Palladium-catalyzed alpha-arylation of sulfoximines

[reaction: see text] Palladium-catalyzed alpha-arylation of N-benzoyl sulfoximine ethyl ester with various aryl bromides leads to alpha-arylated products that can easily be hydrolyzed, giving the corresponding N-protected benzyl phenyl sulfoximines. In this manner, new sulfoximine derivatives are accessible that have so far been difficult to prepare in enantiopure form.     

Reactivity of silyl-substituted heterobimetallic iron-platinum hydride complexes towards unsaturated molecules: Part II. Insertion of trifluoropropyne and hexafluorobutyne into the platinum-hydride bond

Insertion of hexafluorobutyne into the Pt-H bond of the heterobimetallic complexes [(OC)₃Fe{Si(OMe)₃}(μ-Ph₂PXPPh₂)Pt(H)(PPh₃)] (1a X = CH₂; 1b X = NH) yields the σ-alkenyl complexes [(OC)₃Fe{μ-Si(OMe)₂(OMe)}(μ-Ph₂PXPPh₂)Pt{C(CF₃)C(H)CF₃}] (3a X = CH₂; 3b X = NH). This insertion reaction is accompanied by dissociation of the platinum bound PPh₃ ligand and saturation of the vacant coordination site by a dative μ−η²-Si-O → Pt interaction. Addition of the Pt-H bond of 1a across the triple bond of 3,3,3-trifluoropropyne affords in a regiospecific manner [(OC)₃Fe{μ-Si(OMe)₂(OMe)}(μ-dppm)Pt{C(CF₃)CH₂}] (2) having the trifluoromethyl substituent on the α-carbon. Addition of RNC to 3 affords the isocyanide adducts [(OC)₃Fe{Si(OMe)₃}(μ-Ph₂PXPPh₂)Pt(CNR){C(CF₃)C(H)CF₃}] (4a R = t-Bu, X = CH₂; 4b R = 2,6-xylyl, X = CH₂; 4c R = 2,6-xylyl, X = NH). In dichloromethane solution 3a is gradually transformed into the C₄F₆-bridged compound [(OC)₃Fe(μ-dppm)(μ-CF₃CCCF₃)Pt(CO)] 5. The Pt-bound carbonyl ligand of 5 is displaced by xylylisocyanide or trimethylphosphite affording the derivatives [(OC)₃Fe(μ-dppm)(μ-CF₃CCCF₃)Pt(CNxylyl)] 6 and [(OC)₃Fe(μ-dppm)(μ-CF₃CCCF₃)Pt{P(OMe)₃}] 7. The molecular structures of 4a, 5 and 6 have been determined by X-ray diffraction studies.     

Synthesis and use of alpha-silyl-substituted alpha-hydroxyacetic acids

[reaction: see text] Rhodium-catalyzed oxygen transfer was used to generate benzyl 2-silyl-2-oxoacetates in good yields. The hydrogenation of these compounds led to chiral alpha-silyl-substituted alpha-hydroxyacetic acids. Resolution by means of HPLC using a chiral stationary phase afforded an enantiomerically pure representative of this class of compounds, which was successfully applied as a chiral ligand in an asymmetric aldol-type reaction.     

Synthesis,spectral, thermal and structural characterization of {[Cu(H2O)3][Cu(MAL)2] · 2H2O}∞ and [Cu(MAL)(TEA)] · H2O (MAL = malonate and TEA = triethanolamine)

A polymeric malonato-bridged copper(II) complex, {[Cu(H₂O)₃][Cu(MAL)₂]· 2H₂O}, and a mononuclear malonato-copper(II) complex with triethanolamine, [Cu(MAL)(TEA)]·H₂O, have been prepared and characterized by elemental analyses, i.r., u.v.–vis, magnetic measurements and single crystal X-ray diffraction. The polymeric complex consists of one-dimensional chains containing the MAL bridged [Cu(H₂O)₃]²⁺ and [Cu(MAL)₂]^2– ions and each MAL ligand simultaneously exhibits chelating bidentate (at one copper atom) and bridging (at the adjacent copper atom) coordination modes. The intrachain Cu1...Cu2 separation is 4.963 Å and the polymeric complex exhibits antiferromagnetic behaviour. In the mononuclear complex, the copper(II) ion is octahedrally coordinated by one bidentate MAL and one tetradentate neutral TEA ligands. The i.r. spectra and thermal decompositions of both complexes are described.     

Modeling chemoadaptive behavior: X-ray structure of the trimethylamine oxide-urea (1∶4) complex

The structure of a trimethylamine oxide (TMAO)-urea 14 complex was investigated by x-ray crystallographic methods. C₃H₉NO, 4CH₄N₂O, M_r=315.33, monoclinic P2₁/n, a=11.004(2), b=9.8259, c=15.419(2),=106.88(4), V=1595.4(2) å₃, Z=4, D_x=1.313(1) g cm^–3, monochromatized Cu (=1.5418 å),=8.94 cm^–1, F(OOO)=680, temperature = 110K, final R=0.067, for 1786 unique observed reflections. Based on these studies and comparison with related compounds a model of the interaction of urea and TMAO with proteins, especially enzymes, is proposed. This is important in the physiology of many organisms, especially elasmobranchs. The counteracting effect of TMAO on urea perturbation of protein structure and function is interpreted in terms of water structure as a balance between the structure breaking effect of urea and the structure-stabilizing effect of TMAO.     

Many-to-many location-routing with inter-hub transport and multi-commodity pickup-and-delivery

In this paper, we consider a variant of the many-to-many location-routing problem, where hub facilities have to be located and customers with either pickup or delivery demands have to be combined in vehicle routes. In addition, several commodities and inter-hub transport processes are taken into account. A practical application of the problem can be found in the timber-trade industry, where companies provide their services using hub-and-spoke networks. We present a mixed-integer linear model for the problem and use CPLEX 12.4 to solve small-scale instances. Furthermore, a multi-start procedure based on a fix-and-optimize scheme and a genetic algorithm are introduced that efficiently construct promising solutions for medium- and large-scale instances. A computational performance analysis shows that the presented methods are suitable for practical application.     

Heterotrimeric liquid crystalline thiadiazole derivatives

Abstract

Various trimeric co-oligomers combining 2-phenyl-1,3,4-thiadiazole mesogenic moieties with a biphenyl mesogenic moiety were synthesized and their mesomorphic behaviour investigated by polarizing microscopy, calorimetry and X-ray scattering. Such co-oligomeric structures provide an opportunity to combine different mesogenic units. Thus readily accessible homochiral biphenyl mesogenic units were connected with thiadiazole mesogenic units leading to an oligomeric liquid crystal material with ferroelectric properties.