bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural studies of PdCl2L2 complexes with fluorinated phosphines, phosphites, and phosphinites as precursors of benzyl bromide carbonylation catalysts, and and X-ray crystal structure of cis-PdCl2[PPh2(OEt)]2
Authors: Trzeciak Anna M , Bartosz-Bechowski Hubert , Ciunik Zbigniew , Niesyty Katarzyna , Ziólkowski Józef J
Published: April 2011

PdCl2L2-type complexes with phosphines (L = PPhx(C6F5)3-x (x = 0-3)), phosphites (L = P(OMe)3, P(OPh)3, P(OEt)3), and phosphinites (L = PPh2(OC6F5), PPh2(O-3,5-F2C6H3), PPh2(OEt), PPh2(O-n-Bu), PPh2(O-t-Bu)) were synthesized and characterized by UV-vis and 31P NMR methods. PdCl2L2 complexes with less sterically demanding phosphines (Θ < 140°) exist as cis isomers, which is confirmed by the X-ray structure of cis-PdCl2[PPh2(OEt)]2. These complexes react with CO in the presence of NEt3 forming Pd(CO)xLy (x + y = 4) type carbonyls characterized by IR spectra. All PdCl2L2 complexes studied are active as precursors of benzyl bromide carbonylation catalysts at 40°C and 1 atm CO; however, the activity of the cis isomers is higher than that of the trans isomers. The highest yields of the carbonylation product, phenylacetic acid methyl ester, were obtained using cis-PdCl2[P(OMe)3]2 (92%), cis-PdCl2[P(OPh)3]2 (89%), and cis-PdCl2[PPh2(O-n-Bu)]2 (78%) as catalyst precursors.Key words: palladium complexes, fluorinated phosphines, benzyl bromide carbonylation.
(para-Diphenylphosphino)benzenesulfonic acid and its ruthenium(II) complexes: an old water soluble phosphine ligand in a new perspective
Authors: Papp Gábor , Kovács József , Bényei Attila Cs , Laurenczy Gábor , Nádasdi Levente , Joó Ferenc
Published: April 2011

Chloro- and hydrido-complexes of ruthenium(II) with potassium (4-diphenylphosphino)benzenesulfonate (pTPPMS) were prepared and their properties were compared with those of the related complexes of (3-diphenylphosphino)benzenesulfonates. An X-ray crystal structure determination revealed that the para-sulfonated ligand has a Tolman cone angle slightly smaller than that of PPh3. It was established by pH-potentiometric measurements and by1H and31P NMR studies that the distribution of the hydride derivatives [RuClH(pTPPMS)3] and [RuH2(pTPPMS)3,4] is strongly pH-dependent. Hydrogenation of trans-cinnamaldehyde in aqueous-organic mixtures is catalyzed by [RuCl2(pTPPMS)4] and is also strongly influenced by the pH of the aqueous phase due to the pH-dependent formation of the above hydrides. In acidic solutions (pH < 2) an exclusive C=C reduction takes place, while in alkaline solutions (pH > 6) a selective C=O hydrogenation was observed.Key words: ruthenium, water soluble, hydrogenation, hydrides, sulfonated phosphines, biphasic.
Transition metal phthalocyanine and porphyrin complexes as catalysts for the polymerization of alkenes
Authors: Long Gregory S , Snedeker Benjamin , Bartosh Kyle , Werner Michelle L , Sen Ayusman
Published: April 2011

Vanadium phthalocyanine and porphyrin complexes, in conjunction with methylaluminoxane (MAO) or EtAlCl2 cocatalyst, have been found to catalyze the homopolymerization of ethene. In addition, the copolymerization of ethene with propene and 1-decene was achieved with the vanadium phthalocyanine complex and MAO. Nickel phthalocyanine complex was also found to catalyze the polymerization of ethene in the presence of MAO. However, only dimerization was observed when EtAlCl2 was used as the cocatalyst.Key words: phthalocyanine, porphyrin, polymerization, copolymerization, ethene, propene, 1-decene.
Tetraacetatodirhodium(II) complexes with tris(methoxyphenyl)phosphines, their reactivity, structure, and antitumor activity
Authors: Pruchnik Florian P , Starosta Radoslaw , Ciunik Zbigniew , Opolski Adam , Wietrzyk Joanna , Wojdat Elzbieta , Dus Danuta
Published: April 2011

Reactions of [Rh2(µ-OAc)4(H2O)2] ([1·(H2O)2]) with tris(3-methoxyphenyl)phosphine at 1:1 and 1:2 molar ratios yield, first, the appropriate adducts: [1·(H2O){P(C6H4-3-OMe)3}] and [1·{P(C6H4-3-OMe)3}2], and then [Rh2(µ-OAc)3{µ-(C6H3-3-OMe)P(C6H4-3-OMe)2}(HOAc)2] ([2·(HOAc)2]), and [Rh2(µ-OAc)2{µ-(C6H3-3-OMe)P(C6H4-3-OMe)2}2(HOAc)2] ([3·(HOAc)2]) complexes, respectively. They have been characterized by spectroscopic methods. The molecular structure of [3·(HOAc)(H2O)] has been determined crystallographically. The complexes [3·(HOAc)2], [Rh2(µ-OAc)3{µ-(C6H3-4-OMe)P(C6H4-4-OMe)2}(HOAc)2] ([4·(HOAc)2]), and [Rh2(µ-OAc)2{µ-(C6H3-4-OMe)P(C6H4-4-OMe)2}2(HOAc)2] ([5·(HOAc)2]) reversibly react with CO giving mono- and biadducts. Antitumor activity of binuclear rhodium(II) compounds [3·(HOAc)2], [Rh2(µ-OAc)3{µ-(C6H3-2-O)P(C6H3-2-OMe)2}(HOAc)] ([6·(HOAc)]), and [Rh2(µ-OAc)3{µ-(C6H3-6-OMe-2-O)P[(C6H3-2,6-(OMe)2]2}(HOAc)] ([7·(HOAc)]) have been investigated in vitro. The most active agent for investigated tumor lines is complex [6·(HOAc)]. It shows higher activity than cisplatin (cis-[PtCl2(NH3)2]). Antitumor activity decreases in the series: [6·(HOAc)] > [7·(HOAc)] > [3·(HOAc)2]. Activity of all investigated rhodium(II) complexes is higher than that of [1·(H2O)2].Key words: dirhodium(II) complexes, functionalized phosphines, aryl phosphines, ferrocenylmethylphosphines, adducts with CO, antitumor activity, orthometallation reactions.
Synthesis, structure, and reactivity of diamidophosphine complexes of yttrium and the lanthanides
Authors: Fryzuk Michael D , Yu Peihua , Patrick Brian O
Published: April 2011

The reaction of the dilithiodiamidophosphine ligand precursor PhP(CH2SiMe2NPh)2Li2(THF)2([NPN]Li2(THF)2) with LnCl3(THF)3 (Ln = Y, Sm, Ho, Yb, Lu; THF = tetrahydrofuran) in refluxing toluene generates the mononuclear complexes [NPN]LnCl(THF) in good yield. The molecular structures have been shown to be five-coordinate in the solid state and in solution. Attempts to prepare alkyl derivatives have only met with partial success; the reaction of MeMgCl with [NPN]YCl(THF) generates the partially characterized mixed-metal derivative [NPN]YMe2MgCl. The reaction with LiAlH4 results in complete ligand exchange and the formation of the tetranuclear lithium aluminum hydride derivative {[NPN]AlH2Li(THF)}2. Reduction of the lutetium derivative with KC8 and naphthalene generated the dinuclear naphthalene-bridged species {[NPN]Lu}2(µ-η4:η4-C10H8) wherein each Lu centre engages in η4-coordination to opposite sides of the arene moiety. X-ray crystallography was used to characterize the four complexes.Key words: lanthanides, yttrium, mixed-donor ligands, aluminum, lithium, naphthalene.
Binding of anti-inflammatory drug indomethacin with cyclodextrin and DNA: solubility, spectroscopic, and voltammetric studies
Authors: Shehatta I S , Ibrahim M S
Published: April 2011

The interaction of the anti-inflammatory drug indomethacin (IMC) with α-, β-cyclodextrins (CDs) and calf thymus deoxyribonucleic acid (ct-DNA) have been investigated in the Britton-Robinson (BR) buffer (pH = 7.2) using solubility, spectroscopic, and voltammetric methods. The measurements show that the IMC molecule, acting as an intercalator, is inserted, from the p-chlorobenzoyl part, into the cavity of the cyclodextrins as well as into the base-stacking domain of the ct-DNA double helix. Upon addition of β-CD in a buffered IMC solution, the solubility of IMC increases and the Gibbs free energies of transfer of the drug from aqueous solution to the cavity of β-CD are negative and increase negatively with increasing β-CD concentration. The interaction of IMC with CDs and ct-DNA causes hypochromism and bathochromic shifts in the absorption spectra, along with pronounced changes in the electrochemical behaviour of the drug. The stoichiometry of complexes formed in solution is inferred to be 1:1. The binding constants were calculated from the increase of the solubility, the strong hypochromism, and the decrease in peak current of IMC upon the addition of the host molecules. IMC has a higher affinity for β-CD than for α-CD, as the IMCβ-CD interaction is the most exergonic. Binding is interpreted in terms of the intercalative (hydrophobic) interactions with the ct-DNA helix (i.e., the stacked base pairs) or within CD cavity.Key words: cyclodextrin, ct-DNA, anti-inflammatory drug, indomethacin, binding constant, solubility, spectra, voltammetry.
Sol-gel synthesis of ternary phosphate-ZrO2-SiO2 catalysts for alcohol dehydration
Authors: Zhuang Quan , Miller Jack M
Published: April 2011

PhosphateZrO2Si2O catalysts were synthesized by sol-gel method using tributyl phosphite, zirconium propoxide, and tetraethyl orthosilicate as precursors. They were characterized by N2 adsorption, 31P CP MAS NMR, and DRIFTS. At lower P content, monomeric phosphates were formed on the surface of the catalysts, which were mainly responsible for the isopropanol dehydration activity. At higher P content, polyphosphates were formed, and thus, the dehydration activity decreased. An optimum P content for dehydration activity was found to be at 10 mol%.Key words: sol-gel synthesis, ternary oxides, phosphate, acid catalyst, alcohol dehydration, 31P CP MAS NMR, N2 adsorption, DRIFTS.
One-pot sol-gel synthesis of sulfated ZrO2-SiO2 catalysts for alcohol dehydration
Authors: Zhuang Quan , Miller Jack M
Published: April 2011

Sulfated ZrO2SiO2 catalysts were synthesized by one-pot sol-gel method using ammonium sulfate, zirconium propoxide, and tetraethyl orthosilicate as precursors. The catalysts were characterized by N2 adsorption and DRIFTS. On calcining the gel at elevated temperature, the ammonium sulfate decomposed, giving a sulfated zirconiasilica catalyst. By adding ammonium sulfate to the sol-gel synthesis system, the surface area, pore size, and pore volume of the resultant catalyst were increased. The one-pot sol-gel synthesized catalyst with an optimum loading of SO42 14 mol% showed significantly higher catalytic activity, with a selectivity of 100%, for isopropanol dehydration when compared to the impregnated catalyst. The one-pot sol-gel synthesis method is an effective way to prepare sulfated zirconia catalyst.Key words: sulfated zirconia, sol-gel synthesis, acid catalyst, alcohol dehydration, N2 adsorption, DRIFT.
Cadmium complexes of thiones. Part II.1 A synthetic, solution, and solid-state MAS 111/113Cd NMR study of cadmium complexes of 1,3-thiazolidine-2-thione, and the structures of [tetrakis(1,3-thiazolidine-2-thione)cadmium] trifluoromethanesulfonate ([Cd(C3H5NS2)4](CF3SO3)2) and [tetrakis(1,3-thiazolidine-2-thione)cadmium][tetrakis(nitrato-O,O')cadmate] ([Cd(C3H5NS2)4][Cd(O2NO)4])
Authors: Rajalingam Umarani , Dean Philip AW , Jenkins Hilary A , Jennings Michael , Hook James M
Published: April 2011

Treatment of Cd(O3SCF3)2 with the stoichiometric quantity of 1,3-thiazolidine-2-thione (tztH) allows isolation of [Cd(tztH)4](O3SCF3)2 (1). When tztH:Cd [Formula: see text] 2 the reaction of Cd(NO3)2·4H2O with tztH leads to [Cd(tztH)4][Cd(O2NO)4] (2). The structures of both 1 and 2 have been determined by single crystal X-ray analysis. Colourless crystals of 1 are orthorhombic, space group Fdd2, with eight molecules per unit cell (Z = 8) of dimensions a = 20.139(3), b = 23.332(5), c = 14.214(3) Å. Those of 2 are tetragonal, space group I [Formula: see text], with four molecules per unit cell (Z = 4) of dimensions a = 13.8853(11), c = 8.077(2) Å. The discrete homoleptic cation [Cd(tztH)4]2+ is characterized for the first time in 1 and 2. The cations are of point group symmetry C2 and S4 in 1 and 2, respectively. In both cases the ligands are S-bound, and the CdS4 kernel is a squashed tetrahedron. In 2, the eight-coordinate anion [Cd(O2NO)4]2- is characterized for the second time. 113Cd CP MAS NMR data are reported for solid 1 and 2, and also for solids produced by fusing Cd(NO3)2·4H2O with different molar ratios amounts of tztH, and by fusing Cd(O3SCF3)2 with six mol equivalents of tztH. In the Cd(NO3)2·4H2O:tztH mixtures, species identified include unreacted cadmium salt 2 ([Cd(tztH)4](NO3)2) and possibly Cd(tztH)3(NO3)2. [Cd(tztH)4](NO3)2 becomes the major species only when a significant excess of tztH is used. In the mixtures with tztH:Cd > 4, neither Cd(NO3)2·4H2O nor Cd(O3SCF3)2 form complexes containing more than four tztH ligands. Reduced-temperature 111Cd NMR data are reported for Cd(ClO4)2·6H2O:tztH mixtures in MeOH. Species identified are Cd(tztH)w2+(solv) (w = 03).Key words: 1,3-thiazolidine-2-thione, cadmium complexes, X-ray analysis, 113Cd CP MAS NMR, solution 111Cd NMR, tetrakis(1,3-thiazolidine-2-thione)cadmium(2+) cation, tetrakis(nitrato-O,O')cadmate(2) anion.
2000 Alcan Award Lecture Adventures in organometallic NMR: steric restraints, slowed rotations, and skeletal rearrangements
Authors: McGlinchey Michael J
Published: April 2011

The structures and NMR fluxionality of a wide variety of organometallic complexes (including tetrahedral cluster cations and systems of the type (CnRn)ML3, where R = Et, Ph) are discussed. Barriers to tripodal and peripheral substituent rotations are reported, and the relevance of correlated rotations to molecular machines is outlined. Haptotropic shifts in (cyclopenta[def]phenanthrenyl)MLn and (cyclopenta[l]phenanthrenyl)MLn complexes are rationalized in terms of the aromatic character of the transition states. Likewise, the barriers to silatropic shifts in polyindenylsilanes can be correlated with the aromaticity of the intermediate isoindenes. Finally, the use of cobalt clusters to control cyclohexane ring conformations is described.Key words: NMR ring currents, fluxionality, correlated rotations, molecular rearrangements, haptotropic shifts.
New low-spin Co(II) complexes with novel tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane ligand: electron transfer kinetics and spectroscopic characterization of Co(II)P6 and Co(II)P3S3 ions in aqueous solution
Authors: Iwatsuki Satoshi , Obeyama Kenji , Koshino Nobuyoshi , Funahashi Shigenobu , Kashiwabara Kazuo , Suzuki Takayoshi , Takagi Hideo D
Published: April 2011

Substitution-inert Co(II) complexes with tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane were produced in aqueous solution by the controlled-potential electrolysis. EPR studies indicated that the Co(II)P6 and Co(II)P3S3 species are in the low-spin t62ge1g state. The analyses of the absorption spectra of the Co(II) species in solution indicated significant JahnTeller distortion in Co(II)P6 and Co(II)P3S3 ions as expected for the low-spin d7 electronic configuration, while less distortion was observed for the Co(II)S6 ion. Kinetic studies of the redox reactions involving these Co(III/II) species confirmed that the electron self-exchange reactions for the Co(III/II)P6 and Co(III/II)P3S3 couples are relatively fast (kex ~ 1 × 104 dm3 mol1 s1), which is consistent with the results for other low-spin  low-spin Co(III/II) couples. It was concluded that the nephelauxetic effect of the P-donor atom stabilizes the low-spin state in Co(II), and that the rather rapid electron exchange rates for these Co(III/II) couples were explained by the lack of the spin reorganization process required for the ordinary low-spin  high-spin Co(III/II) couples.Key words: cobalt(III/II), spin state, EPR study, kinetics, electron transfer.
Calculations on the electronic structure and nonlinear second-order susceptibilities of fulleropyrrolidinetetrathiafulvalene(C60PYTTF) based on donorbridgeacceptor dyads
Authors: Fu Wei , Zhang Hong-Xing , Feng Ji-Kang , Li Wei
Published: April 2011

The semiempirical INDO calculations were carried out to investigate the charge-transfer interaction and to evaluate the second-order nonlinear susceptibilities for a series of fulleropyrrolidinetetrathiafulvalene(C60PYTTF) dyads, C60PY, and C60PY-(CH=CH)n-TTF (n = 06). The equilibrium geometries, electronic structures, and UVvis spectra of these C60PYTTFs DBA dyads were determined by using ZINDO methods. On the basis of electronic spectra, we calculated the β for the dyads using the ZINDO-SOS expression, and found that these dyads have relatively large β. The calculated values of β are 48.78, 62.34, 97.90, 123.24, 183.78, 189.43, 193.45, 195.82 × 1030esu for C60PY and C60PY-(CH=CH)n-TTF (n = 06), respectively, which shows the enhancing effect when TTF is introduced. The β significantly increases as n increases from 03; and it tends to be saturated in the end.Key words: ZINDO-SOS, CI, structure, spectra, C60PYTTF.
A synthesis of 6,11-disubstituted benzo[b]carbazoles
Authors: Fraser Heidi L , Gribble Gordon W
Published: April 2011

Sequential regioselective addition of organolithium reagents to indolo[1,2-b]isoquinoline-6,11-quinone (7) followed by sodium borohydride reduction of the intermediate diol 10, which is not isolated, affords 6,11-disubstituted 5H-benzo[b]carbazoles 11. The tandem combination of methyllithium and lithium triethylborohydride (Super Hydride) gives 6-methylbenzo[b]carbazole (24).Key words: benzo[b]carbazole, organolithiums, indolo[1,2-b]isoquinoline-6,11-quinone, ellipticine, indole.
Lewis acid-mediated intramolecular addition of silyl enol ethers to internal unactivated alkynes
Authors: Imamura Ken-ichiro , Yoshikawa Eiji , Gevorgyan Vladimir , Sudo Tomoko , Asao Naoki , Yamamoto Yoshinori
Published: April 2011

The EtAlCl2-mediated intramolecular addition of silyl enol ethers to both terminal and internal unactivated alkynes, bearing alkyl and phenyl susbstituents at the alkyne moiety, gave mono- and bicyclic β,γ-unsaturated ketones in good to excellent yields. On the other hand, the silyloxy-substituted cyclic vinylsilanes were obtained in moderate to high yields when the reactions were catalyzed by B(C6F5)3 in the presence of triethylsilane. All the reactions proceeded via endo-fashion exclusively. The mechanisms of these regiospecific Lewis acid-assisted carbocyclizations are proposed.Key words: Lewis acid, silyl enol ethers, carbocyclization, alkynes.
Structure assignment of aminoconduritols by 15N NMR correlation spectroscopy; synthesis of a positional isomer of 7-deoxypancratistatin
Authors: Schilling Stefan , Rinner Uwe , Chan Collin , Ghiviriga Ion , Hudlicky Tomas
Published: April 2011

A positional isomer of 7-deoxypancratistatin was synthesized in 12 steps from epoxyaziridines 4 and 5. An intermolecular opening of the aziridine rather than the epoxide in the early stages of the synthesis led to 13, which did not match the properties of tetraacetate 10 derived from 7-deoxypancratistatin. At no stage of the synthesis did standard NMR techniques, involving 1H1H or 1H13C coupling, prove adequate for the structure assignment. Unambiguous structure was assigned by 1H15N correlation NMR spectroscopy as well as by the conversion of epoxide 11 to diol 29 synthesized independently by another route. Experimental and spectral details are reported for all new compounds.Key words: 15N NMR spectroscopy, iso-7-deoxypancratistatin, Lewis acid catalyzed intramolecuar opening of epoxides, aminoconduritols.
Synthetic studies of novel ninhydrin analogs
Authors: Hark Richard R , Hauze Diane B , Petrovskaia Olga , Joullié Madeleine M
Published: April 2011

Ninhydrin is an essential tool in the analysis of amino acids, peptides, and proteins, and the preferred reagent for the detection of latent fingerprints on porous surfaces. The goal of this investigation was to prepare ninhydrin analogs with enhanced chromogenic and fluorogenic properties. Target compounds included structures with extended conjugation and (or) with the presence of sulfur-containing moieties. We have devised general convergent routes for novel heterocyclic and aryl-substituted ninhydrin analogs for use as reagents for amino acid detection.Key words: ninhydrin analogs, synthesis, ketals, Suzuki cross-coupling reactions, Stille cross-coupling reactions.
Ortho-directed metallation of π-deficient heterocycles in connection with palladium-catalyzed biaryl cross-coupling  Synthesis of marine alkaloids of the pyridoacridine series
Authors: Godard A , Rocca P , Guillier F , Duvey G , Nivoliers F , Marsais F , Quéguiner G
Published: April 2011

Connection between ortho-directed metallation of π-deficient heterocycles and Suzuki cross-coupling reactions provides a very efficient and fruitful strategy to polycyclic molecules of biological interest. The methodology is used to synthesize alkaloids or precursors and analogues of natural compounds of the pyrido[2,3,4-k,l]acridine series.Key words: marine alkaloids, pyrido[2,3,4-k,l]acridines, metallation, cross-coupling.
Attempted enantiotopic group selective cyanohydrin formation from α-alkoxy aldehydes by double stereodifferentiation
Authors: Ward Dale E , Sales Marcelo , Hrapchak Matthew J
Published: April 2011

Enantiotopic group selectivity can result from the competition between substrate and reagent double stereodifferentiation. We have examined this approach for enantioselective hydrocyanation of racemic α-alkoxy aldehydes (e.g., 2-(phenylmethoxy)heptanal (1)). Reaction of 1 with TMSCN mediated by chiral nonracemic alkoxy Ti(IV) reagents under conditions known to be reasonably enantioface selective in reactions with achiral aldehydes, proceeded with very low enantiotopic group selectivity (<2:1). It was established that TMSCN can react with Ti(IV) reagents to produce "TiCN" adducts that are capable of hydrocyanation but with low substrate-controlled diastereoselectivity in reactions with 1. The poor enantiotopic group selectivity observed can be rationalized to result from this low diastereoselectivity despite the respectable levels of enantioface selectivity associated with these reagents in hydrocyanation of achiral aldehydes. Highly diastereoselective hydrocyanation of α-alkoxy aldehydes can be achieved with TMSCN in the presence of excess MgBr2·OEt2. High diastereoselectivity was also observed using achiral and chiral TiCN adducts in place of TMSCN. Although the putative TiCN adducts obtained from nonracemic alkoxy Ti(IV) reagents are implicated in enantioface selective hydrocyanation, these reagents were not enantiotopic group selective under these conditions and showed no evidence of double stereodifferentiation. The use of nonracemic bisoxazoline ligands for Mg(II) was also ineffective.Key words: cyanohydrin, 2-alkoxyalkanal, double stereodifferentiation, enantiotopic group selective reaction, kinetic resolution.
Absolute stereochemistry of the spiroxins
Authors: Wang Tao , Shirota Osamu , Nakanishi Koji , Berova Nina , McDonald Leonard A , Barbieri Laurel R , Carter Guy T
Published: April 2011

The absolute configuration of spiroxin A has been determined by exciton-coupled circular dichroism (CD). Namely, the difference CD between spiroxin A  bis-methoxycinnamate, as well as that between spiroxin A  bis-retinoate, both exhibit negative exciton couplings between the acylated phenolic hydroxyl group chromophores. This establishes the absolute configuration as 2S,3R,4S,2'S,3'R,4'S.Key words: circular dichroism, exciton coupling, spiroxins, antitumor, antifungal.
Enantioselective syntheses of (+)- and ()-nephrosteranic acid employing the Nicholas-Schreiber reaction
Authors: Jacobi Peter A , Herradura Prudencio
Published: April 2011

(+)- and ()-Nephrosteranic acid (16) have been prepared in an enantioselective fashion from alkyne acid 19 (or ent-19) by a three step sequence involving debenzylationlactonization, oxidative cleavage, and selective epimerization at C4. Acids 19 and ent-19 were obtained as single enantiomers employing a NicholasSchreiber reaction.Key words: paraconic acids, nephrosteranic acid, butyrolactones, NicholasSchreiber reaction.
Studies of palladium-catalyzed coupling reactions for preparation of hindered 3-arylpyrroles relevant to (-)-rhazinilam and its analogues
Authors: Ghosez Léon , Franc Cécile , Denonne Frédéric , Cuisinier Claire , Touillaux Roland
Published: April 2011

Suzuki cross-coupling reactions of 3-pyrroleboronic acid derivatives with haloaromatics and the reverse process i.e., the coupling of 3-iodo(bromo)pyrroles with arylboronic acids have been investigated as a potential key step in the synthesis of ()-rhazinilam and analogues. It was found that 3-iodo-2-formyl-1-tosylpyrroles efficiently coupled with a variety of arylboronic acids in the presence of PdCl2(dppf) as catalyst. This catalytic system is compatible with a broad spectrum of arylboronic acids  electron-rich, electron-poor, hindered, heterocyclic  which easily coupled with the pyrrole substrate.Key words: 2-substituted-3-arylpyrroles, biaryls, coupling reactions, arylboronic acids, palladium coupling, catalysis.
Solubility of nonpolar gases in 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoropropan-2-ol at several temperatures and 101.33 kPa partial pressure of gas
Authors: Sánchez Miguel Angel , Mainar Ana María , Pardo Juan Ignacio , López María Carmen , Urieta José Santiago
Published: April 2011

Solubilities, expressed as mol fractions, of 14 nonpolar gases (He, Ne, Ar, Kr, Xe, H2, N2, O2, CH4, C2H4, C2H6, CO2, CF4, and SF6) in 2,2,2-trifluoroethanol (TFE) at 268.15 and 283.15 K and 1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) at 273.15 and 283.15 K, with the partial pressure of gas being 101.33 kPa for all measurements, are reported. Standard changes in the thermodynamic functions (enthalpy and entropy) have been calculated from the solubilities and their variation with temperature. The Scaled Particle Theory (SPT) model has been used to determine these thermodynamic functions and also the partial molar volumes of the gases in the formed solutions.Key words: gas solubilities, nonpolar gases, fluoroalcohols, Scaled Particle Theory.
Interaction of human serum albumin with oxovanadium ions studied by FT-IR spectroscopy and gel and capillary electrophoresis
Authors: Purcell M , Neault J F , Malonga H , Arakawa H , Tajmir-Riahi H A
Published: April 2011

Some oxovanadium compounds have shown potential to inhibit RNase activity, while at the same time not inhibiting DNase activity. Some vanadyl complexes also inhibit protein synthesis in rabbit reticulocytes, but induce activation of proteintyrosine kinase. To gain an insight into the interaction of oxovanadium ions with proteins, the present study was designed to examine the bindings of VOSO4and NaVO3salts with human serum albumin (HSA) in aqueous solution at physiological pH with metal ion concentrations of 0.0001 to 1 mM and HSA (fatty acid free) concentration of 2% w/v. Gel and capillary electrophoresis (CE) and Fourier transform infrared (FT-IR) spectroscopic methods were used to determine the metal ion binding mode, association constant, and the secondary structure of the protein in the presence of the oxovanadium compounds. Gel electrophoresis results showed that a maximum of 20 vanadyl cations (VO2+) are bound per HSA molecule with strong (K1= 7.0 × 107M1) and weak (K2= 6.5 × 105M1) bindings. Similarly, capillary electrophoresis showed two major bindings for vanadyl cation with K1= 1.2 × 108M1and K2= 8.5 × 105M1, whereas vanadate (VO3) has only a weak binding affinity (K = 6.0 × 103M1) with HSA molecule. The VO3binds mainly to the lysine ε-amino NH+3groups, while VO2+binds possibly to the histidine nitrogen atom and the N-terminal of the α-amine residue. Infrared spectroscopic analysis showed metal ion binding results in major protein secondary structural changes from that of the α-helix (55.0 to 4344%) to the β-sheet (22.0 to 2326%), β-antiparallel (12.0 to 1316%), and turn (11.0 to 1718%), at high metal ion concentration. The observed spectral changes indicate a partial unfolding of the protein structure, in the presence of oxovanadium ions.Key words: oxovanadium, protein, binding mode, binding constant, secondary structure, electrophoresis, FT-IR spectroscopy.
Tests for aromaticity applied to the pentalenoquinones  A computational study
Authors: Delamere C , Jakins C , Lewars E
Published: April 2011

Criteria for aromaticity and antiaromaticity were applied to the four pentalenoquinones, 1,2-, 1,5-, 1,4-, and 1,6-pentalenoquinone, i.e., bicyclo[3.3.0]octa-4,6,8-triene-2,3-dione (7a), bicyclo[3.3.0]octa-3,5,8-triene-2,7-dione (7b), bicyclo[3.3.0]octa-1(5),3,7-triene-2,6-dione (7c), and bicyclo[3.3.0]octa-1(5),3,6-triene-2,8-dione (7d). Geometry optimizations and frequency calculations were done with the pBP/DN* DFT method as implemented in Spartan, and single-point HF/3-21G calculations to obtain Löwdin bond orders (Spartan), as well as HF/6-31G* NICS calculations (Gaussian 98) were also carried out. Geometries and bond orders, chemical hardness, and NICS values gave no definite indication of aromatic or antiaromatic character. However, homodesmotic ring-opening reactions to give acyclic analogues indicated that 7a and 7b are nonaromatic (resonance energies 11 and 5 kJ mol1) while 7c and 7d are antiaromatic (resonance energies 83 and 54 kJ mol1). The resonance energies were obtained with the aid of an estimate of the strain energy of the molecules 7 (86 kJ mol1) by a novel extrapolation procedure on hydropentalenes. Calculated pBP/DN* activation energies for DielsAlder reactions with ethyne and ethene placed 7a and 7b in an "unreactive" class similar to 1,3-butadiene and fulvene, and 7c and 7d in a "reactive" class, similar to cyclopentadienone.Key words: aromaticity, pentalenoquinones, DFT, hardness, NICS, homodesmotic, resonance energy, bicyclo[3.3.0]octatrienediones.
Total synthesis of polyoximic acid
Authors: Hanessian Stephen , Fu Jian-min
Published: April 2011

The structure and stereochemistry of polyoximic acid, a degradation product of polyoxins, was originally designated as trans-3-ethylidene-L-azetidine-2-carboxylic acid. However, total synthesis revealed that the correct structure was in fact cis-3-ethylidene-L-azetidine-2-carboxylic acid, which was confirmed by X-ray crystallography. The synthesis of the trans-isomer was also done and its identity was confirmed by X-ray analysis as well. The key step for constructing the four-membered ring was a rhodium catalyzed carbenoid insertion into the NH bond of a beta-amino acid derivative. The stereoselectivity of the exo-double bond was controlled by conducting a Horner-Emmons-Wadsworth or a Wittig reaction to generate the trans- and cis-isomers, respectively. Weinreb's amide was used as a latent methyl group for the separation of trans and cis mixtures. The double bond stereochemistry of polyoximic acid in the parent polyoxin was also confirmed to be cis by extensive 2D NMR studies.Key words: diazoinsertion, azetidine, olefination.
Kinetics and mechanistic study of the ruthenium(III) catalyzed oxidative deamination and decarboxylation of L-valine by alkaline permanganate
Authors: Bilehal Dinesh C , Kulkarni Raviraj M , Nandibewoor Sharanappa T
Published: April 2011

The kinetics of ruthenium(III) catalyzed oxidation of L-valine by permanganate in alkaline medium at a constant ionic strength has been studied spectrophotometrically. The reaction between permanganate and L-valine in alkaline medium exhibits 2:1 stoichiometry (KMnO4:L-valine). The reaction shows first-order dependence on the concentration of permanganate and ruthenium(III) and less than unit-order dependence on the concentrations of L-valine and alkali. The reaction rate increases both with an increase in ionic strength and a decrease in solvent polarity of the medium. Initial addition of reaction products did not significantly affect the rate. A mechanism involving the formation of a complex between catalyst and substrate has been proposed. The activation parameters were computed with respect to the slowest step of the mechanism.Key words: oxidation, L-valine, catalysis, ruthenium(III), kinetics.
Rhodium-catalyzed hydroborations of allylamine and allylimines1
Authors: Vogels Christopher M , O'Connor Paul E , Phillips Trevor E , Watson Keith J , Shaver Michael P , Hayes Paul G , Westcott Stephen A
Published: April 2011

The in situ rhodium-catalyzed addition of catecholborane (HBcat, cat = 1,2-O2C6H4) and pinacolborane (HBpin, pin = 1,2-O2C2Me4) to allylamine, allylimine, 2- and 4-vinylpyridines, and a thienyl imine has been examined using multinuclear NMR spectroscopy. Although reactions of allylamine (H2NCH2CH=CH2) and HBcat gave complex product distributions arising from competing dehydrogenative borylation pathways, addition of HBpin to allylamine using a rhodium catalyst afforded only products arising from hydroboration (RN(Bpin)CH2CH2CH2Bpin, where R = H, Bpin) and hydrogenation (RN(Bpin)CH2CH2CH3). Hydroboration of allylimines (RHC=NCH2CH=CH2, R = Ar) with HBcat occurs initially at the more reactive imine functionality to give unsaturated borylamines (RCH2N(Bcat)CH2CH=CH2). Further reaction with HBcat gives varying amounts of hydroboration products RCH2N(Bcat)CH2CH2CH2Bcat and RCH2N(Bcat)CH2CH(Bcat)CH3as well as the diboration product RCH2N(Bcat)CH2CH2CH(Bcat)2, depending on the choice of catalyst. Reactions with related unsaturated pyridine derivatives are complicated by extensive degradation, which can be avoided by coordination of the pyridine nitrogen to a Lewis acid. The first examples of metal-catalyzed hydroboration of imines using HBpin are also reported.Key words: catalysis, hydroboration, boronate esters, dehydrogenative borylation, allylimines.
Kinetic stabilizing effect of the 4-N-methylacetamido substituent on the phenylnitrenium ion
Authors: Ruane Patrick H , McClelland Robert A
Published: April 2011

Photolysis of 4-(N-methylacetamido)phenyl azide in aqueous solution results in quantitative formation of the 4-(N-methylacetamido)phenylnitrenium ion, this cation arising from solvent protonation of an initially formed singlet arylnitrene. The cation is observed by flash photolysis, and is identified through characteristic quenching by azide ion and by 2'-deoxyguanosine, both excellent nucleophiles for arylnitrenium ions in water. The nitrenium ion is protonated in acidic solutions to form the 4-(N-methylacetamido)aniline dication, whose pKa is determined to be 1.5 based on the ratepH profile. This means that the nitrenium ion is relatively basic, which suggests that there is significant positive charge on the N-methylacetamido group. Further evidence for this is seen in the remarkably long lifetime (5 ms) of the nitrenium ion in water. In fact, the 4-(N-methylacetamido)phenylnitrenium ion is 5000-fold longer-lived than the 4-methoxy-substituted analog. A 4-methoxy substituent on a phenyl ring is more electron donating according to σ+ values (0.78 for MeO vs. 0.60 for NMeAc). The dramatic reversal in the arylnitrenium ions is another example of the failure of these to follow the carbocation scale.Key words: nitrenium ion, flash photolysis, amide substituent.
Reaction of arylnitrenium ions with guanine derivatives: N1-methylguanosine and N2,N2-dimethylguanosine
Authors: Cheng Bernice , McClelland Robert A
Published: April 2011

A prior flash photolysis study of the direct reaction of arylnitrenium ions with 2'-deoxyguanosine identified a second intermediate that grew in as the transient nitrenium ion reacted with the nucleoside. This intermediate was identified as the the product of the addition of the nitrenium ion to the C-8 position of guanine prior to loss of the C-8 proton  the C-8 intermediate. A feature of the C-8 intermediate is that it exists in acidbase forms. This behavior was evident in both a spectroscopic analysis as well as in the ratepH profile, which showed a break around pH 4 from a pH-independent reaction to a reaction that was first-order in H+. The present study was designed to identify the structure of the conjugate base form. This involved a kinetic study of the decay of the C-8 intermediate derived from the reaction of the 2-fluorenylnitrenium ion with N1-methylguanosine and N2,N2-dimethylguanosine. The rationale was that the former is unable to lose the N-1 proton, while the latter cannot deprotonate at the NH2 group. The ratepH profiles clearly show that it is the N-1 proton that is acidic. The rate constants for the C-8 intermediate of N2,N2-dimethylguanosine show the same downward break observed with 2'-deoxyguanosine and guanosine associated with conversion to the conjugate base form. In contrast, the rate constants for the N1-methylguanosine intermediate are independent of pH. Rate constants for the reaction forming the C-8 intermediate are also reported. These show that the reaction of nitrenium ions with the N2,N2-dimethylguanine derivative is significantly faster (except where the reactions are diffusion controlled). This is consistent with the initial step of the reaction of an arylnitrenium ion and guanine occurring by direct addition at C-8. The developing positive charge in such a reaction can be delocalized to the C-2 position where π donors such as NH2 and NMe2 can exert a stabilizing effect.Key words: nitrenium, arylnitrenium, guanosine, DNA adduct.
Microwave-assisted Diels-Alder synthesis
Authors: Jankowski Christopher K , LeClair Gaëtan , Bélanger Jacqueline MR , Paré Jocelyn RJ , VanCalsteren Marie-Rose
Published: April 2011

The synthesis of isoquinolinone carboxylates was performed using arecoline or its isomer N-methyl tetrahydro pyridine carboxylate with Danishefsky's diene via thermal or microwave assisted Diels-Alder reaction. The comparison of both condensation modes showed that the microwave method not only afforded higher yields of the adducts, but also lead to the formation of a new α,β-unsaturated pyridyl ketone. All structures were identified with the help of high resolution 2D NMR.Key words: Diels-Alder microwave assisted reaction, microwave synthesis, Michael, diene, isoquinoline carboxylate synthesis, Danishefsky diene synthesis, MAP Diels-Alder2.
The chemistry of the processes involved in the production of lanthanide titanates by the polymerized-complex method
Authors: Todorovsky Dimitr S , Getsova Miroslava M , Milanova Maria M , Kakihana Masato , Petrova Nikolina L , Arnaudov Michail G , Enchev Venelin G
Published: April 2011

The composition, some spectral characteristics, and thermal decomposition of solid lanthanide–titanium (lanthanide (Ln) = Y, La, Ce) and lanthanide–titanium citrates (CA) and tartrates (TA) have been studied. The complexes have been prepared in ethylene glycol medium at conditions modeling those of the polymerized-complex method applied for Ln2Ti2O7 preparation. Special attention has been paid to the chemical nature of the bimetallic products as well as to the factors influencing the deprotonation of the alcoholic OH groups of the acidic ligands. The results contribute to further elucidation of the complexation and thermal decomposition processes involved in the polymerized-complex method.Key words: inorganic compounds, sol–gel chemistry, infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis (TGA).
LINEAR FREE ENERGY RELATIONSHIPS CONCERNING EQUILIBRIA IN MODERATELY CONCENTRATED MINERAL ACIDS: A SIMPLE METHOD FOR ESTIMATING pK's OF WEAK BASES
Authors: Bunnett J. F. , Olsen Fredric P.
Published: April 2011

Linear relationships exist between the logarithms of equilibrium quotients, [SH+]/[S][H+], of diverse bases as they vary with acid concentration in moderately concentrated mineral acids. For purposes of formulating these linear free energy relationships in standard form, the equilibrium quotient for protonation of a hypothetical aromatic primary amine of pKa zero has been chosen as horizontal coordinate; this is given by (−H0 − log [H+]). Log ([SH+]/[S]) + H0 is plotted against (H0 + log [H+]). The slope, [Formula: see text] of the linear plot is a parameter which characterizes the response of the equilibrium quotient to changing acid concentration. The intercept represents the thermodynamic pKa of the base. This constitutes a general method for estimating the pKa of any base which undergoes protonation in moderately concentrated mineral acid, with reference to the single acidity function, H0. For bases of diverse type, pK's estimated by this method are in good agreement with those estimated by the acidity function method. Use of the new correlation procedure as a check on the validity of several acidity functions and its application to equilibria not involving proton gain or loss are also discussed.
COULOMB PARAMETERS IN SIMPLE HUCKEL AND OMEGA TECHNIQUE MOLECULAR ORBITAL METHODS
Authors: Baird N. C. , Whitehead M. A.
Published: April 2011

The well-known similarities of the simple Huckel and omega technique molecular orbital procedures for pi electrons to Pople's self-consistent field method are extended by considering systematic approximations to the latter. From the relationships found, Huckel-method Coulomb integrals and omega values for a variety of atoms (Be, B, C, N, O, F, Mg, Al, Si, P, S, Cl, Ge, As, Se, Sn, Sb, Te) are derived. The Huckel and omega Coulomb integrals are shown to be directly related to a recent definition of orbital electronegativity. The ability of the omega techniques to improve upon the Huckel-method charge distributions is discussed by use of an arbitrary but typical example.
ELECTRON SPIN RESONANCE SPECTRA OF 15N-CENTERED RADICALS AT LOW TEMPERATURES: II. THE RADIOLYSIS OF POTASSIUM SULFAMATE
Authors: Morton J. R. , Smith D. R.
Published: April 2011

Single crystals of potassium sulfamate, KNH2SO3, enriched in the isotope 15N, were irradiated, and examined at 77° K by electron spin resonance. Two intermediates, neither of which are present on examination at 300 °K, have been identified as NH2 and NH2SO3. A possible radiolysis mechanism is discussed.
ELECTRON SPIN RESONANCE SPECTRA OF N2H4+ AND PF2
Authors: Wan J. K. S. , Morton J. R. , Bernstein H. J.
Published: April 2011

The radicals N2H4+ and PF2 have been detected by electron spin resonance in -γ-irradiated NH4PF6. The radical N2H4+ was shown to be formed from NH3+ radicals detectable after low-temperature irradiation.
ULTRAVIOLET, INFRARED, AND RAMAN SPECTRA OF PROTONATED CARBOXYLIC ACIDS
Authors: Hoshino Sumie , Hosoya Haruo , Nagakura Saburo
Published: April 2011

Ultraviolet, infrared, and Raman spectra were measured for acetic acid and propionic acid in sulfuric acid solutions of various acidities. Infrared spectra of acetic acid and benzoic acid were measured in deuterosulfuric acid and aqueous deuterated sodium hydroxide solutions. From the detailed analyses of the ultraviolet absorption change the pKBH+ values of acetic and propionic acids were found to be −6.12 and −6.33, respectively. In the infrared and Raman spectra of the protonated acids, the C=O stretching band at about 1700 cm−1 disappeared and a new strong infrared absorption band appeared at about 1600 cm−1. The frequency of the latter band, which can be assigned to antisymmetric C—O stretching band, is very similar to that of the carboxylate group. The acidity dependence of these infrared spectra was parallel with that of the ultraviolet absorption. These facts confirm that the protonated carboxyl group has a skeleton [—C(OH)2]+ similar to the carboxylate group [—CO2]−.
THE PHOTOLYSIS OF CO2 AT 1 470 Å
Authors: Ung A.-Y. , Schiff H. I.
Published: April 2011

The apparatus used to study the photolysis contained a collimating region which minimized the effect of divergent light, and permitted the temperature of the cell and lamp to be controlled separately. Analytical sensitivity was such that conversions less than 0.2% were possible.Although CO and O2 were the only stable products, the CO/O2 ratios were higher than those required by mass balance. The product yields were found to be independent of CO2 pressure and to be linear with irradiation time at 25 °C. At higher temperatures the quantum yields decreased and at 200 °C were no longer linear functions of irradiation time. The O2 yields decreased when CO was added, the effect increasing with temperature. The overall quantum yield was less than unity. Reactions were observed with CH4, H2, and N2O when these were added in small amount. These results indicated the presence of a reactive species, capable of promoting back reactions and of being adsorbed on the walls. A mechanism is suggested which best fits the results and which postulates CO3 as the reactive species.
PREPARATION OF FREMY'S SALT, POTASSIUM NITROSODISULFONATE
Authors: Singh R. P.
Published: April 2011

not available
Étude quantitative des réactions d'ozonolyse. IV. Ozonation de l'indène
Authors: Fliszār S. , Belźecki Cz. , Chylińska J. B.
Published: April 2011

The ozonolysis of indene in ethanol yields 3-hydroxy-4,5-benzo-7-ethoxy-l,2-dioxacyclo-heptane and 3-ethoxy-4,5-benzo-7-hydroxy-1,2-dioxacycloheptane, roughly in a 1:1 ratio, thus showing that the cleavage of the primary indene ozonide follows the two possible courses: via the zwitterions [Formula: see text] and [Formula: see text], respectively.
13C n.m.r. studies. X. 13C spectra of some substituted methyl benzoates
Authors: Dhami K. S. , Stothers J. B.
Published: April 2011

The 13C spectra of the methyl esters of 20 substituted benzoic acids have been recorded, and the chemical shifts of the carbon nuclei of the carbomethoxyl group and aromatic ring have been measured. These shielding results are discussed and compared with the corresponding data for similar series of acetophenones and anisoles. Some evidence of steric inhibition of conjugation is presented for certain diortho-substituted examples.
Mechanism of the α-silylcarbinol to silyl ether rearrangement
Authors: Brook A. G. , LeGrow G. E. , MacRae D. M.
Published: April 2011

The rates of rearrangement of a wide variety of α-silylcarbinols have been measured. Hammett plots of log k vs. σ have been made for several systems, and values for ρ, for the energy of activation, and for the entropy of activation have been obtained. A mechanism which is consistent with the above data, and which involves a cyclic three-membered transition state, has been proposed for the α-silylcarbinol to silyl ether rearrangement.
The synthesis, separation, and identification of the methyl ethers of arabinose and their derivatives
Authors: Williams S. C. , Jones J. K. N.
Published: April 2011

A study has been made of various methods available for the identification and separation of the methyl ethers of arabinose. Gas–liquid partition chromatography has been used to separate the acetylated glycosides and the acetylated alditols of the methyl ethers of arabinose. All of the methyl ethers of arabinopyranose and arabinofuranose have been separated by paper chromatography. Several spray reagents have been used to distinguish between those methyl ethers with similar rates of movement. Thin-layer chromatography has been used to separate the methyl glycosides, acetylated methyl glycosides, and glycitols of the methyl ethers of arabinose, as well as the methyl ethers of the reducing sugar. The optical rotations of the reducing sugars and of the methyl glycosides of the methyl ethers of arabinose provide information about the ring form and, in the case of the glycosides, about the anomer present. The rotations of the acetylated and unacetylated O-methyl arabinitols aid in the determination of the position of the methyl substitutents. In connection with this study, all of the mono-O-methyl and tri-O-methyl, and most of the di-O-methyl ethers of arabinose have been synthesized. New syntheses have been devised for 4-O-methyl and 2,3-di-O-methyl arabinose, and the other sugars have been synthesized by known or partially revised syntheses. During this work, previously unreported derivatives of these sugars have been prepared.
A new synthesis of twistane
Authors: Gauthier Jean , Deslongchamps Pierre
Published: April 2011

A new synthesis of twistane (IX) has been realized in seven steps, starting from a readily available decalin system.
Cyclobutenyl derivatives of phosphorus and sulfur
Authors: Cullen W. R. , Dawson D. S. , Dhaliwal P. S.
Published: April 2011

Diethylphosphine and methanethiol react with the cyclobutenes

[Formula: see text](X = Cl, F) to give the compounds (C2H5)2

[Formula: see text] (Y = Cl, F) and

[Formula: see text] (Y = F, Cl, C2H5). The disubstituted compound

[Formula: see text] is also obtained from CH3SH and

[Formula: see text].The related di(tertiary phosphine) (C6H5)2-

[Formula: see text] can similarly be prepared. Methanethiol adds to

[Formula: see text] to give the cyclobutane, but reacts with

[Formula: see text]to give

[Formula: see text]and with

[Formula: see text] to give the cyclobutenone

[Formula: see text]. Tetra-methyldiphosphine and

[Formula: see text] yield the disubstituted compound

[Formula: see text], whereas a cyclobutenone is obtained when (C6H5)2P—P(C6H5)2 reacts with

[Formula: see text]. In some reactions, the phosphorane (C6H5)2PF3 is obtained, probably from (C6H5)2PF.