Iridium-catalyzed enantioselective Pauson-Khand-type reaction of 1,6-enynes

Iridium-chiral diphosphine complex catalyzes an enantioselective intramolecular Pauson-Khand-type reaction to give various chiral bicyclic cyclopentenones. The enantioselective reaction proceeds more smoothly and enantioselectively under a lower partial pressure of carbon monoxide. Moreover, aldehyde can be used as a CO source in the enantioselective carbonylative coupling.     

Short communication: An alternative and effective catalyst for the silastannation of arylacetylenes with Me3SiSnBu3 at room temperature

The palladium‐catalyzed silastannation of acetylenes with tributyl(trimethylsilyl)stannane in the presence of triethylphosphite is reported for the first time. The reaction occurs at room temperature to give (Z)‐silyl(stannyl)ethenes in high yields. The protodemetallation of the resulting adducts with HCl–tetraethylammonium chloride is described first, which demonstrates that the reaction is governed only by the stability of a carbonium ion arising from the protonation to (Z)‐silyl(stannyl)ethenes rather than the hard and soft acid and base principle, i.e. the β‐cation stabilization effect (σ–π stabilization one) of a stannyl group in the carbonium ion is rather significant. Copyright © 2004 John Wiley & Sons, Ltd.     

Dynamic behaviour attributed to chiral carbohydrate substituents of N-heterocyclic carbene ligands in square planar nickel complexes

Nickel complexes having acetylated glucopyranosyl group incorporated N-heterocyclic carbene (NHC) ligands with methyl or benzyl groups as an N-substituent exhibit two kinds of dynamic behaviours in solution (1)H NMR spectroscopy. One of the dynamic behaviours is attributed to the anti- and syn-rotamers, which occur by the rotation of the unsymmetrical NHC ligands around the axes of the Ni-C bonds. The other is attributed to the diastereomers of the syn-rotamers, which occur by opposite rotation of the imidazolylidene rings and the chiral carbohydrate group incorporated into the NHC ligands. Crystallographic analysis of the nickel complex having the NHC ligand with acetylated glucopyranosyl and benzyl groups as N-substituents showed CH-π interaction between the glucopyranosyl unit of each NHC ligand and the phenyl ring of the other NHC ligand in the complex in the solid state.     

Ir(I)-catalyzed enantioselective secondary sp3 C-H bond activation of 2-(alkylamino)pyridines with alkenes

A cationic Ir(I)-tolBINAP complex catalyzed an enantioselective C-C bond formation initiated by secondary sp(3) C-H bond cleavage adjacent to a nitrogen atom. The reaction of 2-(alkylamino)pyridines with various alkenes gave chiral amines in good yields with high enantiomeric excesses.     

Chemoselective Suzuki coupling of diborylmethane for facile synthesis of benzylboronates

The chemoselective Pd-catalyzed Suzuki-Miyaura cross-coupling reaction using a diborylmethane is reported. The use of an equimolar amount of base with a diborylmethane realized chemoselective coupling for the synthesis of various benzylboronate derivatives. Sterically hindered aryl bromides can give products in moderate to excellent yields.     

Metal-catalysed cleavage of carbon-carbon bonds

Reactions cleaving carbon-carbon bonds with the assistance of transition metals as the catalyst have provided various molecular transformations that are otherwise difficult to execute, opening a scenic avenue along organic synthesis. Construction of structural motifs like medium-sized carbocycles and chiral quaternary carbon centres have been set within an access of such paradoxical approaches in the past decade.     

Total synthesis of kehokorins A and B

The total synthesis of a dibenzofuran rhamnoside, kehokorin A, and its aglycone, kehokorin B, was achieved via a route including Suzuki-Miyaura cross-coupling followed by Ullmann ether synthesis to form a dibenzofuran, stepwise bromination at C7 of the dibenzofuran, a second Suzuki-Miyaura cross-coupling to install a 4-methoxyphenyl group at C7, and rhamnosylation.     

Asymmetric Colliding-Pulse Mode-Locking in InGaAsP Semiconductor Lasers

Asymmetric colliding-pulse mode-locking was successfully demonstrated in an InGaAsP laser. This laser had a single saturable absorber section located partway along the cavity length, and showed mode-locking operation at harmonics of the cavity roundtrip frequency. The method verified that optical pulse repetition up to subterahertz rates can be generated with nearly 1-mm-long mode-locked InGaAsP lasers.     

Determination of crystallinity of swollen poly(vinyl alcohol) by laser Raman spectroscopy

Laser Raman spectra of atactic poly(vinyl alcohol) (PVA) after heat treatment and/or swelling in water have been obtained. An amorphous Raman band is observed at 1124 cm^?1, while a crystalline Raman band is found at 1147 cm^?1. A new method for crystallinity determination is proposed, in which the amorphous band is used instead of the crystalline band. The method is superior to others for water-swollen PVA samples. Laser Raman spectra of swollen PVA revealed that swelling causes destruction of a major fraction of the crystalline regions and the remaining intact crystalline part increases with increasing temperature of heat treatment.     

Correction method for X-ray fluorescent determination of chromium in high-alloy steels and nickel-base alloys

Summary A new interelement correction method has been developed for the X-ray fluorescent determination of chromium in high-alloy steels and nickel-base alloys. The calibration equation which was derived from the JIS (Japanese Industrial Standards) model is applicable over wide ranges of compositions by preparation of only Fe-Cr binary standards.The new approach gave better accuracy than that based on Rasberry-Heinrich correction model. The accuracies (_d) were 0.08% for high-alloy steels and 0.14% for nickel-base alloys.

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Korrekturmethode für die röntgenfluorescenzspektrometrische Bestimmung von Chrom in hochlegierten Stählen und Nickellegierungen

Zusammenfassung Die Eich-Gleichung für das neue Korrekturverfahren wurde vom JIS-Modell (Japanese Industrial Standards) abgeleitet und ist über einen weiten Bereich von Zusammensetzungen durch Herstellung von lediglich binären Fe-Cr-Standards einsetzbar. Das beschriebene Verfahren bietet eine bessere Genauigkeit als die Methode nach dem Korrekturmodell von Rasberry-Heinrich. Sie betrug 0,08% für hochlegierte Stähle und 0,14% für Nickellegierungen.