首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
On photolysis in methanol the diarylphosphinic azides AR2P(O)N3 (Ar = phenyl,p-tolyl,p-anisyl,p-chlorophenyl) rearragement with loss of nitrogen to form (monemeric) metaphosphonimidates which are trapped by the solvent to give methyl NP-diarylphosphonamidates (7) (41–53%). Diarylphosphinic amides (18–42%) are also usually formed, presumably from (triplet) nitrenes. The limited evidence available suggests that the rearrangements take place directly from the photo-excited azides rather than via (singlet) nitrene intermediates. One of the products of rearrangement, methyl NP-di(p-chlorophenyl)phosphonamidate, suffers extensive photochemical dechlorination giving methyl N-phenyl-P-p-chlorophenylphosphonamidate.  相似文献   

2.
Reduction of exo-2-methyl-3, 4-dichlorobicyclo[3.2.1]oct-2-ene and the exo-2-phenyl-3,4-dibromo analogue with lithium aluminium hydride proceeds mainly with allylic rearrangement. Moreover, hydride enters and bromide leaves synfacially. The stereochemistry of the process is discussed in the light of the favourable energy of a quasi-cyclic transition state in which reagent and halide are complexed.  相似文献   

3.
The allyl anisole derivatives 1 , d2- 1 , 3 , 5 and 7 (Scheme 1), on exposure to UV. light in benzene, acetone or methanol solution, cyclize to yield the corresponding cyclopropyl anisole derivatives 2 , d2- 2 , cis- and trans- 4, 6 and 8 , respectively. Under the above conditions the N, N-dialkyl-2-allyl anilines 9 , 10 and 11 give similar results (Scheme 2). On the other hand, N-alkyl-2-allyl anilines ( 15 and 19 , Scheme 3) are transformed by UV. light in cyclohexane or benzene solution into 2-methyl-indolines ( 16 and 20 , resp.), whereas in methanol solution the corresponding 2′-methoxy compounds 18 and 21 are formed in addition to 16 and 20 , respectively.  相似文献   

4.
Irradiation of 3-phenyl-( 4 ), 2-methyl-3-phenyl-( 8 ), and 2,3-diphenyl-2H-azirine ( 10 ), in benzene solution in the presence of aldehydes, yields the corresponding aryl-3-oxazolines. Photochemical reaction of 4 and 10 with carbon dioxide leads to the formation of 4-phenyl- ( 15 ) and 2,4-diphenyl-3-oxazolin-5-one ( 16 ), respectively.  相似文献   

5.
Broadband irradiation (lambda > 320 nm) of hemicarceplex H(.)1 between -74 degrees C and -84 degrees C, produces encapsulated didehydroazepine (2), triplet phenylnitrene ((3)PN), 2-azabicyclo[3.2.0]hepta-1,3,6-triene (6), and 4-azaspiro[2.4]hepta-1,4,6-triene (7). The highly strained anti-Bredt imine 6 is formed from 2 via a photochemical four-electron electrocyclization. Under the irradiation conditions, 6 rearranges further to azaspirene 7. In addition, 6 thermally rearranges to 7 via a 1,5-sigmatropic shift (DeltaG(267K) = 20.0 +/- 0.5 kcal/mol), yielding a final equilibrium composed of [7]/[6] = 5 at room temperature. The observation of a photochemical rearrangement of 2 to 6 contrasts earlier results of narrow band irradiations (lambda = 334 nm) of matrix-isolated 2, which gave (3)PN (Hayes, J. C.; Sheridan, R. S. J. Am. Chem. Soc. 1990, 112, 5879-5881). Encapsulated (3)PN is remarkably stable due to the prevention of its dimerization by the surrounding hemicarcerand. Above 255 K, it slowly decays with a rate constant k = 10(7.7+/-0.4) s(-1) x exp {(13300 +/- 500 cal/mol)/RT}. The isolation of substantial amounts of a hemicarcerand lacking one acetal spanner suggests that (3)PN decays preferentially by inserting into an inward-pointing acetal C-H bond of H.  相似文献   

6.
Adducts of [2 + 2]-cycloaddition to the 3–4 bond were isolated in the photochemical cycloaddition of vinyl butyl ether and acrylonitrile to 4-methyl-7-diethylaminocoumarin. The stereochemical structures of the compounds obtained as isomers of the head-to-tail type with an endo or exo orientation of the substituents were established by means of PMR spectroscopy. As a result of an evaluation of the effect of sensitizers and one-electron oxidizing and reducing agents it was found that the investigated reactions proceed through the singlet excited states of 7-aminocoumarins. It is assumed that the regiospecificity of the [2 + 2]-cycloaddition is determined by the C(3) reaction center of the coumarin fragment.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1169–1175, September, 1988.  相似文献   

7.
Regiospecific addition of benzeneselenenyl bromide to ethyl vinyl ether followed by alcoholysis of the initially formed β-bromoalkyl selenide 1 by primary, secondary or tertiary allylic alcohols 2a-e gave the mixed acetals 3a-e . Subsequent oxidation and thermal treatment of the corresponding selenoxides 4a-e furnished after saponification the γ, δ-unsaturated acids 7a-e in excellent overall yields. The entire sequence (Scheme 2) represents a new version of the ester Claisen rearrangement.  相似文献   

8.
A number of 3-aryl-4-methyl-7-diethylaminocoumarins were obtained as a result of the photolysis of 3-iodo-4-methyl-7-diethylaminocoumarin in the presence of benzene, chlorobenzene, fluorobenzene, benzonitrile, toluene, and diphenyl ether. On the basis of an analysis of the PMR spectra it was established that photosubstitution leads to o- and p-isomeric products. The mechanism of the reaction was studied.See [1] for Communication 7.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1172–1176, September, 1990.  相似文献   

9.
On acid-catalyzed hydrolysis, the tricyclic compounds 2 and 10 , incorporating cyclopropyl-silyl-ether moieties undergo rearrangement to the cis-decalones 3 and 7 , respectively. Hydrolysis of 2 and 10 in the presence of oxygen leads additionally to the formation of the 1,2-dioxolan-3-ols 9 and 13 , respectively, which involves an electron-transfer oxygenation process as could be demonstrated by photooxygenation of the silyl ether 10 and the cyclopropanol 14 in the presence of 9,10-dicyanoanthracene. The configurations of 3 and 9 were assigned by X-ray analysis of the latter compound as well as of the p-nitrobenzoate 8 of 3 .  相似文献   

10.
11.
12.
It is quite apparent that the use of photoinitiated electron transfer has become a powerful, if not dominating, technique in the study of biological electron transfer. It provides a means to measure directly very fast processes and, through the choice of approach (flavin semiquinones or related, metal substitution in hemes or modification with ruthenium) and experimental conditions, provides the ability to probe different features of the electron transfer mechanism. Nevertheless, much remains to be done to fully understand biological electron transfer. The use of photoinitiated electron transfer has clearly established a role for a number of factors involved in controlling the kinetics of electron transfer, including driving force, distance, intervening media, dynamics (conformational gating) and orientation of redox centers. However, we have only scratched the surface in regard to understanding in molecular terms the details of electron transfer in physiologically relevant systems. Thus, even relatively simple and well characterized systems like cytochrome c-cytochrome c peroxidase remain obscure in terms of the through-protein electron paths (intervening media) and the role of protein dynamics in controlling electron transfer kinetics. Indeed, it is the through-protein paths and conformational gating that are unique to biological systems and provide nature with the capability of modulating electron transfer kinetics to optimize biological function. Of the techniques described here, the use of flavin semiquinones is clearly the least invasive in that there is no evidence that flavin semiquinones bind to or perturb physiologically relevant systems. However, this approach is constrained in that precise distances and orientations are not always known, and the range of driving forces available is limited. In contrast, metal substitution and ruthenation allow the positions of interacting redox centers to be reasonably well defined and can provide a very large range of driving force. This latter point is particularly important since it provides a means to discriminate between rate limiting electron transfer and conformational gating. Nevertheless, chemically modifying redox proteins runs the risk of structural and electrostatic alterations which can be difficult to detect but have profound effects on the redox kinetics. Moreover, the intrinsic protein dynamics can be affected, resulting, in the worst case, in changes in conformational gating which cannot be resolved from rate limiting electron transfer. Given the early stage of development of photo-initiated electron transfer, substantial progress can be expected in the next few years. No doubt new approaches will be developed and existing approaches further refined. Especially important, the theoretical basis for interpreting and understanding electron transfer will continue to evolve.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   

13.
Photochemical reactions of triphenylcyclopropenium tetrakis(pentafluorophenyl)gallate (TPCPGa) and diphenyl-(2-methoxy-1-naphthyl)-cyclopropenium tetrakis(pentafluorophenyl)gallate (DPMNCPGa) (Chart 1) have been investigated in acetonitrile. Traces of water were required for the photochemical reactions to proceed. The disappearance of both TPCPGa and DPMNCPGa obeys zero-order kinetics with rate constants (k) having a linear dependence on the concentration of water. Electron-transfer from water to the cyclopropenium cation is proposed as the primary process in the formation of the cyclopropenyl radical. The latter dimerizes leading to the photoproducts.  相似文献   

14.
On singlet excitation (λ = 254 nm), the epoxydiene (E)- 3 underwent (E)/(Z)-isomerization, electrocyclic ring closure of the diene side chain leading to the cyclobutenes 4A + B , and rearrangement to the cyclohexanones 5A + B . Compounds 5A + B were presumably formed in a series of processes including a 1,3-acyl shift of the homoconjugated ketone 8 , arising from (Z)- 3 by a 1,5-H-shift accompanied by cleavage of the C,O-bond of the oxirane.  相似文献   

15.
Vicinal perfluorodi-t-butoxycycloalkanes and isomers have been prepared in 50 to 70% yields through photochemical reactions of (CF3)3COOC(CF3)3 with perfluorocycloolefins (c-C5F8 and c-C6F10) under a 200-watt Hg lamp at ?20°C. The two isomers of vic-C5F8[OC(CF3)3]2 in 1:4 ratio have been fractionated and identified as cis- and trans-isomers respectively. The three isomers for vic-C6F10[OC(CF3)3]2 in 1:4:2 ratio have been fractionated and tentatively identified as equatorial-equatorial, axialequatorial and axial-axial respectively.New 2,2′ -perfluorodimethoxycycloalkyls have been prepared in 60 to 80% yields through photolysis of CF3OOCF3 with perfluorocycloolefins under a 2500-watt Hg-Xe lamp at ?20°C. The attempted separations of the rotational isomers have been unsuccessful. The need of a strong ultra-violet source for primary perfluorodialkyl peroxide is discussed and the mechanism and the radical chain sequences are presented.Another new synthesis of bis(perfluoro-t-butyl) peroxide [D(CF3)3CO-OC(CF3)3 ?34.5 kcal] from (CF3)3COF using difluoroamino radicals as the fluoroxy fluorine atoms acceptor is described.  相似文献   

16.
17.
18.
Photolysis of cyanoacetylene with 185- or 206-nm light yields 1,3,5-tricyanobenzene while 254-nm radiation yields a mixture of tetracyanocyclooctatetraenes, 1,2,4- and 1,3,5-tricyanobenzene. A polymer of cyanoacetylene is the major photoproduct. 1,3,5-Tricarbomethoxybenzene was the only photoproduct identified from the irradiation of methyl propiolate at 254 nm. Mono-, di-, and tricyanobenzenes are formed by irradiation of mixtures of acetylene and cyanoacetylene at 185, 206, and 254 nm along with trace amounts of cyclooctatetraenes. No photoadducts were detected on photolysis of mixtures of cyanoacetylene and CO or HCN. The tetracyanocyclooctatetraene structures were established by UV, MS, and NMR analyses. The 1H NMR of the product mixture exhibited a singlet at delta 7.028 consistent with either 1 or 2 and two singlets at delta 6.85 and 6.91 assigned to 3. Photolysis of mixtures of dicyanoacetylene and acetylene with either 185- or 206-nm light yielded 1,2-dicyanobenzene and (E,Z)-1-buten-3-yne-1,4-dicarbonitrile. These products were also obtained using 254-nm light along with a mixture of tetracyanocyclooctatetraenes. The same three singlets were observed in this product mixture as were observed in the tetracyanocyclooctatetraenes obtained from cyanoacetylene. From this observation it was concluded that the delta 7.02 signal is due to 2 and not 1. The photolysis of cyanoacetylene and dicyanoacetylene in the presence of ethylene with 185-nm light yields 1-cyanocylobutene and 1,2-dicyanocyclobutene, respectively. 2-Cyanobutadiene and 2,3-dicyanobutadiene are the photoproducts with 254-nm light. Reaction pathways are proposed to explain these findings.  相似文献   

19.
20.
Photochemically initiated reactions of aliphatic aldehydes, namely acetaldehyde, propionaldehyde and butyraldehyde, with methyl trifluoroacrylate afforded γ-ketoesters of the type R-CO-CF2CHF-COOCH3 in the liquid phase. In the gas phase reaction further products were formed by addition of the aldehyde fragments to the olefinic bond of the methyl trifluoroacrylate.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号