Sacculatal and isosacculatal,two new exceptional diterpenedials from the liverwort, trichocoleopsis sacculata

The stereostructures of the two new exceptional diterpene dialdehydes from the liverwort, Trichocoleopsis sacculata: sacculatal (1), responsible for the characteristic pungent taste, and isosacculatal (2) have been determined by the spectral evidence and by comparison with polygodial (3), isopolygodial (4), and drimanediol (6) of known relative configurations.     

(S)-citramalic acid,a useful chiral synthon for the synthesis of 15-deoxy-16(S)-hydroxy-16-methylprostaglandins

(S)-Citramalic acid, a readily available microbial metabolite has been efficiently transformed into (2S)-2-methyl-2-hydroxy-1-hexanol ($\text{7}$), an important chiral synthon for the synthesis of 15-deoxy-16(S)-hydroxy-16-methylprostaglandins.     

Synthesis of polyamideamines from 5-oxazolones

Polyamideamines with a sequence of two amide and one amine linkage in a main chain were synthesized from the polyaddition of 2-isopropylidene-4-alkyl-3-oxazolin-5-ones and primary diamines. The polyaddition reaction proceeded through 1,4-conjugate addition of an amine group to 3-oxazolin-5-one and subsequent ring opening of the intermediate addition product with another amine. Although aliphatic diamines gave oily polymers, xylylenediamines afforded amorphous solid polymers. The reduced viscosities and polymer melt temperature of the polymers were 0.05–0.12 and 90–130°C., respectively.     

Synthesis of 2,3-disubstituted benzofurans by platinum-olefin-catalyzed carboalkoxylation of o-alkynylphenyl acetals

The PtCl2-catalyzed cyclization reaction of o-alkynylphenyl acetals 1 in the presence of 1,5-cyclooctadiene produces 3-(alpha-alkoxyalkyl)benzofurans 2 in good to high yields. For example, the reaction of acetaldehyde ethyl 2-(1-octynyl)phenyl acetal (1a), acetaldehyde ethyl 2-(cyclohexylethynyl)phenyl acetal (1c), and acetaldehyde ethyl 2-(phenylethynyl)phenyl acetal (1f) in the presence of 2 mol % of platinum(II) chloride and 8 mol % of 1,5-cyclooctadiene in toluene at 30 degrees C gave the corresponding 2,3-disubstituted benzofurans 2a, 2c, and 2f in 91, 94, and 88% yields, respectively.     

Heterosubstituted allylic carbanion based stereocontrol,regio- and stereo- selective reaction of O and S substituted allylic carbanions with aldehydes

Regio- and diastereoselective reaction of oxygen and sulfur substituted allylic carbanions with aldehydes is described. Either threo or erythro isomer can be obtained predominantly or exclusively by merely choosing an additive.     

Preparation of CH3SiO3/2 film from methyltriethoxysilane

An oligomer solution was prepared from methyltriethoxysilane with HNO₃ catalyst. Aluninum acetylacetonate was introudced into the solution to eliminate crystalline precipitates (CH₃SiO_3/2)₈. Self-sustained film was attempted by dropping the solution onto an aqueous solution, into which NaCl was added to elevate the solution density. The film formation greatly depended both on the reaction time and on the supporting solution. The structure of the film thus obtained was investigated by FTIR attenuated total reflectance spectroscopy.     

Polarization-maintaining photonic crystal fibers with near-zero flattened dispersion in 1.06 μm waveband for medical applications

In this paper we present the design of a modified hexagonal photonic crystal fiber (PCF) having high birefringence and a near-zero flattened dispersion. Using the finite-difference method (FDM), it is shown that the proposed multiple Gedoped core hexagonal PCF exhibits a high birefringence of order 10⁻³ and a nearly zero flattened dispersion in the optical coherence tomography (OCT) waveband. In addition, the proposed PCF has a confinement loss of less than 10⁻⁸ dB/m at 1.06 μm. PCFs with such properties are considered suitable for both endoscopic OCT and other experimental setups employing 1.06 μm lasers.     

Measurements of mode field diameter and effective area of photonic crystal fibers by far-field scanning technique

We have demonstrated that the correction factor k _n = A _eff/(πw ²), where ω = MFD/2 (MFD: mode field diameter), is above 1.20 for photonic crystal fibers (PCFs) with structural parameters in the range of d/Λ ≅ 0.40 to 0.90 (d/Λ ratio of hole diameter d and pitch Λ). By using the far-field scanning (FFS) technique and the finite difference method, the results of experimental measurements and numerical simulations differed by only 0.9 to 3.0% for two types of PCFs. The finding that k _n ≠ 1.0 for PCFs indicates that their electrical field distribution is non-Gaussian and cannot be determined by assuming a conventional step-index distribution for PCFs. It was also found that the ITU-T Petermann II definition is the most suitable for MFD measurements of PCFs with non-Gaussian distribution.     

Three-dimensional GaN-Ga2O3 core shell structure revealed by x-ray diffraction microscopy

In combination of direct phase retrieval of coherent x-ray diffraction patterns with a novel tomographic reconstruction algorithm, we, for the first time, carried out quantitative 3D imaging of a heat-treated GaN particle with each voxel corresponding to 17 x 17 x 17 nm3. We observed the platelet structure of GaN and the formation of small islands on the surface of the platelets, and successfully captured the internal GaN-Ga2O3 core shell structure in three dimensions. This work opens the door for nondestructive and quantitative imaging of 3D morphology and 3D internal structure of a wide range of materials at the nanometer scale resolution that are amorphous or possess only short-range atomic organization.