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1.
Robert W. Hicklin Tania L. López Silva Prof. Paul J. Hergenrother 《Angewandte Chemie (International ed. in English)》2014,53(37):9880-9883
Fenestranes are an intriguing class of highly strained molecules possessing a quaternary carbon with bonds that deviate from the canonical tetrahedral geometry. Herein we report the discovery that the natural product pleuromutilin can be used as a structurally complex starting material for the synthesis of a series of bridged cis,cis,cis,cis‐[4.5.5.5]‐ and cis,cis,cis,cis‐[4.5.7.5]oxafenestranes through a carbocation rearrangement cascade. X‐ray crystallographic analysis of several cis,cis,cis,cis‐[4.5.5.5]oxafenestranes shows a significant planarization of the central tetracoordinate carbon atom and demonstrates the influence of bridgehead substituents and bridging rings on planarity. 相似文献
2.
Irradiation of benzofurazan ( 1 ) in benzene solution yields the azepine derivative 3 as the main photoproduct. Addition of methanol in the dark to the irradiated benzene solution of 1 results in the isolation of 3 together with a new product, methyl-1-cis, 3-cis-N-(4-cyano-buta-1, 3-dien-1-yl)-carbamate (1-cis, 3-cis- 2 ). Irradiation of 1 in methanol solution gives a mixture of the stereoisomeric methyl N-(4-cyano-buta-1, 3-dien-1-yl)-carbamates, from which the 1-trans, 3-cis isomer of 2 could be isolated in pure form. The observed photoproducts are formed via the reactive intermediates a , a nitrile-(nitrile oxide), and c , a nitrene, neither of which was isolated. 相似文献
3.
The principal decomposition routes of molecular ions of cis, cis, cis-2,4,6-octatriene, cis, cis, trans-2,4,6-octatriene, trans, cis, trans-2,4,6-octatriene, trans-5,6-dimethyl-1,3-cyclohexadiene and cis-5,6-dimethyl-1,3-cyclohexadiene were studied using ion kinetic spectroscopy. The loss of radicals from [M]+· appears to proceed via a ground state, while loss of a neutral molecule appears to involve either complete equilibration of structure within the system or both ground state and excited state pathways. 相似文献
4.
The oxidative addition of XRCN to PtL4 yields cis-and/or trans-PtX(RCN)L2 (X = Cl, Br; R = (CH2)n, n = 1, 2, 3; L = PPh3, PPh2CH3, AsPh3). L is readily displaced by more basic phosphines or by a diphosphine. In each case the trans complex is the thermodynamically more stable isomer and cis-trans isomerization catalyzed by free L occurs in dichloromethane. Insertion of CO in the σ Pt? C bond takes place quantitatively in the case of cyanoethyl and cyanopropyl. Abstraction of X by AgBF4 gives cis or trans cationic complexes with N-bonded CN group. 相似文献
5.
Sven Hernestam 《Journal of heterocyclic chemistry》1983,20(6):1681-1685
Treatment of 1,1′-iminobis-2-butanols with 70% w/w sulfuric acid gives cis- and trans-2,6-diethylmorpholines, 3-ethyl-4-methylpyridine and unsaturated 3-ethyl-4-methylpiperidines. Hydrogenation of the unsaturated 3-ethyl-4-methylpiperidines gives cis- and trans-3-ethyl-4-methylpiperidines. With 50% w/w sulfuric acid cis- and trans-2,6-diethylmorpholines and a small amount of cis- and trans-2-ethyl-7-methyl-hexahydro-1,4-oxazepines are obtained. 相似文献
6.
1-cis, 2-cis-Dipropenylbenzene (cis, cis- 1 ) isomerises thermally at 215–235° with 1st order kinetics to give trans, cis- 1 and vice versa. At equilibrium 89% trans, cis- and 11% cis, cis- 1 are present. It is shown by thermal rearrangement of cis, cis-2′, 2″-d2- 1 that the isomerisation is attributable to aromatic [1, 7a]-sigmatropic H-shifts. trans, trans- 1 rearranges thermally at 225–245° to yield 2, 3-dimethyl-1, 2-dihydronaphthalene ( 2 ). The formation of 2 can be visualized by disrotatory ring closure followed by an aromatic [1, 5s]-sigmatropic H-shift. 2 is also formed when, cis, cis- or trans, cis- 1 are heated for 153 h at 225°. Besides 2 a small amount (3%) of 1-ethyl-1, 2-dihydronaphthalene ( 5 ) is formed. The rearrangement of trans, trans- 1 and trans, trans-2′, 2″-d2- 1 shows a secondary isotope effect kH/kD = 0,90. 相似文献
7.
Daniel Townsend Prof. Dr. Kenneth Shankland Dr. Alex Weymouth-Wilson Dr. Zofia Komsta Dr. Tim Evans Dr. Alexander J. A. Cobb 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(16):3504-3508
A highly enantioselective, organocatalytic, and scalable synthesis of a very unusual cis-decalin-cis-hydrindane tricyclic diterpenoid system has been achieved. Despite the prevalent pharmacological space that the related trans,trans and trans,cis-systems occupy, there have been no reports of an asymmetric synthesis of the cis,cis systems in the literature until now. We demonstrate the flexibility of our approach not only through access to a diverse range of products, all of which are attained in exceptionally high selectivities, but also by showing their easy conversion to the corresponding trans,cis-system and other derivatives. 相似文献
8.
Planarisation of Tetracoordinate Carbon Atom, Synthesis of the Brigded all-cis-[5.5.5.5]Fenestrane 13-Oxapentacyclo[5.5.2.11,7.04,15.010,15]pentadecan-14-one The synthesis of the ketolactone 23 from (Z,Z)-1,5-cyclooctadiene is reported. Transannular carben insertion, achieved via photolysis of the deprotonated (2,4,6-trisisopropylphenylsulfonyl)hydrazone of 23 gives the bridged all-cis-[5.5.5.5]fenestrane 3 . 相似文献
9.
Akiko Asano Mitsunobu Doi Kenji Yoza 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(6):o323-o325
Ceratospongamide (CS) is a potent inhibitor of secreted phospholipase A2, and cis,cis and trans,trans isomers, related with respect to the two proline amide bonds, are known. Crystals of cis,cis‐CS were grown from N,N‐dimethylacetamide solution, giving the title compound, the cyclic ester of isoleucyloxazolinylphenylalanylprolylthiazolylphenylalanylproline [cyclo(‐Ile–Oxz–Phe–Pro–Thz–Phe–Pro‐)] N,N‐dimethylacetamide hemisolvate, C41H49N7O6S·0.5C4H9NO. The structure is the third example of cis,cis‐CS to be investigated and comprises twinned crystals, in which the a and b axes are interchanged. The ratio of co‐existing twin crystals is approximately 50%. The peptide has a `saddle‐like' structure and is very similar to previously reported structures of cis,cis‐CS, which implies that the structure of cis,cis‐CS is very stable in spite of differences in crystallization conditions. 相似文献
10.
Reaction of 9-methyl-cis-decalin-1,8-dione ( 2 ) and of its trans-isomer ( 3 ) with (2R,3 R)-2,3-butanediol ( 8 ) gives in both cases the monoacetals in high yield. While no enantiotopic differentiation is found for 3 , a strong preference for the (9S,10 R)-monoacetal 9 is found for the cis-decalin-dione 2. The differentiation, reaching a maximal ratio of 9:1, is found to increase by conditions, which slow down the rate of reaction, e. g. lowering the temperature, the concentration of the acid catalyst, or by using a sterically encumbered catalyst. The use of this procedure for the preparation of optically active compounds is exemplified by the transformation of monoacetal 9 (obtained in 76% yield from 2 ) into (9 R, 10 R)-9-methyl-1-decalone ( 12 ). The differing behaviour of diketones 2 and 3 is discussed in terms of steric and electronic effects. 相似文献
11.
The photochemical isomerization of trans and cis-difluorostilbenes has been studied. In the presence of a photosensitizer (biacetyl, 0.05 mol·?1) about 75% of the trans form can be converted into the crystalline cis form. The reactions of difluorocarbene (CF2) from the Seyferth reagent (PhHgCF3) with cis- and trans-stilbene obey the Skell rule, i. e., stereospecific cycloaddition. However, although the reaction of CF2 with trans-1,2-difluorostilbene yields trans-1,2-diphenyl-perfluorocyclopropane (9) as the only isolable product, the reaction of CF2 with cis-difluorostilbene also gives the same trans-cycloadduct as the only isolable product. A possible mechanistic path involving the homolytic cleavage of the highly activated cyclopropane C—C bond facing the CF2 group is discussed. 相似文献
12.
S. D. Simova N. V. Bozhkova A. S. Orahovats 《Magnetic resonance in chemistry : MRC》1984,22(7):431-433
The 1H and 13C NMR spectra of the trans,trans-, cis,cis- and cis-C-3–C-4, trans-C-7–C-8-germacrones and of the cis-C-2–C-3, trans-C-7–C–8, trans-C-2–C-3, cis-C-7–C-8- and cis,cis-isogermacrones are analysed. The last two isogermacrones are new compounds. The C-2–C-3 double bond in the previously described isogermacrone is found to be of cis configuration, contrary to the hitherto accepted trans arrangement. 相似文献
13.
Peter Uebelhart Andreas Baumeler Andreas Haag Roland Prewo Jost Hans Bieri Conrad Hans Eugster 《Helvetica chimica acta》1986,69(4):816-834
Optically Active 4,5-Epoxy-4,5-dihydro-α-ionones; Synthesis of the Stereoisomeric 4,5:4′,5′-Diepoxy-4,5,4′,5′-tetrahydro-?,?-carotenes and the Steric Course of their Hydrolysis We prove that epoxidation with peracid of α-ionone, contrary to a recently published statement, predominantly leads to the cis-epoxide. Acid hydrolysis affords a single 4,5-glycol whose structure, established by an X-ray analysis, shows that oxirane opening occurred with inversion at the least substituted position (C(4)). Stable cis-and trans-epoxides are prepared by epoxidation of the C15-phosphonates derived from α-ionone. Both the racemic and optically active form are used for the synthesis of the 4,5:4′,5′-diepoxy-4,5,4′,5′-tetrahydro-?,?-carotenes having the following configuration in the end groups: meso-cis/cis, meso-trans/trans, rac-cis/trans, rac- and (6R, 6′ R)-cis/cis, rac- and (6R, 6′R)-trans/trans, rac- and (6R, 6′R)-cis/trans, and (6R, 6′ R)-cis/?. Acid hydrolysis of the cis/cis-epoxycarotenoids under relatively strong conditions occurs again with inversion at C(4)/C(4′) in case of the cis/cis-epoxycarotenoids, but at C(5)/C(5′) in case of the trans/trans-epoxycarotenoids. An independent synthesis of this 4,5,4′,5′-tetrahydro-?,?-carotene-4,5,4′,5′-tetrol is presented. The irregular results of the oxirane hydrolysis are explained by assumption of neighbouring effects of the lateral chain. 400-Mz-1H-NMR data are given for each of the stereoisomeric sets. In the visible range of the CD spectra, the (6R, 6R′)-epoxycarotenoids compared with (6R, 6R′)-?,?-carotene exhibit an inversion of the Cotton effects. 相似文献
14.
The photoisomerization of retinal 总被引:1,自引:0,他引:1
Abstract— –Quantum efficiencies have been measured for the photoisomerization of four stereoisomers of retinal (all-trans, 13-cis, 11 cis, and 9-cis) in two solvents at different wavelengths of irradiation and at various temperatures. In heane at 25°C the quantum efficiencies for isomerization at 365 nm are: 9-cis to trans, 0.5; 13-cis to trans, 0.4; 11-cis to trans, 0.2; all-trans to monocis isomers, 0.2-0.06, depending upon assumptions made regarding the stereo-isomeric composition of the product. These values vary somewhat with the wavelength of the irradiating light. The quantum efficiency for the photoisomerization of all-trans retinal in hexane decreases by a factor of 30 when the temperature is lowered from 25° to – 65°C; the activation energy for this photoisomerization is about 5 kcal/mole. The quantum efficiencies for the isomerization of the monocis isomers to all-trans retinal in hexane are virtually independent of temperature. In ethanol the rates of photoisomerization from trans to cis or cis to trans depend only slightly on the temperature between 25° and – 65°C. The photosensitivities of the stereoisomers of retinal are of the same order of magnitude as those of the retinylidene chromophores of rhodopsin (11 -cis), metarhodopsin I (all-trans), and isorhodopsin (9-cis); but it is not yet possible to derive the photochemistry of rhodopsin uniquely and quantitatively from that of retinal. 相似文献
15.
《Journal of Coordination Chemistry》2012,65(7):1208-1218
Three cis-Ru(dppm)2XY complexes (XY?=?C2O4, 1; X?=?Cl, Y?=?N3, 2; X?=?Y?=?N3, 3) were prepared by reactions of cis-Ru(dppm)2Cl2 with (NH4)2C2O4, a mixture of NaN3 and NaPF6, and only NaN3, respectively, while 3 could also be obtained from further reaction of 2 with NaN3 undergoing a facile chloride abstraction. All complexes have been characterized by IR, NMR, UV–vis, and luminescence spectroscopic analyses as well as X-ray diffraction studies. Of these structures, 1 shows oxalate coordinates to Ru as a chelating ligand, while 2 displays Ru and azide linear, and 3 gives two azide groups cis to each other, which are different from two substituting ligands commonly lying in trans positions in Ru(P–P)2 complexes by using cis-Ru(dppm)2Cl2 as a precursor. 相似文献
16.
Frank A. L. Anet N. Roy Easton Issa Yavari 《Magnetic resonance in chemistry : MRC》1979,12(5):299-301
The natural-abundance 13C NMR spectra of cis,cis-1,5-cyclooctadiene monoepoxide and cis,syn,cis-1,5-cyclooctadiene diepoxide have been investigated over the temperature range of – 10 to – 180°C. Whereas the spectra of the former showed no dynamic NMR effect, two different conformations in the ratio of 3:1 were observed at low temperatures for the latter. The free-energy barrier (ΔG≠) for conversion of the major conformation to the minor conformation is calculated to be 5.9°0.2 kcal mol?1 from a line-shape analysis of spectra obtained at intermediate temperatures. It is shown that cis,syn,cis-1,5-cyclooctadiene diepoxide exists in solution in chair (major) and in twist-boat (minor) conformations of slightly different energies. Interconversion paths between these conformations are discussed. The monoepoxide is suggested to have a twist-boat conformation that is rapidly pseudorotating via a boat conformation even at – 180°C. 相似文献
17.
The circular dichroism (CD.) spectra of all-trans-(3S, 3′S) astaxanthin diacetate and its 9-cis, 13-cis, 9,9′-di-cis, 9,13′-di-cis, and 9,13-di-cis isomers conform to the rules previously formulated for optically active carotenoids with a 4-oxo-β-end ring containing an asymmetric C-atom [1]. Thus the CD. bands of the all-trans and the di-cis isomers show the same signs whereas those of the mono-cis isomers have opposite signs. The CD. spectra of all the astaxanthin diacetate isomers invert sign upon cooling to ?180°. The CD. spectra of the 9-mono-cis and 9,9′-di-cis isomers and to a lesser extent also those of the 9, 13′-di-cis and 9, 13-di-cis isomers are concentration dependent at ?180°, with the longest wavelength band giving at the higher concentration a bisignate CD. curve under the main absorption characteristic of aggregation. This phenomenon has been observed only in isomers with a 9-cis linkage. It is suggested that steric hindrance prevents such aggregation taking place in the other isomers. 相似文献
18.
Alkylation of bicyclo[3.3.0]octane-2,8-dione ( 1 ), which is prepared by a modification of the procedure described in the literature, gives the methyl- and propynyl-derivatives 6 and 7 (Scheme 1). In addition to the method described previously (Scheme 2), 9-methyl-cis-decalin-1,8-dione 9 is obtainable stereoselectively either by cyclization of keto-acid 16 , or by aldol cyclization of keto-aldehyde 26 and oxydation of the resulting alcohols 24 and 25 (Scheme 4). The β-keto-alcohols 24 and 25 undergo a base-catalyzed isomerization; the trans-decalin isomers 27 and 28 are not detected in this equilibrium mixture (Schemes 4 and 5)l. Monoreduction of cis-dione 9 gives the endo-alcohol 25 , while 27 is the favored product of the reductin of trans-dione 10 (Scheme 4). Optically pure (+)- 25 can be prepared from (9S,10R)-monoacetal 29 (Scheme 5). 相似文献
19.
Akira Uchida Masatoshi Hasegawa Hiroshi Manami 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(8):o435-o438
cis,cis,cis‐1,2,4,5‐Cyclohexanetetracarboxylic acid, C10H12O8, (I), contains a mirror plane and the cyclohexane ring exhibits a chair conformation. Two crystallographically independent hydrogen bonds form (14), (16) and (16) ring motifs, and propagation of these two hydrogen bonds along the c and b axes generates (16) and (7) chains. cis,cis,cis‐1,2:4,5‐Cyclohexanetetracarboxylic dianhydride, C10H8O6, (II), was prepared by the reaction of (I) with acetic anhydride. The cyclohexane ring of (II) exhibits a boat conformation and the dihedral angle between the two anhydro rings is 117.5 (1)°. 相似文献
20.
The isomerization of cis-Pt(PPh3)2(I)(CH2P(O)(OCH3)2), 1 , was studied by an NMR technique. An Arrhenius plot for the isomerization gives an activation energy of 99.2 KJ/mol, ΔH≠ = 97 KJ/mol and ΔS≠ = ?8.3 J/mol-K. Under a CO atmosphere the cis isomer catalytically isomerized to its trans form. Free PPh3 did not catalyze the cis-trans isomerization. In the proposed isomerization mechanism the reaction goes through an intramolecular assisted phosphine dissociation, followed by dimer formation. The addition of phosphine to the dimer then completes the isomerization of the original monomer from cis to trans. 相似文献