bluuebunny/crossref_metadata_2025 huggingface dataset:
Dimeric rhodium(II) complexes containing bridging mandelate ligands
Authors: Pruchnik Florian , James Brian R. , Kvintovics Pál
Published: May 2006

The syntheses and characterization of some dimeric rhodium(II) complexes containing bridging mandelato ligands and a metal–metal bond are described. The compounds isolated are Rh2(O2CR)4(H2O)2, previously described by Shchelokov and coworkers, and derivatives of the type Rh2(O2CR)2(N—N)2X2•nH2O (R = (R)—CH(OH)Ph, N—N = o-phenanthroline or 2,2′-dipyridyl, X = Cl, Br, I, and n is 4, 2, or 1). A mixture of species containing both bridged acetate and mandelate was isolated also. Infrared and electronic spectral data are reported. The chloride ligands of the dimers are displaced readily by alcohols, phosphines, phosphites, and amines; the metal centre also may be reduced by alcohols, P(OEt)3, and nBu2NH. Preliminary studies point to the conditions necessary for the rhodium(II) mandelate and derivatives (phosphine or (N—N) substituted) to activate H2 for catalytic hydrogenation of olefins and ketones, including prochiral substrates.
Acid-catalyzed hydrolysis of 2-methylene-1,3-dithiolane. 2. Remarkable effects of β substitution on reversibility of the carbon protonation
Authors: Okuyama Tadashi , Toyoda Masayoshi , Fueno Takayuki
Published: May 2006

Hydrolyses of 2-ethylidene-(1b), 2-isopropylidene-(1c), and 2-benzylidene-1,3-dithiolane (1d) were kinetically investigated in aqueous solution. All the individual rate constants involved in this three-step reaction were evaluated. Initial carbon protonation is only partially reversible (k2/k−1 = 1.33, 0.68, and 1.02 for 1b, 1c, and 1d, respectively) at higher pH, while the protonation becomes completely reversible below pH 2 where the third step is rate determining. Complete H–D isotope exchange at the β-carbon of 1b and 1d was observed in deuterium media before appreciable hydrolysis took place. It was demonstrated that reversion from the tetrahedral intermediate 3 to 1 occurs extensively during the reaction in the latter acidity range. Relative stabilities and reactivities of the olefinic substrates 1 are discussed.
Kinetics and mechanism of nucleophilic displacements with heterocycles as leaving groups. Part 23. Studies at the borderlines between reactions proceeding (i) via free carbocations, (ii) via rate-determining formation of ion–molecule pairs, and (iii) via rate-determining nucleophilic attack on ion–molecule pairs
Authors: Katritzky Alan R. , Brycki Bogumil
Published: May 2006

Evidence is presented to demonstrate that at the borderline between first-order reaction via nucleophilic trapping of intimate ion–molecule pairs and first-order reaction via the formation of free carbocations, both mechanisms proceed independently, without merging. Similarly at the borderline between first-order (rate-determining formation) and second-order (rate-determining nucleophilic attack) reactions of intimate ion–molecule pairs, both reactions again proceed independently.
Solvolytic rearrangement studies with 14C or 13C labeled (E)- and (Z)-1,2-diphenyl-2-tolylvinyl bromides
Authors: Lee Choi Chuck , Wanigasekera Dave
Published: May 2006

The reaction of (E)-, (Z)-, or a 2:3 mixture of (E)- and (Z)-1,2-diphenyl-2-tolyl[2-14C]vinyl bromide ((E)-, (Z)-, or (E,Z)-3-Br-2-14C) in HOAc–AgOAc gave a 1:1 mixture of the structurally unrearranged but isotopically scrambled (E)- and (Z)-1,2-diphenyl-2-tolyl[1,2-14C]vinyl acetates ((E,Z)-3-OAc-1,2-14C), with an average of 18.3% scrambling of the 14C label from C-2 to C-1 arising from 1,2-tolyl shifts in the 1,2-diphenyl-2-tolylvinyl cation (3). No detectable amount of the structurally rearranged 2,2-diphenyl-1-tolylvinyl acetate (4-OAc) was formed. Solvolysis of (E,Z)-3-Br-2-14C in TFE-2,6-lutidine gave as products 62% 4-OTFE-1,2-14C and 38% of a 1:1 mixture of (E)- and (Z)-3-OTFE-1,214C. Only (Z)-3-OTFE-1,2-14C could be isolated as a pure product and it showed an average of 44.7% scrambling of the label from C-2 to C-1. Similar trifluoroethanolyses of (E,Z)-3-Br-2-13C coupled with gas chromatographic - mass spectral analyses of the diphenyl and phenyl tolyl ketones from ozonolysis of the product mixture showed 44.6% scrambling in the (E,Z)-3-OTFE-1,2-13C, confirming the 14C results for the (Z) isomer. Nondegenerate rearrangements from 1,2-phenyl shifts before and after the degenerate 1,2-tolyl shifts to give 4-OTFE-1-13C and 4-OTFE-2-13C were also observed, demonstrating the occurrence of successive 1,2-aryl shifts in these triarylvinyl cations.
The structure of fusarochromanone: new mycotoxin from Fusariumroseum, "Graminearum"
Authors: Pathre Sadanand V. , Gleason William B. , Lee Yin-Wan , Mirocha Chester J.
Published: May 2006

An isolate of Fusariumroseum "Graminearum" obtained from overwintered oats in Alaska produced toxic cultures when grown on rice. The toxic principle called fusarochromanone isolated from these cultures reproduced the signs of tibial dyschondroplasia in poultry and also reduced hatchability of fertile eggs. Spectroscopic data (nmr, ir, and ms) indicated the mycotoxin to be a chromanone derivative. The chromanone ring structure was also confirmed by single crystal X-ray.
New physostigmine related bromoalkaloids from the marine bryozoan Flustrafoliacea
Authors: Laycock Maurice V. , Wright Jeffrey L. C. , Findlay John A. , Patil Ashok D.
Published: May 2006

Methylene chloride extracts of the bryozoan Flustrafoliaceae show strong antimicrobial activity. Chemical investigation of the metabolites has led to the identification of a series of new bromoalkaloids belonging to the physostigmine class, which are responsible for this activity.
Detection of deuterium labelling by two-dimensional 1H,13C nuclear magnetic resonance shift correlation with 2H decoupling
Authors: Reese Paul B. , Trimble Laird A. , Vederas John C.
Published: May 2006

Methylene groups that are stereospecifically labelled with deuterium can be easily observed using deuterium-decoupled 2-dimensional proton/carbon nmr shift correlation spectroscopy in either normal or CH-selective mode. Application of the technique to [3-2H]camphors 2, 3, and 4 shows that overlap of other 13C resonances does not interfere with the 2H detection. Such experiments with [3-2H]-N-benzoylphenylalanine methyl esters 6 and 7 demonstrate that identification of labelled diastereotopic hydrogens can be done if they are separated by 0.1 ppm in the 1H nmr spectrum. Fully deuterated carbons (e.g., CD3 methyl, CD2 methylene, CD methine) cannot be observed by this approach, as seen by the study of pregnenolone acetate (9) randomly deuterated at C-17 and C-21. The technique is ideal for cases with extensive overlap of other proton and carbon resonances because high chemical shift dispersion in two dimensions separates the signals of interest. This nmr method was used to show that hydrogenation of cholesteryl acetate (10) with deuterium gas and palladium catalyst exchanges the C-7 α-hydrogen to give 12. The detection limit is estimated at 10% deuterium per site unless 13C-labelled compounds are used.
Synthesis of 8-methylene-des-AB-cholestan-9-one by cholesterol degradation
Authors: Morzycki Jacek W. , Jurek Jaroslaw , Rodewald Wladyslaw J.
Published: May 2006

The short synthetic route from 3β-acetoxy-5β-methyl-19-norcholest-9(10)-en-6-one (1) to 8-methylene-des-AB-cholestan-9-one (8) is described. Compound 8 is a convenient intermediate for the synthesis of relatives of vitamin D3 by the A → CD route.
Open chain nitrogen compounds. Part XI. 3,7-Bis(arylazo)-1,3,5,7-tetraazabicyclo[3,3,1]nonanes: the reaction of diazonium ions with ammonia–formaldehyde mixtures
Authors: Singer Robert D. , Vaughan Keith , Hooper Donald L.
Published: May 2006

Reaction of a series of diazonium salts with either hexamine or an aqueous mixture of ammonia–formaldehyde affords 3,7-bis(arylazo)-1,3,5,7-tetraazabicyclo[3,3,1]nonanes; several new examples of this novel class of bicycloheterocycle have been prepared and characterized. Analysis of the low-temperature nmr spectra of one compound in this series shows that the bicyclic system prefers the chair–chair conformation. The bis(arylazo)tetraazabicyclononanes, which are surprisingly stable in aqueous buffer compared to analogous triazenes of open-chain structure, do undergo slow decomposition at slightly acidic pH in an acetone–buffer mixture. The apparent product of this decomposition is the arylamine, which is observed as the Mannich condensation product, ArNH•CH2CH2COCH3.
Synthesis of cyclopentane analogs of (2′- and 3′-deoxy-erythro-pentofuranosyl and ribofuranosyl)-2-thiouracil nucleosides
Authors: Hronowski Lucjan J.J. , Szarek Walter A.
Published: May 2006

Three new carbocyclic analogs of nucleosides having the 2-thiouracil base have been synthesized. The cyclopentyl groups in these nucleosides are (±)-{(1β,3α,4β)-3-hydroxy-4-(hydroxyrnethyl)cyclopentyl} (see 31), (±)-{(1β,2α,4β)-2-hydroxy-4-(hydroxymethyl)cyclopentyl} (see 32), and (±)-{(1β,2α,3α,4β)-2,3-dihydroxy-4-(hydroxymethyl)cyclopentyl} (see 33). The nucleosides were prepared by coupling the appropriate hydroxy derivatives of cis-3-aminocyclopentanemethanol with 3-ethoxypropenoyl isothiocyanate (21) followed by cyclization in 15 N aqueous ammonia to give the 2-thiouracil nucleosides. In addition a modified and shortened synthetic route is described for the synthesis of (±)-(1β,2α,3α,4β)-4-amino-2,3-dihydroxy-cyclopentanemethanol (19). The 1H nmr spectra at 200 MHz of all of the synthetic intermediates, the 2-thiouracil nucleosides, and of the corresponding carbocyclic analogs of uracil nucleosides are discussed. It is shown that each nucleoside has a characteristically unique 1H nmr spectrum and that in general the protons in the sulfur-containing compounds resonate at lower fields than those in the corresponding oxygen-containing compounds. The magnitude of this downfield shift is inversely related to the number of bonds separating a particular proton from the sulfur atom.
Reactions of alicyclic ketones in carbon tetrachloride. I, The kinetics of the chlorination of cyclopentanone and cyclohexanone catalyzed by hydrogen chloride
Authors: Stamhuis Eize J. , Maatman Henk , Stinissen Henk , Joosten Geert E. H.
Published: May 2006

The kinetics of the direct chlorination of cyclopentanone (cp) and cyclohexanone (ch) in carbon tetrachloride, catalyzed by hydrogen chloride, was studied. The rate of chlorination, measured by flow and stopped-flow techniques, is zero order in chlorine; the order in cp and ch increases from 1 at [cp] and [ch] of 0.01 M concentration to 2 at concentrations of 1 M. This is explained by self-association of the ketones in carbon tetrachloride solutions. The order in hydrogen chloride is 1. Since this compound is one of the products, the reaction is autocatalytic. Deuterium isotope effects and the kinetic data strongly point to a mechanism in which the oxygen-protonated monomeric ketone is α-carbon deprotonated in a rate-determining step. This step, which is catalyzed by the bases cp or ch, respectively, leads to the corresponding enol as intermediate. The enol is then chlorinated very rapidly. In addition to the chloro ketone, very reactive chloride anions are formed. A small fraction of these anions deprotonate α- or α′-carbon atoms of the oxygen-conjugate acid of the monochloro ketone. The remainder are captured by HCl to form energetically more favored Cl--(HCl)n complexes with n = 1, 2, or 3. This explains why, even at low conversions of the ketones, substantial amounts of the various dichloro isomers are formed in addition to monochloro products. A rate expression is derived, which excellently describes the experimentally obtained rates of chlorination of cp and ch over a range of reaction rates of more than three decades.
An MNDO study of dipyridopyrazinium and relation cations: instability of certain fused heteroaromatic dications with two bridgehead nitrogens
Authors: Eaves Jeffrey G. , Parker David , Rudgewick-Brown Nigel
Published: May 2006

MNDO calculations are reported for the series of closed shell aromatic and heteroaromatic molecules and cations 1 to 7. The 14π dipyrido-dications 1a and 2a are considerably less stable than their dihydro-analogues 1b and 2b and perhaps should not be considered to be "aromatic" cations.
Composés du phosphore dicoordonné: action des amines sur les triazaphospholes-1,2,4,3 substitués en 2,5. Étude thermodynamique de l'équilibre de formation des triazaphospholines et caractérisation de leurs dérivés tétracoordonnés
Authors: Boisdon Marie-Thérèse , Lopez Lucien , Malavaud Christian , Barrans Jean , Chabane Abdelaziz , Mathis Raymonde
Published: May 2006

The oxidation of 2,5-disubstituted 1,2,4,3-triazaphospholes with amines gives 1,2 addition products by an equilibrium reaction. This equilibrium has been proved by temperature lowering and also by chemical reaction: addition of sulfur, selenium, or azide (X) shifts the equilibrium to the 1,2 addition products:[Formula: see text]The thermodynamical parameters associated with this equilibrium have been determinated in some cases.
Synthesis and structural studies of rhodium complexes of phosphorus—sulfur ligands
Authors: Dick David G. , Stephan Douglas W.
Published: May 2006

Rhodium complexes of the phosphorus—sulfur ligands, 2-diphenylphosphinoethyl methyl sulfide (MeSP), 1, and 2-diphenylphosphinothiophene (PTH), 2, have been prepared and studied by single crystal X-ray diffraction methods. [Rh(MeSP)2]BF4•H2O, 3, crystallizes in the space group P21/n with a = 16.939(6) Å, b = 17.152(5) Å, c = 12.049(9) Å, β = 106.50(4)°, and Z = 4. The MeSP ligands chelate to Rh yielding a distorted square-planar geometry. The disposition of the methyl groups on the cis sulfur atoms is transoid. Average Rh—P and Rh—S bond distances were found to be 2.225(3) and 2.347(3) Å, respectively. [Rh(PTH)2(COD)]BF4, 4, crystallizes in the space group Cc with a = 15.862(2) Å, b = 15.112(3) Å, c = 16.029(3) Å, β = 103.32(1)°, and Z = 4. The Rh atom in 4 also has essentially a square-planar coordination geometry. 2 does not chelate but rather is monohapto through phosphorus. Rh—P distances of 2.319(3) and 2.378(3) Å and Rh—C distances of 2.17(1), 2.22(1), 2.24(1), and 2.27(1) Å were found. The small variations in the Rh—P and Rh—C bonds distances appear to be a result of steric interactions between 2 and the COD ligand.
Acyclic nucleoside analogues: methods for the preparation of 2′,3′-secoguanosine, 5′-deoxy-2′,3′-secoguanosine, and(R,S)-9-[1-(2-hydroxyethoxy)-2-hydroxyethyl]guanine
Authors: McGee Danny P. C. , Martin John C.
Published: May 2006

A high yielding, one-pot method for the preparation of 2′,3′-secoguanosines 5 and 6 by treatment of 5′-deoxyguanosine (4) and guanosine (2), respectively, with sodium periodate and then sodium borohydride is described. The final products 5 and 6 were purified from contaminating salts by passage of the reaction mixture over a column of activated charcoal. An additional acyclic derivative 14 was prepared in racemic form by an approach involving a novel condensation reaction. Alkylation of N2,9-diacetylguanine (8) with 2,3-dichlorotetrahydrofuran (7) resulted in selective N-9 alkylation to give adduct 9a. Compound 9a was deacylated with ammonium hydroxide to give 10, which was monomethoxytritylated to 11. Elimination of hydrogen chloride from 11 using potassium tert-butoxide afforded 12, which was reacted with OsO4–NaIO4 followed by treatment with NaBH4 to give 13, which was then deprotected with acid to 14. Compounds 5, 6, 14, and 16 were tested in vitro against herpes simplex virus types 1 and 2 and were found to be inactive.
Cobalt carbonyl catalyzed reaction of mercaptans with Schiff bases and carbon monoxide
Authors: Antebi Shlomo , Alper Howard
Published: May 2006

Thiophenols and p-methylbenzyl mercaptan react with Schiff bases and carbon monoxide in benzene, in the presence of cobalt carbonyl, to give amides as the principal products. These amides arise from cleavage of the carbon–nitrogen double bond of the reactant imine. The reaction is applicable to a variety of Schiff bases (i.e. aliphatic, benzylic, aromatic). Thioesters and olefins are usually obtained as reaction by-products.
Motional and conformational dynamics in a homologous series of smooth muscle relaxing agents
Authors: Valensin Gianni , Gaggelli Elena , Lepri Andrea , Sega Alessandro
Published: May 2006

Dynamic features were investigated in a homologous series of synthesized drugs having pharmacologic activity, with particular emphasis on relative motions of the two side chains anchored to a backbone of two aromatic rings linked by an amide bridge. A general and deep insight was reached by using a model-free approach. Conformational and motional dynamics within the compound exhibiting maximum activity were delineated and the most relevant parameters for pharmacologic action were defined.
Acyl migration from N6 to N7 of a 2′,3′-O-isopropylideneadenosine derivative accompanied by cyclonucleoside formation
Authors: Anzai Kentaro , Uzawa Jun
Published: May 2006

Reaction of 2′,3′-O-isopropylideneadenosine (1) with p-NCC6H4COCl in 1:6 Et3N–CH2Cl2 afforded the cyanoimidazole nucleoside 8 (53%) and the 8,5′-O-cycloadenosine derivative 7 (29%). Treatment of N6,N6-di-p-toluyl-2′,3′-O-isopropylideneadenosine (23) with ZnBr2 in p-dioxane resulted in acyl migration from N6 to N7 to give the cycloadenosine derivative 4. The coordination site of the zinc cation on the base moiety of adenosine derivatives was determined by 15N nmr spectra.
Far ultraviolet induced decomposition of thymine in deaerated and aerated aqueous solutions
Authors: Ohtani Bunsho , Nagasaki Hiroshi , Nishimoto Sei-Ichi , Sakano Koichi , Kagiya Tsutomu
Published: May 2006

Thymine in aqueous solution was decomposed with quantum yields of 0.3 and 0.4 under N2-saturated and aerated conditions by far-ultraviolet light (> 180 nm, far-uv), and quantum yields of 2 × 10−4 and 3 × 10−4 by near-ultraviolet light (> 220 nm, near-uv), respectively. The main photolytic products by far-uv were 5,6-dihydrothymine (DHT) (selectivity: S (DHT) = 0.2) and 5-hydroxymethyluracil (HMU) (S(HMU) = 0.1) under N2-saturated conditions, cis- and trans-5,6-Dihydroxy-5,6-dihydrothymine (TG), 6(5)-hydroperoxy-5(6)-hydroxy-5,6-dihydrothymine (HTP) (S(TG) + S (HTP) = 0.2), and N1 -formyl-N2-pyruvylurea (FPU) (S(FPU) = 0.4) were obtained under aerated conditions. These products were attributed to the reactions of thymine with the H and OH produced by photolysis of water.
Comparative sulphur cation chemistry in a hydrocarbon flame with H2S, OCS, and SO2 additives
Authors: Karellas Nicholas S. , Goodings John M.
Published: May 2006

A fuel-rich, conical, premixed, methane–oxygen flame at atmospheric pressure was doped separately with 0.2 mol% of H2S, OCS, and SO2 to probe the chemistry of sulphur at its source during combustion. These three additives represent a broad range of fuel-sulphur contaminants since they occur early, intermediate, and late in the sulphur oxidation sequence. A wide variety of sulphurous cations, formed by chemical ionization reactions, is observed for each additive by sampling the flame into a mass spectrometer. The total ionization profile measured along the flame axis is enhanced in the reaction zone when a sulphur additive is present; the mechanism involves the formation of sulphurous negative ions which reduces the rates of cation loss by electron–ion recombination and ambipolar diffusion. Mass spectra measured in the mass range 10–110 u at fixed points on the flame axis are very similar for all three additives, and are not helpful in the identification of the additive. However, the general presence of sulphur is evident from large signals measured near the reaction zone at five principal mass numbers; namely, 45 u (CHS+), 47 u (CH3S+), 58 u (C2H2S+), 59 u (C2H3S+), and 69 u (C3HS+) related to CS, thioformaldehyde, thioketene, and C3S.
The chlorination of acetone: a complete kinetic analysis
Authors: Guthrie J. Peter , Cossar John
Published: May 2006

not available
β-Lactams. XII.: A study of the synthesis of N-unsubstituted β-lactams, and of 4-styryl monobactams
Authors: Dugat Denise , Just George , Sahoo Soumya
Published: May 2006

A few types of amines XNH2 were investigated for the formation of β-lactams via the cycloaddition of the corresponding Schiff bases with azidoacetyl chloride. Among the β-lactams formed, only the N-p,p′-dimethoxybenzhydryl compounds could be transformed to N-unsubstituted azetidinones by removal of the N-substituent with ceric ammonium nitrate. Conversion of those N-unsubstituted intermediates to 3-acylated monobactams was studied in the 4-styryl series.
Thermolysis of geminal diazides: a novel route to 1,3,4-oxadiazoles
Authors: Ogilvie William , Rank Werner
Published: May 2006

The geminal diazides ethyl α,α-diazidoacetoacetate and α,α-diazidobenzoylacetate were prepared from the corresponding dibromo precursors by nucleophilic azide displacement. Thermolysis of the diazido compounds led to the formation of 2,5-disubstituted 1,3,4-oxadiazoles in high yield.
Influence of solvent on the magnitude of the anomeric effect
Authors: Praly J.-P. , Lemieux R. U.
Published: May 2006

A novel application of 13C nuclear magnetic resonance provided the effects of solvent polarity and hydrogen-bond formation on the conformational equilibria for a range of 2-substituted tetrahydropyrans and the results are interpreted in terms of how solvent affects the competition between the endo- and exo-anomeric effects in determining the magnitude of the anomeric effect. In accord with the generally accepted origin of the endo- and exo-anomeric effects (anti-periplanar n–σ* interaction of the oxygen lone-pair orbital with the antibonding orbital of the adjacent C—O bond), the exo-anomeric effect for the α anomer is expected to be weaker because charge delocalization from the glycosidic oxygen to anomeric center is in competition with delocalization from the ring-oxygen atom. The effects of solvent on the relative magnitudes of the endo- and exo-anomeric effects are then considered to arise from the formation of specific complexes with the solvent, and the exo-anomeric effect of a β-glycoside is more strongly influenced. It is contended that hydrogen bonding of solvent to the ring oxygen increases the exo-anomeric effects. For this reason water is particularly effective for the strengthening of the exo-anomeric effect and, thereby, the conformational rigidity of glycosides. Experimental evidence is presented that indicates that the anomeric hydroxyl groups of free sugars dissolved in water tend to prefer the equatorial orientation because these provide stronger hydrogen bonds as proton donors to water.
1,2,6-Thiadiazin-3,5(2H,6H)-dione 1,1-dioxide derivatives: crystal structure, physico-chemical and biological properties
Authors: Goya Pilar , Nieves Rosa , Ochoa Carmen , Rodellas Carmen , Martinez-Ripoll Martín , García-Blanco Severino
Published: May 2006

Crystal structure, 1H and 13C nmr spectroscopy and pKa measurements of 1,2,6-thiadiazin-3,5(2H,6H)-dione derivatives related with phenylbutazone are reported. An anomalous variation in the pKa values of compounds 1,2, and 3 has been observed. Antiinflammatory, analgesic, and antipyretic activities of these compounds have been evaluated.
Chloration de l'acétanilide et de la benzanilide en présence des cyclodextrines et de l'amylose
Authors: Chênevert Robert , Ampleman Guy
Published: May 2006

The ratio of ortho to para isomers in chlorination of acetanilide and benzanilide is changed in favour of the para isomer when the reactants are entrapped in cyclodextrins or amylose. The dissociation constant and the time-averaged position of acetanilide in the α-cyclodextrin cavity have been determined by proton and carbon-13 nuclear magnetic resonance spectroscopy.
Preparation of (4R,5S)-(5-methyl-2,2-dimethyl-1,3-dioxolane-4-ylmethyl)-phosphonium iodide. A synthetic approach to olguine: further model studies
Authors: Valverde Serafin , Herradon Bernardo , Rabanal Rosa M. , Martin-Lomas Manuel
Published: May 2006

The enantiomerically pure title compound ((4R,5S)-(5-methyl-2,2-dimethyl-1,3-dioxolane-4-ylmethyl)-phosphonium iodide) has been synthesized starting from (R,R)-(+)-tartaric acid. The synthesis of an olguine analog has been carried out. Attempts have been made to improve the stereoselectivity and yield of key steps.
Electrochemical oxidation of squaric and croconic acids on Pt and Pt surfaces modified by underpotential heavy metal monolayers in acid solutions
Authors: Sazou D. , Kokkinidis G.
Published: May 2006

The electrochemical oxidation of squaric and croconic acids on platinum in aqueous perchloric acid solutions has been investigated by means of cyclic voltammetry, rotating disc electrode, potentiostatic transients and controlled-potential electrolysis. The kinetic parameters (Tafel slopes, reaction orders) have been determined on the foot of the wave by varying the sweep rate, the angular velocity, depolarizer concentration, and perchloric acid concentration. A probable mechanism has been proposed for the overall oxidation processes. It involves two charge-transfer steps followed by the desorption of product, which is the rate-determining step. The oxidation product is immediately deactivated by a rapid hydration reaction. Also, the effect of underpotential Tl, Pb, and Bi monolayers on the electrochemical behaviour of squaric and croconic acids has been examined.
Mécanisme des réactions du chlorite et du dioxyde de chlore. 5. Cinétique de la réaction chlorite–bromure
Authors: Schmitz Guy , Rooze Henri
Published: May 2006

In acidic solutions of chlorite and bromide two processes occur simultaneously, the disproportionation of chlorite and an autocatalytic reaction leading to a rapid production of ClO2. The unusual features of this reaction are described. In this complex system the rate of HClO2 + Br− + H+ → HClO + HBrO cannot be measured. It can be, however, with added ortho-tolidine to remove the HBrO and HClO. We obtained r = k[HClO2][Br−][H+] with k = 1.48 × 10−2 M−2 s−1 at 25 °C. Without added ortho-tolidine this reaction initiates the autocatalytic reaction for which we suggest a kinetic scheme.
Calculations of the energetics of silane–N2O2 exciplexes
Authors: Bell Thomas N. , Perkins Kathryn A. , Perkins Peter G.
Published: May 2006

Calculations have been made on the enthalpies of the singlet and triplet N2O2 species generated from 2πNO + 4πNO, and the exciplexes which result from reaction of N2O2 with some methyl fluorosilanes. Both the ground-state singlet and the first excited triplet of the latter systems have been studied and are discussed in relation to the mechanism for the decomposition of NO after initial excitation with Hg(63P1) atoms.
The reactivity of aliphatic amines and morpholines in dioxane–water solvent systems
Authors: Kalsi Sabrina , Laframboise Rita , Scott Ronald M.
Published: May 2006

Using the titration of tertiary aliphatic amines as a model a linear relationship for the log equilibrium constant versus the log dielectric constant over a broad range of dioxane–water mixtures is established. Primary and secondary amines are less responsive to changes in dielectric constant, producing linear data of shallower slope. A study of morpholine and N-alkyl-morpholines produces curves that plateau in high dielectric constant regions and display decreasing slope as water concentrations approach zero. Similar behavior for morpholines is observed in low water mixtures where they form proton transfer complexes with p-nitrophenol. Possible reasons for the behavior are discussed.
Preparation of chiral allylic alcohols using Rhizopusnigricans. Use of the Harada–Nakanishi exciton chirality method for verifying configurational assignments of allylic alcohols
Authors: Ito Satoru , Kasai Masaji , Ziffer Herman , Sllverton J. V.
Published: May 2006

A series of (R) acyclic and cyclic allylic alcohols was prepared by enantioselective hydrolysis of acetates using Rhizopusnigricans. The configurations of the alcohols formed were established by chemical methods and, in the case of 1,2-benzocyclohepta-1,3-dien-5-yl camphanate, by X-ray crystallography. In conjunction with the Harada–Nakanishi rule, the chiroptical properties of the p-bromobenzoate esters were used to verify configurations tentatively assigned from their method of preparation.
Speciation of soluble manganese in lakewater with Chelex-100 and polyacrylate resin, XAD-7
Authors: Corsini Alfio , Wade Gwen , Wan Chi-Chung , Prasad Shareen
Published: May 2006

Two fractions of (soluble) manganese in Lake Ontario water have been detected and measured with the aid of sequential preconcentration on the polyacrylic ester resin, XAD-7, and Chelex-100. One fraction, consisting of free Mn(II), was retained on the XAD-7 column; the second fraction, consisting of one or more unidentified forms, was retained on Chelex-100. After elution from the columns, the concentration of manganese in each fraction in the lakewater was determined by graphite-furnace AAS. Because both fractions are retained by Chelex-100, the second fraction could also be determined by difference on passage of two separate aliquots through Chelex-100 and XAD-7. Analysis of samples from three locations in the western basin of Lake Ontario showed that about 12–22% of total (soluble) manganese was present as free Mn(II).
The voltammetric determination of Mo in seawater after adsorptive accumulation of the Eriochrome Blue Black R complex
Authors: Willie S. N. , Berman S. S. , Page J. A. , VanLoon G. W.
Published: May 2006

A method for direct determination of molybdenum in seawater has been developed, and uses linear sweep voltammetry after adsorptive accumulation of the Erichrome Blue Black R (EBBR) complex on a static mercury drop electrode. To an acidified (pH 1.6) seawater (SW) sample, 6.0 × 10−6 M EBBR is added and preconcentration by adsorption is carried out for 30 s at a potential of −0.05 V vs. the Ag/AgCl/SW reference electrode. The potential is then scanned in the negative direction, giving a current peak for the reduction of the Mo—EBBR complex at −0.17 V. Under these conditions the limit of detection is 0.50 ng/mL. Experimental results for Mo in seawater using this technique agree well with certified values for two reference seawater samples (NASS-1, CASS-1).
Selective extraction of trace metals associated with hydrous aluminum oxides
Authors: Slavek Janece , Pickering William Frederick
Published: May 2006

In soil/sediment analysis, subdivision of trace metal content into different categories is usually based on selective extraction schemes. To assess the disposition of metal ions bound to aluminum hydrous oxides in such schemes, suspensions of Al(OH)3gel, gibbsite, or alumina were loaded with up to 5 μ mol of Cu, Pb, Cd, or Zn ions prior to being extracted for 24 h with one of fifteen different chemical solutions. The percentage of sorbed ion retrieved varied along the reagent sequence: NaCl, CaCl2 < MgCl2, NH4NO3 < CH3COONH4, Na citrate, Na4P2O7 < EDTA, DTPA < CH3COOH, H2C2O4, HCl, HNO3. In each system, the recovery value varied with the initial surface loading (a function of sorption pH) and reflected changes in metal species form, e.g., bonded M2+, (MOH+), M(OH)2. With low loading levels up to 40% was displaced by salt solutions; with 1 to 2 μ mol sorbed, as little as 10% was displaced by acids or complex formers but this increased to ~90% with higher loadings. The relationship between sorption pH, amount sorbed, and extraction value was complex, and since in selective extraction schemes classification is based on recovery values, changes in initial retention parameters (e.g. system pH) lead to varying fractions of the different metal ions being classified as "ion exchangeable", "chemisorbed", and "incorporated in the lattice".
Kinetics and mechanisms of the reaction of 2,4,6-trinitrocumene and 2,4,6-trinitroethylbenzene with 1,1,3,3-tetramethylguanidine in N,N-dimethylformamide solvent
Authors: Biswas Mihir K. , Jarczewski Arnold , Leffek Kenneth T.
Published: May 2006

The reaction of tetramethylguanidine (TMG) with trinitrocumene (TNC) and trinitroethylbenzene (TNEB) in dimethylformamide solvent has been studied with respect to products and kinetics. For TNC only σ-complex formation with the benzene ring was observed, for which the equilibrium constant, rate constants, and activation parameters were measured. For TNEB, both σ-complex formation and proton transfer from the σ-carbon atom of the ethyl group were observed. The equilibrium constants, rate constants, and activation parameters were separately determined for each reaction and a primary deuterium isotope effect, kH/kD = 13.6 (at 20 °C), was found for the proton transfer. The reaction parameters are compared to those for proton transfer from TNT to tetramethylguanidine in DMF solvent.
Cyclic single drop square wave polarography at spherical electrodes — the reversible case
Authors: Ramaley Louis , Tan Wee Tee
Published: May 2006

The influence of electrode sphericity and the results of sweep reversal are examined for square wave voltammetry and the square wave polarography in which an entire polarogram is obtained on a single drop. An expanding sphere treatment obtained by adding a spherical correction to expanding plane theory gives the best fit to the experimental data. Amalgam forming reactions fit the simple theory developed to a lesser extent than other reactions, especially on the reverse sweep. The shape of the differential polarogram is not significantly affected by sphericity and the reverse peak potential is approximately equal to the forward peak potential. Small differences in these potentials are due to the distortion of the square wave by the stairstep used for the sweep and the distortion of the polarogram due to drop growth. The ratio of the forward and reverse peak currents depends on the phasing of the square wave and stairstep in all cases and on other parameters for a growing drop.
Extraction and spectrophotometric determination of molybdenum(VI) with N-phenylbenzohydroxamic acid and phenylfluorone
Authors: Gunawardhana H. Dasaratha , Fernando S. Amarasiri
Published: May 2006

N-Phenylbenzohydroxamic acid reacts with molybdenum(VI) in 3.5–6.0 M hydrochloric acid to give a complex that is extractable into chloroform. The chloroform extract of the molybdenum complex, on second extraction from a dilute hydrochloric acid medium (0.2–0.3 M) in the presence of phenylfluorone and ethanol, forms an intensely coloured complex possessing an absorption maximum at 518 nm. Job's method of continuous variation reveals that the complex is Mo(VI)—2NPBHA—PF. The molar absorptivity under optimum conditions is 7.4 × 104 cm3 mol−1 cm−1. The system obeys Beer's law up to 0.6 ppm of molybdenum(VI). Considerable amounts of many cations and anions can be tolerated. The interference from vanadium(IV) and vanadium(V) can be eliminated by the addition of sodium metabisulphite, whereas the interference from titanium(IV) is mitigated by oxalate ions. The method has been successfully applied for the determination of molybdenum in a standard steel sample.
Reactions of 4-tert-butyl-5-methylene-3,3-dimethyl-Δ1-1,2,4-triazoline with dimethyl acetylenedicarboxylate
Authors: Schwan Adrian L. , Warkentin John
Published: May 2006

4-tert-Butyl-5-methylene-3,3-dimethyl-Δ1-1,2,4-triazoline (1) reacts rapidly with dimethyl acetylenedicarboxylate (2) to afford dienamines 3 and 4 from Michael addition and enamine 5 by extensive skeletal rearrangement. Assignments of their structures and probable mechanisms of their formation are discussed.
New positive mixed alkali and mixed anion effects on fast Na+ ion conductivity in Na2SO4
Authors: Gundusharma U. M. , Secco E. A.
Published: May 2006

The ac conductivity data for the binary alkali sulfate Rb+:Na2SO4 reveal a new positive mixed alkali effect in contrast to the so-called mixed alkali effect observed in β-aluminas. The binary alkali sulfate Rb+:Li2SO4 exhibits conductivity behavior intermediate between the two mixed alkali effects. A new positive mixed anion effect is also reported for the [Formula: see text] system. The higher Na+ conductivity in the Rb+:Na2SO4 and [Formula: see text] solid solutions is attributed to lattice expansion in a hexagonal structure effected by the larger radius isovalent guest ion and is interpreted in terms of a percolation type of transport mechanism.
Evidence for an intermediate phosphaborene
Authors: Couret Claude , Escudie Jean , Garrigues Bernard , Lazraq Mohamed , Satge Jacques
Published: May 2006

Addition of tert-butyllithium to chloroborylphosphine 2 to give 3 and 4 provides evidence for the phosphaborene 1, a compound with dicoordinated double-bonded boron and phosphorus.
Étude en résonance magnétique nucléaire du 13C des F-méthyl-4 coumarines
Authors: Pastor Raphaël E. , Fabron Joëlle , Cambon Aimé , Hu You-Chuan
Published: May 2006

Analysis of 13C nuclear magnetic resonance spectra of six 4-F-methyl coumarins are reported. This 4-F-alkyl substituent has a very slight effect on the chemical shifts of different carbon atoms. Only the C-10, C-4, and C-5 atoms are really affected and are shifted towards higher fields. The size of these effects was evaluated and compared with the corresponding effects of a 4-methyl substituent. The most important fact is the appearance of a 4JCF (and 5JCF for 6) coupling constant. We have shown that this effect is a through-space coupling.
The total synthesis of (±)-4-demethoxy-10-nordaunomycinone
Authors: Wong C. M. , Gordon P. M. , Chen A. G. , Lam H. Y. P.
Published: May 2006

4-Demethoxy-10-nordaunomycinone (4) is synthesized starting with 4,7-dimethoxy-1-indanone (8). Nucleophilic addition of ethynyl magnesium bromide to 8 followed by mercuric acetate oxidation and iron pentacarbonyl – tri-n-butyltin hydride reduction gave 4,7-dimethoxy-1-acetylindane (16). Condensation of 16 with phthalic anhydride followed by methylation with dimethylsulfate and oxidation gave 22, which was epimerized to 24 by 2,2-dimethoxypropane and trifluoroacetic acid. Demethylation of 24 with aluminum chloride gave the 4-demethoxy-10-nordaunomycinone (4).
Target factor analysis of bond dissociation energies
Authors: Howery Darryl G. , Rubenstein Matthew
Published: May 2006

Six data matrices of bond dissociation energies ranging from a 6 × 6 matrix involving only hydrocarbon radicals to a 14 × 14 matrix involving several types of radicals are target factor analyzed. The number of factors to reproduce the data near experimental error range from two to four for the six matrices. The hydrogen and fluorine radicals are shown to be the most unique radicals. Combination sets of vectors from the data matrices reproduce the data within experimental error, with the hydrogen, fluorine, and hydroxyl radicals being the most important ones. Using target testing, a few of the properties of the radicals are identified as basic factors.
Total synthesis of leukotriene B4 analogues: 3-thia-LTB4 and 3-thia-20,20,20-trifluoro-LTB4
Authors: Guindon Yvan , Delorme Daniel
Published: May 2006

Using C-furanosides as chiral precursors of (Z,E) 1,3-dienes has permitted the synthesis of two leukotriene B4 analogues: 3-thia-LTB4 and 3-thia-20,20,20-trifluoro-LTB4.
A chiral approach to 2-deoxystreptamine
Authors: Baer Hans H. , Arai Isamu , Radatus Bruno , Rodwell June , Chinh Nguyen
Published: May 2006

A new synthesis of 2-deoxystreptamine (21), a component of numerous antibiotics, was developed. Starting from D-mannose, it proceeds through chiral intermediates and is designed to furnish starting points for the preparation of stereospecifically modified derivatives of the meso compound 21. 1,2-Dideoxy-1-nitro-D-manno-heptitol (2), obtainable from mannose by the nitromethane method, was protected as the 4,5:6,7-di-O-isopropylidene derivative 4, which was mesylated or triflated in position 3. From the sulfonic esters (5 and 6) two different routes involving displacement by azide, partial deacetonation at O-6,7, periodate oxidation, and cyclization of the resulting nitroaldohexose derivatives converged to give 1L-(1,3/2,4,6)-6-azido-1,2-O-isopropylidene-4-nitro-1,2,3-cyclohexanetriol (19) as a key intermediate. Catalytic hydrogenation then afforded optically active 4,5-O-isopropylidene-2-deoxystreptamine (23), isolated as its N,N′-diacetyl derivative 24. Deacetonation of 19 gave the azidonitrotriol 15, which was reduced to 21. The potential utility of the chiral intermediates for stereospecific syntheses of deoxystreptamine-containing aminoglycosides is discussed.
Structural studies of organoboron compounds. XXVI. 8-Methyl-6,6-diphenyl-5,7-dioxa-8-azonia-6-borata-6,7-dihydro-5H-benzocycloheptene
Authors: Kliegel W. , Lauterbach U. , Rettig Steven J. , Trotter James
Published: May 2006

Crystals of 8-methyl-6,6-diphenyl-5,7-dioxa-8-azonia-6-borata-6,7-dihydro-5H-benzocycloheptene are triclinic, a = 12.917(1), b = 13.285(1), c = 10.567(1) Å, α = 94.183(8), β = 90.094(5), γ = 72.176(6)°, Z = 4, space group [Formula: see text]. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.045 and Rw = 0.042 for 2914 reflections with I ≥ 2σ(I). The envelope-like conformation adopted by the seven-membered chelate ring places one B-phenyl group above the plane of the fused-ring system facilitating a thermally-induced 1,4-migration of a B-phenyl group to the nitrone carbon atom. Mean bond lengths (corrected for libration) are (N)O—B = 1.559(6), (C)O—B = 1.496(3), C—B = 1.610(4) Å.
A new series of mono- and dipiperidine, oxazoline, and oxazolidine crown ethers. Stability constants, ion transport rates, and nuclear magnetic resonance studies
Authors: Desroches J. , Dugas H. , Bouchard M. , Fyles T. M. , Robertson G. D.
Published: May 2006

A series of monopiperidine, 1, dipiperidine 2, 3 (syn and and), as well as the corresponding oxazoline and oxazolidine crown ethers have been prepared and their ionophoric properties evaluated. The syn-dipiperidine 2c turned out to be a particularly efficient Ca2+ ligand (log K = 9.7). 13C and 23Na nuclear magnetic resonance spectroscopy was used to evaluate the nature of the complex between the monopiperidine 1c, the syn-dipiperidine 2c, and Ca2+ and Na+ ions. In methanol–water solution, the dimeric salt (2c)2Ca exhibits both a tight or asymmetric and a symmetric or loose ion pair between the cation and the carboxylate groups. Sodium-23 chemical shifts and line-width variation both support a 1:1 complex with 1c and 2c. The structural results correlate with observations from ion transport experiments.
Specific patterns of short range solvation — aliphatic amines in benzene–dimethylsulfoxide mixed solvents
Authors: Berman Edward D. , Thomas Rosemarie , Stahl Philip , Scott Ronald M.
Published: May 2006

The trends in the values of equilibrium constants for the formation of proton transfer complexes between 2,4-dinitrophenol and various aliphatic amines are used to infer the nature of the short range solvation of the amines in benzene–DMSO solvent mixtures. Hydrogen bonds between the DMSO oxygen and the amine proton increase the basicity of the primary and secondary amines. Equilibrium constants for this bond formation are estimated for secondary amines.
Synthesis of oligosaccharide structures unique to pituitary glycoprotein hormones
Authors: Hindsgaul Vandana , Hindsgaul Ole , Baenziger Jacques U.
Published: May 2006

The trisaccharide βDGalNac(1 → 4)βDGlcNAc(1 → 2)αDMan (2) and its 4″-O-sulfate ester (3) have been chemically synthesized as their 8-methoxycarbonyloctyl glycosides. Structures 2 and 3 contain oligosaccharide sequences unique to the asparagine-linked carbohydrate chains of pituitary glycoprotein hormones. The characteristic chemical shift for H-4 of the βDGalNAc residue in the sulfate ester 3 (4.692 ppm) is identical to that in the 1H nuclear magnetic resonance spectrum of glycopeptides isolated from bovine lutropin (luteinizing hormone), thus establishing the position of sulfation in the natural structures.
Photochemistry of substituted cyclic enones. Part 6. Photochemical reactions of 5-arylmethyl-3-phenylcyclopent-2-enones. A photostationary state
Authors: Clements Michael T. M. , McMurry T. Brian H.
Published: May 2006

Photolysis of 5-(1- and 2-naphthylmethyl)-3-phenylcyclopent-2-enones affords [2 + 2] cycloaddition products, the 7,8- and 5,6-benzo-fused 10-phenyltetracyclo[7.2.1.03,10.04,9]dodeca-5,7-dien-2-ones respectively, in equilibrium with the starting enones. A similar dibenzo-fused photoproduct is formed from the corresponding 9-phenanthrylmethyl substituted cyclo-pentenone. The photoproducts revert to the respective enones on acid treatment, or pyrolysis, and on photolysis.
The products of the reaction of thiiranium ions with competing nucleophiles
Authors: Schmid George H. , Strukelj Mark , Dalipi Snezana
Published: May 2006

The reaction of the stable thiiranium ion, prepared by the reaction of trifluoromethanesulfonic acid and methyl-3-(4-chlorophenylthio)propene with tetraethylammonium chloride in either 3.5 or 36% v/v methanol/dichloromethane with urea as a buffer, forms 2-methoxy-2-methyl-1-propyl 4-chlorophenyl sulfide, 2-chloro-2-methyl-1-propyl 4-chlorophenyl sulfide, and 1-chloro-2-methyl-2-propyl 4-chlorophenyl sulfide as products. While these same products are formed by the addition of 4-chlorobenzenesulfenyl chloride to methylpropene in the same solvents, their proportions differ. This is one of the rare examples in which there is a difference in the product composition of thiiranium ions formed in different ways and allowed to react under identical conditions. One possible explanation for this difference may be that the two thiiranium ions form products by different paths involving different kinds of ion pairs.
Electronegativity in density functional theory: diatomic bond energies and hardness parameters
Authors: Orsky A. R. , Whitehead M. A.
Published: May 2006

New definitions of the rate of change of electronegativity with charge, the hardness η, of an atom, are developed for acids A and bases B, where [Formula: see text] and [Formula: see text]. These definitions reproduce the experimental ordering of hard and soft acids and bases, and produce good trends in diatomic bond energies.
A general synthesis of dihydrobenzofurans by intramolecular conjugate addition
Authors: Weeratunga Gamini , Jaworska-Sobiesiak Alina , Horne Stephen , Rodrigo Russell
Published: May 2006

ortho Iodophenoxy crotonates 3e–7e cyclize to dihydrobenzo[b]furans 1 and 9–12 when subjected to lithium–iodine exchange at −100 °C. Naphtho[2,1-b]furan 13 can be similarly obtained from α-iodonaphthoxy crotonate 8e. Methylation of this reaction mixture insitu provides a single diastereomer 14; its relative configuration is assigned by 1H nuclear magnetic resonance, and its formation rationalized by steric arguments. Diastereoselective deuteration is also observed in this case.
Synthesis and 13C nuclear magnetic resonance spectral analysis of some diterpenoids related to the cleistanthane type hydrocarbon isolated from Amphibolisantarctica
Authors: Kaufman Teodoro S. , Mischne Mirta P. , Gonzalez-Sierra Manuel , Ruveda Edmundo A.
Published: May 2006

The synthesis of the cleistanthane-type diterpene 13 (8-β(H), 14-β-ethyl, 13-methylene podocarpane), a dihydro epimer of the natural product 6, is described. By comparison of the 13C nuclear magnetic resonance spectral data of 13 and related compounds with those reported for 6, the stereochemistry of the C-14 side chain of the latter was confirmed.
Effets de solvant sur les complexes par transfert de charge iode – composés thiocarbonylés
Authors: Guiheneuf Georges , Abboud José-Luis M. , Bouab Widded
Published: May 2006

The effects of solvents on different iodine – thiocarbonyl base charge-transfer complexes of variable stability have been examined and these are compared with the effects of solvents of the iodine – carbonyl compound complexes. There is an inversion of the effect of those solvents that can form hydrogen bonds on going from one series to the other, which is attributed to the fact that the carbonyl compounds are hard bases while the thiocarbonyl compounds are soft bases. [Journal translation]