摘要:

The total synthesis of the title compound22and methyl 14α-hydroxy-5β,13α,8-androstene-1,7,17-trioxo-10β-oate21isomer is reported. We also describe the 1,6-Michael addition of 2-methyl-1,3-cyclopentanedione on dienone14and the protic ammonium salt catalyzed intramolecular Michael addition of cyclic β-ketoester on the conjugated acetylenic ketone13.Keywords: cardenolides, steroid synthesis, aldol, Michael addition.

ISSN:0008-4042    

DOI:10.1139/v90-296

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Carbanion sources (organolithium and Grignard reagents) react with [(mesitylene)2Fe]2+and [(mesitylene)(Ch)Fe]+cations (Ch = cyclohexadienyl) to afford neutral Ch2Fe and ChCh′Fe ("pseudoferrocene") complexes, respectively. Addition of R−(R− = methyl, phenyl, benzyl, andt-butyl) occurs stereospecifically viaexoaddition at an unsubstituted carbon atom of the arene ring. The synthesis and characterization of these complexes is detailed and the structure of bis(η5-exo-6-phenyl-1,3,5-trimethylcyclohexadienyl)iron(II),3b, has been determined by single crystal X-ray diffraction analysis.3bcrystallizes in the triclinic space group, witha = 11.947(2),b = 12.784(1),c = 8.865(2), α = 108.59(1)°, β = 108.19(1)°, γ = 84.91(1)°, andDcalcd1.227 g cm−3forZ = 2. Least-squares refinement gave a conventionalRvalue of 0.0452 for 2080 independent observed reflections. The structure reveals that the complex adopts agauche-eclipsed conformation. The variable temperature (vt)1H NMR spectra of pseudoferrocenes are interpreted in terms of restricted ring rotation around the ligand—metal—ligand axis.Keywords: arene, cyclohexadienyl, pseudoferrocene, variable temperature NMR, X-ray diffraction.

ISSN:0008-4042    

DOI:10.1139/v90-297

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A two-wavelength method was applied to the determination of free, ionic calcium with Arsenazo III in solutions containing calcium-binding ligands. By this procedure impurities in the indicator can be corrected for, thereby allowing the use of commercial indicator preparations with purities as low as 80%. Only a 1:1 complex with a conditional log stability constant of 4.28 ± 0.13 at pH 4.6 and ionic strength 0.1 was found under the conditions studied.Key words: free metal ion determination, calcium ion speciation, spectrophotometry, arsenazo III, ion increment method for speciation.

ISSN:0008-4042    

DOI:10.1139/v90-298

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

A new method to calculate the enthalpy and entropy of cavity formation in liquids is proposed. The reference cavity formation process is identified with the vaporization of liquid in the absence of order and Corresponding States Principle is used to eliminate the order contribution to vaporization enthalpy. The proposed method agrees very well with Claverie's modification of the Pierotti's method but strongly disagrees with the Sinanoglu's method, particularly in the context of entropy of cavity formation.The new method is checked by applying it to the description of solution process in alkane binary mixtures at infinite dilution and is used to study the solvent effect on the solvolysis oft-butyl chloride and bromide.Keywords: cavity formation, enthalpy and entropy of cavity formation, Corresponding States Principle, alkanes, intermolecular interactions, acentric factor, solvent effect.

ISSN:0008-4042    

DOI:10.1139/v90-299

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The products, plausible intermediates, and their mechanisms of formation in the aprotic diazotization of 2-[(2-acetoxyethyl)-sulfinyl (and sulfonyl)]anilines with isoamyl nitrate have been investigated by experimental and quantum chemical methods. Oxidation of 1,2,3-benzthiadiazole with hydrogen peroxide in acetic acid affords 1,2,3-benzthiadiazole-1-oxide,13. The thermal stability of13up to 135 °C, together with EPR evidence which disfavors an aryldiazenyl radical precursor, discount13as an intermediate in the formation of benzoxathiete14or its valence tautomer17during aprotic diazotization of the sulfinylanilines. Electron paramagnetic resonance evidence in conjunction with spin trapping indicates an intermediate arylaminyl radical. This evidence, taken together withabinitiocalculations of optimized geometries energies and energy differences for biradical intermediate15, favors a mechanism of formation of benzoxathiete14via aryldiazoate anhydride5thence to rapid ring closure of carbon-centered radical8. Further oxidation of 1,2,3-benzthiadiazole-1-oxide,13, with hydrogen peroxide in methanol – acetic acid affords biphenylene and dibenzo-1,4-oxathiane-S-oxide,38. Rose bengal sensitized photooxidation of 1,2,3-benzthiadiazole affords13, biphenylene, and38. Formation of the latter, in which one of the original S—O bonds has been broken, requires the formation of benzoxathiete-S-oxide,34, and its rapid valence tautomerism to ketosulfine36and (2 + 4) cycloaddition of36to the simultaneously generated dehydrobenzene to give38. Both ring closure of singlet biradical35to34and valence tautomerism of the latter to36are predicted byabinitiocalculations to be facile and exothermic. In contrast to the aprotic diazotization of 2-[(2-acetoxyethyl)sulfinyl]anilines, the reaction of isoamyl nitrite with the corresponding sulfonyl anilines may plausibly follow a mechanism via 1,2,3-benzthiadiazole-1,1-dioxide33owing to the thermal instability of the latter and supported byabinitiotreatments of the energetics of the processes involved. In addition EPR evidence, in conjunction with spin trapping of carbon centered radicals, support the viability of the pathway via23,25,28, and16to biphenylene20. Theabinitiocalculations of the energy differences between the reaction intermediates and estimates of the activation energies elucidated several aspects of these novel reactions.Keywords: benzoxathiete,abinitiocalculations, valence tautomerism.

ISSN:0008-4042    

DOI:10.1139/v90-300

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The photochemistry of 2-trifluoromethylnorbornene in pentane solution has been investigated. Direct photolysis with 193 nm light yields 1-trifluoromethyl-2-norcarene in 90% yield, due to formal [1,3]-sigmatropic rearrangement, in addition to three other minor products. Chlorobenzene-sensitized photolysis affords photoreduction products, principallyexo- andendo-2-trifluoromethylnorbornane and decane isomers, in addition to several products of higher molecular weight. On the basis of comparisons of the photochemistry of this compound to that previously reported for norbornene and 2-cyanonorbornene, as well as spectroscopic evidence, it is suggested that the lowest excited singlet state (the photoreactive state in solution) in 2-trifluoromethylnorbornene is the π, π* state. The results indicate that trifluoromethyl substitution has the effect of significantly raising the energy of the π,R(3s) Rydberg state in simple alkenes, without altering the high energy (ca. 6.5 eV) or the localized character of the alkene π, π* state. Furthermore, they lend additional support to the view that the carbene-derived products typically formed upon photolysis of alkenes in solution are derived from π,R(3s) excitation.Keywords: Rydberg, photolysis, far-uv, alkene, solution phase, singlet, triplet.

ISSN:0008-4042    

DOI:10.1139/v90-301

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Valence and inner-shell (C1s) electronic excitation spectra of norbornene, 2-methylnorbornene, and 2-trifluoromethylnorbornene have been measured by electron energy loss spectroscopy. These data have been complemented with gas- and solution-phase UV absorption spectra in the 5–6.7 eV range, HeI UV photoelectron spectra, and AM1 semi-empirical calculations for the three compounds. The valence shell energy loss and UV absorption spectra show marked variations throughout the series of compounds, suggesting the presence of at least three low-lying electronic excited states. The spectral bands have been assigned as due to π,R(3s), π,π*, and π, R(3p) excitations on the basis of their term values and the differences between their intensities in the solution and gas phase absorption spectra. The valence shell spectra indicate that while the vertically-excited π,R(3s) state is substantially lower in energy than the (vertically-excited) π,π* state in norbornene and the 2-methyl derivative, they are nearly isoenergetic in 2-trifluoromethylnorbornene. This difference in excited state manifolds is reflected in profound differences between the solution phase photochemistry of norbornene and the 2-trifluoromethyl derivative.The carbon 1sspectra are even more sensitive to substituent than the valence shell energy loss spectra. An interpretation is proposed which reflects the spatially localized character of inner-shell excitation and a "group orbitals" picture of the unoccupied MO's as accessed by C1sexcitation.Keywords: Rydberg, electron energy loss, UV absorption, UV photoelectron spectroscopy, alkene, gas-phase.

ISSN:0008-4042    

DOI:10.1139/v90-302

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Spectrophotometric titration of tetrahydropterins with incremental amounts of•N3showed that 6,7-dimethyl-7,8-dihydropterin was an intermediate in the oxidation of 6,7-dimethyltetrahydropterin at the two electron-equivalent oxidation point. The eventual end product at four electron equivalents was 6,7-dimethylpterin. In the case of unsubstituted tetrahydropterin, the dihydro form was clearly not an exclusive product at the two electron equivalent point, and this was attributed to the disproportionation of different forms of dihydropterin to tetrahydropterin and pterin.The azide radical oxidized tetrahydropterins to trihydropterin radicals,•PnH3, with overall second-order rate constants at pH 7 of 4.1, 3.8, and 2.9 × 109 M−1s−1for tetrahydropterin, 6,7-dimethyltetrahydropterin, and 6-carboxylated tetrahydropterin, respectively. At pH 10 the rate constants are slightly larger due to the presence of the deprotonated enolate forms of tetrahydropterins. Spectra vary somewhat with substitution in the pterin molecule, but all species have a strong peak (ϵ ~9000 M−1cm−1) near 320 nm and lower absorption above this, with a tail extending to 580 nm.Keywords: tetrahydropterin oxidation, tetrahydropterin, trihydropterin radical, azide radical, trihydropterin spectrum.

ISSN:0008-4042    

DOI:10.1139/v90-303

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The thermal reactions of dicarbonyl-η5-cyclopentadienyl(2-thienoyl)iron with a series of substituted acetylenes to give indenones and cyclopentathiophenones have been reinvestigated. The results obtained support a reaction mechanism involving initial acetylene insertion followed by that of carbon monoxide, in contradiction to the previously reported results. The reaction products were identified and characterized primarily using 2D1H nmr spectroscopy.Keywords: acetylene, carbon monoxide, iron, indenone, mechanism, thienyl.

ISSN:0008-4042    

DOI:10.1139/v90-304

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The photochemical ring opening ofcis- andtrans-3,4-dimethyl-, 1,3,4-trimethyl-, and 1,2,3,4-tetramethylcyclobutene (1,3, and4, respectively) has been investigated in hydrocarbon solution with 193 nm and 214 nm light sources. Ring opening is non-stereospecific in all cases at both wavelengths. The ratio of dienes formed by the formally allowed to formally forbidden pathways in the photolysis of these compounds is highest (ca. 2) for the trimethylcyclobutenes, and approximately 1 for bothcisandtransisomers of the di- and tetramethylcyclobutenes with 193 nm excitation. The diene distributions from photolysis of all compounds butcis-3show slight wavelength dependence. Gas- and solution-phase UV absorption spectra are reported for3and4, and indicate that there are at least three singlet excited states accessible in the 185–230 nm region in these molecules. The π,R(3s) state is the lowest energy state in the gas phase in3and4. The results verify that orbital symmetry factors do not play a role (or a consistent one, at least) in controlling the stereochemistry of the reaction, but they do not allow a firm assignment of the excited state(s) responsible for ring opening. Direct photolysis of these compounds also results in fragmentation to yield Z-2-butene (fromcis-3and4) orE-2-butene (fromtrans-3and4) in addition to propyne or 2-butyne. The 2-butenes are formed with greater than 90% stereospecificity in all cases. The structures of the four 3-methyl-2,4-hexadiene isomers obtained from photolysis of3have been assigned on the basis of1H NMR spectroscopy and the results of thermolysis of the two cyclobutene isomers.Keywords: cyclobutene, photolysis, Rydberg, orbital symmetry, far-UV, solution phase, UV spectra.

ISSN:0008-4042    

DOI:10.1139/v90-305

出版商:NRC Research Press    

年代:1990

数据来源: NRC