Rudolph Ernst K. Winter

Alkali metal and ammonium cation–arene interactions with tetraphenylborate anion

Sodium, potassium, rubidium, caesium, ammonium and tetramethylammonium tetraphenylborates were studied by both positive and negative ion electrospray mass spectrometry. An affinity order of Cs+ > Rb+ > K+ ∼ Na+ was obtained. The results obtained were compared with both calculations and solid-state structures, where available. The previously reported high affinity of caesium for tetraphenylborate concluded from NMR experiments was confirmed for the gas phase. The affinity does not appear to result from steric effects and a cation–pi interaction seems likely. In the positive ion mode, a unique acetonitrile complex of NaBPh4 was observed.

Discrimination by the Potato Leafhopper (Hemiptera: Cicadellidae) of Host Volatiles from Resistant and Susceptible Alfalfa, Medicago sativa L.

Abstract Varieties of glandular-haired alfalfa, Medicago sativa L., with resistance to the potato leafhopper, Empoasca fabae (Harris), have been commercially released. To assess the role of volatile organic compounds in leafhopper resistance, stem and leaf volatiles were collected using vacuum steam distillation from the resistant genotype M. sativa G98A and the susceptible M. sativa Ranger. Whole-plant volatiles were collected using head-space analysis. Gas chromatography–mass spectrometry determined that steam distillates from both G98A and Ranger were composed mainly of alcohols and esters, with 1-octen-3-ol, (Z)-3-Hexenyl acetate, and (Z)-3-hexen-1-ol as major components. (Z)-3-hexenyl acetate was the only major component in head-space samples from G98A and Ranger. No volatiles were unique to either G98A or Ranger, but different ratios of volatiles were detected. Two-choice bioassays of leaf steam distillates and head-space samples found significantly more potato leafhoppers oriented toward volatiles from Ranger than G98A. Leafhoppers were attracted to a 0.0001% solution of 1-octen-3-ol, but not to (Z)-3-hexenyl acetate. Instead of producing volatile repellents, resistance of G98A to the potato leafhopper might be based, in part, on decreased attraction.

The photoisomerization of dihydrocostunolide

Abstract Photoisomerization of the germacranolid dihyrocostunolide (2) proceeds with a high degree of regio-and stereoselectivity to give the guaianolide photunolide (16) as the only major product. The conversion of photunolide to two guaianolides of known structure (8 and 9) and synthesis from O-acetylisophotosantonic lactone (11) provide unambiguous proof of both the structure and the stereochemistry of photunolide. The photoisomerization of 2 to 16 appears to involve an intramolecular hydrogen shift.

Unique properties of a perfluoroalkyl-modified 2,2′-bipyridyl ruthenium complex in a Nafion™ membrane: attenuated leaching of a potential biofuel cell redox mediator

The synthesis and characterization are described for the complex salt [Ru(κ2-2,2′-N2C10H6{(CH2)3(CF2)5CF3}2-4,4′)(κ2-2,2′-N2C10H8)2][PF6]2, where one of the 2,2′-bipyridyl ligands bears terminal bis(perfluoralkyl) chains, the purpose of which is to exploit ‘like-dissolves-like’ intermolecular forces as an anchoring mechanism for the complex in Nafion™ membranes. TBAB-modified-Nafion™ thin films (sulfonic acid protons exchanged for NBun4+ cations) were cast or spin-coated onto electrodes and glass microscope slips, exposed to CH2Cl2 solutions of the complex and then examined by fluorimetry and cyclic voltammetry. Steady state and time-resolved luminescence analysis revealed quite different behavior in comparison with tris-2,2′-bipyridyl ruthenium in unmodified Nafion™ films. Exposure to methanol solutions indicated mitigation of the swelling effect of this solvent along with sustained structural integrity of the mediator complex among the various microenvironmental domains of the TBAB-modified-Nafion™ polymer. The dramatic leaching evident for samples of regular tris-2,2′-bipyridyl ruthenium dications in unmodified and modified Nafion™ films is not apparent for the new [Ru(κ2-2,2′-N2C10H6{(CH2)3(CF2)5CF3}2-4,4′)(κ2-2,2′-N2C10H8)2]2+/TBAB-modified-Nafion™-coated electrodes. Thus CVs of the latter show sustained peak current densities in excess of 1.0 mA cm−2 for the Ru3+/2+ couple and thus decent mediator retention over multiple potential cycles when exposed to mixed methanol–phosphate buffer solutions.

Rare excitatory amino acid from flowers of zonal geranium responsible for paralyzing the Japanese beetle

The Japanese beetle (JB), Popillia japonica, exhibits rapid paralysis after consuming flower petals of zonal geranium, Pelargonium x hortorum. Activity-guided fractionations were conducted with polar flower petal extracts from P. x hortorum cv. Nittany Lion Red, which led to the isolation of a paralysis-inducing compound. High-resolution–MS and NMR (1H, 13C, COSY, heteronuclear sequential quantum correlation, heteronuclear multiple bond correlation) analysis identified the paralytic compound as quisqualic acid (C5H7N3O5), a known but rare agonist of excitatory amino acid receptors. Optical rotation measurements and chiral HPLC analysis determined an l-configuration. Geranium-derived and synthetic l-quisqualic acid demonstrated the same positive paralytic dose–response. Isolation of a neurotoxic, excitatory amino acid from zonal geranium establishes the phytochemical basis for induced paralysis of the JB, which had remained uncharacterized since the phenomenon was first described in 1920.

The nuclear magnetic resonance spectra of bicyclo[2.1.0]pentanes: A comparative study

Abstract The detailed, computer analyzed NMR spectra of the isomeric 2.3-diphenylbicyclo[2.1.0] pentanes ( 1–3 ) are presented. It is noted that in the absence of special substituent effects, the endo protons on both the three- and four- membered rings are shielded relative to the exo hydrogens although comparison of chemical shifts for 1–3 with those of bicyclo[2.1.0]pentane itself reveals general deshielding of all protons by phenyl substituents. Restrictions imposed on the free rotation of the phenyl groups in the cis, syn isomer 2 are suggested to be responsible for the reversal in chemical shift order observed in this isomer. Vicinal coupling constants in both the three- and four-membered rings are consistently greater for protons in a cis rather than trans arrangement. Significant long range coupling ( 4 J > 1 Hz) in isomers 1–3 is observed even for protons which are not in a “ W ” arrangement indicating that caution should be used in assigning stereochemistry solely on the basis of the presence (or absence) of long range coupling. The availability of multiple paths and the special properties of the cyclopropane ring may account for the long range “non- W ” coupling observed.

Synthesis and characterization of 1,9-difluoro-5-methyl-5-phenyl-10,11-dihydro-5H-dibenzo[b,f]silepin

Abstract The synthesis of 2,2′-difluoro-6,6′-dichlorobibenzyl, a precursor to dibenzometallepins, has been accomplished from bromination of 2-chloro-6-toluene followed by coupling of the benzyl bromide produced with PhLi. A variety of conditions were studied for conversion to a diGrignard reagent the most successful of which involved activated magnetism (Mg ∗ ) produced from reduction of MgBr 2 and K. Reaction of the diGrignard with PhMeSiCl 2 produced 1,9-difluoro-5-methyl-5-phenyl-10,11-dihydro-5 H -dibenzo[b,f]silepin ( 3a ). The silepin was characterized by an X-ray crystal structure in the solid state and in solution by 1 H, 13 C, 29 Si and 19 F NMR spectroscopy. The solid structure reveals a folded boat conformation for the central seven-membered ring and a butterfly angle for the tricyclic framework of 124°. The 1 H NMR data in solution exhibits a complex, unsymmetrical multiplet associated with the ethano-bridge protons. The conformations of 3a were generated by MM2 calculations and the results demonstrated that there were four enantiomeric pairs of similar energy. The configuration with an axially oriented phenyl group corresponded closely to the configuration observed in the solid state. energy. The configuration with an axially oriented phenyl group corresponded closely to the configuration observed in the solid state.

Synthesis of an allene-containing germacranoid

Abstract The anion-induced cyclization of the farnesol derivative IV furnished germacranoid V . Desulfurization of the corresponding sulfoxide gave an allene analogue of the sesquiterpene alcohol, hedycaryol.

On Guaiol Oxygenation Products

Abstract The photosensitized oxygenation of guaiol (I) results primarily in allylic hydroperoxides; cyclopentenyl compounds predominate with an apparent preference for reaction at the α-face. Ozonolysis of hydroperoxide IVb furnished the hydroperoxy hemiperoxyacetal IX as a crystalline solid.