Efficient synthesis of optically active atropisomeric anilides through catalytic asymmetric N-arylation reaction

In the presence of (R)-DTBM-SEGPHOS-Pd(OAc)2 catalyst, N-arylation of ortho-tert-butyl-NH-anilides with 4-nitroiodobenzene proceeds with high enantioselectivity (89-95% ee) to give optically active atropisomeric anilides possessing N-C chiral axis. Furthermore, the intramolecular version of the present catalytic asymmetric N-arylation gave atropisomeric lactams with high optical purity (94-96% ee).     

Stereocontrolled synthesis of 7-hydroxy- and 7-acetoxy-PGI2: New stable PGI2 analogues

Stable analogues of PGI₂, 7-hydroxy- and 7-acetoxy-PGI₂, were synthesized from protected PGI₂ methyl ester $\text{1b}$via sulfoxides $\text{6a}$, $\text{6b}$ through stereocontrolled sulfoxide-sulfenate rearrangement.     

The Synthesis of Damascenone and β-Damascone and the possible mechanism of their formation from carotenoids

A brief synthesis of damascenone ( 5 ) from the acetylenic diol 2 and also that of β-damascone ( 8 ) from β-ionol, resembling the biogenetic synthesis, are described. A possible mechanism for the formation of damascenone from neoxanthin is proposed.     

Synthesis of new crown ethers and their metal complexes: 1H and 13C NMR study

A new type of crown ethers containing a diphenyl ether unit has been prepared, the ring size ranging from 12 to 36. ¹H and ¹³C NMR spectra of both free ligands and their metal-ion complexes have been recorded. For 18- and 21-membered compounds a general downfield shift was observed for both methylene and aromatic proton resonances on metal-ion complexation. The stoichiometry of K⁺ and Na⁺ complexes was deduced from chemical shift dependence on metal-ion concentration. The K⁺ and Na⁺ complexes of 18- and 21-membered rings have a guest to host ratio of 1:1, whereas the K⁺ salt of the 15-membered ring exists as a 1:2 complex in solution. The ¹H shift observed on salt formation was attributed to electric-field and conformational effects. The ¹³C resonances for the aryl carbons, C-1, C-2 and C-3, and the α-methylene carbon in 15- and 18-membered rings were shifted upfield when an equivalent amount of KSCN was added in CDCI_3?DMSO-d₆. The shift changes were independent of the anion, and similar results were obtained for SCN^?, Br^?, and I^? salts. The upfield shift is explained by conformational factors. The spectral changes were slight for 12- and 36-membered rings. In 15- and 18-membered rings, complexation induces conformational changes which force the C-α carbon into the plane of the benzene ring. The solution conformation of these molecules is discussed.     

Third-order potential constants and dipole moment of SeO2 by microwave spectroscopy

The third-order potential constants of SeO₂ have been recalculated using the vibrational frequencies reported for matrix-isolated SeO₂. General trends of the constants are in good accord with the results obtained for other triatomic molecules, such as SO₂, O₃, and OF₂. The dipole moment was measured more accurately to be 2.62 ± 0.05 D.     

A numerical method for the solution of multi-point problems for ordinary differential equations with integral constraints

We propose a method for the solution of a system of nonlinear ordinary differential equations with integral constraints, by transforming to multi-point boundary value problems. Examples are given.     

Improvements in Carrier-to-Noise-Ratio (CNR) of Lightwave Amplitude Modulated Vestigial-Sideband (AM-VSB) Transmission Systems by the Use of Optical Isolators

In lightwave community antena television (CATV) systems as well as other optical fiber communication networks, a transmitted optical signal is known to be degraded by an intensity noise produced within the fiber due to the interference between the signal and doubly reflected light. We report on the improvements to the signal degradation due to the double Rayleigh backscattering by inserting optical isolators in the trunk lines of the systems. A carrier-to-noise ratio (CNR) has been calculated as a function of the number and the insertion loss of the isolators. The calculated results indicate that there is an optimum number of isolators, and if the insertion loss is less than 0.3 dB, the CNR degradation can be restored by more than 60%. To test the calculated results, we conducted experiments for the specific case of employing one isolator, and obtained good agreements between the two.