Domino "Staudinger/semi-aza-Wittig/fragmentation" reactions of gamma-azido-beta-hydroxyketones

Treatment of gamma-azido-beta-hydroxyketones with triphenylphosphine resulted, depending on the structural features of the starting materials, in a domino "Staudinger/semi-aza-Wittig/fragmentation" reaction rather than a normal aza-Wittig reaction. 2-Azido-1-hydroxy-1-(2,4-dioxoalkyl)cyclopentanes, readily available by condensation of 1,3-dicarbonyl dianions with 2-azidocyclopentanone, proved to be optimal starting materials for these reactions which afforded 1-(1,3-dioxoalkyl)amino-2-(alkylidene)cyclopentanes.     

"Contact voltage" in nanoparticle/molecule connections

This work presents conclusive evidence that connecting Pt and Co nanoparticles stabilized by an aluminum-organic shell with molecular spacers interacting with this shell can induce notable changes in the electronic structure of the metal. X-ray absorption spectroscopy measurements at the Al K-, the Pt L(III)-, and the Co K-edge provide consistent evidence for this effect. The changes induced by cross-linking with an acidic spacer are discussed in detail as an example to elucidate the mechanism of this effect. It turns out that a reconfiguration of the protection shell that occurs upon networking is responsible for the observed changes.     

Solvent-free synthesis of 4-chalcogenophosphorylpyridines viaSNHAr reaction of pyridines with secondary phosphine chalcogenides

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ISO/TC 158: "Analysis of Gases"

This paper presents an overview of the work of ISO/TC 158: "Analysis of Gases". The standardisation of general and specific aspects of gas analysis, focusing on the preparation and use of calibration gases, to facilitate traceable and comparable measurements. ISO/TC 158 follows "market-oriented" objectives and is an advocate of the consistent use of a coherent set of ISO standards aimed at reinforcing "Good Analysis Practice" in organisations dealing with gas analysis. ISO/TC 158 acts as a centre of information in the field of gas analysis and is an active intermediary between suppliers and users of calibration gases.     

Diastereoselective synthesis of N-acetyl-D,L-acosamine and N-benzoyl-D,L-ristosamine

N-Acyl derivatives of $\text{D}$,$\text{L}$-acosamine and $\text{D}$,$\text{L}$-ristosamine were synthesized with high stereo selectivity utilizing intramolecular Michael addition of γ- and δ-carbomoyloxy-α,β-unsaturated esters.     

"Click" saccharide/beta-lactam hybrids for lectin inhibition

Hybrid glycopeptide beta-lactam mimetics designed to bind lectins or carbohydrate recognition domains in selectins have been prepared according to a "shape-modulating linker" design. This approach was implemented using the azide-alkyne "click" cycloaddition reaction, and as shown by NMR/MD experiments, binding of the resulting mimetics to Ulex Europaeus Lectin-1 (UEL-1) occurred after a "bent-to-extended" conformational change around a partially rotatable triazolylmethylene moiety.     

Stereoselective synthesis of 1,8- and 1,5-diketo-trans-syn-trans-perhydroanthracenes

A stereOselective conversion of 1,8- and 1,5-diethoxy-9,10-anthraquinone to 1,8- and 1,5-diketo-$\text{trans}$-$\text{syn}$-$\text{trans}$-perhydroanthracenes by successive sodium borohydride, metal-ammonia, and catalytic reductions is described.     

Steroidal antifeedants from the dorid nudibranch Aldisasanguineacooperi

Two steroids, 3-oxo-chol-4-ene-24-oic acid ($\text{2}$) andi ts unsaturated analog $\text{4}$ have been isolated from the dorid nudibranch $\text{Aldisa}$$\text{sanguinea}$$\text{cooperi}$, and the acid $\text{2}$ has been shown to have antifeedant properties.     

Advanced sedex (sensitive detector of exothermic processes)

The instrument described is suitable for the investigation of the thermal behaviour of substances and reaction mixtures under production conformable conditions; this is made possible by the sophisticated design of the sample chamber: easy stirring of the samples, measuring under any gas atmosphere and while bubbling gas through the sample, choice of the sample container and visual observation during the measurement. The control device allows the choice of one of three operational modes: constant temperature, linear increase in temperature, and adiabatic control; this permits the application of the SEDEX apparatus for a variety of methods including dynamic scanning, isoperibolic measurements, and (quasi) adiabatic studies.     

Graphitic molecules with partial "zig/zag" periphery

A new synthetic protocol that affords novel hexa-peri-hexabenzocoronene (HBC) derivatives with partial "zig/zag" periphery and dramatically different electronic properties has been developed, which represents an important step toward understanding structure-property relationships of graphitic materials. The scope of this methodology was broadened by application to a much larger polycyclic aromatic hydrocarbon (PAH) with a more extended "zig/zag" character.     

"H/Vinyl" and "Alkyl/Vinyl" conical intersections leading to carbene formation from the excited states of cyclohexene and norbornene

The photochemical [1,2]-shifts leading to carbene intermediates from cyclohexene and norbornene have been studied using CASSCF calculations and a 6-31G* basis set. In each case, a S(1)/S(0) conical intersection hyperline was identified that extends from the region of the reactant excited state to the carbene product. It is traditionally thought that the Rydberg R(pi,3s) state is responsible for carbene formation on photolysis of cyclic alkenes, but these new results indicate an efficient mechanism for carbene formation following excitation to the (1)(pipi*) state. This pathway is essentially barrierless and involves internal conversion to the ground-state surface via conical intersections between the excited zwitterionic valence state and the ground-state surface, similar to those responsible for cis-trans isomerization in ethene and other acyclic alkenes. These results are in excellent agreement with recent experimental data obtained using femtosecond spectroscopy.     

Stereocontrolled (E,Z and erythro, threo) synthesis of ⊙-hydroxyallylic sulphides

All four isomers of substituted 3-alkylthio-4-hydroxybutenes have been synthesised: both the geometry of the double bond and the relative stereochemistry of the two chiral centres are controlled.     

Preparation of halo-F-methanes via potassium fluoride-halogen cleavage of halo-F-methylphosphonium salts

Treatment of halo-$\text{F}$-methylphosphonium salts with potassium fluoride and halogen (I₂, Br₂, ICl, IBr) gives modest yields of halo-$\text{F}$-methanes. This method of preparation augments the classical Hunsdiecker approach to these materials.     

Synthesis of N-benzoyl-L-daunosamine from D-threonine

The synthesis of N-benzoyl-$\text{L}$-daunosamine (14) from the C₄$\text{threo}$ aldehyde (2b), prepared from $\text{D}$-threonine, through the intermediacy of the C₇ adduct (7a) is reported     

The ipso-nitration of p-cresol

The nitration of $\text{p}$-cresol by nitric acid in aqueous sulphuric acid involves ~40% $\text{ipso}$-substitution at C^Me. The 4-methyl-4-nitrocyclohexa-2,5-dien-1-one (I) formed undergoes an acid-catalysed rearrangement to 4-methyl-2-nitrophenol.     

MIRC (Michael Initiated Ring Closure) Reactions Formation of Three,Five, Six and Seven Membered Rings

The term MIRC reaction is defined. Examples of the construction of three, five, six and seven membered rings using alkylthiolates and LDA as nucleophiles are presented.     

Empirical determination of medium effects on the equilibrium between transcis and transtrans 1,2-dibromo-4-t-butylcyclohexanes

Head space analysis, GLC retention time data, and solution calorimetry are used to determine the effect of medium on the thermodynamic parameters for the equilibrium (1) ? (2). It is shown that changes in ΔG° and ΔH° can be evaluated for the transfer of the equilibrium from a series of solvents to the gaseous phase which is used as the reference medium.