Absolute stereochemistry of TT-1 (rasfonin), an α-pyrone-containing natural product from a fungus, Trichurus terrophilus

The absolute stereochemistry of TT-1 (1=rasfonin), an α-pyrone-containing natural product from a Fungi Imperfecti, Trichurus terrophilus, was determined as 5R,6R,7S,9R, and 6′S on the basis of synthesis of diastereomers of two fragments of 1 in optically active forms, and comparison of their spectral and optical data with those of natural specimens.     

Iron-catalyzed 1,6-addition of aryl Grignard reagents to 2,4-dienoates and -dienamides

1,6-Addition of aryl Grignard reagents to 2,4-dienoates or -dienamides was nicely catalyzed by iron salt to give 5-aryl-3-enoates or the corresponding amides in a highly regio- and stereoselective manner.     

Supramolecular catalysts by encapsulating palladium complexes within dendrimers

Dendrimers are well-defined and highly branched macromolecules. By utilizing their capsular architectures, dendrimers encapsulating various catalytically active species can be prepared, which often bring about unique catalysis. Treatment of the alkylated PPI dendrimer with 4-diphenylphosphinobenzoic acid and [PdCl(C3H5)]2 afforded the dendrimer-encapsulated Pd complex using ionic interactions. The dendrimers encapsulating Pd complexes acted as unique supramolecular catalysts for the Heck reaction and allylic amination. The specific nanoenvironment created by the dense amino groups inside the dendrimers can provide high catalytic activity and stability for the Pd complexes. Facile recovery of the dendritic catalysts could be achieved by thermomorphic systems.     

Asymmetric synthesis of allyl- and alpha-allenylamines from chiral imines and alkynes via (eta(2)-imine)Ti(O-i-Pr)2 complexes

[reaction: see text] The reaction of a divalent titanium reagent Ti(O-i-Pr)(4)/2i-PrMgX with optically active arylaldimines derived from arylaldehydes and O-methylphenylglycinol provided, in a highly diastereoselective manner, chiral (eta(2)-imine)Ti(O-i-Pr)(2) complexes, which in turn reacted with 1-alkynes or propargyl compounds to give optically active allyl- and alpha-allenylamines, respectively.     

Hydroxyapatite-supported palladium nanoclusters: a highly active heterogeneous catalyst for selective oxidation of alcohols by use of molecular oxygen

Treatment of a stoichiometric hydroxyapatite (HAP), Ca10(PO4)6(OH)2, with PdCl2(PhCN)2 gives a new type of palladium-grafted hydroxyapatite. Analysis by means of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray (EDX), IR, and Pd K-edge X-ray absorption fine structure (XAFS) proves that a monomeric PdCl2 species is chemisorbed on the HAP surface, which is readily transformed into Pd nanoclusters with a narrow size distribution in the presence of alcohol. Nanoclustered Pd0 species can effectively promote the alcohol oxidation under an atmospheric O2 pressure, giving a remarkably high turnover number (TON) of up to 236,000 with an excellent turnover frequency (TOF) of approximately 9800 h(-1) for a 250-mmol-scale oxidation of 1-phenylethanol under solvent-free conditions. In addition to advantages such as a simple workup procedure and the ability to recycle the catalyst, the present Pd catalyst does not require additives to complete the catalytic cycle. The diameters of the generated Pd nanoclusters can be controlled upon acting on the alcohol substrates used. Oxidation of alcohols is proposed to occur primarily on low-coordination sites within a regular arrangement of the Pd nanocluster by performing calculations on the palladium crystallites.     

Site-selective iodine-magnesium exchange reaction of 1,4-diiodo-1,3-alkadienes by an organomagnesium ate complex,and its application to synthesis of polysubstituted styrenes and phenols

When 1,4-diiodo-1,3-alkadienes were treated with i-PrBu2MgLi, highly site-selective iodine-magnesium exchange reaction took place to afford, after the reaction with electrophiles, a variety of 1-iodo-1,3-alkadiene derivatives. Synthetic utility of the reaction was demonstrated by an efficient preparation of polysubstituted styrenes and phenols.     

Generation of protonic acid sites originating from molecular hydrogen over H-ZSM-5

Infrared studies of adsorbed pyridine and OH groups on H-ZSM-5 zeolite demonstrate that protonic acid sites are generated on the surfaces by exposure to molecular hydrogen above 373 K. By evacuation of gas phase hydrogen, the protonic acid sites are eliminated.

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, H-ZSM-5 373 . .

     

Creation of a chain-like cationic iron species in montmorillonite as a highly active heterogeneous catalyst for alkane oxygenations using hydrogen peroxide

A chain-like Fe3+ species containing an Fe-O-Fe unit has been prepared within the interlayer space of a montmorillonite, which showed a very high catalytic activity (turnover frequency 386 h-1 and turnover number 23,200) for the oxidation of cyclohexane with H2O2, affording cyclohexyl hydroperoxide as a major product.     

Capillary electrophoresis with laser induced-fluorescence detection of profens derivatized with the water-soluble fluorogenic reagent 4-N-(4-N'-aminoethyl)piperazino-7-nitro-2,1,3-benzoxadiazole

Profens, including pranoprofen, fenoprofen, flurbiprofen, ketoprofen and ibuprofen (Ib), were derivatized by a water-soluble benzofurazan fluorescent reagent, 4-N-(4-N'-aminoethyl)piperazino-7-nitro-2,1,3-benzoxadiazole and then were run on capillary electrophoresis in a NH4Ac-HAc buffer of pH 3.1 containing 2.4 mM beta-cyclodextrin. At room temperature, the derivatization reaction was catalyzed by triphenyl phosphine and diphenyl disulfide in acetonitrile medium, and the derivatives fluoresce around 530 nm when excited at 488 nm. With the CE running on a 50 cm x 50 microm I.D. length fused-silica capillary of by using Ar+ laser induced-fluorescence detection, the detection limits attained were in the range of 0.16 to 0.3 fmol.