[2 + 2] Cycloaddition reactions of unsymmetrically substituted carbodiimides

N-Alkyl-N′-arylcarbodiimides add alkyl and aryl isocyanates to the N-alkyl substituted CN double bond to yield 4-arylimino-1,3-diazetidine-2-ones 3. In the case of bulky alkyl substituents the reaction still proceeds across the sterically hindered CN double bond. N-Aryl-N′-[(4-dimethylamino)phenyl]carbodiimides form [2 + 2] cycloadducts with aryl isocyanates preferentially across the CN double bond not attached to the electron-rich aryl groups. However, steric crowding on this CN double bond directs the reaction to the adjacent double bond of the heterocumulative system. The rate of the [2 + 2] cycloaddition reaction of N'-methyl-N′-phenylcarbodiimide with 4-nitrophenylisocyanate is about 2.5 times faster in acetonitrile than in benzene.     

Librational relaxation and IR line broadening of matrix isolated CO

The IR line profile corresponding to the fundamental vibrational transition of CO isolated in an Ar matrix has been studied as a function of the temperature. The spectrum consists of two superimposed bands, a sharp one and a broad one whose linewidths are respectively 0.45 and 2.7 cm^?1 at 10 K. The strong temperature dependence of the CO lineshape is mainly due to the large change in the intensity ratio of the two components. Such a behaviour is accounted for by relaxation of librational populations. The calculated contributions of the processes connecting the ground and first excited librational states to the IR linewidth are of the same order of magnitude as the values experimentally measured. However the experimental lineshape of the sharp component being rather gaussian than lorentzian, it is concluded that librational relaxation contributes significantly to the broadening of the infrared CO band but not exclusively.     

Benzoporphyrins and Acetylene-Substituted Porphyrins as Improved Photosensitizers in the Photodynamic Tumor Therapy with Porphyrin Platinum Conjugates

Summary.  A combination of a cisplatinum-like fragment and a porphyrin in the same molecule should not only result in the additivity of the dark toxicity of the platinum fragment and the phototoxicity of the porphyrin moiety, but also in the enrichment of the porphyrin platinum conjugates in tumor tissue, which cisplatinum alone does not show. To increase the penetration depth of the red light used in the photodynamic tumor therapy the conjugated system of the porphyrin components in porphyrin platinum conjugates had to be expanded. Sixteen new (NH₃)₂Pt derivatives of benzoporphyrins and acetylene-substituted porphyrins were synthesized, characterized, and tested with respect to their antitumor activity on the mammary carcinoma cell line MDA-MB-231. Received November 12, 2001. Accepted November 20, 2001     

Determination of 1,3-dichloropropanol in soy sauce and related products by headspace gas chromatography with mass spectrometric detection: interlaboratory study

An interlaboratory study was performed to evaluate the effectiveness of a headspace gas chromatography (GC) method for the determination of 1,3-dichloro-propan-2-ol (1,3-DCP) in soy sauce and related products at levels above 5 ng/g. The test portion is mixed with an internal standard (d5-1,3-DCP) and ammonium sulfate in a sealed headspace vial. After achieving equilibrium, the headspace is sampled either by gas-tight syringe or solid-phase microextraction (SPME) and analyzed by GC with mass spectrometric detection. 1,3-DCP is detected in the selected-ion mode (monitoring m/z 79 and 81 for 1,3-DCP and m/z 82 for the deuterated internal standard) and quantified by measurement against standards. Test materials comprising soy, dark soy, mushroom soy, and teriyaki sauces, both spiked and naturally contaminated, were sent to 9 laboratories in Europe, Japan, and the United States; of these, 5 used SPME and 4 used syringe headspace analysis. Test portions were spiked at 5.0, 10.0, 20.0, 100.0, and 500.0 ng/g. The average recovery for spiked blank samples was 108% (ranging from 96-130%). Based on results for spiked samples (blind pairs at 5, 10, 20, 100, and 500 ng/g) as well as a naturally contaminated sample (split-level pair at 27 and 29 ng/g), the relative standard deviation for repeatability (RSDr) ranged from 2.9-23.2%. The relative standard deviation for reproducibility (RSDR) ranged from 20.9-35.3%, and HorRat values of between 1.0 and 1.6 were obtained.     

Reaktivität der M-M-mehrfachbindung in metallcarbonyl-derivaten: VII. Aktivierung von carbodiimiden durch [η-C5H5(CO)2Mo]2 als μ(η1:η2) ligand unter erhalt der Mo—Mo-Dreifachbindung

The reaction of Cp(CO)₂MoMo(CO)₂Cp (Cp = η-C₅H₅) with an excess of carbodiimides RN=C=NR′ results in the substitution of two carbonyl groups to give the new asymmetrically bridged complexes Cp₂(CO)₂Mo₂μ(η¹:η²-RN=C=NR′) with Cp₂(CO)₄Mo₂μ(η¹:η²-CNR) complexes as by products.     

Synthesis and proton NMR stereochemical study of 7,8,9-substituted-7,8-dihydro-4H,9H-furo[2′,3′,4′:4,4a,5]-naphth[2,1-e][1,3]oxazin-4-ones

7,8,9-Substituted-7,8-dihydro-4H,9H-furo[2′,3′,4′:4,4a,5]naphth[2,1-e][1,3]oxazin-4-ones were stereospecifically obtained as a single pair of enantiomers. Their relative trans configuration and the conformation of the dihydro oxazine ring were established by ¹H nmr 2D NOESY experiments.     

Optisch aktive übergangsmetall-komplexe: LXXXV. Darstellung,eigenschaften und konformationsanalyse von optisch aktiven CpCo-Komplexen

The Schiff bases from 2-pyridine-carbaldehyde, 2-acetylpyridine, 2-benzoylpyridine, 2-pyrrole-carbaldehyde, and 2-acetylpyrrole with (?)-1-phenylethylamine and (?)-3-aminomethylpinane were synthesized. The pyridine Schiff bases αγ were used as neutral compounds and the pyrrole Schiff bases δHζH were used as anions δζ in the reaction with CpCo(CO)I₂ and CpCo(CO)(C₃F₇)I. In place of the covalently bonded iodine ligand different monodentate ligands bp were incorporated. Compounds of the type CpCo(αζ)(ap) and [CpCo(αζ)(ap)]X with X = I, PF₆ are formed.All the complexes consist of pairs of diastereomers differing only in the Co configuration. The diastereomers exhibit different ¹H NMR spectra. The Co configuration in all the compounds is labile except the C₃F₇ derivatives. A conformational analysis establishes which of the diastereomers is the thermodynamically more stable one, on the basis of the following arguments and methods: NOE-difference spectroscopy, diastereomer ratios at equilibrium, chemical shifts of the Cp signals, and CD spectra.     

Relative susceptibility of the Iα and Iβ phases of cellulose towards acetylation

The relative reactivity of the I and I phases of Valonia cellulose toward partial homogeneous acetylation was investigated by FT-IR and CP/MAS ¹³C-NMR spectroscopy. At the beginning of the acetylation and when only partial reaction was achieved, it was found that the reactivity of the I phase was substantially higher than that of the corresponding I component. At a later stage of acetylation, the difference in reactivity between the two phases was less pronounced. In correlation with previous ultrastructural observations (Sassi and Chanzy, 1995), it can be concluded that at equivalent accessibility, the I phase of cellulose is indeed more reactive toward acetylation than the I phase. The homogeneous acetylation of cellulose is essentially a surface reaction that affects only the accessible parts located at the surface of the microfibrils. The decrease in the rate of I phase disappearance with acetylation time confirms therefore that the microstructure of Valonia is made of domains that are distributed throughout the thickness of its microfibrils.     

Sels de n-alcoxypyridinium porteurs d'une fonction cetone dans leur chaine alcoxyle: Synthese et reactivite vis-à-vis d'amines secondaires

Reaction of α-bromoisobutyrophenone on pyridine l-oxide and γ and β-picoline l-oxide, in the prosence of silver nitrate, leads to N-alkoxypyridinium and picolinium salts, bearring a keto group on their alkoxyl chain. On treatment with pyrrolidine, these salts, are converted to 4-ω-pyrrolidinobutadienyl-3-isoxzolinols, substituted or not by a methylgroup in their chain. The reaction proceeds according to the PARC-ANRO mechanism(Poton Abstraction, Ring Closure-Addition of a Nucleopile, Ring Opening), as demonstrated by isolation of the bicyclic isoxazolino pyridinium intermediates which result form the first phase of this process, In addition, steric hindrance towards ring opening caused by the methyl group in the adduct derived from β-picoline N-oxide, allow observation of a competiting novel mode of fragmentation alkoxylogous of Katritxky's mode A of decmposition of N0-alkoxypyridinium salts.