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121.
Jos M. Villalgordo Adelheid Enderli Anthony Linden Heinz Heimgartner 《Helvetica chimica acta》1995,78(8):1983-1998
Diphenyl phosphorazidate (DPPA) was used as the azide source in a one-pot synthesis of 2,2-disubstituted 3-amino-2H-azirines 1 (Scheme 1). The reaction with lithium enolates of amides of type 2 , bearing two substituents at C(2), proceeded smoothly in THF at 0°; keteniminium azides C and azidoenamines D are likely intermediates. Under analogous reaction conditions, DPPA and amides of type 3 with only one substituent at C(2) gave 2-diazoamides 5 in fair-to-good yield (Scheme 2). The corresponding 2-diazo derivatives 6–8 were formed in low yield by treatment of the lithium enolates of N,N-dimethyl-2-phenylacetamide, methyl 2-phenylacetate, and benzyl phenyl ketone, respectively, with DPPA. Thermolysis of 2-diazo-N-methyl-N-phenylcarboxamides 5a and 5b yielded 3-substituted 1,3-dihydro-N-methyl-2H-indol-2-ones 9a and 9b , respectively (Scheme 3). The diazo compounds 5–8 reacted with 1,3-thiazole-5 (4H)-thiones 10 and thiobenzophenone ( 13 ) to give 6-oxa-1,9-dithia-3-azaspiro[4.4]nona-2,7-dienes 11 (Scheme 4) and thiirane-2-carboxylic acid derivatives 14 (Scheme 5), respectively. In analogy to previously described reactions, a mechanism via 1,3-dipolar cycloaddition, leading to 2,5-dihydro-1,3,4-thiadiazoles, and elimination of N2 to give the ‘thiocarbonyl ylides’ of type H or K is proposed. These dipolar intermediates with a conjugated C?O group then undergo either a 1,5-dipolar electrocyclization to give spirohetrocycles 11 or a 1,3-dipolar electrocyclization to thiiranes 14 . 相似文献
122.
Accurate lower and upper bounds for the nonrelativistic lowest energies1
E
0 and3
E
0 of the singlet and triplet-system of the4He-Isotop are calculated with the linearized method of variance minimization. The same was done for1
E
1 the energy of the first excitedS-state 21
S.
The results especially for1
E
0 and3
E
0 in a.u. are −2.90330769975 ≤1
E
0 ≤ −2.90330769218 −2.17493242637 ≤3
E
0 ≤ −2.17493242459 i.e. the values are determined with an absolute error smaller than 0.00167 cm−1 for1
E
0 and 0.00039 cm−1 for3
E
0. 相似文献
123.
Halochromic Molecules. Synthesis and Acidobasic Properties of 3′-substituted 6,11-dihydrospiro[[1]benzopyrano[4,3-b]indol-6,9′?9′9′H-xanthenes] We have synthesized a series of 3′-substituted 6,11-ihydrospiro[6H-chromeno[4,3-b]indol–6,9′?9′H-xanthenes] and one of their respective aza analogues. 1H-MR data as well as the fragmentation in the mass spectra of starting and final products supported the postulated structures. With acid, the spiro compounds form ring-opened intensely coloured xanthylium salts. UV/VIS spectra of these salts are listed and discussed. The ?pH* curves in buffered MeOH/H2O solutions and the pK* values are determined. The title compounds could possibly be used in ‘pressure sensitive papers’. 相似文献
124.
Serge Mignani Francis Lahousse Robert Merényi Zdenek Janousek Heinz Gunter Viehe 《Tetrahedron letters》1985,26(38):4607-4608
Carbanions carrying captodative substitution are readily oxidized to their dimers. 相似文献
125.
The preparation of the title compounds was achieved via the ‘azirine/oxazolone method’ starting from the corresponding γ‐hydroxy acids. Upon subjecting the γ‐hydroxy‐N‐[1‐(dimethylcarbamoyl)ethyl]butanamides 4 to the so‐called ‘direct amide cyclization’ (DAC) conditions, chlorinated acids 11 or imino lactones 12 were obtained as the sole products instead of the expected cyclodepsipeptides A or their cyclodimers (Scheme 4). Variation of the substituents in 4 did not affect the outcome of the reaction and a mechanism for the formation of both products from the intermediate oxazolone 13 has been proposed. Under the acidic conditions of the DAC, the imino lactones are formed as their HCl salts 12 , which, in polar solvents or on silica gel, reacted further to give the chlorinated acids 11 . Stabilization of the imino lactones was achieved by increasing the substitution in the five‐membered ring, and their structure, in the form of the hydrochlorides, was established independently by X‐ray crystallography (Fig. 4). A derivative 15 of the imino lactone 12a was prepared by the reaction with the 2H‐azirin‐3‐amine 10a ; its structure was also established by an X‐ray crystal‐structure determination (Fig. 3). Furthermore, the structures of the ω‐chloro acids 11a and 11b were determined by X‐ray crystallography (Fig. 2). 相似文献
126.
Doz. Dr. Heinz Falk Otmar Hofer Alfred Leodolter 《Monatshefte für Chemie / Chemical Monthly》1975,106(4):983-990
The structure of squaric acid derivatives was investigated on the basis of the PPP—SCF—LCAO—MO—CI method utilizing the π-electron densities and bond orders. The parameters used in the calculations were modified to fit the experimental data for representative compounds. The data were obtained by X-ray photoelectron spectrometry and electron absorption spectroscopy (including the polarization of the bands as determined by liquid crystal induced circular dichroism measurements). 相似文献
127.
Formation of Thietane Derivatives via Intramolecular (2+2) Cycloaddition On irradiation, the two 4-vinyl-1,3-thiazole-5(4H)-thiones 1a, b , synthesized from thiobenzoic acid and the corresponding 3-amino-2H-azirines 2a , b , undergo an intramolecular (2+2)-cycloaddition reaction of the C?S and C?C bonds to give the tricyclic thietane derivatives 3a , b . 相似文献
128.
Solvolysis of 4-Alkydenbicyclo[3.2.0]hept-2-en-6-oles. Synthesis of 1-Vinylfulvenes and 8,8-Diphenylheptafulvene Four 4-alkylidenebicyclo[3.2.0]hept-2-en-6-ones 2–5 , obtained via ketene cycloaddition to fulvenes, were reduced to separated mixtures of the ‘endo’ -alcohols ‘endo’- 6 to ‘endo’- 9 (68–73%) and ‘exo’- 6 to ‘exo’- 9 (3–20%). Treatment of some of these alcohols with (CF3SO2)2O in CH2Cl2/pyridine caused a spontaneous solvolysis to yield unsaturated 7-membered rings as pyridinium triflates 10–12 or 1-vinylfulvenes 13 and 14 , a new class of reactive tetraenes: Both ‘endo’- 9 and ‘exo’- 9 , having two methyl groups at C(7), were converted into the vinylfulvene 13 (≈ 80%). The alcohols with two H-atoms at C(7) exhibited a stereochemically controlled reaction selectivity, inasmuch as ‘endo’- 6 to ‘endo’- 8 afforded only the corresponding 7-membered-ring pyridinium salts 10–12 (66–79%), while ‘exo’- 6 produced only the vinylfulvene 14 (77%). A stereoelectronic control argument explains the C(1), C(5)-bond cleavage with ‘endo’- B and ‘endo’– 6 -‘endo’- 8 , as well as the C(1), C(7)-bond cleavage with ‘exo’- B , ‘exo’- 6 , and with both ‘endo’- and ‘exo’- 9 . Thermolysis (120°) of the pyridinium triflates 10 and 11 yielded the 3-isopropenyl-cycloheptatrienes 18 and 19 , respectively (≈90%); similar conditions (145°) applied to the triflate 12 produced the doubly cyclized fluorene derivative 21 (60%). When the iodide 22 derived from the triflate 12 with Nal was heated in refluxing toluene, 8,8-diphenylheptafulvene ( 23 , 86%) was obtained. 相似文献
129.
Kurt Dietliker Paul Gilgen Heinz Heimgartner Hans Schmid 《Helvetica chimica acta》1976,59(6):2074-2099
Photochemistry of 4-substituted 5-Methyl-3-phenyl-isoxazoles. 4-Trideuterioacetyl-5-methyl-3-phenyl-isoxazole ([CD3CO]- 27 ), upon irradiation with 254 nm light, was converted into a 1:1 mixture of oxazoles [CD3CO]- 35 and [CD3]- 35 (Scheme 13). This isomerization is accompagnied by a slower transformation of ([CD3CO]- 27 ) into [CD3]- 27 . Irradiation of the isoxazole derivatives 28, 29, 30 and (E)- 31 yielded only oxazoles 36, 37, 38 and (E), (Z)- 39 ; no 4-acetyl-5-alkoxy-2-phenyl-oxazole, 2-acetyl-3-methyl-5-phenyl-pyrrole or 2-acetyl-4-methoxycarbonyl-3-methyl-5-phenyl-pyrrole, respectively, were formed (Scheme 9 and 10). Similarly (E)- 32 gave a mixture of (E), (Z)- 40 only (Scheme 11). Upon shorter irradiation, the intermediate 2H-azirines (E), (Z)- 41 could be isolated (Scheme 11). Photochemical (E)/(Z)-isomerization of the 2-(trifluoro-ethoxycarbonyl)-1-methyl-vinyl side chain in all the compounds 32, 40 and 41 is fast. At 230° the isoxazoles (E)- and (Z)- 32 are converted into oxazoles (E), (Z)- 40 . The same compounds are also obtained by thermal isomerization of the 2H-azirines (E), (Z)- 41 . The most probable mechanism for the photochemical transformations of the isoxazoles, as exemplified in the case of the isoxazole 27 , is shown in Scheme 13. A benzonitrile-methylide intermediate is postulated for the photochemical conversion of the 2H-azirines into oxazoles. 2H-Azirines are also intermediates in the thermal isoxazole-oxazole rearrangement. It is however not yet clear, if the thermal 2H-azirine-oxazole transformation involves the same transient species as the photochemical reaction. A mechanism for the photochemical isomerization of the 2H-azirine 11 to the oxazole 15 is proposed (Scheme 3). 相似文献
130.
Karl Heinz Neeb Herbert Neidl und Heinz Stöckert 《Fresenius' Journal of Analytical Chemistry》1972,259(4):265-268
Zusammenfassung Zur Bestimmung der U- und Th-Gehalte in 0,5–1,5mg wiegenden Mikroproben von ThO2-UO2-Kernbrennstoffen wurde die Neutronenaktivierungsanalyse mit zerstörungsfreier-Spektrometrie eingesetzt. Bei Gehalten über 0,1% beträgt die relative Standardabweichung 6%. Der Th-Gehalt der Mikroproben wird durch-spektrometrische Messung des233Pa ermittelt; bei Natur-Uran enthaltenden Proben wird der U-Gehalt über239Np bestimmt, bei hochangereichertes UO2 enthaltenden Proben über131J. Mit der beschriebenen Methode können sowohl unbestrahlte als auch bestrahlte ThO2-UO2-Kernbrennstoffe untersucht werden.
Teil I siehe [3].
Herrn G. Hofmann danken wir für die Entnahme der Mikro-Bohrproben aus den bestrahlten und unbestrahlten Brennstoffschliffen. 相似文献
Use of a Ge(Li) detector in radiochemical analysisII. determination of U and Th contents in microsamples of ThO2-UO2 nuclear fuels
Neutron activation analysis with non-destructive-spectrometry has been used to determine U and Th in microsamples (0.5–1.5 mg) from ThO2-UO2 nuclear fuels. With U contents of more than 0.1% the relative standard deviation amounts to 6%. Th in the microsamples is estimated by measuring233Pa; in natural UO2 containing samples239Np ist measured for U determination, in highly enriched UO2 samples131J. Fresh und spent ThO2-UO2 nuclear fuels can be investigated by the method described.
Teil I siehe [3].
Herrn G. Hofmann danken wir für die Entnahme der Mikro-Bohrproben aus den bestrahlten und unbestrahlten Brennstoffschliffen. 相似文献