conclude that the net absorption CIDEP is produced during the triplet quenching if theJ value of radical-triplet encounter pair is positive. This is the first report of the radical-triplet encounter pairs with positiveJ value. The mechanism for this unusual positive sign ofJ value is discussed on the basis of the spin-selective configuration interaction between the doublet spin correlated states of radical-triplet and charge transfer encounter pairs.