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Two N-heterocyclic phosphines with exocyclic SCN substituents were synthesised via metathesis of chlorophosphine precursors with KSCN and fully characterised. The crystallographic studies reveal that the products exhibit pronounced structural differences. The thiocyanato unit binds in one case via the nitrogen atom to yield a molecular structure with a slightly elongated P-N single bond and, in the other case, via the sulfur atom to form a structure that is best described as an ion pair and forms a one-dimensional coordination polymer in the crystal. DFT calculations suggest that the P-N and P-S interactions can be described as covalent and dative bonds, respectively, and that the structural differences correlate with the different cation stabilities of the individual phosphenium cation fragments. Key words: N-heterocyclic phosphines, ambident Lewis bases, dative bonds, coordination isomerism. Nous avons synthétisé deux phosphines N-hétérocycliques portant des substituants SCN exocycliques par voie de métathèse de précurseurs chlorophosphine avec le KSCN, et nous les avons soumis à une caractérisation complète. Les analyses cristallographiques révèlent que les produits présentent des différences structurales importantes. L'unité thiocyanate se lie dans un cas par l'atome d'azote pour produire une structure moléculaire caractérisée par une liaison simple P-N légèrement allongée, et dans l'autre cas, par l'atome de soufre pour former une structure qui s'apparente davantage à une paire d'ions créant un polymère de coordination unidimensionnel dans le cristal. Les calculs DFT indiquent que les interactions P-N et P***S pourraient être décrites comme des liaisons covalentes et bipolaires, respectivement, et que les différences structurales sont corrélées avec la stabilité des différents fragments cationiques de phosphénium. [Traduit par la Rédaction] Mots-clés: phosphines N-hétérocycliques, bases de Lewis ambidentates, liaisons bipolaires, isomérisme de coordination., Introduction The reaction between a Lewis acid (electron pair acceptor) and a Lewis base (electron pair donor) to form a complex (or Lewis pair) is one of the most fundamental [...]

The previously unreported carbene-phosphine adduct (IPr)P[Cl.sub.2][N.sub.3] [IPr = [(HCNDipp).sub.2]C:; Dipp = 2,6-[sup.i][Pr.sub.2][C.sub.6][H.sub.3]] was synthesized and used as a synthon toward the elusive dichlorophosphazene monomer unit, [[Cl.sub.2]P=N]. (IPr)P[Cl.sub.2][N.sub.3] was found to undergo halide and azide abstraction when combined with various electrophiles and its thermolysis yielded the unexpected Staudinger reaction product (IPr=N)P[Cl.sub.2]. Key words: Staudinger reaction, phosphazenes, carbene, phosphine. Nous avons réalisé la première synthèse de l'adduit carbène-phosphine (IPr)P[Cl.sub.2][N.sub.3], [IPr = [(HCNDipp).sub.2]C:; Dipp = 2,6-[sup.i][Pr.sub.2][C.sub.6][H.sub.3]] et l'avons employé comme synthon en vue de préparer l'unité monomérique dichlorophosphazène hypothétique [[Cl.sub.2]P=N]. Nous avons observé qu'en présence de divers électrophiles, l'adduit (IPr)P[Cl.sub.2][N.sub.3] subissait une abstraction des atomes d'halogène et de l'azoture, et que sa thermolyse donnait lieu à un produit inattendu, le (IPr=N)P[Cl.sub.2], issu de la réaction de Staudinger. [Traduit par la Rédaction] Mots-clés: réaction de Staudinger, phosphazènes, carbène, phosphine., Introduction Originally referred to as 'inorganic rubber', poly(dichlorophosphazene) [[[Cl.sub.2]P=N].sub.n] was first reported by Stokes in 1895. (1) This important parent polymer is typically synthesized by the ring-opening polymerization (ROP) of [...]

Methyl substituted 3-hydroxypyridin-4([.sup.1]H)-ones have been synthesized. The p[K.sub.a] values and [Fe.sup.3+] affinity constants of these ligands were studied. The introduction of an electron-donating methyl group at a different position of pyridinone ring markedly influences the p[K.sub.a] values of 3-hydroxy and 4-oxo groups. The p[Fe.sup.3+] values were also affected and are in the range of 17.6-20.7. The findings can be used to guide a design of 3-hydroxypyridin-4-ones with desirable p[K.sub.a] and p[Fe.sup.3+] values. Key words: iron chelators, 3-hydroxypyridin-4-ones, methyl substituted, p[Fe.sup.3+], electron-donating group, p[K.sub.a]. Resume : Nous avons synthetise des 3-hydroxypyridin-4([.sup.1]H)-ones substituees par un groupe methyle. Nous avons etudie les p[K.sub.a] de ces ligands et leurs constantes d'affinite pour le [Fe.sup.3+]. La position d'un groupe methyle electrodonneur sur le noyau pyridinone influence considerablement les valeurs de p[K.sub.a] des groupes 3-hydroxy et 4-oxo, et modifie egalement les valeurs de p[Fe.sup.3+], qui se situent dans un intervalle de 17,6 a 20,7. Ces resultats peuvent permettre d'orienter la conception de 3-hydroxypyridin-4-ones qui poss-dent des valeurs souhaitables de p[K.sub.a] et de p[Fe.sup.3+]. [Traduit par la Redaction] Mots-cles : chelateurs du fer, 3-hydroxypyridin-4-ones, substitue par un groupe methyle, p[Fe.sup.3+], groupe electrodonneur, p[K.sub.a]., Introduction Deferiprone (6) is an orally active iron-selective chelator that is widely used to treat systemic iron overload associated with regular blood transfusion. (1,2) It is highly effective at removing [...]

Abstract: Competitive 5-exo and 6-endo anionic intramolecular cyclization reactions in heterocyclic alkynylamides were explored via experimental and computational analysis. The 5-exo-dig cyclization pathway is usually disfavoured in heterocyclic systems, and [...]

Abstract: Sorption of d-metal ions ([Cu.sup.2+], [Fe.sup.2+], and [Ni.sup.2+]) from aqueous media using modified heterocyclic biopolymers takes place with the participation of sorption sites, with the following acidic groups: α-hydroxycarboxylic [...]

A catalyst-free, direct, high regio-, and chemo-selective method is reported for the facile conversion of a wide variety of epoxides to their corresponding 2-thiocyanatoalkyl alkanoates, which contain two important functional groups (ester and thiocyanate). using a mixture of tetrabutylammonium rhodanide ([(n-Bu).sub.4]NSCN) and an aliphatic or aromatic carboxylic anhydride under neutral and solvent-free conditions. Key words: epoxide, 2-thiocyanatoalkyl alkanoate, carboxylic anhydride, tetra butyl ammonium rhodanide. On a mis an point une methode hautement regio- el chimio-selective directe et n'impliquant aucun catalyseur pour la transformation facile d'une grande variete d'epoxydes en alcanoates de 2-thiocyanatoalkyles correspondants qui contiennent deux groupes fonctionnels importants (ester et thiocyanate): elle comporte l'utilisation d'une melange de rhodanide de tetrabutylammonium [(n-Bu).sub.4]NSCN et l'anhydride d'un acide carboxylique aliphatique ou aromatique, dans des conditions neutres et sans solvant. Mots-cles : epoxyde, alcanoate de 2-thiocyanatoalkyle, anhydride d'acide carboxylique, rhodanide de tetrabutylammonium, [Traduit par la Redaction], Introduction Epoxides are important intermediates in organic synthesis. (1) Their facile regio- and stereo-selective ring-opening reactions with a wide variety of nucleophiles provide a powerful strategy in organic chemistry. (1-6) [...]

Synthesis of some oxygen, nitrogen, and sulfur based condensed heterocycles by the condensation of dimedone with aromatic monoaldehyde under different solvent conditions has been achieved. Key words: dimedone, heterocyclization, dimerization. On a realise la synthase de derives heterocycliques a base d'oxygene, d'azote et de soufre par condensation de la dimedone avec un monoaldehyde aromatique dans divers solvants. Mots-cles: dimedone, heteerocyclisation, dimerisation. [Traduit par la Redaction], Introduction 1,3-Dicarbonyl derivatives constitute important synthetic intermediates, incorporating multiple functionalities that can be either nucleophilic or electrophilic species in a large variety of synthetic transformations. (1) Their versatility and effectiveness [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.tibs.2009.02.004 Byline: Christoph Parthier (1), Steffen Reedtz-Runge (2), Rainer Rudolph (1)(3)(4), Milton T. Stubbs (1)(3)(4) Abstract: G-protein-coupled receptors (GPCRs) represent the largest constellation of validated drug targets. Crystal structures of class A GPCRs have facilitated major advances in understanding the principles underlying GPCR activation. By contrast, relatively little is known about class B GPCRs, a family of receptors for a variety of therapeutically relevant peptide hormones. Encouraging progress has recently been made through the structural elucidation of several extracellular hormone-binding domains of class B GPCRs in complex with their natural ligands or synthetic analogues. The structures reveal similar modes of ligand binding, with concomitant [alpha]-helical structuring of the ligand. The latter suggests an attractive mechanical model for class B GPCR activation. Author Affiliation: (1) Institut fur Biochemie und Biotechnologie, Martin-Luther-Universitat Halle-Wittenberg, Kurt-Mothes-StraAe 3, D-06120 Halle (Saale), Germany (2) Department of Structure and Biophysical Chemistry, Novo Nordisk, 2760 MA[yen]lA[cedilla]v, Denmark (3) Mitteldeutsches Zentrum fur Struktur und Dynamik der Proteine, Martin-Luther-Universitat Halle-Wittenberg, D-06120 Halle (Saale), Germany (4) ZIK HALOmem, Martin-Luther-Universitat Halle-Wittenberg, D-06120 Halle (Saale), Germany

Pd-catalyzed aminocarbonylation in the presence of Xantphos as a ligand was used to transform lactam-, lactone-, and thiolactone-derived triflates into N-methoxy-N-methyl or morpholine Weinreb amides. The method could also be applied to synthesize dienones in which one of the double bonds is embedded in a heterocyclic moiety, as useful substrates for Nazarov cyclization.

The full details, scope, and limitations of copper-catalyzed one-step functionalization of pyridines and related nitrogen-containing heterocycles with various simple alkynes is reported. The method provides an alternative catalytic route to nucleophilic or cross-coupling to enantioenriched alkynylated heterocycles.

A three step efficient strategy is described for synthesizing substituted -nitropiperidones by using Michael addition of N-p-tolylsulfinyl [beta]-nitroamines to [alpha],[beta]-unsaturated esters, hydrolysis of the sulfonyl group and cyclization of the resulting free amines. The main features of the process have involved a very simple experimental process involving mild conditions and only one chromatographic purification process.

A sterically encumbered [[N.sub.2][S.sub.6]] macropentacycle related to diazamacrobicycles and cryptands is prepared by the [1!] condensation reaction between functionalized macrocyclic and macrotricyclic precursors. Adoption of the in, out form by macropentacycle in the crystal and in solution at low-temperature has resulted from the steric crowding and strain introduced by the [15]ane-[N.sub.2][S.sub.2] macrocyclic bridging subunits.

The hetero-Diels-Alder reactions of 4-alkenylthiazoles with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) has produced new heteropolycyclic systems in excellent yields and high levels of stereocontrol through a suprafacial approach. The results have highlighted the convertible mechanism of the [4@] cycloaddition of triazolinediones with dienes.

The ene reaction between 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) and tetramethylethylene is examined by using quantum mechanical (QM)/molecular mechanical (MM) calculations in water, methanol, DMSO and acetonitrile. The analysis of solute-solvent interactions and charges have shown that larger activation barriers in the protic solvents compared to aprotic solvents have come from greater stabilization of the electron density at the N[double bond]N atoms in PTAD in the reactants.

The synthesis and structures of four Bi-Ni heteroatomic clusters closo-[[[Bi.sub.3][Ni.sub.4][(CO).sub.6]].sup.3-], closo-[[[Bi.sub.3][Ni.sub.4][(CO).sub.6]].sup.2-], the open cluster [[[Bi.sub.3][Ni.sub.4][(CO).sub.9]].sup.3-], and the intermetalloid closo-[[[Ni.sub.x]@{[Bi.sub.6][Ni.sub.6][(CO).sub.8]}].sup.4-] are presented. The clusters are characterized in compounds with potassium cations sequestered by 2,2,2-crypt or 18-crown-6 ether.

The photochromism of mixed crystals containing bisthienyl-, bisthiazolyl-, and bisoxazolyethene derivatives is described. The mixed crystal is found to change color from colorless to yellow, red, and blue upon irradiation with light of appropriate wavelengths.

A complete assignment of the Raman active modes of 1,10-phenanthroline-5,6-dione is described using density functional theory (DFT). The DFT calculations have revealed the presence of couplings in the phendione system, where the couplings are attributed to the presence of carbonyl groups in the phendione ring system and are shown to have a major effect on fundamental vibrations.

A stannane-free hydrodehalogenation of 4-halotetrahydropyran is developed under very mild conditions. This method has allowed selective one-pot dehalogenation and/or debenzylation depending on the type of halide-substrate used and its applicability is shown in the synthesis of a key intermediate toward the enantioselective synthesis of (+)-SCH 351448.

The synthesis and characterization of the reaction of heterocyclic methanol derivatives that led to the isolation of a novel family of OR-substituted titanium alkoxide precursors are described. It is demonstrated that the isolation of a novel family of structurally characterized compounds is successful.

A study gives a complete structural and functional analysis of the pyocyanin, a biologically active phenazine that is produced by the human pathogen Pseudomonas aeruginosa and acts as a virulence factor in various diseases like AIDS. The results indicate that PhzM has no ability to produce pyocyanin and it is P. aeruginosa that prevents the formation and release of an unstable and potentially deleterious intermediate and ensures the production of pyocyanin.

The [super 15]N solid-state nuclear magnetic resonance (SS-NMR) is proposed as a tool for directly observing reactive positions of the flavin ring and thereby obtaining information on their frontier orbitals. The [super 15]N chemical shift principal values are valuable tools for understanding electronic differences that underlie variations in flavin reactivity, as well as the reactivities of other heterocyclic cofactors.

A pure ruthenium hydride complex with N-heterocyclic carbene ligand was efficiently generated from the reaction of a second-generation Grubbs ruthenium catalyst with vinyloxytrimethylsilane and unambiguously characterized. This ruthenium hydride complex showed high catalytic activity for the selective isomerization of terminal olefin and for the cycloisomerization of 1,6-dienes.

The investigation of unimolecular photochemical reactions of 2H-thiopyran-2-one (TP) and 2H-pyran-2-thione (PT) is conducted. The work revealed a series of phototransformations leading to generation of a series of photoproducts.

The stereochemical outcome of the alkylation of a variety of phenyglycinol-derived oxazolopiperidone lactams is studied. The synthetic utility of the alkylation reactions is illustrated with the synthesis of cis and trans 3,5-disubstituted, 2,5-disubstituted and 2,3,5-trisubstituted enantiopure piperidines and the indole alkaloids 20R- and 20S-dihydrocleavamine.

The reduction of dipyridil[3,2-a:2'3'-c]phenazine, dppz, by pulse radiolytically generated e(super -)(sub sol) or by the reaction of the dppz excited states with electron donors produces the radical dppzH(super .). The dimer radical, (dppz)(sub 2)H(super .), exists in equilibrium with dppz with an association constant, K = 10(super 3) M(super -1).

A series of (NHC)Pd(R-allyl)Cl complexes (NHC: lPr = N,N-bis(2,6-diisopropylphenyl)imidazol-2-ylidene, SIPr = N,N-bis(2,6-diisopropylphenyl)-4,5-dihydroimidazol-2-ylidene; R = H, Me, gem-Me2, Ph) are synthesized and fully characterized. Higher catalytic activity in the Suzuki-Miyura and Buchwald-Hartwig reactions allow for the coupling of unactivated aryl chlorides at room temperature in minutes.

The photophysical properties of the phenazine-based dye neutral red are examined in aqueous solution in the presence of the macrocyclic host molecule cucurbit[7]uril (CB7) by using ground-state absorption as well as steady-state and time-resolved fluorescence measurements. The comparison of the complexation behavior of neutral red toward CB7 with that toward beta-cyclodextrin (beta-CD) has revealed that although both hosts have a hydrophobic cavity, additional recognition elements such as cation receptor sites at the portals of the cavity are quintessential to promote a strong and selective binding of fluorescent dyes.

Evidence for a proposed mechanism of C-H activation of 3-methyl-3,4-dihydroquinazoline by (PCy3)(sub 2)RhCl is presented. The consequences of the mechanism for coupling reactions of N-heterocycles that occur through Rh-catalyzed C-H bond activation are discussed.

An efficient methodology for the synthesis of 4-phenylthiopyrimido[4,5-b][1,4]benzothiazepines was developed. This transformation can be rationalized by a mechanism similar to the Bischler-Napieralski-type reaction and the aryl sulfide group of the resulting 4-arylthiopyrimido[4,5-b][1,4]benzothiazepines can be subjected to selective oxidation and subsequent nucleophilic substitution.

The EPR spectra of dications at 123K in a butyronitrile matrix that showed the population of a tripled state are discussed. Theoretical analysis of the exchange interaction of the dications and the rented (m-and p-phenylene)bisphenothiazine dications at the perpendicular geometry are also provided.

The scope and the limitations of aza-Baylis-Hillman reactions and the Lewis base and solvent effects in the reactions that are investigated are described. A series of nitrogen-containing heterocyclic compounds as 'abnormal' aza-Baylis-Hillman reaction products could be formed in the presence of an appropriate Lewis base promoter.

The derivation of the standard molar enthalpies of formation in the gaseous state of a new phenazine derivative, 2-hydroxyphenazine-di-N-oxide, is reported. The mean molar dissociation enthalpy of the (N-O) bonds is derived for the 2-hydroxyphenazine-di-N-oxide species.

The mechanism of cycloaddition reaction involving the formation of a germanic hetero-polycyclic compound between alkylidenegermylene and ethylene is examined. The mechanism involves formation of a three-membered ring intermediate INT1 by the two reactants through a barrier -free exothermic reaction of 35.4 kJ/mol, isomerization of the intermediate into an active four-membered ring product and formation of the germanic hetero-polycyclic compound due to the reaction of P2.1. with ethylene.

One, five-Diamino-1 H-tetrazole could easily be protonated by reaction with strong mineral acids, yielding the poorly investigated 1, 5-diaminotetrazolium nitrate and perchlorate. The salts examined show good to reasonable physical properties that include high densities, good thermal stabilities, and distinctive melting points around 100 degree Celsius.

The fast-flow-discharge technique is used to determine the absolute rate coefficients for the gas--phase reactions of the NO3 radical with a series of five-membered heterocycles. The experiments involve monitoring the NO3 radical by laser-induced fluorescence.

The synthesis of Rhenium (V) oxo complexes with N-heterocyclic carbenes is described. The results show that the equatorial coordination spheres of the rhenium atoms are essentially planar irrespective of the steric demands of the individual carbene ligands.