Synthesis of an Optically Active Trisubstituted α,β-Butenolide, (S)-4, 6-Dihydroxy-2, 3-dimethyl-2-hexesoic Acid 1, 4-Lactone,from 2-Deoxy-D-ribose

The title compound has been synthesized efficiently from 2-deoxy-D-ribose. The synthesis involves : 1) an aldol like carbon-carbcr. bond formation of (S)-3, 5-dibenzyioxy-2-pentanor.e (8) with a lithium enolate of methyl propanoate, and 2) O-de-benzylation of the aldol adducts (11) for a γ-lactonization followed by β-elimination of the desired butenolide skeleton.     

Regioselective beta-metalation of meso-phosphanylporphyrins. Structure and optical properties of porphyrin dimers linked by peripherally fused phosphametallacycles

meso-Diphenylphosphanylporphyrins were successfully prepared via Pd-catalyzed C-P cross-coupling reaction of the corresponding meso-iodoporphyrins with diphenylphosphane. The meso- phosphanylporphyrins underwent regioselective metalation at the beta carbon to produce novel classes of porphyrin dimers linked by peripherally fused phosphametallacycles. A Pd-mononucler complex was structurally characterized by X-ray crystallography, which revealed a flat structure of the Pd-linked porphyrin pi systems. Both experimental and theoretical results demonstrate that the orbital interaction between the pyrrolic ppi orbitals and the metal dpi orbital affects optical and electrochemical properties of the metal-linked coplanar porphyrin dimers.     

Theoretical study of C-H and N-H sigma-bond activation reactions by titinium(IV)-imido complex. Good understanding based on orbital interaction and theoretical proposal for N-H sigma-bond activation of ammonia

The C-H sigma-bond activation of methane and the N-H sigma-bond activation of ammonia by (Me3SiO)2Ti(=NSiMe3) 1 were theoretically investigated with DFT, MP2 to MP4(SDQ), and CCSD(T) methods. The C-H sigma-bond activation of methane takes place with an activation barrier (Ea) of 14.6 (21.5) kcal/mol and a reaction energy (DeltaE) of -22.7 (-16.5) kcal/mol to afford (Me3SiO)2Ti(Me)[NH(SiMe3)], where DFT- and MP4(SDQ)-calculated values are given without and in parentheses, respectively, hereafter. The electron population of the CH3 group increases, but the H atomic population decreases upon going to the transition state from the precursor complex, which indicates that the C-H sigma-bond activation occurs in heterolytic manner unlike the oxidative addition. The Ti atomic population considerably increases upon going to the transition state from the precursor complex, which indicates that the charge transfer (CT) occurs from methane to Ti. These population changes are induced by the orbital interactions among the d(pi)-p(pi) bonding orbital of the Ti=NSiMe3 moiety, the Ti d(z2) orbital and the C-H sigma-bonding and sigma*-antibonding orbitals of methane. The reverse regioselective C-H sigma-bond activation which leads to formation of (Me3SiO)2Ti(H)[NMe(SiMe3)] takes place with a larger Ea value and smaller exothermicity. The reasons are discussed in terms of Ti-H, Ti-CH3, Ti-NH3, N-H, and N-CH3 bond energies and orbital interactions in the transition state. The N-H sigma-bond activation of ammonia takes place in a heterolytic manner with a larger Ea value of 19.0 (27.9) kcal/mol and considerably larger exothermicity of -45.0 (-39.4) kcal/mol than those of the C-H sigma-bond activation. The N-H sigma-bond activation of ammonia by a Ti-alkylidyne complex, [(PNP)Ti(CSiMe3)] 3 (PNP = N-[2-(PH2)2-phenyl]2-]) ,was also investigated. This reaction takes place with a smaller E(a) value of 7.5 (15.3) kcal/mol and larger exothermicity of -60.2 (-56.1) kcal/mol. These results lead us to predict that the N-H sigma-bond activation of ammonia can be achieved by these complexes.     

Divergent synthesis of withasomnines via synthesis of 4-hydroxy-1H-pyrazoles and Claisen rearrangement of their 4-O-allylethers

4-Hydroxypyrazoles were synthesized by the alkaline hydrolysis of the Baeyer-Villiger oxidation products of 4-formylpyrazoles. This new synthesis of 4-hydroxypyrazoles was applied to the divergent synthesis of withasomnine alkaloids in a unique strategy, for which the key steps included the regioselective Claisen rearrangement of their 4-O-allyl-4-hydroxy-1H-pyrazoles and a Suzuki coupling of 4-trifluoromethanesulfonyloxy-1H-pyrazoles and arylboronic acids.     

Low temperature adsorption and site-conversion process of CO on the Ni(111) surface

Low-temperature (25 K) adsorption states and the site conversion of adsorbed CO between the ontop and the hollow sites on Ni(111) were studied by means of temperature programmed desorption and infrared reflection absorption spectroscopy. The activation energy and pre-exponential factor of desorption were estimated to be 1.2 eV and 2.6 × 10¹³ s^? 1, respectively, in the limit of zero coverage. At low coverage, CO molecules preferentially adsorbed at the hollow sites below 100 K. With increasing temperature, the ontop sites were also occupied. Using a van't Hoff plot, the enthalpy and the entropy differences between the hollow and ontop CO were estimated to be 36 meV and 0.043 meV K^? 1, respectively, and the vibrational entropy difference was estimated to be 0.085 meV K^? 1. The positive entropy difference was the result of the low-energy frustrated translational mode of the ontop CO, which was estimated to be 4.6 ± 0.3 meV. With the harmonic approximation, the upper limit of the activation energy of site hopping from ontop sites to hollow sites was estimated to be 61 meV. In addition, it was suggested that the activation energy of hollow-to-hollow site hopping via a bridge site was less than 37 meV.     

Ambipolar behavior of hydrogen-bonded diketopyrrolopyrrole-thiophene co-oligomers formed from their soluble precursors

Organic field-effect transistors with hydrogen-bonded diketopyrrolopyrrole-thiophene co-oligomers were fabricated by a solution-process method with annealing at 200 °C, showing ambipolar charge-carrier transfer with field-effect mobilities up to μ(h) = 6.7 × 10(-3) cm(2) V(-1)s(-1) and μ(e) = 5.6 × 10(-3) cm(2) V(-1) s(-1).     

The effect of a lateral substituent on the mesomorphic properties of 4-cyanophenyl 4-(4-alkyloxybenzoyloxy)benzoates

The thermal properties of 4-cyanophenyl 4-(4-alkyloxybenzoyloxy)benzoates having a lateral substituent have been examined. Commencing with the nonyloxy homologue the hydrogen derivative shows a smectic A phase having a partially bilayered arrangement (SA_Ad). When the substituents are introduced at position X, the S_Ad phase commences from the octyloxy homologue, and the chlorine and bromine derivatives show an additional S_Ad phase in the low temperature region. When the substituents are introduced at position Y, the S_Ad phase commences either from the undecyloxy or the dodecyloxy homologue, and the nitro derivative shows two tilted phases in the low temperature region. Compounds having a methoxy group at position Z have difficulty in forming the S_Ad phase. The effect of the substituent on the thermal properties of the smectic phases has been discussed in terms of the electrostatic and structural properties of the substituents. A driving force for the formation of the partially bilayered arrangement is also discussed.     

Selective determination of gallium by flow injection fluorimetry

Gallium can be determined fluorunetrically, with linear response in the range 2.2 × 10^-5 M–1.08 × 10^-4 M, by means of chelate formation with lumogallion ; fluorescence is enhanced by mixing with a polyethylene glycol monolauryl ether solution. Up to 10-fold molar amounts of aluminum can be tolerated, because of the slow formation rate of the aluminum—lumogallion chelate.