Palladium-catalyzed regiocontrolled alpha-arylation of trimethylsilyl enol ethers with aryl halides

Inter- and intramolecular arylations of trimethylsilyl enol ethers with aryl halides are accomplished regiospecifically in the presence of a palladium catalyst and tributyltin fluoride in refluxing benzene or toluene. The optimal catalyst system called for the use of Pd2(dba)3 and tri-tert-butylphosphine in ca. 1:2 ratio. Aryl iodides, bromides, and chlorides are all effective arylation partners in this reaction. [reaction: see text]     

Promotion of the γ‐phase of polyamide 6 in its nanocomposite with phosphate glass

The effect of tin fluorophosphate‐glass (Pglass) nanoparticles on the polyamide‐6 (PA6) matrix in Pglass/PA6 hybrids has been investigated by ¹³C solid‐state nuclear magnetic resonance (NMR). The crystallinity determined by direct‐polarization ¹³C NMR combined with longitudinal relaxation‐time (T_1C) filtering varied between 31 and 44%. T_1C‐filtered ¹³C spectra with cross polarization clearly showed resonances of both the α‐ and γ‐crystalline phases of PA6, typically at ratios near 45:55, while the similarly processed neat polymer contained only the α‐phase. This suggests that the Pglass promotes the growth of the γ‐crystalline phase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 857–860, 2008     

Stereospecific synthesis of highly substituted skipped dienes through multifunctional palladium catalysis

[reaction: see text] Multifunctional palladium catalysis is utilized in the one-pot stereocontrolled synthesis of tetrasubstituted alkenes. The homogeneous palladium dihalide catalyst utilized for bromo-/chloroallylation of alkynes is then reused in situ for a subsequent Suzuki cross-coupling reaction.     

Au Nanoparticles Supported Nanoporous ZnO Sphere for Enhanced Photocatalytic Activity Under UV-Light Irradiation

Monodispersed 200 nm-sized ZnO spheres (SPs) with porous structure emanating from 8 nm zinc oxide nanoparticles (NPs) composing the SPs were synthesized by dissolving zinc acetate dihydrate in diethylene glycol at 160 °C. The prepared SPs were employed in fabricating the gold (Au) loaded ZnO (Au/ZnO SP) composite materials, exhibiting high photocatalytic activity in decomposing salicylic acid under UV-light irradiation. It is deduced that its high catalytic activity originates from the charge separation by transferring photoinduced electrons from the conduction band (CB) of ZnO to Au, since the CB level of ZnO (?0.5 V vs. NHE) is located more negative side than that of Au (+0.5 V vs. NHE). The evidence for the charge separation was provided by monitoring^.OH radical with bare ZnO SPs and Au/ZnO SP produced in the solution which readily react with 1,4-terephthalic acid (TA) inducing 2-hydroxy terephthalic acid (TAOH) that shows unique fluorescence peak at 426 nm.     

Chiral squaramide derivatives are excellent hydrogen bond donor catalysts

Thioureas represent the dominant platform for hydrogen bond promoted asymmetric catalysts. A large number of reactions, reported in scores of publications, have been successfully promoted by chiral thioureas. The present paper reports the use of squaramides as a highly effective new scaffold for the development of chiral hydrogen bond donor catalysts. Squaramide catalysts are very simple to prepare. The (-)-cinchonine modified squaramide (5), easily prepared through a two-step process from methyl squarate, was shown to be an effective catalyst, even at catalyst loadings as low as 0.1 mol%, for the conjugate addition reactions of 1,3-dicarbonyl compounds to beta-nitrostyrenes. The addition products were obtained in high yields and excellent enantioselectivities.     

Unexpected regioselective debenzylation leading to modification of both rims of α-cyclodextrin

Diisobutylaluminum hydride-mediated debenzylation of perbenzylated α-cyclodextrin was investigated using modified conditions. It was found that the reaction proceeded much slower to allow a more controlled removal of benzyl groups. Prolonged reaction time led to the unprecedented observation that a cleavage of up to two benzyl groups can occur at the secondary rim in a highly regioselective manner.     

Total synthesis of N-methylwelwitindolinone D isonitrile

Described is a concise total synthesis of N-methylwelwitindolinone D isonitrile, the first in a family of complex bicyclo[4.3.1]decane-containing indole alkaloids to yield to synthesis. The complete carbon core of the natural product was assembled rapidly through a Lewis acid-mediated alkylative coupling followed directly by a palladium-catalyzed enolate arylation reaction. The final ring of the pentacycle was introduced by an indole oxidation/cyclization, and the isonitrile was installed through the rearrangement of an aldehyde to an isothiocyanate followed by desulfurization.