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排序方式: 共有157条查询结果,搜索用时 31 毫秒
1.
John Bethke Jürgen Kopf Paul Margaretha Bernard Pignon Léon Dupont Léon E. Christiaens 《Helvetica chimica acta》1997,80(6):1865-1868
Irradiation (λ = 350 nm) of 1H-[2]benzothiopyran-1-one ( 2 ) in the solid state affords selectively and in good yield 6aα, 6bα, 12bα, 12cα -tetrahydrocyclobuta[1, 2-c:4, 3-c′]bis([2]benzothiopyran)-5, 8-dione ( 3 ), the head-to-head (HH) cis-cisoid-cis-cyclodimer of 2 , X-Ray analysis of 2 confirms that this reaction proceeds according to the well-established topochemical principles. The same dimer 3 is obtained in low yields on irradiation of 10−1 M solutions of 2 in either MeOH or MeCN, while no conversion at all is observed in benzene. On irradiation of 2 in MeCN in the presence of tetrachloroethene, the [2 + 2] photocycloadduct 4 is formed in good yield, the conversion 2 → 4 being efficiently quenched by naphthalene. In contrast, no reaction is observed -on irradiation of 2 in the presence of 2, 3-dimethylbut-2-ene, neither in polar nor in apolar solvents. 相似文献
2.
Pablo Wessig Philipp Wettstein Bernd Giese Markus Neuburger Margaretha Zehnder 《Helvetica chimica acta》1994,77(3):829-837
The chiral N-(2-benzoylethyl)-N-tosylglycinamides 1a-c were prepared from the C2-symmetric pyrrolidines 5a-c . Irradiation of these ketones 1a-c gave cis-3-hydroxyprolinamides 10-12 in moderate to good yields (Scheme 3). The de of the photocyclizations depended on the size of the substituents in positions C(2) and C(5) of the chiral pyrrolidine auxiliaries. In addition, the de varied with the reaction temperature, allowing the determination of activation-parameter differences. The structure of products 10-12 were established by NMR and X-ray analyses. 相似文献
3.
The title compound 3g is obtained via two different routes, either in a multistep synthesis starting from 2-amino-2-methylpropionic acid (methylalanine) or by light-induced, oxidative dealkylation of the corresponding N-isopropyl derivative 3c . 相似文献
4.
Irradiation (λ = 254 nm) of N-(4,4,6,6-tetramethyl-2-cyclohexen-1-ylidene)-1,1,3,3-tetramethyl-2-cyclohexen-1-ylidene-1,1,3,3-tetramethylbutylamine (7d) , which in turn is photodecomposed by light of the same wavelength, but at a four times slower rate than it is formed. The rate of formation of photoproduct 7d is a function of the concentration of starting material 1d , suggesting the involvement of a bimolecular ( 1d * + 1d ) step. The structure of 7d was established by spectroscopy and by its hydrolysis to 3-cyclohexyl-4,4,6,6-tetramethyl-2-cyclohexenone ( 8 ). The previously made assumption that N-(2-cyclohexen-1-ylidene)cyclohexylamine ( 1a ) and 2,3,4,4a,5,6-hexahydroquinolines 2 photorearrange to N-cyclohexylidenecyclohexanamine 3a and 3,4,4a,5,6,8a-hexahydroquinolines 4 , respectively, via a light-induced 1,3-hydrogen shift proves incorrect. 相似文献
5.
Michael Beyer Ramin Ghaffari-Tabrizi Michael Jung Paul Margaretha 《Helvetica chimica acta》1984,67(6):1535-1539
On acetone-sensitized irradiation the title compounds 3a–c are converted to 2-allyl-3-hydroxy-1H-pyrrole-2-carboxylates 4 in reasonable yields. 相似文献
6.
Irradiation (λ > 340 nm) of the title compound 2a in t-BuOH affords 3,3,10,10-tetramethyl-2,8-dioxatricyclo-[4.3.2.01,6]undecane-5,9-dione (3) via photoextrusion of 2-methylpropene and subsequent photocycloaddition of 2a to the alkene. The same regioisomer 3 is formed selectively and in much higher yields on irradiating 2a in the presence of excess 2-methylpropene. Irradiation of 3 (λ = 300 nm) in t-BuOH in the presence of the same alkene gives a 6:1 mixture of spirooxetanes 7a and 7b but not α-cleavage products. In 2-propanol, 2a is photoreduced to a 2:1 mixture of diastereoisomeric hydrodimers 9 . 相似文献
7.
Dihydrothiinone 9a undergoes photocycloaddition regioselectively to all three C?C bonds of penta‐1,2,4‐triene ( 10 ), the relative stabilities of the biradical intermediates determining the product distribution. In contrast, cyclohexenone 9b and dihydropyranone 9c afford more complex mixtures of bicyclo[4.2.0]octanones, which also turn out to be less stable on chromatographic workup, reflecting the higher strain due to the shorter bond lengths (C? O and C? C vs. C? S) in the six‐membered rings, respectively. 相似文献
8.
The reaction of the 4,4-dialkylated 2-cyclohexenones 1 or 2 with a twofold excess of a secondary amine 3 affords the 2-amino-1,3-cyclohexadienes 4 and 5 , respectively. Irradiation (λ ≧ 300 nm) of the morpholino derivative 4a yields a mixture of the isomeric 3-morpholino-6-methyl-1,3,5-heptatrienes 6 and 7 , while 5 gives only one corresponding product 8 . The reaction of enone 1 with an equimolar amount of pyrrolidine ( 3c ) affords the bis-enamine 9 which is converted to the unsaturated diketone 10 by oxidative hydrolysis. 相似文献
9.
Zusammenfassung Während verschiedene Basen mit organischen Lewissäuren stabile Anbadone liefern, führt die Umsetzung mit Hydrazin zu Aldazinen bzw. Hydrazonen.
13. Mitt.:P. Margaretha undO. E. Polansky, Mh. Chem.100, 576 (1969). 相似文献
Reaction of electrically neutral organic lewis acids with hydrazine (organic lewis acids, XIV)
While several bases reacting with organic Lewis-acids form stable anbadons, the reaction with hydrazine leads to aldazines (azines) and hydrazones.
13. Mitt.:P. Margaretha undO. E. Polansky, Mh. Chem.100, 576 (1969). 相似文献
10.
Christian P. Klaus Carolin Thiemann Jürgen Kopf Paul Margaretha 《Helvetica chimica acta》1995,78(5):1079-1082
Irradiation (λ > 390 nm) of 2H-1-benzothiopyran-2-one ( 1 ) in the solid state affords selectively 6aα,6bα,12bα,12cα -tetrahydrocyclobuta[1,2-c:4,3-c′]bis[1]benzothiopyran -6,7-dione ( 2 ), the head-to-head (HH) cis-cisoid-cis-dimer, while irradiation of 1 in the solid state using shorter wavelengths (λ > 340 nm) affords a mixture of all four cis-fused tricyclic dimers 2 – 5 . These results represent a novel wavelength effect in solid-state photochemistry. 相似文献