共查询到20条相似文献,搜索用时 0 毫秒
1.
Takehiko Nishio Peter Mathies Kurt Job Bruno Frei Oskar Jeger 《Helvetica chimica acta》1989,72(5):943-951
Photo-oxygenation of (E)-7-methyl-β-ionone ((E)? 1 ) and (E)-8-methyl-β-ionone ((E)? 2 ) gave rise to the formation of the hydroperoxy-enones (E)? 10 and (E)? 15 , respectively, which, in part, underwent intramolecular epoxidation to the hydroxy-epoxy-ketones 11 and 16 , respectively, The product distribution of the photo-oxidation of (Z)? 1 shows a marked influence of the skewed ground-state conformation of the dienone chromophore. Thus, singlet oxygen (1O2) was added to C(γ) of the dienone chromophore leading to the spirocyclic peroxy-hemiacetal 12 and to the endoperoxide 13 . In addition, the tricyclic peroxide 14 was formed as a new type of product via primary addition of 1O2 to C(γ) of the dienone chromophore. The structure of 14 was established by X-ray crystal-structure analysis of the hemiacetal 22 . 相似文献
2.
The wavelength dependence of the photolysis of 7-methyl-β-ionone ((E)- 1 ) was investigated. Irradiation of (E)- 1 with light of λ > 347 nm leads primarily to (E/Z)-isomerization followed by transformation to the tricyclic enol ether 3 as the only secondary photoproduct. On photolysis of (E)- 1 with light of shorter wavelength (λ > 280 nm or λ = 254 nm), however, a series of other products was formed (via a) photocyclization of the dienone chromophore (→ 5 ), (b) photo-enolization (→ 8 ), and (c) a 1,5-sigmatropic H-shift (→ (E/Z)- 7 ). For the structure elucidation of the new products, 7-[13C]methyl-β-ionone ((E)-[7-methyl-13C]- 1 ) was prepared and irradiated furnishing the corresponding 13C-labelled photoproducts. 相似文献
3.
Alfons Pascual Norbert Bischofberger Bruno Frei Oskar Jeger 《Helvetica chimica acta》1988,71(2):374-388
The photolysis of 7,8-dihydro-4-hydroxy-β-ionone ( 6 ) was investigated together with its acetate and isopropyl ether 7 and 8 , respectively. Irradiation (λ > 245 nm) of 6 in MeCN or i-PrOH at temperatures between 25° and ?65° leads to the tricyclic ethers 9 , 10 and 13A + B , and to the spirocyclic ethers 11 and 12 , which are all known types of photoproducts, previously obtained on photolysis of 7,8-dihydro-β-ionone ( 1 ). The same types of products are obtained on irradiation of the acetate 7 and the isopropyl ether 8 . On the other hand, irradiation of the hydroxy compound 6 in MeCN or i-PrOH at temperatures between ?35° and ?65° leads to the new tricyclic tertiary alcohols 14 and 15 as the major products. Their formation involves an intramolecular trapping of a carbocation by the neighbouring OH group, thus, supporting the previously proposed mechanism of the transformation 1 → 5. For structure proof, the tricyclic alcohol 14 and the pheny1 carbamate 42 , derived from 9 , were subjected to X-ray analysis. 相似文献
4.
Irradiation of a pentane solution of (E)-dehydro-β-ionone-epoxide ( 1 ) with light from a medium pressure mercury lamp using acetone as filter led to formation of the isomers 2 , 3, 4 and 5 by novel photochemical processes. 相似文献
5.
(E)-5-Demethyl-4-oxo-β-ionone ( 2 ), (E)-4-oxo-β-ionone ( 3 ), (E)-4-oxo-β-irone ( 4 ), and the five-membered ring analogs 36 – 41 were synthesized by a novel, convergent route starting from 2-methylfuran ( 1 ). A recently discovered, intramolecular reaction of 2-(diazoacyl)furans, catalyzed by dirhodium tetraacetate, leading to dienediones served as key step, thereby testing its utility in natural-product synthesis for the first time. 相似文献
6.
The syntheses, photolyses, and thermolyses of the α,β-unsaturated silyl ketones (E/Z)-7, (E)- 8 , and (E)- 9 are described. On n,π*-excitation (λ > 347 mm), the aforementioned compounds undergo (E/Z)-isomerization followed by γ-H abstraction. The intermediate enols are trapped intermolecularly by siloxycarbenes leading to the dimeric acetals 27A + B, 30A + B , and 31A + B . In addition, the acylsilanes (E/Z)- 7 undergo photoisomerization by δ-H abstraction furnishing the acylsilanes 29A + B . Flash vacuum thermolyses (FVT) of (E/Z)- 7 , (E/Z)- 8 , and (E)- 9 give rise to intramolecular reactions of the siloxycarbene intermediates. Thus, FVT (520°) of (E)- and (Z)- 7 selectively leads to the enol silyl ethers 32 and (E)- 33 , respectively, arising from carbene insertion into an allylic C–-H bond. FVT of (E/Z)- 8 (560°) and (E)- 9 (600°) affords the trienol silyl ethers 34A + B and the cyclic silyl ethers 37A + B , respectively, which are formed by CH insertion of the siloxycarbenes. As further products of (E)- 8 and (E)- 9 , the bicyclic enol ethers 35 and 36 are formed, presumably via siloxycarbene addition to the cyclohexene C?C bond. 相似文献
7.
8.
9.
On π,π*-excitation of the epoxyenone (E)- 1 (λ = 254 nm, MeCN), in addition to the previously isolated compounds 2 – 9 , the new products 10 – 12 , derived from the ylide intermediate c were isolated. Further evidence for the ylide c was obtained by the rapid racemization of the optically active epoxyenone (?)-(E)- 1 . 相似文献
10.
Daniel Grenier Robert E. Prud'Homme Alain Leborgne Nicolas Spassky 《Journal of polymer science. Part A, Polymer chemistry》1981,19(7):1781-1793
S(?) and R(+) enantiomers of α-methyl-α-ethyl-β-propiolactone (MEEPL) were prepared in an eight-step synthesis with respective optical purities of 99 and 97% determined by 1H-NMR (250 MHz) spectroscopy. Polymers (PMEPL) of different enatiomeric compositions were prepared with an anionic-type initiator. Substantial differences in physical properties were observed between the racemic and optically pure polymers; for example, the melting point of the latter is 42°C higher than that of the former. Chiroptical properties of PMEPLs are reported. The 13C-NMR (100.62 MHz) spectra of the polymers indicated that the distribution of configurational units in the macromolecular chain is random. 相似文献
11.
Antoni Siewnski Barbara Henggeler Hans Richard Wolf Bruno Frei Oskar Jeger 《Helvetica chimica acta》1984,67(1):120-128
1n, π*-Excitation of the γ,δ-epoxy-enone (E)- 3 leads exclusively to the conformers (Z)- 3A + B . On 1π, π*-excitation of (E)- 3 , in addition to (Z)- 3A + B , products 6–9 arising from a carbene intermediate e are formed. However, products of an isomerization via C(γ), O-bond cleavage of the oxirane were not formed on either mode of excitation. On thermolysis, at 80° the conformer (Z)- 3A is transformed into (Z)- 3B , which on photolysis returns to (Z)- 3A and (E) -3 . At 160°, however, (Z) -3B rearranges to the isomers 6, 10 and 11 . 相似文献
12.
13.
14.
(Z)-1,3-Dibromo-2-methoxypropene is prepared in 90% yield by dehydrohalogenation of 1,2,3-tribromo-2-methoxypropane with diisopropylamine in dichloromethane. The E-isomer can be obtained as the only product in almost quantitative yield by UV irradiation of the Z-isomer. Nucleophilic displacement reactions of the allylic bromide and palladium-catalyzed coupling reactions of the vinylic bromide in (E)- and (Z)-1,3-dibromo-2-methoxypropene have been studied. 相似文献
15.
16.
17.
18.
D. Carbone S. Fisichella S. Occhipinti G. Scarlata 《Journal of heterocyclic chemistry》1982,19(6):1505-1509
The mass spectra of some (Z)α-(4-R′-phenyl)-β-(2-thienyl-5-R)acrylonitriles (R = H, CH3, Br; R′ = H, CH3O, CH3, Cl, NO2) at 70 eV are reported. Mass spectra exhibit pronounced molecular ions. The compound's where R = H, and CH3 are characterized by the occurrence of a strong [M - H]+ peak. Moreover, in all the compounds a m/z 177 peak occurs. In the compounds where R = H, [M - HS]* and [M - CHS]* ions are present except the nitroderivatives. Where R = CH3, [M - HS]+ ion occurs. 相似文献
19.
Stereospecific syntheses of (E)- and (Z)-α-bisabolenes have made revision of the configuration of natural (+)-α-bisabolene from Opoponax oil necessary. 13C-NMR. spectroscopy has been used for the differentiation of these isomers. 相似文献