Pd(II) acts simultaneously as a Lewis acid and as a transition-metal catalyst: synthesis of cyclic alkenyl ethers from acetylenic aldehydes

The reaction of carbon-tethered acetylenic aldehydes with alcohols in the presence of a catalytic amount of Pd(OAc)2 in 1,4-dioxane at room temperature gave the 5- or 6-membered acetal products in high yields. The 13C NMR studies suggested that a Pd(II) catalyst exhibited dual roles in the present reaction; the attack of ROH to aldehyde is catalyzed by Lewis acidic Pd(OAc)2, and the nucleophilic oxygen of the resulting hemiacetal reacts with alkyne complexed by Pd(II), giving the alkenyl ethers.     

Ring transformation of pyrimidines to pyridines. Synthesis of 4-alkylaminopyridin-2-ones by alkaline hydrolysis of 6-(2-dimethylaminovinyl)uracils

Alkaline hydrolysis of 1,3-disubstituted 6-(2-dimethylaminovinyl)uracils 2 induced a novel ring transformation giving 4-alkylaminopyridin-2-ones 3 via ring-opening and ring-closure processes. The 4-methylamino-3-nitropyridin-2-one ( 3a ) thus obtained was employed for the synthesis of 3-deazahypoxanthine derivative 8. 4-Alkylamino-3-cyanopyridin-2-ones 11 , ricinine analogs, were also prepared by the reaction of 4-chloro-3-cyano-1-methylpyridin-2-one ( 10 ) with amines.     

Electrostatic manipulation of enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylate within gamma-cyclodextrin cavity through chemical modification. inverted product distribution and enhanced enantioselectivity

In the enantiodifferentiating supramolecular photocyclodimerization of 2-anthracenecarboxylate using gamma-cyclodextrin with a dicationic side chain, a dramatic switching of the product selectivity and a significant enhancement of the enantiomeric excess were achieved by introducing a flexible dicationic sidearm to native gamma-cyclodextrin and also by lowering the temperature and solvent polarity.     

Heterodimerization of dye-modified cyclodextrins with native cyclodextrins

The heterodimerization behavior of dye-modified beta-cyclodextrins (1-6) with native cyclodextrins (CDs) was investigated by means of absorption and induced circular dichroism spectroscopy in an aqueous solution. Three types of azo dye-modified beta-CDs (1-3) show different association behaviors, depending on the positional difference and the electronic character of substituent connected to the CD unit in the dye moiety. p-Methyl red-modified beta-CD (1), which has a 4-(dimethylamino)azobenzene moiety connected to the CD unit at the 4' position by an amido linkage, forms an intramolecular self-complex, inserting the dye moiety in its beta-CD cavity. It also associates with the native alpha-CD by inserting the moiety of 1 into the alpha-CD cavity. The association constants for such heterodimerization are 198 M(-1) at pH 1.00 and 305 M(-1) at pH 6.59, which are larger than the association constant of 1 for beta-CD (43 M(-1) at pH 1.00). Methyl red-modified 2, which has the same dye moiety as that for 1 although its substituent position is different from that of 1, does not associate even with alpha-CD due to the stable self-intramolecular complex, in which the dye moiety is deeply included in its own cavity of beta-CD. Alizarin yellow-modified CD (3), which has an azo dye moiety different from that of 1 and 2, caused a slight spectral variation upon addition of alpha-CD, suggesting that the interaction between 3 and alpha-CD is weak. On the other hand, phenolphthalein-modified beta-CD (4), which forms an intermolecular association complex in its higher concentrations, binds with beta-CD with an association constant of 787 M(-1) at pH 10.80, where 4 exists as the dianion monomer in the absence of beta-CD. p-Nitorophenol-modified beta-CDs (5 and 6), each having p-nitorophenol moieties with a different connecting part with an amido and amidophenyl group, respectively, associated with alpha-CD with association constants of 66 and 16 M(-1) for 5 and 6, respectively. The phenyl unit in the connecting part of 6 may prevent the smooth binding with alpha-CD. All these results suggest that the dye-modified CDs, in which the dye part is not tightly included in its CD cavity, associate with the native CD to form heterodimer composed of two different CD units by inserting the dye moiety into the native CD unit. The resulting heterodimers have a cavity that can bind another appending moiety of host molecules. On this basis, more ordered molecular arrays or the supramolecular hereropolymers can be constructed.     

Synthesis,stability and bonding situation of tris-, bis- and mono[9-(azuleno[1,2-b]thienyl)]methyl cations

Stable tris-, bis- and mono[9-(azuleno[1,2-b]thienyl)]methyl cations (7a, 8a and 9a) and their derivatives, with a 6-isopropyl substituent on each azuleno[1,2-b]thiophene ring (7b, 8b and 9b) were prepared by the hydride abstraction reaction of the corresponding methane derivatives. The bonding situation of these compounds including the methane derivatives was examined by analysis of the 3J(H,H) values for the seven-membered ring from the 1H NMR spectra. The methane derivatives exhibited a significant alternating pattern in the 3J(H,H) values, which indicated that the pi-system of the azulene core is perturbed by the fused thiophene ring, showing a tendency towards a localized heptafulvene substructure. The 3J(H,H) values of 7b and 8b in the seven-membered ring revealed that the alternating C-C bond lengths in the azulene core still existed. The cations 9a and 9b, which exhibited nearly equal 3J(H,H) values in the seven-membered ring, exhibit the development of a delocalized tropylium substructure in the azulene core. X-ray crystal analysis of 6-isopropylazuleno[1,2-b]thiophene revealed substantial bond-length alternation in the seven-membered ring. Significant bond-length equalization in the seven-membered ring was also confirmed by the X-ray crystal analysis of 9b. The stability of these carbocations was examined by measurement of the pKR+ values and the redox potentials, which revealed that the bond-length alternation in the azulene core does not significantly affect the stability of the carbocations.     

Copolymerization of carbon dioxide and N-phenylethylenimine

Copolymerizations of carbon dioxide and N-phenylethylenimine were carried out with the use of various catalysts and solvents. The infrared spectrum of the polymer produced showed the characteristic absorption peak at 1730–1735 cm^?1 based on the urethane linkage. The content of the urethane linkage decreased in the following order: Mn(acac)₂ ≈ MnCl₂4H₂O > Al(OBu)₃ > Ti(OBu)₄ > ZnCl₂ ? BF₃OEt₂ = VCl₃ = Mn(acac)₃ = FeCl₃ = CrCl₃ · 6H₂O = 0. The manganase (bivalent) catalyst in combination with n-hexane solvent was found to be the best system for the copolymerization, and this system received detailed study. Generally speaking, both the polymer yield and the content of the urethane linkage increased with increasing content of carbon dioxide in the feed as well as with increasing polymerization temperature. From the fractionation of polymer in methanol, it was found that the produced polymer is composed of both homopolymer of N-phenylethylenimine and copolymer of N-phenylethylenimine and carbon dioxide. The content of the urethane linkage of the copolymer thus fractionated was as high as about 80%.     

Electric-field effects on photoluminescence properties in a GaAs/AlAs marginal type-I superlattice

We have investigated the electric-field effects on the cw and time-resolved photoluminescence (PL) properties in a marginal type-I GaAs/AlAs superlattice (SL) whose lowest X state (X₁) is situated in the lowest Γ(Γ₁) miniband. In the low bias voltage regime, the PL spectra reveal the transition between type-I and type-II radiative recombination processes caused by Wannier–Stark localization. In contrast, in the high bias voltage regime, the decay time of the time-resolved PL is prolonged. This is because of delayed carrier transport caused by Γ–X transfer. From these results, it was found that marginal type-I SLs present various interesting phenomena that originate from the competitive carrier transport among the Γ miniband, the localized Γ Stark–ladder states, and the X₁ state.     

An extended doubly-adaptive quadrature method based on the combination of the Ninomiya and the FLR schemes

An improvement is made to an automatic quadrature due to Ninomiya (J. Inf. Process. 3:162–170, 1980) of adaptive type based on the Newton–Cotes rule by incorporating a doubly-adaptive algorithm due to Favati, Lotti and Romani (ACM Trans. Math. Softw. 17:207–217, 1991; ACM Trans. Math. Softw. 17:218–232, 1991). We compare the present method in performance with some others by using various test problems including Kahaner’s ones (Computation of numerical quadrature formulas. In: Rice, J.R. (ed.) Mathematical Software, 229–259. Academic, Orlando, FL, 1971).      

Influence of surface roughness on adhesion between elastic bodies

We study the influence of surface roughness on the adhesion between elastic solids. We present experimental data for the force necessary to pull off rubber balls from hard rough substrates. We show that the effective adhesion (or the pull-off force) can be calculated accurately from the surface roughness power spectra obtained from the measured surface height profile.