Helicity amplitudes A1/2 and A3/2 for the D13(1520) resonance obtained from the gamma-->p-->-->ppi(0) Reaction

The helicity dependence of the gamma-->p-->-->ppi(0) reaction has been measured for the first time in the photon-energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4pi-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D13(1520) resonance and are used to determine its helicity amplitudes.     

Synthesis and properties of fluorene‐based fluorinated polymers

Fluorene‐based polymers containing various fluorinated benzene (fluorobenzene, p‐difluorobenzene, and tetrafluorobenzene) moieties were synthesized. In addition, perfluorooctylation of poly‐[(9,9‐dioctylfluorene‐2,7‐diyl)‐co‐(fluorene‐2,7‐diyl)] was carried out to afford fluorene‐based polymers with perfluorooctyl moiety at the 9‐position on the fluorene ring. To evaluate the effect of fluorine moiety, polymers containing nonfluorinated benzene moieties and nonfluorinated octyl groups were synthesized. The photoluminescence measurements indicated that all these polymers exhibited blue emission in solution, but a polymer containing a perfluorooctyl group did not emit in the film state. Polymers containing various fluorinated benzene moieties showed higher fluorescence quantum yields and thermal stability than those containing nonfluorinated benzene. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3143–3150, 2001     

Synthesis and hydrolysis of p‐toluoyl and acetyl 9‐triptycyl diselenides: A study on generation of triptycene‐9‐selenenoselenoic acid

p‐Toluoyl 9‐triptycyl diselenide ( 9 ) was prepared by reaction of Se‐9‐triptycyl triptycene‐9‐selenoseleninate ( 7 ) with p‐toluenecarboselenoic acid ( 8 ) and by reaction of triptycene‐9‐selenenoselenolate salt with p‐toluoyl chloride. Acetyl 9‐triptycyl diselenide ( 13 ) was prepared by reaction of triptycene‐9‐selenenoselenolate salt with acetyl chloride. Hydrolysis of the two diselenides, 9 and 13 , provided triptycene‐9‐selenol ( 10 ) and di‐9‐triptycyl triselenide ( 12 ), suggesting the generation of triptycene‐9‐selenenoselenoic acid ( 3 ). © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:525–528, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20155     

Asymmetric Total Synthesis of Indole Alkaloids Containing an Indoline Spiroaminal Framework

The total synthesis of the indole alkaloids, neoxaline, oxaline and meleagrin A, all containing a unique indoline spiroaminal framework, was accomplished through the stereoselective introduction of a reverse prenyl group to the congested benzylic carbon of furoindoline, a two‐pot transformation of indoline (containing three nitrogen atoms at appropriate positions) to the featured indoline spiroaminal framework, and elimination of carbonate assisted by the adjacent imidazole moiety to construct the (E)‐dehydrohistidine. The absolute stereochemistry of neoxaline was elucidated through our total synthesis. In addition, we evaluated the bioactivity, especially the anti‐infectious properties, of neoxaline and oxaline, and of some synthetic intermediates.     

Construction of complex STO-NG basis sets by the method of least squares and their applications

The goals of electronic structure theory are to make quantitative predictions of molecular properties and to provide qualitative insight into bonding as well as features of potential energy surfaces. Oftentimes, the two goals are at odds as an accurate treatment requires a complicated wave function that obscures chemical insight. The multifacet graphically contracted function (MFGCF) method offers a new approach that allows both goals to be addressed simultaneously. The recursive product structure of the MFGCF wave function reduces the exponential scaling of the exact wave function and allows the computation of molecular properties with polynomial scaling with respect to system size. Additionally, the graph density concept provides an intuitive tool for visualizing and analyzing the qualitative features of the wave function. In this work, the graph densities for model systems are examined to demonstrate their utility in analyzing the changes in wave function character along potential energy surfaces and near avoided crossings. Finally, we demonstrate that the graph density exposes the structure of the exact wave function for a system of noninteracting molecules as a product of the fragment wave functions.     

Formal meta-specific intramolecular Friedel–Crafts allylic alkylation of phenols through a spirocyclization–dienone–phenol rearrangement cascade

Formal meta-specific intramolecular Friedel–Crafts allylic alkylation of phenols was achieved based on spirocyclization–dienone–phenol rearrangement cascades. Systematic screening of acid catalysts revealed that Sc(OTf)₃ was a highly effective catalyst for dienone–phenol rearrangement of spiro[4.5]cyclohexadienones. Using 5 mol % of Sc(OTf)₃ as the promoter, various spirocyclic substrates were transformed into the corresponding phenol derivatives in good to excellent yield. Furthermore, the one-pot sequential spirocyclization–dienone–phenol rearrangement proceeded using a palladium and scandium multi-catalytic system or a triphenylmethyl cation single-catalyst system, providing the corresponding meta-allylated phenol derivatives in excellent yield.     

Very fast magic angle spinning (1)H-(14)N 2D solid-state NMR: sub-micro-liter sample data collection in a few minutes

Substantial resolution and sensitivity enhancements of solid-state (1)H detected (14)N HMQC NMR spectra at very fast MAS rates up to 80 kHz, in a 1mm MAS rotor, are presented. Very fast MAS enhances the (1)H transverse relaxation time and efficiently decouples the (1)H-(14)N interactions, both effects leading to resolution enhancement. The micro-coil contributes to the sensitivity increase via strong (14)N rf fields and high sensitivity per unit volume. (1)H-(14)N HMQC 2D spectra of glycine and glycyl-L-alanine at 70 kHz MAS at 11.7 T are observed in a few minutes with a sample volume of 0.8 μL.     

Isolation of a Labile Homoleptic Diazenium Cation

Following our interest in nitrogen chemistry, we now describe the synthesis, structure, and bonding of labile disilylated diazene, its GaCl₃ adduct, and the intriguing trisilylated diazenium ion [(Me₃Si)₂N?N‐SiMe₃]⁺, a dark blue and highly labile (T_decomp>?30 °C) homoleptic cation of the type [R₃N₂]⁺. Although direct silylation of Me₃Si‐N?N‐SiMe₃ failed, the [(Me₃Si)₂N?N‐SiMe₃]⁺ ion was generated in a straightforward two‐electron oxidation reaction from mercury(II) dihydrazide and Ag[GaCl₄]. Moreover, previous structure data of Me₃Si‐N?N‐SiMe₃ were revised on the basis of new data.     

A novel stereocontrolled approach to steroid side chain construction: asymmetric synthesis of potential synthon of the vitamin D series

Stereocontrolled synthesis of (?)-de-AB-8-oxa-cholest-14-en-9-one (2) as an optically active form was achieved starting from the methylene ketone (7). This work constitutes a formal synthesis of de-AB-cholestan (1).