Stereoselective Ring Opening of Electronically Excited Cyclohexa-2, 4-dienones: Cause and effect

The two conformers of a cyclohexa-2, 4-dienone with different substituents at C(6) on irradiation are believed to undergo ring opening stereospecifically affording a mixture of two configurationally isomeric diene-ketenes (and descendents thereof)- Exceptions are generally found for those dienones with one C and one O substituent or even with two C substituents, if one of them carries a polar group at a site able to interact through space with the ring C?O group. In these cases, only one of the two anticipated diene-ketenes (and descendents thereof) is produced. A thorough investigation of the photochemistry of a series of structurally different cyclohexa-2, 4-dienones on analytical as well as on preparative scale extends our mechanistic knowledge of the various routes from diene-ketenes into a variety of compound classes. Novel compound classes accessible to diene-ketenes are seven-membered carbocycles (by intramolecular aldolization of the zwitterion of appropriately substituted, transiently formed diene-(N, O)-ketene acetals) and β-lactams (by Staudinger reaction).     

Absolute Configuration of 3-Substituted 1-Azabicyclo[2.2.1]heptanes

The l-azabicyclo[2.2.1]heptan-3-exo-ol ( 2 ) was resolved by fractional crystallisation of its hydrogen tartrate salts. The enantiomers (+)- and (?)- 2 were oxidised to the ketones (?)- 4 and (+)- 4 , respectively (Scheme). CD spectroscopy suggested that (?)- 4 possesses the (1R,4S)-configuration. This absolute configuration was confirmed by single-crystal X-ray diffraction of the derivative (+)-(1R,4R)-3-(1,3-dithian-2-ylidene)-1-azabicyclo [2.2.1]-heptane ((+)- 5 ).     

Protein analysis of laser capture micro-dissected tissues revealed cell-type specific biological functions in developing barley grains

Both the nucellar projection (NP) and endosperm transfer cells (ETC) of the developing barley grain (harvested 8 days after flowering) were isolated by laser capture micro-dissection combined with pressure catapulting. Protein extracts were analyzed by nanoUPLC separation combined with ESI-Q-TOF mass spectrometry. The majority of the ～160 proteins identified were involved in translation, protein synthesis, or protein destination. The NP proteome was enriched for stress defense molecules, while proteins involved in assimilate transport and the mobilization of nutrients were common to both the NP and the ETC. The combined qualitative and quantitative protein profiling allowed for the identification of several proteins showing tissue specificity in their expression, which underlines the distinct biological functions of these two tissues within the developing barley grain.     

The Unexpected Formation of a 2,2′-Di( N -ethyl-acetamino)substituted Diphenyl Disulfane on Oxidation of 3-Ethyl-2-methylbenzothiazolium Tetrafluoroborate

Attempts at the oxidation of 3-ethyl-2-methylbenzothiazolium salt 2 with a variety of oxidizing reagents did not lead to the desired isochiral S -oxide 3 or achiral S , S -dioxide 4 , in some cases, however, unexpectedly to the ring-opened dimeric 2,2'-di( N -ethyl-acetamino)substituted diphenyl disulfane 5 , the molecular structure of which was confirmed by x-ray analysis. The synthesis of 2-methylbenzothiazole- S , S -dioxide 14 , reported by Zincke et al. in 1915, turned out to be not reproducible. \centerline{\epsfbox{:art:fig-01.jpg}}     

Self-organization of gold atoms on a polar FeO(111) surface

The spatial distribution of single Au atoms on a thin FeO film has been investigated by low-temperature scanning tunneling microscopy and spectroscopy. The adatoms preferentially adsorb on distinct sites of the Moiré cell formed by the oxide layer and the Pt(111) support and arrange into a well-ordered hexagonal superlattice with 25 angstroms lattice constant. The self-organization is the consequence of an inhomogeneous surface potential within the FeO Moiré cell and substantial electrostatic repulsion between the adatoms.     

Local Entropy Conditions in Transonic Potential Flow Problems

The transonic potential flow problem is handled as a variational problem over a closed convex set which is given by a bound for the gas velocity and by a local entropy condition. It can be shown that the minimum problem has a solution though the functional need not be convex and the given set is not compact. Furthermore, the convergence of an approximation method (KATCHANOV'S method) for the solution to the corresponding variational inequality is proved.     

Fulven-Dimere: Synthese,Strukturbeweis and thermisches Verhalten

Fulvene-Dieters: Synthesis, Structure Elucidation and Thermal Behaviour In contrast to earlier assumptions, thermal reaction of pure fulvene ( 1a ), 6-methylfulvene ( lb ) and 6, 6-dimethylfuivene ( 1c ) at 227deg; gives oligomeric mixtures consisting mainly of the endo-[4 + 2]-eycloaddition products 2a , 2b and 2c . Thermal reactivity of the fulvenes decreases strongly in the series 1a > 1b > 1c . While the dimers 2b and 2c equilibrate very easily in solution above room temperature with 1b and 1c , respectively, 2a equilibrates with the isomer 5a (? 1, 6-Dimethyliden3a α, 3bβ, 6a α, 6bβ-tetrahydro-1-H), 6 H-bi (cyclopentadienylen). This surprising rearrangement envolves a formal 1,3-shift of the 1, 2-dihydrofulvene-unit of 2a (s. Scheme 4).