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51.
Helmut Sprdizer Andrea Pichler Wolfgang Holzer Irene Toth Bettina Zuchart 《Helvetica chimica acta》1997,80(1):139-145
Khusimone (1), one of the main odor-donating compounds of vetiver oil is subject of the following study on structure/odor relationship. The omittance of the ethano bridge of the tricyclic khusimone leads to a bicyclic system. The stereoselective approach to this degraded structure is described, and the olfactory properties are studied. The key step of the synthesis of the hydrindane nucleus is based on a highly diastereoselective conjugate addition to a chiral oxo-cyclopentene-2-carboxylate. 相似文献
52.
Hetero- or homocoupling of protected 1,4-cis-diethynylated 1,5-anhydroglucitols leads to two isomeric cyclotrimers and to four isomeric cyclotetramers. The C3-symmetric cyciotrimer 31 , the C4-symmetric cyclotetramer 35 , and the D2-symmetric cyclotetramer 6 have been prepared before. We have now synthesized the C1-symmetric cyciotrimer 13 , and the C1- and the C2-symmetric cyclotetramers 22 and 27 , respectively. The cyclotrimer 13 was prepared by intramolecular, oxidative homocoupling and, alternatively, by a one-pot trimerization/cyclization of the monomer 36 (Schemes 1 and 5, resp.). Oxidative homocoupling was used for the cyclization of the tetramers 19 and 25 , leading to 22 and 27. The tetramer 19 was made by sequential Cadiot-Chod-kiewicz coupling (Scheme 2)and the tetramer 25 by a combination of a Cadiot-Chodkiewicz reaction and an intermolecular, oxidalive homocoupling (Scheme 3). The acetates 34 and 38 , corresponding to 35 and 27 , respectively, were also made by a one-pot dimerization/cyclization of the dimer 37 (Scheme 5). Intramolecular oxidative heterocoupling is also feasible and results in an alternative, more convenient synthesis of the acetylated cyclotrimer 30 and the acetylated cyclotetramer 34 (corresponding to 31 and 35 , resp.; Scheme 4). The solid-state conformation of the C4-symmetric cyclotetramer 34 corresponds well to the one predicted by force-field calculations. We compared the water-solubilities of the cyclotrimers 13 and 31 and the tetramers 6, 22, 27 , and 35 , their calculated conformations (MM3*), and the D -adenosine binding properties of the cyclotetramers 6, 27 , and 35 . 相似文献
53.
New spirocyclic heterocycles 8, 16, 19/20, 25, 27 , and 30 derived from pyrimido[4,5‐b][1,4]diazepin]‐8′(9′H)‐one were synthesised by a tandem nitroso‐ene/Diels–Alder reaction of 4‐(alkenoylamino)‐5‐nitrosopyrimides. The crystal structure of 16 was established by X‐ray analysis. It is characterised by four pairs of intermolecular H‐bonds linking every two molecules in the unit cell. Sequential imine reduction and intramolecular condensation of the C(4′)‐(acylamino)‐pyrimido[4,5‐b][1,4]diazepines 27 and 30 led to the [1,4]diazepino[1,2,3‐gh]purines 28 / 29 and 31 , respectively. 相似文献
54.
55.
DFT computational study of the mechanism of allyl halides carbonylation catalyzed by nickel tetracarbonyl 总被引:1,自引:0,他引:1
Bottoni A Miscione GP Novoa JJ Prat-Resina X 《Journal of the American Chemical Society》2003,125(34):10412-10419
A theoretical investigation at the DFT(B3LYP) level on the carbonylation reaction of allyl bromide catalyzed by nickel tetra-carbonyl Ni(CO)(4) is discussed. The computational results show the following: (i) Three main steps characterize the catalytic cycle: (a) an oxidative addition step, (b) a carbonylation step, and (c) a reductive elimination step where the acyl product is obtained and the catalyst is regenerated. (ii) Both Ni(CO)(3) and Ni(CO)(4) complexes can behave as "active" catalytic species. (iii) The oxidative addition leads to the formation of either eta(3) or eta(1)-allyl nickel complexes, which are involved in a fast equilibrium. (iv) The carbonylation occurs much more easily on the eta(1) than on the eta(3) intermediates. 相似文献
56.
57.
Andrea Szép András Szabó Nikoletta Tóth Péter Anna György Marosi 《Polymer Degradation and Stability》2006,91(3):593-599
The effects of non-treated (MMT), organophilic (OMM), and olefin/silicone polymer intercalated (IMM) montmorillonites on the thermal stability of ethylene-vinyl acetate copolymer (EVA) and on the flammability of magnesium hydroxide filled EVA were studied. The influence of various treatments on the delamination of montmorillonites in EVA was detected by rheological measurements and by Raman microscopy. The latter was a unique method for rapid detection of the dispersion also in highly filled EVA. Enhancement of thermo-oxidative stability of EVA and flame-retarded EVA could be observed by thermal analysis in the presence of variously treated montmorillonites. The flame-retardant efficiency of magnesium hydroxide was improved by simultaneous application of MMT and IMM. The increased performance of magnesium hydroxide was explained by the rheological effect of the IMM, catalytic effect of MMT and chemical interactions of montmorillonites with the metal hydroxide. 相似文献
58.
For ν≥0 let cνk be the k-th positive zero of the cylinder functionC v(t)=J v(t)cosα-Y v(t)sinα, 0≤α>π whereJ ν(t) andY ν(t) denote the Bessel functions of the first and the second kind, respectively. We prove thatC v,k 1+H(x) is convex as a function of ν, ifc νk≥x>0 and ν≥0, whereH(x) is specified in Theorem 1.1. 相似文献
59.
Andrea Ricci 《Tetrahedron》2004,60(1):115-120
The photochemistry of five 11-hydroxy-1,5-cyclopregn-3-en-2-ones (‘lumi’ products from the corresponding pregna-1,4-dien-3-ones) has been investigated. In all cases the photoproducts were 1,11-oxy derivatives, resulting from intramolecular attack of the hydroxyl group to the incipient positive charge at C-1. When a fluorine atom was present at C-6, HF elimination took place concurrently with the nucleophilic addition and led to linearly conjugated dienones, rather than the enones obtained in the other cases. Quantum yields were in the range 0.06-0.2, the lower values applying when a fluorine atom was present in position 6 (not in position 9). The results add new evidence on the role of zwitterionic intermediates in the photochemistry of cross-conjugated dienones and the corresponding lumi photoproducts. 相似文献
60.
An unprecedented combination of photochromism and electrochromism is observed for two 1,2-bis(dithienyl)cyclopentene derivatives; the ring-opening reactions are photochemically driven while the ring-closing reactions can be triggered by electrochemical oxidation. 相似文献