Novel enhancement of diastereoselectivity of [2 + 2] photocycloaddition of chiral cyclohexenones to ethylene by adding naphthalenes

The additive effect on the diastereoselective [2 + 2] photocycloaddition of chiral cyclohexenones 1 to ethylene is examined. A novel and fairly efficient method of increasing the diastereoselectivity in the reaction of 1a was elucidated. The de value increased from 56% to 83% by the addition of 1-phenylnaphthalene. The major product 2a was isolated by the recrystallization of the diastereomeric mixture (major/minor = 11/1), of which X-ray analysis confirmed the absolute configuration of the bicyclic system of 2a. Hydrolysis for removing the chiral auxiliary and subsequent esterification afforded the optically pure bicyclo[4.2.0]octanone derivative 5. From the fluorescence spectral analyses and other experimental results, the additive effect is attributed to the complex formation of chiral cyclohexenone 1a and added naphthalenes.     

The possible way to evaluate the purity of double-walled carbon nanotubes over single wall carbon nanotubes by chemical doping

Here, we carried out Raman study on chemically doped single wall carbon nanotube (SWNT)/double-walled carbon nanotube (DWNT) mixed bucky-papers. Their highly different Raman responses (e.g., a large upshift of tangential mode of SWNT and no large changes in the frequencies of tangential mode assigned to the outer tubes of the DWNT) upon doping with the sulfuric acid could be used as a qualitative indicator of the purity of the DWNT samples with the concentration of its SWNTs contents.     

Asymmetric 1,3-dipolar cycloaddition reaction of nitrones and acrolein with a bis-titanium catalyst as chiral Lewis acid

A mu-oxo-type chiral bis-Ti(IV) oxide (S,S)-1 can be successfully utilized in the asymmetric 1,3-dipolar cycloaddition reactions between various nitrones 2 and acrolein to give the corresponding isoxazolidines with high to excellent enantioselectivities. For instance, the reaction between nitrone 2 (R = t-Bu) and acrolein in the presence of 10 mol % of bis-Ti(IV) catalyst (S,S)-1 in dichloromethane at -40 degrees C gave the corresponding endo cycloadduct with 97% ee.     

Site selectivity switch in Lewis acid catalysis. Mechanism and kinetic simulation of skeletal rearrangement of cyclobutene-fused homoquinones

[reactions: see text] We investigated the site selectivity switch in BF3-catalyzed dual skeletal rearrangements of cyclobutene-fused diarylhomobenzoquinones by changing the stoichiometric amount of acid concentration. From the lower to the higher equivalency of BF3 x Et2O, the branching product ratios (path A/path B) obeyed nonlinear sigmoid curves against the equivalency of BF3 x Et2O. The observed selectivity profiles were simulated to elucidate factors that govern thermodynamic aspects (binding affinity K of each carbonyl function with acid) and kinetic aspects (rate constants k for the cyclobutene-ring cleavage).     

Solid-phase synthesis of oligosaccharides and on-resin quantitative monitoring using gated decoupling (13)C NMR

A general strategy for solid-phase oligosaccharide synthesis capable of nondestructive quantitative monitoring has been developed. The synthesis was carried out on TentaGel using thioglycosides as glycosylating agents and dimethylthiomethylsulfonium triflate as the activator. An acylsulfonamide linker was introduced to cleave the oligosaccharide from the resin. The solid-phase reactions were monitored quantitatively by using the inverse gated decoupling technique of (13)C NMR, where two (13)C-enriched markers were used to monitor the reactions: one was (13)C-enriched glycine incorporated as a part of the linker and as an internal standard, and the other was a (13)C-enriched acetyl group used as a protecting group of the glycosylation reagent. A representative synthesis of sialyl Lewis X branched tetrasaccharide was demonstrated.     

Thermodynamics of the N2/N3- redox couple in a LiBr-KBr-CsBr melt

Nitrogen electrode reaction has been investigated in a LiBr-KBr-CsBr melt containing Li3N. The reaction N3- --> 1/2N2 + 3e- is confirmed by quantitative analysis of anodically evolved gas. The Nernst relation holds for the rest potential of Ni electrodes at a nitrogen gas pressure, pN2, of 0.05-1.0 atm and an anion fraction of the N3- ions, xN3-, of 0.003-0.010 (anion fraction). Then, the standard formal potential of the N2/N3- couple, , is evaluated to be 0.251 +/- 0.009 V versus Li+/Li (pN2 = 1 atm, xN3- = 1) at 673 K. The dependence of on the temperature (570-730 K) gives a linear relation, whose slope is (-0.930 +/- 0.117) x 10(-3) V K(-1). Thermodynamic quantities for the formation of Li3N in the melt are also estimated.     

Asymmetric syntheses of diarylheptanoid natural products (−)-centrolobine and (−)-de-O-methylcentrolobine via hetero-Diels-Alder reaction catalyzed by dirhodium(II) tetrakis[(R)-3-(benzene-fused-phthalimido)-2-piperidinonate]

Catalytic asymmetric syntheses of (−)-centrolobine and (−)-de-O-methylcentrolobine have been achieved, incorporating a hetero-Diels-Alder (HDA) reaction between 4-aryl-2-silyloxy-1,3-butadienes and phenylpropargyl aldehyde derivatives as a key step. The HDA reaction using dirhodium(II) tetrakis[(R)-3-(benzene-fused-phthalimido)-2-piperidinonate], Rh₂(R-BPTPI)₄, as a chiral Lewis acid catalyst provides exclusively cis-2,6-disubstituted tetrahydropyran-4-ones in up to 93% ee.     

Development of a certified reference material of nitrous oxide in nitrogen for emission gas measurement

A reference gas mixture of nitrous oxide (N₂O) in nitrogen, filled in a 10-L high-pressure aluminum alloy gas cylinder, has been developed as a certified reference material for emission measurement of exhaust gases from automobiles. As an example of certified values, mole fraction of N₂O is 302.36 μmol/mol. An electronic mass comparator with a home-made automatic cylinder exchanger, gas-filling equipment, and a gas chromatograph with a thermal conductivity detector have been used for the production of this CRM. The gas chromatographic analysis has of sufficient precision. The mole fraction of N₂O has good long-term stability for 10 years and is independent of inner pressure in the gas cylinder. As these results, a relative expanded uncertainty (coverage factor is 2) of the certified value has become 0.28 %. This sufficiently small uncertainty of the N₂O mole fraction will be advantageous in the calibration of analytical instruments for emission gas analysis.     

Extending Babuška-Aziz’s theorem to higher-order Lagrange interpolation

We consider the error analysis of Lagrange interpolation on triangles and tetrahedrons. For Lagrange interpolation of order one, Babu?ka and Aziz showed that squeezing a right isosceles triangle perpendicularly does not deteriorate the optimal approximation order. We extend their technique and result to higher-order Lagrange interpolation on both triangles and tetrahedrons. To this end, we make use of difference quotients of functions with two or three variables. Then, the error estimates on squeezed triangles and tetrahedrons are proved by a method that is a straightforward extension of the original one given by Babu?ka-Aziz.     

General Form of Non-Symmetric Spin Models

A spin model (for link invariants) is a square matrix W with non-zero complex entries which satisfies certain axioms. Recently (Jaeger and Nomura, J. Alg. Combin. 10 (1999), 241–278) it was shown that ^t WW ^–1 is a permutation matrix (the order of this permutation matrix is called the index of W), and a general form was given for spin models of index 2. In the present paper, we generalize this general form to an arbitrary index m. In particular, we give a simple form of W when m is a prime number.