A simple catalyst system for the palladium-catalyzed coupling of aryl halides with terminal alkynes

A convenient catalyst system consisting of Pd(OAc)₂, PPh₃, K₃PO₄ and DMSO was found to be effective for the coupling reaction of aryl halides with terminal alkynes as well as the deacetonative coupling reaction using a 4-aryl-2-methylbut-3-yn-2-ol as a terminal alkyne precursor. An iminophosphine as a ligand worked more effectively for some combination of substrates than triphenylphosphine.     

Comment on ‘Step structure of vicinal Ge(001) surfaces’ by B.A.G. Kersten, H.J.W. Zandvliet, D.H.A. Blank and A. van Silfhout

We have investigated detailed structures of monatomic steps on Ge(001) at room temperature by using high-resolution scanning tunneling microscopy. Our conclusions are different from those of Kersten et al. [Surf. Sci. 322 (1995) 1] for the same system. The most crucial difference is that we have not observed the nonbonded SB step. We have pointed out a possible reason for the different conclusions.     

Infrared absorption spectra and compositions of evaporated silicon oxides (SiOx)

Clear and simple relationships among oxygen content, peak position in the 9–10 μm region and intensity of infrared absorption were obtained for a wide range of x value in evaporated silicon oxides (SiO_x). Using these relationships, the origin of 875 cm⁻¹ peak was proposed to be due to a vibrational mode from a structural combination of Si---(O_ySi_4-y) (y = 2, 3 and 4).     

Proton and Li-7 NMR study on the effect of the OH− anion upon the Li+-ion conduction in the solid solution Li5NI2LiOH

From ¹H and ⁷LiNMR relaxation times T₁, T₂ and T_1ρ in Li₅NI₂ and the solid solution Li₅NI₂?0.77LiOH, the diffusive motion of the Li⁺ ion was studied to make clear the role of the OH^? ion in improving the Li⁺ ionic conduction. At temperatures as low as 140 K, each Li⁺ ion jumps among four available positions. Its activation energies are 9.26 and 11.8 kJ mol^?1 for Li₅NI₂ and Li₅NI₂?0.77LiOH, respectively. Diffusive motion was observed in T₂ and T_1ρ above 240 K. The mode of the cation distribution and the diffusion mechanism are not affected by the presence of the OH^? anion. The most noticeable fact is that the OH^? ion is substituted selectively for the N^3? ion that is the nearest neighbour of the Li⁺ ion. This selective substitution increases the concentration of the Li⁺ vacancy most effectively up to 4.2% of the total Li positions. At the same time it diminishes the strong attractive force of the N^3? anion binding the Li⁺ ion to the position, and thus the activation energy. For the diffusion, an anomalously low attempt frequency of 3̃ × 10⁹Hz was obtained from T_1ρ, while the normal value of 4.8 × 10¹²Hz was obtained from the ionic conductivity. The large discrepancy was attributed to the collective nature of the Li⁺ diffusive motion.     

Heteroatom-facilitated ortho carbon-carbon bond formation in nucleophilic F-phenyl substitution

Regioselective ortho-substitutions in F-phenyl carboxylic acid and its derivatives were accomplished by conversion into F-phenyloxazoline (1a) or F-phenyldihydrooxazine (1b), followed by nucleophilic displacements of one or two ortho-fluorines with organometallic reagents in nonpolar solvents. Requisite 1a and 1b were readily prepared by treating F-benzoyl chloride with 2-amino-2- methyl-1-propanol, and F-benzonitrile with 2-methyl-2,4- pentanediol, respectively. Treating 1a or 1b with either Grignard reagents (CH₃MgI, C₂H₅MgBr, nC₃H₇MgBr) or organolithium reagents (CH₃Li, nC₄H₉Li) gave appreciable yields of the 2-substituted F-phenyloxazoline (2a) or F- phenyldihydrooxazine (2b), while no 4-substituted ones were identified. The use of an excess of the organometallic reagents afforded 2,6-disubstitution in preference to 2,4-disubstitution. The ortho-directing effects here observed are conceivably caused through a mechanism like that suggested by Meyers(Tetrahedron Lett., 223(1978)).

     

Reaction of diphenyldiacetylene by annealing under elevated pressure

Reaction of diphenyldiacetylene (1,4-diphenylbutadiyne) by annealing under elevated pressure (0.1–500 MPa) was carried out. Diphenyldiacetylene reacted at 210°C with appearance of gas, and this temperature was independent of the pressure. The measurement of high pressure differential thermal analysis (DTA) revealed that the reaction temperature under elevated pressure was below 24–42°C of the exothermic peak temperature. This implied that exothermic reaction occurred under elevated pressure. Elementary analysis, gel permeation chromatography (GPC), FTIR, Raman scattering, and high resolution ¹³CNMR experiments were performed to characterize the structure of the product. It was indicated that the product was a mixture of derivative of condensed polycyclic aromatic compound with phenyl group and diphenyldiacetylene oligomer. The fraction of the derivatives increased with increasing pressure, and pressure accelerated the dehydrogenation of the derivatives. The number-averaged molecular weight (M_n) of the diphenyldiacetylene oligomer was 470–610 and the weight-averaged molecular weight (M_w) was 1700–2300. It was considered that the oligomer had a polyacene-based structure. © 1994 John Wiley & Sons, Inc.     

Absolute stereochemistry of amphidinolide C: synthesis of C-1-C-10 and C-17-C-29 segments

Two of each diastereomers of the C-1-C-10 and C-17-C-29 segments of amphidinolide C (1) were synthesized. Comparing the ¹H NMR chemical shifts of its MTPA esters with those of linear methyl ester of 1, the absolute configurations at C-7, C-8, C-20, C-23, and C-24 in amphidinolide C (1) were confirmed to be all R.     

Urinary metabolites of nobiletin orally administered to rats

During the course of our systematic investigation of the metabolism of flavonoids, the polymethoxyflavone nobiletin, occurring in the fruits of Citrus depressa, was orally administered to rats. The urinary metabolites were separated and identified by three-dimensional HPLC equipped with a photodiode array detector and the structure was determined by spectroscopic methods to be 4'-hydroxy-3',5,6,7,8-pentamethoxyflavone (1).