Synthese von Triafulven-Vorstufen aus trisubstituierten Cyclopropanen

Synthesis of Triafulvene-Precursors from Trisubstituted Cyclopropanes Trisubstituted cyclopropanes 5a–f are prepared by carbene addition to the appropriate olefins. While 5a (Y = OAc) and 5c (Y = Cl) rearrange in the presence of BuLi, 5d (Y = SPh) is stable enough to allow the envisaged sequence for triafulvene (Scheme 2) : halogen-Li exchange, followed by methylation of 6d , gives 7d in a 93% yield; after base-induced elimination of HB r from 7d , the key precursor 1-methylene-2-(phenylthio)cyclopropane ( 9 , 70% yield) is isolated. Compound 9 is transformed into the corresponding sulfoxide 10 (83%), sulfone 11 (80%), and sulfonium fluoroborate 12 (95% yield) by subsequent oxidation and methylation, respectively. Some ¹H-NMR results of cyclopropanes 5a–f and 7d as well as of methylidene-cyclopropanes 9–11 are discussed.     

Strukturaufklärung eines Dimethylfulven-Trimeren. Hinweis auf eine [6 + 4]-Cycloaddition von 6, 6-Dimethylfulven

Structure Elucidation of a Dimethylfulvene-trimer. Evidence for a [6+ 4]-Dimerization of 6, 6-Dimethylfulvene Thermal reaction of pure 6, 6-dimethylfulvene ( 1c ) at 60° gives an oligomeric mixture consisting mainly of fulvene-trimers. The structure of the main product 3c is partially elucidated by ¹H-NMR. investigations at 400 MHz and definitely confirmed by X-ray analysis. The formation of 3c is explained in terms of a [6+4] dimerization, followed by a 1, 5-proton-shift and a final Diels-Alder reaction.     

Chloracylierung und Bromacylierung von Carbonylverbindungen. III. Lage des Gleichgewichts

Chloroacylation and Bromoacylation of Carbonyl Compounds III. Reactant/Product Equilibria Aliphatic, α, β-unsaturated and aromatic aldehydes 1 as well as aliphatic ketones react with acyl halides 2 to α-haloalkyl esters 3 . In the presence of Lewis acids there is an equilibrium between reactants and product. The position of the equilibrium depends on the nature of the carbonyl compound as well as that of the acyl halide: The products 3 are favoured in the case of aldehydes, cyclobutanone and cyclohexanone, and the equilibrium constant increases in the series F < Cl < Br < I. Low reaction temperature, nonpolar solvents as well as high reactant concentrations favour the product 3 .     

The influence of lithium excess in the target on the properties and compositions of Li<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript>2</Subscript>O<Subscript>4−<Emphasis Type="Italic">δ</Emphasis></Subscript> thin films prepared by PLD

Li–Mn–O thin films were deposited by pulsed laser deposition (PLD) onto stainless steel substrates using targets containing different concentrations of added Li₂O. The influence of the target composition on the stoichiometry of the resulting thin films, the surface morphology and the electrochemical properties was studied. The application of the target with added 7.5 mol% Li₂O results in an almost ideal lithium content, while all films were still oxygen deficient. The thin films were applied as electrodes in Li//Li_1+x Mn₂O_4−δ cells (i.e. model cells for a rechargeable Li-ion battery) and characterized by cyclic voltammetry and galvanostatic charge/discharge experiments. The electrochemical measurements of the thin films confirmed that the thin films can serve as good model systems and that they show a sufficient cyclability.     

Further Synthetic Attempts towards Calicene

First synthetic attempts towards the so‐far‐unknown calicene (=5‐(cycloprop‐2‐en‐1‐ylidene)cyclopenta‐1,3‐diene) precursors 3‐(cyclopenta‐2,4‐dien‐1‐ylidene)tricyclo[3.2.2.2^2,4]nona‐6,8‐diene ( 4 ; Scheme 1), 1,4‐di(cyclopenta‐2,4‐dien‐1‐ylidene)cyclohexa‐2,5‐diene ( 5 ; Scheme 2), and (2‐bromocycloprop‐1‐en‐1‐yl)cyclopentadiene ( 6 ; X=Br; Scheme 5) are reported, which would represent very attractive compounds for gas‐phase pyrolysis ( 4 ), matrix photolysis ( 5 ), and low‐temperature HBr eliminations in solution ( 5 ).