Stereoselective synthesis of 1,4-disubstituted 1,3-diene

New synthetic methods for the preparation of 1,3-dienes are described.     

Determination of chemical form of antimony in contaminated soil around a smelter using X-ray absorption fine structure.

Only limited information is available about the behavior of antimony (Sb) in contaminated soils. However, understanding the behavior of Sb in contaminated soils is important, because the toxicity or solubility of this element depends on its chemical state. In this study, we investigated the levels of Sb and the chemical forms of Sb in the soil around a smelter using X-ray absorption fine structure (XAFS) spectra. The highest Sb concentration in the contaminated soil was 2900 mg/kg dry soil. According to Sb-K edge X-ray absorption near edge (XANE) spectra, the Sb in the soil was in the form of Sb(V) compounds. The similarity of extended XAFS (EXAFS) spectra suggests that Sb speciation was independent of the sampling site, which indicates that Sb or Sb2O3 emitted from the smelter was converted into Sb(V) compounds in the soil.     

Synthesis of poly(2-cyclohexenone-4-yl methacrylate) and acidolysis of pendant protecting groups in the polymer

4-Acetoxy-2-cyclohexenone (ACH) and 2-cyclohexenone-4-yl methacrylate (CHM) were obtained from the condensation reaction of 4-bromo-2-cyclohexenone (BCH) with acetic acid and methacrylic acid using 1,8-diazabicyclo-[5,4,0]-7-undecene (DBU), respectively. Poly(2-cyclohexenone-4-yl methacrylate) ( P-1 ) containing acid-sensitive 2-cyclohexenone-4-yl group was prepared from the radical polymerization of CHM and the esterification of poly(methacrylic acid) with BCH using DBU. Furthermore, P-1 and CHM copolymers ( P-2 and P-3 ) were easily synthesized from the radical polymerization of methacrylic acid and comonomers in dimethylsulfoxide using 1 mol % of 2,2′-azobis (isobutyronitrile) followed by esterification of the resulting polymers with BCH using DBU by one-pot method. The deprotection reaction of ACH and P-1 was carried out in dichloromethane using an acid catalyst. The reaction proceeded smoothly in solution to give phenol and the corresponding carboxylic acid. Therefore, the 2-cyclohexenone-4-yl group is a useful protecting group for carboxylic acids, because the protection and deprotection reactions are very easy. In the case of polymer films, however, the acid was trapped by carbonyl group on the 2-cyclohexenone-4-yl group, and did not cause the deprotection reaction. © 1993 John Wiley & Sons, Inc.     

Synthesis and properties of bowl‐shaped homotriazacalix[3 and 6] arenes and the acyclic analogues

Bowl‐shaped chiral homotriazacalixarenes were prepared by the cyclization reactions of chiral triamines with three equimolar amounts of bis(chloromethyl) phenols or bis(chloromethyl) phenol‐formaldehyde dimers in moderate yields. The corresponding acyclic phenol‐formaldehyde oligomers were also synthesized. The structural analysis of the macrocycles by nmr and circular dichroism spectra imply the existence of chiral transmission from the point chirality of the cysteine bridge to the cyclophane moiety. Their cyclic and acyclic compounds have a π‐base cavity large enough to include the ammonium ion.     

Lewis acid promoted cyclization of enyne triesters and diesters

Reactions of enynes with three or two ester groups (1-4) in the presence of halogen-ligand Lewis acids gave cyclized products with halide incorporation (5-8) with high generality. The cyclization process was also analyzed in a theoretical study. Facile isomerization and dehydrohalogenation of five-membered products 5 and 8 by Al(2)O(3) or Et(3)N were also observed; this process introduces conjugated moieties into the products.     

Measurement of dioxygen by electrocatalytic reduction on microelectrodes modified with Nafion and methyl viologen

Nafion/methyl viologen (MV) has been chemically modified on a gold disk microelectrode (GDME). The electrochemistry of the Nafion/MV modified GDME is investigated by cyclic voltammetry (CV). Linear sweep voltammetry (LSV) and differential pulse amperometry (DPA) show that the Nafion/MV modified GDME exhibits very high electrocatalytic activity toward dioxygen reduction with good reproducibility and high sensitivity. The electrocatalytic peak current is found to be linear with the dioxygen concentration in the range of 3.44x10(-7) to 2.59x10(-4) mol l(-1) (at 25 degrees C), with a correlation coefficient of 0.9978. The detection limit (signal/noise=3) is calculated to be 0.19 mumol l(-1). The response time of the microsensor for dioxygen measurement is less than 15 s. For ten parallel measurements for 8.50 mumol l(-1) dioxygen, the relative standard deviation (RSD) is found to be 2.7%. The sensitivity of the microsensor is 0.17 nA mumol(-1) l(-1). This microsensor has been successfully employed to measure the concentration of dioxygen in real samples. The quantity of dioxygen, released from the three kinds of chloroplasts of plant leaves under different illumination, is monitored by the Nafion/MV modified gold microsensor. In order to survey the dioxygen concentration in vivo, a Nafion/MV modified carbon fiber microelectrode (CFME) is fabricated by a modification procedure similar to that of the Nafion/MV GDME. As a preliminary test, the dioxygen levels in the different areas of rat brain are determined by the Nafion/MV modified carbon fiber microsensors. The mechanism of the catalytic reaction is also addressed.     

Synthesis of 1,2-dihydroisoquinolines via the reaction of ortho-alkynylarylimines with bis-π-allylpalladium

The reaction of the ortho-alkynylarylimines 1 with allyltributylstannane and allyl chloride in the presence of allylpalladium chloride dimer (5 mol %) and Cu(OAc)₂ (20 mol %) in CH₃CN at 50 °C gave the 1,4-diallyl-1,2-dihydroisoquinolines 2 in good yields. Most probably, the reaction proceeds through tandem bis-allylation of the imine-alkyne functional groups with bis-π-allylpalladium.     

Photocyclization of n-[ω-(cycloalken-1-yl)alkyl]-and n-[ω-(inden-3-yl)alkyl]phthalimides : Synthesis of spiro-nitrogen multicyclic systems

Photolysis of the N-[ω-(cycloalken-1-yl)alkyl]phthalimides 6b-$\text{e}$ in each case gave a pair of stereoisomers of spiro-nitrogen multicyclic systems (9b-$\text{e}$) in moderate yields, whose stereochemistry was determined by means of chemical and spectroscopic analyses. Similarly, in N-[ω-(inden-3-yl)alkyl]-phthalimides (8), spiro-nitrogen macrocycles up to 13-membered 13a-$\text{c}$ were obtained in good yields     

Characterization and quantitation of clarithromycin polymorphs by powder X-ray diffractometry and solid-state NMR spectroscopy

Characterization of clarithromycin polymorph was performed by solid-state cross polarization and magic angle spinning (CP/MAS) 13C-NMR spectroscopy. Two polymorphs, form II and form I, of clarithromycins indicated characteristic resonances of C1 carbonyl carbon at 176.2 and 175.2 ppm, respectively. Since each peak of C1 carbon was well separated in the spectrum of the two polymorphs, we performed quantitative analysis of the polymorphic fraction from the peak area of these peaks. The peak area of form I was found to linearly increase with an increase of its content, with a correlation coefficient of above 0.99. Solid-state NMR was found to be a useful technique to determine the characteristics of the polymorphic forms.     

Stepwise delivery of two methoxy groups of arylaldehyde acetals across the phenyl ring. Vacant site-controlled palladium catalysis

A new catalytic cyclization of o-alkynylbenzaldehyde acetals 1 to the functionalized indenes 2 was found to be strictly controlled by the number of triphenylphosphine ligands on the Pd catalyst. Only complexes with three available coordination sites on Pd catalyze this reaction. Mechanistic study suggests that pi-coordination of Pd to the benzene ring is a key step controlled by the number of vacant coordination sites.