Highly enantioselective organocatalytic α-amination reactions of aryl oxindoles: developing designer multifunctional alkaloid catalysts

An enantioselective α-amination of aryl oxindoles catalyzed by a dimeric quinidine has been developed. The reaction is general, broad in substrate scope, and affords the desired products in good yields with good to excellent enantioselectivities. This study provides the first examples of a general organocatalytic method for the creation of nitrogen-containing, tetrasubstituted chiral centers at C(3) of various aryl oxindoles. Furthermore, new catalysts and insights into structural elements of the catalysts that significantly influence enantioselectivities are disclosed.     

On the correlation between the X‐ray absorption chemical shift and the formal valence state in mixed‐valence manganites

Here the correlation between the chemical shift in X‐ray absorption spectroscopy, the geometrical structure and the formal valence state of the Mn atom in mixed‐valence manganites are discussed. It is shown that this empirical correlation can be reliably used to determine the formal valence of Mn, using either X‐ray absorption spectroscopy or resonant X‐ray scattering techniques. The difficulties in obtaining a reliable comparison between experimental XANES spectra and theoretical simulations on an absolute energy scale are revealed. It is concluded that the contributions from the electronic occupation and the local structure to the XANES spectra cannot be separated either experimentally or theoretically. In this way the geometrical and electronic structure of the Mn atom in mixed‐valence manganites cannot be described as a bimodal distribution of the formal integer Mn³⁺ and Mn⁴⁺ valence states corresponding to the undoped references.     

Bidirectional Chemo‐Switching of Spin State in a Microporous Framework

The ins and outs of spin : Using the microporous coordination polymer {Fe(pz)[Pt(CN)₄]} ( 1 , pz=pyrazine), incorporating spin‐crossover subunits, two‐directional magnetic chemo‐switching is achieved at room temperature. In situ magnetic measurements following guest vapor injection show that most guest molecules transform 1 from the low‐spin (LS) state to the high‐spin (HS) state, whereas CS₂ uniquely causes the reverse HS‐to‐LS transition.

     

Inside Cover: Bidirectional Chemo‐Switching of Spin State in a Microporous Framework (Angew. Chem. Int. Ed. 26/2009)

Bidirectional chemo‐switching of magnetism occurs in a microporous coordination polymer containing spin‐crossover subunits, as described by M. Ohba, J. A. Real, S. Kitagawa, and co‐workers in their Communication on page 4767 ff. In situ magnetic measurements reveal that most guest molecules transform the framework spin state from diamagnetic low spin (red) to paramagnetic high spin (yellow), whereas the guest CS₂ stabilizes the low‐spin state. These induced spin states are retained as a memory effect after the release of the guest.

     

On multistage Stochastic Integer Programming for incorporating logical constraints in asset and liability management under uncertainty

We present a model for optimizing a mean-risk function of the terminal wealth for a fixed income asset portfolio restructuring with uncertainty in the interest rate path and the liabilities along a given time horizon. Some logical constraints are considered to be satisfied by the assets portfolio. Uncertainty is represented by a scenario tree and is dealt with by a multistage stochastic mixed 0-1 model with complete recourse. The problem is modelled as a splitting variable representation of the Deterministic Equivalent Model for the stochastic model, where the 0-1 variables and the continuous variables appear at any stage. A Branch-and-Fix Coordination approach for the multistage 0–1 program solving is proposed. Some computational experience is reported.      

Transfers,contracts and strategic games

This paper analyses the role of transfer payments and strategic contracting within two-person strategic form games with monetary payoffs. First, it introduces the notion of transfer equilibrium as a strategy combination for which individual stability can be supported by allowing the possibility of transfers of the induced payoffs. Clearly, Nash equilibria are transfer equilibria, but under common regularity conditions the reverse is also true. This result typically does not hold for finite games without the possibility of randomisation, and transfer equilibria for this particular class are studied in some detail.     

Dearomatizing anionic cyclization of N-methyl-N-benzyldi(1-naphthyl)phosphinamide: a route for access to a new class of functionalized tricyclic azaphospholes with antitumor properties

The dearomatizing anionic cyclization of N-alkyl-N-benzyldi(1-naphthyl)phosphinamide 1d followed by trapping with a series of carbonyl reagents and α,β-unsaturated ketones under optimized conditions provided new tetrahydro-1H-naphtho[1,2-c][1,2]-azaphosphole 1-oxides from moderate to high yields and diastereoselectivities. In addition, two doubly dearomatized compounds as a result of double dearomatization on the two naphthalene rings of 1d have been isolated at first time. Three functionalized azaphospholes have been evaluated on three different human tumor cell lines showing growth inhibition factors (GI₅₀) at a micromolar scale. One of these heterocycles has also shown cytostatic properties.     

Acid-catalysed,nucleophile-catalysed and thermal decomposition of 2-amino-3-(2′,2′-dimethylaziridino)-1,4-naphthoquinone

The course of the thermal, acid-catalysed and iodide-catalysed decomposition of 2-amino-3-(2′,2′-dimethylaziridino)-1,4-naphthoquinone (III) was investigated. Thermal and iodide-catalysed decompositions gave mainly 2,3-diamino-1,4-naphthoquinone (VI) and 2-amino-3-(2′-methylallylamino)-1,4-naphthoquinone (V) together with low amounts of 2,2-dimethyl-1,2,3,4,5,10-hexahydrobenzo[g]quinoxaline (IV) and 2-isopropyl-1H-naphthoimid-azole-4,9-dione (VII). The acid catalysed isomerization of the aziridinonaphthoquinone III with halohydric acids or with acetic acid readily gave the opening of the aziridine ring; the corresponding salts of 2-amino-3-(2′-haloisobutylamino)-1,4-naphthoquinones (VIIIa-c) and 2-amino-3-(2′-acetoxyisobutylamino)-1,4-naphthoqunone (X) were formed by cleavage of the carbon-nitrogen bond at the substituted carbon atom. Hypotheses on the mechanism of these reactions are given.     

Electrodeposited Pt-Ir electrodes: characterization and electrocatalytic activity for the reduction of the nitrate ion

The activity of Pt-Ir deposits on titanium for the reduction of the nitrate ion in 0.5 M perchloric acid was studied. The electrodes were characterized by SEM-EDAX, XPS and cyclic voltammetry. The activity of the electrodes for the nitrate reduction depended on the Pt-Ir ratio. Repetitive cyclic voltammograms produced an enrichment of the electrode surface with Ir and a decrease of the catalytic activity. A synergistic effect in the electrodes with low iridium content is discussed. Received: 2 June 1997 / Accepted: 28 August 1997