bluuebunny/crossref_metadata_2025 huggingface dataset:
A systematic investigation of the reaction of SiF2 with ethylene and six methyl-substituted ethylenes. I. Product yields and mechanistic conclusions
Authors: Reynolds William F. , Thompson James C. , Wright A. P. Gerald
Published: May 2006

SiF2 produced by the quartz tube reaction has been reacted with ethylene and six methyl-substituted ethylenes. All major products (polymers, disilacyclobutanes, disilacyclohexanes, and open chain compounds) have been characterized by a combination of 19F, 1H, 13C, and 29Si nmr spectroscopy. While polymer is always formed in highest yield, the relative proportions of other products vary significantly from alkene to alkene.Key observations concerning structures and stereochemistries and product yields are summarized. Consideration of this evidence leads to a mechanism involving attack of SiF2 on the olefin to form an excited silirane which either ring opens or relaxes to its ground state, followed in either case by further reaction.
Photoelectron spectra of substituted acetophenones. Correlations with reactivity
Authors: McAlduff E. J.
Published: May 2006

Ultraviolet photoelectron spectra of 4-R-acetophenones (R = N(CH3)2, t-Bu, Cl) have been determined and the three lowest ionization potentials assigned. Combination of these data with literature data on other 4-R-acetophenone allows correlations of nO IP with redox potentials, nmr chemical shifts of acetyl protons, and chemical reactivity data. Both PhS and nO IP's correlate with Hammett σP constants of the substituent and PhS IP's are found to be linearly related to the first IP's of the analogous monosubstituted benzenes.
A new synthesis of 2,10,11-trioxatricyclo[4.4.4.01,6]tetradecane
Authors: Beaulieu Normand , Deslongchamps Pierre
Published: May 2006

A simple and convenient synthesis of tricyclic orthoester 1 (2,10,11-trioxatricyclo[4.4.4.01,6]tetradecane) is described.
Reactions of cyclopropylcarbinol in dilute hydrochloric acid
Authors: Lee Choi Chuck , Cessna Allan J.
Published: May 2006

The treatment of cyclopropylcarbinol (1-OH) with dilute HCl bas been used as a method for the preparation of cyclobutanol (2-OH). While 2-OH is the major product in this reaction, a careful investigation showed the presence of a total of 13 products, namely, the alcohols 1-OH, 2-OH, and allylcarbinol (3-OH), cyclopropylcarbinyl, cyclobutyl and allylcarbinyl chlorides (1-Cl, 2-Cl and 3-Cl, respectively), dicyclopropylcarbinyl, cyclobutyl cyclopropylcarbinyl, allylcarbinyl cyclopropylcarbinyl, dicyclobutyl and allylcarbinyl cyclobutyl ethers (1-O-1, 2-O-1, 3-O-1, 2-O-2, and 3-O-2, respectively), as well as butyraldehyde and isobutyraldehyde. The alcohols, chlorides, and ethers likely arose from reactions of the bicyclobutonium ion with available nucleophiles in the reaction mixture. The minor amounts of the two aldehydes may be due to a ring opening isomerization of 2-methylcyclopropanol, the latter in turn resulted from a net 1,3-hydride shift in the cyclopropylcarbinyl cation, probably via an edge-protonated cyclopropane-type of species. Treatment of [α-14C]cyclopropylcarbinol (1-OH-α-14C) with dilute HCl gave samples of 1-OH-x-14C, 2-OH-x-14C, and 3-OH-x-14C the degradation of which showed that ail three methylene groups in these alcohols have become equivalent, indicating a complete equilibration between isotope-position labeled bicyclobutonium ions.
A high field proton magnetic resonance study of the solution conformation of thromboxane B2
Authors: Kotovych George , Aarts Gerdy H. M.
Published: May 2006

The solution conformation of thromboxane B2 (TXB2) has been studied using high-field nuclear magnetic resonance techniques. In CDCl3, both anomers are present in solution with 76% 11α-OH TXB2 and 24% 11β-OH TXB2. In CD3OD, the predominant anomer is 11β-OH TXB2 (80%) while the concentration of 11α-OH TXB2 is 20%. The proton resonances were assigned at 400 MHz using double resonance techniques. The analysis of the vicinal coupling constants indicates that the six-membered ring is present in solution in a chair conformation with both of the aliphatic side chains equatorial. Proton longitudinal relaxation times were measured at 25 °C in CDCl3 for H-2, H-11β, H-12, H-13, H-14, and H-17 to H-19, both at 200 MHz and at 400 MHz. From the frequency dependence of these dipolar relaxation times, the rotational correlation times were evaluated. Within experimental error, all of the values are similar in magnitude (~ 2.0 × 10−10 s) indicating that this is the molecular rotational correlation time.
Dissociation kinetics of potassium anion in methylamine
Authors: Harima Y. , Kurihara H. , Aoyagui S.
Published: May 2006

The potential-sweep voltammograms of solvated electrons in methylamine containing KI as the supporting electrolyte demonstrate the coexistence of one- and two-electron species in equilibrium. The it1/2 vs. log t curve obtained with potential-step chronoamperometry exhibits a transient part between two plateaux. The analysis of this curve yields the approximate value of 102 s−1 for the first-order rate constant of the dissociation of the two-electron species, K−.
Conformational preferences of the fluoromethyl group in p-methylbenzyl fluoride and some derivatives
Authors: Schaefer Ted , Niemczura Walter P. , Sebastian Rudy , Kruczynski Leonard J. , Danchura Werner
Published: May 2006

The coupling over seven bonds between 19F nuclei and protons in p-methylbenzyl fluoride and a series of ring-substituted derivatives is used to estimate the value for a conformation in which the C—F bond lies in a plane perpendicular to the benzene ring. The J method is then used to show that in CS2 solution, the Conformational preference of the fluoromethyl group is very weak in 3,5-dichloro-4-methylbenzyl fluoride and in 3,5-dibromo-4-methylbenzyl fluoride. The barrier to rotation about the exocyclic carbon—carbon bond is perhaps as large as 0.2 kcal/mol. In p-methylbenzyl fluoride, the C—F bond prefers a plane perpendicular to the benzene plane by ca. 0.9 kcal/mol. Good agreement is found with the Conformational preferences based on couplings over six or seven bonds between the methylene protons and the para ring or methyl protons. The deductions are compared with calculations at various levels of molecular orbital theory.
Synthesis of substituted hydrindanes. Part II. Approaches to the synthesis of fawcettimine
Authors: Burnell Robert H. , Humblet Alain , Pelletier Jacques , Badripersaud Santynand
Published: May 2006

Several unsaturated hydrindanones have been prepared to assess various synthetic routes which could lead to the Lycopodium alkaloid fawcettimine. Comparison with an earlier model series starting from dimedone shows that this dihydroorcinol based sequence must be modified considerably.
The photochemistry of 4-phenyl-1-iodobutane and 4-phenyl-2-iodomethyl-1-butene
Authors: Charlton James Leslie , Williams Gaynor Jane , Lypka Gerald Nicholas
Published: May 2006

The photochemistry of 4-phenyl-1-iodobutane 3 and 4-phenyl-2-iodomethyl-1-butene 4 has been studied to investigate the effect of structure on the character of the intermediates generated on photolysis. The irradiation of the simple primary iodide 3 appears to yield only radical intermediates. By contrast the photolysis of the allylic iodide 4 yields products that are more consistent with cationic intermediates.
Magnitudes of 18O isotope shifts in 13C nuclear magnetic resonance spectra of ketones and alcohols
Authors: Diakur James , Nakashima Thomas T. , Vederas John C.
Published: May 2006

The magnitudes of 18O-induced isotope shifts in 13C nmr spectra of ketones and aldehydes are dependent on structure and range from about 0.05 ppm to 0.03 ppm for the carbon attached to 18O. An increase in negative charge density on the carbonyl oxygen or conjugation to an aromatic ring reduces the size of the upfield shift. The shifts in [18O]alcohols are solvent-dependent, range from 0.03 ppm to 0.01 ppm, and tend to decrease in the order tertiary ≥ secondary ≥ primary ≥ phenols.
Tricyclic aromatic ketones by cycliacylation of carboxylic acid derivatives of indan, tetralin, and benzosuberane
Authors: Isabelle M. Elaine , Wightman Robert H. , Avdovich Hajro W. , Laycock David E.
Published: May 2006

The synthesis of a homologous series of new carboxylic acids substituted in the α-position of indan, tetralin, and benzosuberane is accomplished using an efficient general procedure. Cycliacylation of these acids and their corresponding β-isomers produces a complete series of tricyclic aromatic ketones.
A new synthesis of 2, 10, 11-trioxatricyclo[4.4.4.0.1,6]tetradecane
Authors: Beaulieu Normand , Deslongchamps Pierre
Published: May 2006

not available
A highly asymmetric synthesis of the O-2-isocephem class of β-lactam antibiotics
Authors: Tenneson Sheila M. , Belleau Bernard
Published: May 2006

Starting from D-threonine, an asymmetric synthesis of the dextrorotatory bioactive enantiomer of 3-methyl-7-phenylacetamido-O-2-isocephem was accomplished. The key step, where asymmetric cycloaddition of azidoacetyl chloride to the cinnamylidene Schiff base of protected D-threonine is induced, generates the desired cis-β-lactam in 90% optical yield. The absolute configuration of the final product was confirmed by comparing its antimicrobial activity with that of its corresponding racemate.
Structure and conformation of the hydrochloride of pseudoisocytidine, an antileukemic C-nucleoside
Authors: Birnabaum George I. , Watanabe Kyoichi A. , Fox Jack J.
Published: May 2006

The three-dimensional structure of pseudoisocytidine hydrochloride was determined by X-ray crystallography. The crystals belong to the triclinic space group P1 and the cell dimensions are a = 6.623(2), b = 8.053(2), c = 6.201(2) Å, α = 108.35(2), β = 101.36(2), γ = 93.54(2) °. Intensity data were measured with a diffractometer and the structure was solved by a combination of heavy-atom and direct methods. Least-squares refinement, which included hydrogen atoms, converged at R = 0.040. The conformation about the glycosyl bond is anti (χCC = 21.6°), the pucker of the furanose ring is C(1′)exo, and the conformation of the —CH2OH side chain is gauche–trans (t). An examination of bond lengths indicates that of the three main resonance forms of the isocytosine cation the fully conjugated one contributes more to the structure than the cross-conjugated one. Bond angles in the sugar ring reflect its rare conformation.
Direct non-invasive observation of metabolism in living cells by 13C nuclear magnetic resonance spectroscopy
Authors: Burton Gerardo , Baxter Robert L. , Gunn J. Martyn , Sidebottom Philip J. , Fagerness Paul E. , Shishido Kozo , Lee John Y. , Scott A. Ian
Published: May 2006

Applications of 13C nmr in following the metabolism and fate of 13C enriched substrates in whole cells are described. Studies on the elaboration of coproporphyrinogens I (2a) and III (2b) from [5-13C]-δ-aminolevulinic acid (1) and [11-13C-porphobilinogen (PBG, 3), in Rhodopseudomonasspheroides and Propionibacteriumshermanii, respectively, the randomization of 13C from [3-13C]-propionate by P. shermanii, the biosynthesis of citrate, gentisalcohol (4), and patulin (5) from [2-13C]-acetate by Penicilliumurticae, and the anaerobic metabolism of [1-13C]-glucose in rabbit erythrocytes are reported.
An experimental evaluation of nonselective proton spin–lattice relaxation rates: analyses of data for the eight isomeric 2,3,4-tri-O-acetyl-1,6-anhydro-β-D-hexopyranoses
Authors: Bock Klaus , Hall Laurance D. , Pedersen Christian
Published: May 2006

The nonselective spin–lattice relaxation rates (R1-values) have been determined for all of the ring protons of the eight isomers of 2,3,4-tri-O-acetyl-1,6-anhydro-(β-D-hexopyranose as 0.1 molar solutions in benzene-d6. The effects on the proton R1-values of changes in solvent, concentration, temperature, and proton impurities are documented and 13C R1-values are given to show that the first two sets of variations are due to changes in motional correlation times of the molecules. The proton relaxation data can be fitted by regressional analyses to a single set of interproton relaxation contributions, the numerical values of which accord with a 1C4 conformation for the pyranose ring somewhat distorted by the 1,6-anhydro bridge.
A survey of the proton spin–lattice relaxation rates of selected furanose derivatives
Authors: Bock Klaus , Hall Laurance D. , Pedersen Christian
Published: May 2006

The non-selective proton spin–lattice relaxation rates of 3,5-di-O-acetyl-2,6-dibromo-2,6-dideoxy-D-mannono (1), or -glucono (2), 1,4-lactone, methyl-α,(β)-D-ribofuranoside (3), methyl-α,(β)-D-arabinofuranoside (4), methyl-α(β)-D-xylofuranoside (5), 3,5-di-O-acetyl-1-O-benzoyl-2,6-dibromo-2,6-dideoxy-α and β-D-mannofuranose (6) and (7), 3,5-di-O-acetyl-6-bromo-2,6-dideoxy-D-arabino-1,4-lactone (8), and 2,3,5,6-tetra-O-acetyl-1,4-anhydro-D-mannitol (9) have been measured at 270 MHz. Substantial differences are found for the R1-values of epimeric pairs of substances which can be used for structural evidence. The anomalous R1-values in deuteriochloroform for the H-2, H-3, and H-4 resonances of 1 are discussed.
Cycloaddition reactions of meso-ionic oxazolone with cinnamaldehyde anils
Authors: Sain Bir , Thyagarajan Gopalakrishna , Sandhu Jagir S.
Published: May 2006

During the reaction of the azlactone 5 with different cinnamaldehyde anils, we obtained α-pyridones with no evidence for the formation of β-lactams. The products have been characterized through elemental and spectral analyses.
Base-catalysed ring opening of N-(aminothioxomethyl)-5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxamides
Authors: Kulka Marshall
Published: May 2006

The condensation of 5,6-dihydro-2-methyl-1,4-oxathiin-3-carbonyl isothiocyanate (1) with ethyl 3-phenylamino-2-butenoate (2) has yielded a mixture of ethyl 1,4-dihydro-2-(5,6-dihydro-2-methyl-1, 4-oxathiin-3-yl)-6-methyl-1-phenyl-4-thioxo-5-pyrimidine carboxylate (3) and N-[(phenylamino)thioxomethyl]-5,6-dihydro-2-methyl-1,4-oxathiin-3-carboxamide (4, R′ = phenyl). It has been discovered that compounds 4, in general, rearrange to 1-substituted-2,3-dihydro-5-[(2-hydroxyethyl)thio]-6-methyl-2-thioxo-4(1H)-pyrimidinones (5) at room temperature when stirred with dilute aqueous sodium hydroxide. The products of the reaction of 5,6-dihydro-2-methyl-1,4-oxathiin-3-carbonyl isothiocyanate (1) and phenylhydrazine, when treated with dilute aqueous sodium hydroxide, did not yield the rearrangement product 5 (R′ = NHC6H5). Instead, a mixture of the two triazole-3-thiones 9 and 10 was formed. N,2-Bis(5,6-dihydro-2-methyl-1,4-oxathiin-3-carbonyl)hydrazinecarbothioamide (12) with dilute aqueous sodium hydroxide yielded one rearrangement product (out of a possible four), namely, 5-6-dihydro-2-methyl-N-[1,2,3,4-tetrahydro-5-[(2-hydroxyethyl)thio]-6-methyl-4-oxo-2-thioxo-1-pyrimidinyl]-1,4-oxathiin-3-carboxamide (13).
Ozonolysis of olefins containing monochloro substituted double bonds
Authors: Keul Helmut , Griesbaum Karl
Published: May 2006

Ozone cleavage of 12 substituted vinyl chlorides (1) in methanol occurred such that the chlorinated moiety of the double bond afforded the carbonyl fragment (i.e. acyl chloride) and the nonchlorinated moiety afforded the carbonyl oxide fragment. All of these fragments underwent secondary reactions: formyl chloride gave carbon monoxide and hydrogen chloride; all other acyl chlorides yielded the corresponding methyl esters. The carbonyl oxides were converted into the corresponding methoxy hydroperoxides. Under the influence of hydrochloric acid unsubstituted and monosubstituted methoxy hydroperoxides were dehydrated to form the corresponding methyl esters, whereas the disubstituted methoxy hydroperoxide of acetone produced the cyclic trimeric peroxide of acetone.
The adsorption and the reaction of NH3 and NOx on supported V2O5 catalysts: effect of supporting materials
Authors: Takagi-Kawai Maki , Soma Mitsuyuki , Onishi Takaharu , Tamaru Kenzi
Published: May 2006

The effects of supporting materials (Al2O3, SiO2, TiO2) on the catalytic activity and selectivity of V2O5 in the reduction of NOx with ammonia are reported. The adsorbed state and the reactivity of the surface species were examined by an ir spectroscopy together with volumetric measurements, and the electronic state and the surface composition were studied by XPS.The reactivity of an adsorbed ammonia (NH4+) for NO2 over the supported catalysts was in the following increasing order, TiO2 > Al2O3 > SiO2. NH4+(ad) and NO2(ad) were both reactive species in the reaction over V2O5, V2O5/Al2O3, and V2O5/TiO2. Among these catalysts, the oxidized surface of V2O5/TiO2 adsorbs NO as NO2(ad), i.e. the reactive species, whereas other catalysts did not adsorb NO unless oxygen coexisted in the gas phase. In the case of V2O5/SiO2, the reaction between NH4+(ad) and NO2(ad) was very slow, while the surface oxygen was easily removed by the reduction with NH3 and resupplied by the introduction of NO on the surface. This leads to the N2O formation through so-called redox mechanism. The NH4+(ad) on V2O5/SiO2 showed an ir absorption band at 1435 cm−1 which was much higher than those on other catalysts, and XPS measurement suggested that V2O5 on SiO2 is electrically isolated.
Vinyl ether hydrolysis. XIV. 2-Methoxy-2,3-dihydropyran: concurrent reaction of vinyl ether and acetal functional groups
Authors: Burt R. A. , Chiang Y. , Kresge A. J.
Published: May 2006

The hydrolysis of 2-methoxy-2,3-dihydropyran shows a normal isotope effect (kH/kD > 1) under catalysis by the hydrogen ion and gives an accurately linear dependence of reaction rate upon undissociated acid concentration in cyanoacetic acid and formic acid buffer solutions. This substrate, therefore, unlike its higher homolog, 9-methoxyoxacyclonon-2-ene, provides no evidence in support of an anything but a normal mechanism for vinyl ether hydrolysis. Analysis of the hydrogen isotope effect suggests that a minor amount (8%) of this hydrolysis occurs via reaction of the acetal functional group.
Vinyl ether hydrolysis. XV. Methyl β,β-di-tert-butylvinyl ether: buttressing steric effects
Authors: Chiang Y. , Kresge A. J. , Tidwell T. T. , Walsh P. A.
Published: May 2006

The highly congested molecule, methyl β,β-di-tert-butyl vinyl ether, undergoes reaction in dilute aqueous mineral acid solutions by a normal vinyl ether hydrolysis mechanism and gives an unrearranged aldehyde product. The tert-butyl groups retard the rate of hydrolysis, but the effect of cis and trans substituents is not cumulative; this is attributed to a repulsive nonbonded interaction, relieved in the course of reaction, between the ether oxygen atom and the cis-tert-butyl group buttressed by the trans-tert-butyl group.
Oxidation products of arachidonic acid. IV. Model studies on the attachaient of the C(13)—C(20) side-chain in the synthesis of tetrahydrofurans and pyrans 1,2, and 3
Authors: Just George , Crosilla Danilo
Published: May 2006

The synthesis of methyl 15-hydroxy-8(R)-methoxy-11(R)-p-nitrobenzoyloxy-9(S),12(R)-oxy-eicosa-13-ynoate, an arachidonic acid metabolite derivative, is described. As well, methods for the attachment of the C(13)—C(20) prostaglandin side-chain to furanosides were studied and the results are described. The reduction of the C-15 keto group on a model compound was performed and was found to have the same behavior as in the prostaglandins.A partial structure proof of Pace-Asciak's compound, 9,12-oxy-8,11,15-trihydroxy-13-enoic acid is given.
Theoretical and experimental conformational preferences of the aldehyde and fluoroaldehyde groups in 2-methylbenzaldehyde, 2-trifluoromethylbenzaldehyde, and 4-chloro-2-methylbenzoyl fluoride. Proximate couplings
Authors: Schaefer Ted , Salman Salman R. , Wildman Timothy A.
Published: May 2006

On the basis of long-range spin–spin coupling constants, the O-syn conformation of 2-methylbenzaldehyde in CCl4 solution at 305 K is favored over the O-anti form by a free energy of 0.53 kJ/mol. This number is compatible with other experiments, as well as with STO-3G MO calculations in which the geometry of the substituents is optimized. The latter yield 0.52 kJ/mol in the internal energy difference. In benzene solution, 2-trifluoromethylbenzaldehyde exists in the O-anti form to the extent of at least 95% at 305 K. In CCl4 solution at this temperature, the population of the O-syn conformer of 4-chloro-2-methylbenzoyl fluoride is likely 75% or more of the total, in semiquantitative agreement with STO-3G optimization procedures. Substantial proximate couplings exist between 1H and 19F nuclei in the sidechains of the latter two compounds and are compared with INDO MO FPT computations. These yield negative values for [Formula: see text] in 2-trifluoromethylbenzaldehyde, whereas the experimental value is 2.23 Hz.
Synthetic applications of α-hydroxydiazenes. III. Uncatalyzed and phenol catalyzed hydroalkylation of alkenes and of azobenzene with alkylazodiphenylmethanols
Authors: Yeung Dominic W. K. , Warkentin John
Published: May 2006

Alkylazodiphenylmethanols (C6H5)2C(OH)N = NR, (R = CH(CH3)2, CH2CH3, CH3), when decomposed in the presence of olefinic substrates or in the presence of azobenzene, hydroalkylate those substrates. Addition of R and H across the double bond of an unsymmetric alkene occurs with the regiochemistry expected for a radical mechanism, in which the group R adds first. Radical intermediates from decomposition of alkylazodiphenylmethanols have been demonstrated earlier with spin trapping experiments. The fact that addition of phenol can enhance the yield of hydroalkylation product suggests that the process is a radical chain reaction, with chain carrying steps consisting of the reactions:[Formula: see text]One deuterioalkylation and some yield-optimizing experiments are also reported.
Diels–Alder cycloadditions of N-substituted-1,2-dihydropyridines with nitrosobenzene. Synthesis of 3-phenyl-2-oxa-3,6-diazabicyclo[2.2.2]oct-7-enes
Authors: Knaus Edward E. , Avasthi Kamlakar , Giam C. S.
Published: May 2006

The regiospecific (π2 + π4) cycloaddition reaction of N-carbonyl-1,2-dihydropyridines 2 with nitrosobenzene afford a mixture of 3-phenyl-2-oxa-3,6-diazabicyclo[2.2.2]oct-7-ene rotamers 3 and 4. Rotamers 3 and 4, which differ in configuration at the carbonyl to nitrogen (amide) bond, exhibit dual resonances for C(1)H, C(5)H, and the N(6) acetyl (methoxycarbonyl) substituents. An 1H nmr temperature study indicated that rotamers 3a and 4a coalesce at about 100 °C.
Synthesis of camphor-1,4-homoenol (7-hydroxy-1,2-dimethyl[3,3,0,02,7]tricyclooctane)
Authors: Dadson William M. , Money Thomas
Published: May 2006

A simple synthesis of camphor-1,4-homoenol bas been accomplished by reductive cyclization of 8-bromocamphor.
Reactions of phthalans with dienophiles. I. Synthesis of naphthalenes from phthalans and activated acetylenes
Authors: Contreras Luis , MacLean David B.
Published: May 2006

Diethoxyphthalans and activated acetylenes react at temperatures of 140–160 °C to yield substituted naphthalenes. It is proposed that the reaction occurs through the intermediacy of 1-ethoxyisobenzofurans generated thermally from the phthalans. The transient 1-ethoxyisobenzofurans are postulated to add to the acetylenes in a cycloaddition reaction to yield tricyclic intermediates that are transformed to naphthalenes at the elevated temperature of the reaction. Reactions with unsymmetrical acetylenes provided information on the regioselectivity of the reaction.
The barrier to rotation in 2,2″-dimethyl-o-terphenyl and several 3,3″-derivatives (rotational isomers of 1,2-di-o-tolylbenzene)
Authors: Mitchell Reginald H. , Yan Joseph Shue-Hen
Published: May 2006

The synthesis and measurement of the barrier to rotation [Formula: see text] in 2,2″-dimethyl-o-terphenyl (62 kJ/mol) and the following 3,3″-disubstituted derivatives is described (Cl, Cl, 74 kJ/mol), (Cl, CN, 70 kJ/mol), (CM, CN 70 kJ/mol), (CHO, 75 kJ/mol). For 3,3″-bis-CH2Br, Δv, the separation of the —CH3 peaks in the 1Hmr spectrum, was too small to obtain [Formula: see text]
The mass spectrometric behavior of 3α,5-cyclo-5α-cholestan-6β-yl alkyl ethers
Authors: Brown Frederick J. , Massey Ian J. , Djerassi Carl
Published: May 2006

The 3α,5-cyclo-6β-methoxy (i-methyl ether) moiety is a common protective grouping in steroid partial synthesis. Therefore, the mass spectrometric behavior of 6β-hydroxy-3α,5-cyclo-5α-cholestane, the corresponding methyl, ethyl, and tert-butyl ethers, the analogous ketone, and the parent hydrocarbon has been investigated in order to determine the mechanisms of the characteristic fragmentations of these compounds. Such knowledge is essential for unequivocal structure elucidation by mass spectrometry and also bears on the current interest in the stereospecificity of electron impact induced eliminations. Deuterium labeling of carbon atoms 1,2,3,4,7,8,9, and 19 of 6β-methoxy-3α,5-cyclo-5α-cholestane established the course of methanol extrusion and the identity of the highly diagnostic A ring cleavage ion [Formula: see text] Mechanisms are proposed for these key fragmentations. The mass spectra of the methyl, ethyl, and tert-butyl ethers of cholesterol are analyzed, and the features distinguishing these compounds from the isomeric 3,5-cyclosteroids are noted.
Photocyclisation des (oxo-3)-butyl glycopyranosides
Authors: Remy Georges , Cottier Louis , Descotes Gérard
Published: May 2006

3-Oxo butyl glycopyranosides undergo Norrish type II photocyclization giving hydroxyspiroketals. The influence of the anomeric configuration and of different substituents at C-2 has been studied. The favored photocyclization of various β-glycosides occurs with retention of configuration and is interpreted in terms of the greater stability of the radical formed by abstraction of the axial anomeric hydrogen atom.
Catalytic reduction of dimeric acetylated 2-deoxy-2-nitroso-α-D-glycopyranosyl chlorides
Authors: Nagabhushan T. L.
Published: May 2006

Reduction of tri-O-acetyl-2-deoxy-2-nitroso-α-D-glucopyranosyl chloride dimer with hydrogen and platinum oxide in the presence of methanol or ethanol afforded the corresponding alkyl tri-O-acetyl-2-amino-2-deoxy-β-D-glucopyranoside hydrochloride. In the absence of an alcohol the product was tri-O-acetyl-2-amino-1,5-anhydro-2-deoxy-D-glucitol hydrochloride. The glycosylation/reduction process gave similar results with the galacto isomer.A method is described for the ready and large-scale synthesis of D-galactosamine hydrochloride.
Structure of the type XXXIII Streptococcuspneumoniae (pneumococcal) capsular polysaccharide
Authors: Bennett Larry G. , Bishop Claude T.
Published: May 2006

The type XXXIII Streptococcuspneumoniae (pneumococcal) capsular polysaccharide contains D-glucose (2 mol), D-galactose (1 mol), D-glucuronic acid (1 mol), and 2-acetamido-2-deoxy-D-mannose (1 mol). Structural investigations by methylation analysis, specific degradations, and nmr spectroscopy showed that the repeating unit was a linear pentasaccharide of the following structure: → 3)-α-D-Galp-(1 → 3)-β-D-ManpNAc-(1 → 4)-α-D-GlcpA-(1 →.
Reaction des glycosyl isonitriles avec les amines et les alcools
Authors: Marmet Danielle , Boullanger Paul , Descotes Gérard
Published: May 2006

After complexation with metals, glycosylisonitriles 1 react with alcohols to give mainly orthoesters, if C-2 bears a participating group, and/or alkyl glycosides without particular stereoselectivity. In the case of amines, formamidines are obtained by α-addition to 1 in good yields. An example of further heterocyclisation is given with the stereospecific synthesis of the glucosylquinazolinone 15.
2-Alkoxy-5(4H)-oxazolones from N-alkoxycarbonylamino acids and their implication in carbodiimide-mediated reactions in peptide synthesis
Authors: Benoiton N. Leo , Chen Francis M. F.
Published: May 2006

Reaction of N-ethyl,N′-(γ-dimethylaminopropyl)-carbodiimide- HCl with one equiv. of N-tert-butoxycarbonyl-L-valine (3a) in dichloromethane at 23 °C gives, besides the symmetrical anhydride (5a), the optically pure 2-tert-butoxy-4-isopropyl-5(4H)-oxazolone (4a) which can be obtained in 50% yield under selected conditions. The 2-benzyloxycarbonyl-4-isopropyl-5(4H)-oxazolone (4b) is similarly obtainable from N-benzyloxycarbonyl-L-valine (3b). Anhydrous acid converts 4a to the oxazolidinedione. Simple preparations of the N-carboxyanhydrides of valine and isoleucine have been devised from these reactions. Compound 4 reacts with 3 to give 5. Compound 4 reacts with an amino acid ester to give the optically pure peptide even in the presence of salts, but partial racemization occurs for reactions in the presence of a tertiary amine. Evidence for the implication of 2-alkoxy-5(4H)-oxazolones in the couplings of N-alkoxycarbonylamino acids is presented. Compound 4a has been isolated in 6–11% yield from carbodiimide-mediated reactions of 3a with itself or amino acid methyl esters which have been terminated before completion.
Effects of protonation and hydrogen bonding on carbon-13 chemical shifts of compounds containing the group
Authors: Allen Malwina , Roberts John D.
Published: May 2006

The effects of hydrogen bonding and protonation produced by changing solvent from chloroform to 2,2,2-trifluoroethanol to trifluoroacetic acid were determined for the 13C chemical shifts of fourteen imines, four oximes, and two pyridines. Downfield shifts relative to chloroform were observed for the C=N carbon of the imines and oximes in both trifluoroethanol and trifluoroacetic acid, ranging from 1.5 to 27.5 ppm, which contrasts with upfield Cα shifts for the pyridines in trifluoroacetic acid. Substantial downfield and upfield shifts of from +10 to −15 ppm were found for the para and ipso carbons, respectively, of the aromatic rings attached to the C=N group in trifluoroacetic acid. Possible explanations of these shift changes are considered as well as their relation to the corresponding changes in 15N shifts with the identical variations in solvent.
Un nouvel agent de glycosylation: l'anhydride trifluorométhanesulfonique. Synthèse des α et β O-glycosyl-L-sérine, -L-thréonine et -L-hydroxyproline
Authors: Lacombe J. M. , Pavia A. A. , Rocheville J. M.
Published: May 2006

When 2,3,4,6-tetra-O-benzyl-D-glucopyranose, -D-galactopyranose and 2,3,4-tri-O-benzyl-D-xylopyranose were allowed to react in the cold in dichloromethane or acetonitrile as solvent in the presence of trifluoromethanesulfonic (triflic) anhydride, with methyl or benzyl esters of the N-(benzyloxycarbonyl)-L-serine, -L-threonine, and -L-hydroxyproline, an anomeric mixture of the corresponding O-glycosylaminoacids was obtained (55 to 90% overall yield), with the α-anomer being predominant. The same experimental procedure was successfully applied to the condensation of the benzyl ester of the N-(benzyloxycarbonyl)-L-hydroxyproline with 2,3,4-tri-O-benzyl-L-arabinopyranose and 2,3,5-tri-O-benzyl-L-arabinofuranose affording the corresponding condensation products with similar yield. Pure α and β anomers were obtained after column chromatography or crystallization with 30 to 65% yield. Hydrogenolysis of benzyl derivatives afforded the unprotected compounds. Optical rotation, 1H and 13C nmr were the main methods used to assess structure and stereochemistry.
Ipso nitration. XXII. The stereochemistry of 1,4-dimethyl-4-nitrocyclohexa-2,5-dienols and their acetates and methyl ethers
Authors: Fischer Alfred , Henderson George N. , Smyth Trevor A. , Einstein Frederick W.B. , Cobbledick Roger E.
Published: May 2006

The higher melting isomer of 1,4-dimethyl-4-nitrocyclohexa-2,5-dienol has the (E)-configuration. The stereospecific interconversion of the dienols and the corresponding acetates and the stereospecific conversion of dienols to methyl ethers allow the assignment of the configurations of the isomeric acetates and ethers. Parallels in physical properties allow the assignment of the stereochemistry of the isomers of 1-alkyl-4-methyl-4-nitrocyclohexa-2,5-dienyl acetates (alkyl = Et, i-Pr, t-Bu) and of 1-alkyl-4-ethyl-4-nitrocyclohexa-2,5-dienyl acetates (alkyl = Me, Et).
Merostabilization in radical ions, triplets, and biradicals. 5. The thermal cis–trans isomerization of para-substituted tetraphenylethylenes
Authors: Leigh William J. , Arnold Donald R.
Published: May 2006

The cis- and trans-isomers of four para-substituted (three disubstituted and one tetrasubstituted) tetraphenylethylenes have been synthesized, separated, and characterized by either dipole moment or X-ray analysis. The rates of thermal isomerization of the disubstituted derivatives in benzene solution correlate with a substituent parameter reflecting substituent effects on benzylic radical stabilities (σ•), which reflects the biradical nature of the transition state for thermal isomerization in this system. A significant rate enhancement is observed for the tetrasubstituted derivative, in which merostabilization of the transition state is possible.The Arrhenius parameters for thermal isomerization in benzene were determined. From the variation observed for the disubstituted derivatives, an estimate of 35.5 kcal mol−1 for the rotational barrier in tetraphenylethylene is obtained. The activation energy for thermal isomerization of the tetrasubstituted derivative is 2 kcal mol−1 lower than those of the other three; this provides an assessment of the importance of merostabilization in this system.The thermal isomerization of some related olefins (e.g. bianthrylidenes and indigo derivatives) is discussed in light of these results.
Nuclear magnetic resonance study of addition–cyclization involving ethyl thioacetoacetate and α-nucleophiles
Authors: Cocivera Michael , Basu Soumen , Copp Leslie , Malatesta Vincenzo
Published: May 2006

Addition of NH2NH2 or NH2OH to ethyl thioacetoacetate to form the corresponding cyclic product, 3-methylpyrazol-5-one or 3-methylisoxazol-5-one proceeds via cyclization of the carbinolamine formed by addition to the β-keto carbon, i.e., cyclization is faster than dehydration of the carbinolamine to form the imine. In contrast the corresponding carbinolamine derived from ethylacetoacetate undergoes dehydration faster than cyclization. By means of 1H nuclear magnetic resonance spectroscopy, it is possible to detect the cyclic carbinolamine as well as another transient and measure their rates of decay. Based on these results, a mechanism is proposed.
The photovoltaic properties and structure of palladium tetraphenylporphyrin on tin oxide photoelectrochemical cells
Authors: Langford Cooper H. , Hollebone Bryan R. , Nadezhdin Daniel
Published: May 2006

The photovoltaic properties of palladium tetraphenylporphyrin films on n-doped SnO2 transparent electrode in contact with a solution of quinone/hydroquinone are discussed as a function of the preparation of the film and history of its treatment with heat, H2, or O2/H2O. Magnetic circular dichroism (MCD) spectra of the electrodes provide guidance on film structure. There are three important results. First, MCD spectra show that photovoltaic behaviour is independent of crystallinity of the film. Second, the evolution of film behaviour as "doping" by O2/H2O occurs shows that photoprocesses occur at both the interface of the film with SnO2 and the electrolyte, leading to both photoanodic and photocathodic processes. Third, MCD spectra show that "doping" is not a surface or trace phenomenon but affects the axial ligand sensitive region of the spectra of molecules throughout the film. Transport of charge through the film by successive "redox" reactions appears to provide the simplest qualitative explanation of the results. That is, conduction is by hopping in a non-stoichiometrically oxidized film.
Intramolecular hydride shift in some noncyclic isopropyl ketols
Authors: Warnhoff E. W. , Wong Margaret Y. H. , Raman P. Sundara
Published: May 2006

The acyclic ketols [Formula: see text] have been synthesized by a Reformatsky sequence. Each ketol undergoes intramolecular hydride transfer when refluxed in KOH–H2O–t-BuOH solution. When the procedure was applied to the synthesis of 34, hydride transfer occurred during the Reformatsky reaction to yield 33 instead. With longer reaction times, 33 underwent self-acylation and β-dicarbonyl cleavage to 37. Treatment of 33 with aqueous base gave a mixture of ketols 35 and 36 from hydride transfer and β-keto decarboethoxylation. The attempted conversion of the isobutyrate group of the Reformatsky intermediates 21 and 24 to tert-butyl was not practicable.
13C shieldings in syn and anti aldimines and ketimines
Authors: Fraser Robert R. , Banville Jacques , Akiyama Fuminori , Chuaqui-Offermanns Noemi
Published: May 2006

The 13C chemical shifts in a variety of aldimines and in both acyclic and cyclic ketimines have been examined. A comparison of the shieldings at the α carbons in syn versus anti stereoisomers shows a consistent upfield shift of 8–11 ppm in the syn isomer. The greater magnitude found in imines vs. oximes or hydrazones is a clear indication of a steric origin for the differential shieldings. The shifts in the imines of cyclohexanones exhibited stereochemically dependent effects of methyl substitution, very similar to those in analogous oxime and hydrazone derivatives. Chemical shift differences in the syn isomers of the α-phenethylimines of chiral aldimines and ketimines allow a facile measurement of diastereomer ratios for such compounds.
The selective cleavage of permethylated glycopyranosiduronic acid linkages by oxidative decarboxylation with lead tetraacetate
Authors: Aspinall Gerald Oliver , Fanous Hany Kamal , Kumar Nimal Savitri , Puvanesarajah Velupillai
Published: May 2006

Reaction of permethylated glycopyranosiduronic acids with lead tetraacetate furnishes epimeric 5-acetoxypentopyranosides as products of oxidative decarboxylation. Glycoside cleavage then occurs on treatment with sodium borohydride which affords the corresponding pentitols with exposure of aglyconic hydroxyl groups. The reaction sequence has been performed with permethylated derivatives of methyl β-melibiosiduronic acid, methyl β-gentiobiosiduronic acid, gum arabic, leiocarpan A, Sterculia urens gum, and citrus pectic acid. The scope of the reaction sequence in polysaccharide studies is discussed.
The iodination of azetidinone thio compounds. unsym-Azetidinone disulfides from thiazolineazetidinones
Authors: Micetich Ronald G. , Fortier Robert A. , Liew Jennifer
Published: May 2006

The products of the reaction of thiazolineazetidinones with alkyl and aralkyl sulfenyl iodides (generated in situ) are hydrolysed to unsym-azetidinone disulfides.
Products from interaction of aromatic nitrocompounds with argon metastables inside a gas chromatograph
Authors: Aue Walter A. , Paramasigamani Veluppillai , Kim Jae H.
Published: May 2006

The neutral products resulting from the degradation of aromatic nitrocompounds, following interaction with argon metastables (presumably by Penning ionization), have been studied inside a gas chromatographic system. The simplest but typical example, nitrobenzene, yields benzene and phenol. Product ratios sometimes resemble results of mass spectrometry more than they do data obtained by pyrolysis. The ease of elimination of substituents from monohalogenated nitrobenzenes follows the order I > NO2 > Br > Cl. Ratios of the products resulting from loss of NO (rearrangement) versus loss of NO2 have been measured for a variety of compounds. The leaving NO2 group can be replaced by I if the system is doped with iodine vapour. Reduction of the nitro group and ring closures are observed with some of the more complex substrates, similar to results known from discharge chemistry.
Electroreduction of uranyl ion in aqueous calcium nitrate solutions
Authors: Bansal Narottam P. , Plambeck James A.
Published: May 2006

The electroreduction of uranyl ions in buffered and unbuffered 0.5 M calcium nitrate has been studied using polarography, cyclic voltammetry, chronopotentiometry, and chronoamperometry. The results are compared with those in molten calcium nitrate tetrahydrate.
Stability and reactivity of the benzyl and tropylium cations in the gas phase
Authors: Sharma D. K. Sen , Kebarle P.
Published: May 2006

A measurement of equilibrium [4]: t-C4H9+ + BzCl = t-C4H9Cl + C7H7+ led to equilibrium constants K4 which are in fair agreement with earlier work by Abboud etal. However, the present temperature dependence predicts a ΔS40 which is sufficiently different from that by Abboud etal. to put in question the indentification of C7H7+ as Bz+ on the basis of the measured ΔS40 value. Therefore experiments were made to confirm that C7H7+ produced in [4] is Bz+ and not the tropylium cation. A C7H7+ cation was produced by hydride abstraction from 1,3,5-cycloheptatriene. The behaviour of that C7H7+ ion was entirely different from C7H7+ produced by chloride abstraction from BzCl or hydride abstraction from toluene. While the benzyl derived C7H7+ engaged in a number of reactions like hydride abstraction, chloride abstraction, addition, condensation, etc., the C7H7+ from the heptatriene remained completely unreactive. On this basis the C7H7+ ions were identified as Bz+ and tropylium+, respectively. Rate constants for several reactions of Bz+ were determined. It is concluded that a rearrangement from benzyl to tropylium cations and vice versa does not occur at least up to 300 °C. The ions also retain their identity if they are produced with considerable internal excitation energy.
Microbial hydroxylation of steroids. 7. Hydroxylation of B-nortestosterone and related compounds by Rhizopus arrhizus ATCC 11145, and 13C nuclear magnetic resonance spectra of some B-norsteroids
Authors: Holland Herbert L.
Published: May 2006

The incubation of B-norandrost-4-ene-3-ones and B-nor-3β-hydroxyandrost-5-enes with Rhizopus arrhizus ATCC 11145 has been described. The products are consistent with a mechanism of oxidation at C-6 in which the stereochemistry of substitution at C-6 is controlled by stereoelectronic interactions in the substrate, and is not dictated by enzymic constraint during the reaction. The carbon-13 nuclear magnetic resonance spectra of several B-nor-Δ4 and Δ5 steroids have been presented.
The location of the reaction site and discreteness-of-charge effects in electrode kinetics
Authors: Fawcett W. R.
Published: May 2006

Discreteness-of-charge effects for simple heterogeneous electron transfer reactions, namely, the self-image effect, the exclusion disc effect, and the effect of local attractive ion–ion interactions, are considered for a variety of reaction sites in the double layer, both in the presence and in the absence of ionic specific adsorption. An expression is derived for the local activity coefficient of the activated complex; this quantity is shown to be a function of both the potential drop across the inner layer and the adsorbed charge density due to specifically adsorbed ions when the standard state is chosen on the basis of the reaction conditions considered in the classical Frumkin theory (reaction site at the outer Helmholtz plane). The consequences of discreteness-of-charge effects for reactions occuring in three different double layer environments of increasing complexity are described. These effects are discussed on the basis of data obtained earlier for the electroreduction of periodate anion in the presence of specifically adsorbed anions.
Forces between dissimilar colloidal plates for various surface conditions. II. Equilibrium adsorption effects
Authors: Bell G. M. , Peterson G. C.
Published: May 2006

A method previously developed by the authors is used to study the effects of adsorption of ions on the electric double layer interaction between dissimilar colloidal plates immersed in 1:1 electrolyte. For adsorption models which permit the total charge on a plate to change sign, the double layer force remains finite at all plate separations, including zero. For weak adsorption of the ions on the plates the force between two dissimilar plates tends to be repulsive at small separations, looking rather like a weakened constant surface charge density model. Conversely for strong ionic adsorption the force tends to be attractive at small separations, rather as in the constant surface potential model. In this paper we discuss three adsorption models: (1) fixed primary charge density on the plates with secondary adsorption of both counter-ions and co-ions; (2) fixed primary charge density on the plates with secondary adsorption of the counter-ions only, but including the effects of a Stern layer and self-atmosphere potentials; (3) zero primary charge on both plates with equilibrium adsorption of both anions and cations from solution, the net charge density on the plates arising from differential adsorption of the ion types.
A kinetic electron spin resonance study of the reaction of some oxy radicals with vanadyl acetylacetonate
Authors: Howard J. A. , Tait J. C. , Yamada T. , Chenier J. H. B.
Published: May 2006

Reactions of phenoxyl, iminoxyl, nitroxyl, peroxyl, and alkoxyl radicals with VO(acac)2 in solution have been studied by kinetic esr spectroscopy. Rates of reaction are first-order with respect to each reactant and radical reactivity increases in the order galvinoxyl <2,4,6-tri-tert-butylphenoxyl <di(1-adamantyl)methylene-iminoxyl <tert-butylperoxyl. Rates of reaction are retarded by pyridine and accelerated by methanol and there is an isotope effect on the rate when the hydroxyl proton of CH3OH is replaced by deuterium. Vanadium-51 nmr spectroscopy has demonstrated that several vanadium(V) products are formed while conventional product studies have indicated that, in the case of phenoxyl and alkoxyl, the radical is reduced almost exclusively to the parent phenol and alcohol and that VO(acac)2 is eventually regenerated in substantial yields. The net reaction is, therefore, catalytic reduction of the radical. Variable temperature esr studies have shown that phenoxyl and iminoxyl radicals and VO(acac)2 exist in equilibrium with diamagnetic reaction products.
Carbon-13 nmr shifts and C—H coupling constants of deoxybenzoins and related acetophenones
Authors: Jha Hem Chandra , Zilliken Fritz , Offermann Werner , Breitmaier Eberhard
Published: May 2006

13C Chemical shifts and resolved carbon–proton couplings of 39 deoxybenzoins and 11 acetophenones, most of which have naturally occurring substitution patterns, are assigned. Individual benzene rings turned out to have typical parameters not affected by structural variations in the rest of the molecule. Due to substitutional saturation, however, these benzenoid carbon shifts markedly deviate from increment additivity. A few trends of these deviations are described. Phenolic hydrogens, fixed between hydroxyl and carbonyl oxygen due to internal hydrogen bonding, are shown to give rise to additional carbon-splittings.
Synthesis of α-thiohemiaminal derivatives of deoxynupharidine
Authors: Lalonde Robert T. , Eckert Timothy S.
Published: May 2006

Disulfides, sulfenyl chlorides, thiosulfonates, and sulfensuccinimides were evaluated as electrophilic thiating agents for converting the enamine 6-dehydrodeoxynupharidine to α-thiohemiaminal derivatives of the alkaloid deoxynupharidine. Sulfensuccinimides were generally the most useful but other types of agents produced better yields in some individual cases.