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991.
Chrétien A Chataigner I L'Hélias N Piettre SR 《The Journal of organic chemistry》2003,68(21):7990-8002
The reaction between indole-3-carboxaldehyde 1a or indole-3-glyoxalate 1b and 2,3-dimethylbutadiene under thermal activation leads exclusively to the Diels-Alder cycloadducts resulting from the participation of the indole 2,3-carbon-carbon double bond. The concomitant use of zinc chloride and high pressure (16 kbar) induces the primary cycloadduct to react further, and biscycloadducts 11 and 12 are now isolated in high yields, the result of two consecutive [4 + 2] processes on, first, the indole 2,3 C=C bond and, second, the 3-carbonyl unit. The possibility of using two different dienes in a tandem, sequential process is demonstrated by the preparation of tetracycle 13. Interactions between the carbonyl dienophile and Danishefsky diene yield exclusively yet another type of product, namely the gamma-dihydropyranones arising from the sequential [4 + 2] heterocycloaddition, hydrolysis of the silyl enol ether, and loss of methanol. Isolation of the Mukaiyama-type adduct 16 indicates that a stepwise mechanism may be involved, at least under zinc chloride catalysis. N,N-Disubstituted indole-3-glyoxamides undergo the expected, usual Diels-Alder process, with the 2,3 C=C bond acting as dienophile, and cycloadducts of the type 3 are obtained in high yields, regardless of the mode of activation. Remarkably, however, N-monosubstituted indole-3-glyoxamides react almost exclusively as heterodienophiles, the 3-carbonyl unit being now the preferred site of reactivity, and gamma-dihydropyranones of the type 6 are isolated in yields ranging from 72 to 92%. Conformational analysis of the Diels-Alder adducts based on both (1)H NMR spectrometry and X-ray diffraction data indicates that the newly created cyclohexene and cyclohexanone rings adopt a pseudoboat conformation. 相似文献
992.
Youssef Bakkour Gaston Vermeersch Michel Morcellet FranÇois Boschin Bernard Martel Nathalie Azaroual 《Journal of inclusion phenomena and macrocyclic chemistry》2006,54(1-2):109-114
The solubility of cyclodextrin (CD) can be notably improved when it is included in a polymeric structure. CD was reacted with
citric acid, yielding a water-soluble polymer whose inclusion properties towards doxycyclin-hyclate (DOX) as guest molecule
were investigated by NMR. The new DOSY (Diffusion Ordered SpectroscopY) method, based on diffusion coefficient measurements
is convenient study complexes made of large molecules and it was applied to determine the association constants between DOX
and parent β and γ-CD and their polymerised forms. The association constant obtained by DOSY was compared with that determined
more classically by the chemical shift variation measurement using Scott's plot. 相似文献
993.
Rainaldi M Lancelot N Elbayed K Raya J Piotto M Briand JP Kaptein B Broxterman QB Berkessel A Formaggio F Toniolo C Bianco A 《Organic & biomolecular chemistry》2003,1(11):1835-1837
A series of [L-(alphaMe)Leu]n (n = 1-5) homo-peptides have been covalently linked to Tentagel and POEPOP resins and submitted to a conformational study using HRMAS NMR spectroscopy. Whereas the mono- and dipeptide are mainly fully-extended, stable 3(10)-helical structures are formed beginning from the trimer. 相似文献
994.
Guennoun Z Piétri N Couturier-Tamburelli I Aycard JP 《The journal of physical chemistry. A》2005,109(37):8299-8305
Photoreactivity of cyanoacetylene with water was successively studied in cryogenic matrixes and in the solid phase at lambda > 120 nm. These studies were performed using FTIR spectroscopy, isotopic experiments and DFT calculations at the B3LYP/6-31G level of theory. The photolysis of cyanoacetylene complexed with water in an argon cryogenic matrix led to the formation of two products. The first one corresponds to the cyanoketene and the second to the HCN:C2O complex. Trapped in water ice and submitted to UV photolysis, the cyanoacetylene molecule shows great photoreactivity. Indeed, besides the cyanoketene and cyanhydric acid, we characterized and identified the formation of other compounds issued from the addition of water to the CC triple bond of cyanoacetylene. 相似文献
995.
Fettouhi M El-Ali B El-Ghanam AM Golhen S Ouahab L Daro N Sutter JP 《Inorganic chemistry》2002,41(14):3705-3712
Four new mononuclear complexes of formula Cd(PN)(4)(NCS)(2) (A), Cd(PNN)(4)(N(3))(2) (B), Zn(PNN)(4)(N(3))(2) (C), and Zn(PNN)(2)(NCS)(2) (D), where PNN stands for 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and PN for 2-(4-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl, were synthesized and structurally and magnetically characterized. The X-ray structures of compounds B and C were also determined at 90 K. Compounds A[bond]C crystallize in the triclinic space group P 1 macro (No. 2), and D crystallizes in the monoclinic space group P2(1)/m (No. 11). A[bond]C adopt a centrosymmetric distorted octahedral geometry in which the metal ions are bonded to four radical ligands through the nitrogen atom of the pyridyl rings and the azido or thiocyanato ligands occupy the apical positions. Compound D adopts a distorted tetrahedral geometry in which the zinc ion is bonded to two radicals and two thiocyanato ligands. As suggested by their magnetic behavior, the low-temperature X-ray structures of B and C show that these compounds undergo a clear structural change with respect to the room-temperature structures. The experimental magnetic behaviors were perfectly reproduced by a dimer model for A[bond]C and an alternating chain model for D while the sudden breaks observed in the chi(M)T versus T curves for B and C were well accounted for by the high- and low-temperature X-ray structures. For all these complexes the crystal structures favor significant overlap between molecular magnetic orbitals leading to rather strong intermolecular antiferromagnetic interactions. 相似文献
996.
Trabolsi A Elhabiri M Urbani M Delgado de la Cruz JL Ajamaa F Solladié N Albrecht-Gary AM Nierengarten JF 《Chemical communications (Cambridge, England)》2005,(46):5736-5738
Owing to the complementarity between a bis-Zn(II)-porphyrin receptor and a fullerene ligand bearing two pyridine substituents, the substrate can be clicked onto the ditopic receptor, thus leading to a stable non-covalent macrocyclic 1 ratio 1 complex. 相似文献
997.
Florence Babonneau Laurence Yeung Nathalie Steunou Christel Gervais Ainhoa Ramila Maria Vallet-Regi 《Journal of Sol-Gel Science and Technology》2004,31(1-3):219-223
Ibuprofen molecules have been encapsulated in mesoporous MCM-41 type-silica functionalised or not by amino groups. They have been characterised by 13C and 1H solid state NMR spectroscopy. The 13C MAS single pulse or cross polarization NMR spectra, as well as the 1H MAS NMR spectra demonstrate an extremely high mobility of the ibuprofen molecules when the matrix is not functionalised. On the contrary, when the silica matrix is functionalized by amino groups, the 13C NMR response shows less mobility suggesting the existence of interactions between the amino groups and the carboxylic groups. Benzoic acid as well as benzamide have also been encapsulated and their NMR responses compared to that of ibuprofen. 相似文献
998.
999.
Mohamed Saadioui Nathalie Reynier Jean-François Dozol Zouhair Asfari Jacques Vicens 《Journal of inclusion phenomena and macrocyclic chemistry》1997,29(2):153-165
We report the synthesis and complexation properties towards alkalications of a photosensitive azo-modified calix[4]crown 5 in the1,3-alternate conformation. Selectivity of the cis-isomer towards Cs+ andRb+ was observed. 相似文献
1000.
Van Hoof N De Wasch K Poelmans S Noppe H De Brabander H 《Rapid communications in mass spectrometry : RCM》2004,18(23):2823-2829
A multi-residue liquid chromatography/tandem mass spectrometry method (LC/MS2) was developed for the detection of the non-steroidal anti-inflammatory drugs acetylsalicylic acid (via the marker residue salicylic acid), flunixin, phenylbutazone, tolfenamic acid, meloxicam and ketoprofen, in bovine muscle. After extraction of the bovine muscle with acetonitrile, the cleanup was performed using a Oasis HLB column. The evaporated eluate was reconstituted and analysed by LC/MS2. To obtain optimal detection of salicylic acid and phenylbutazone, the ion trap mass spectrometric parameters activation q and maximum ion injection time, respectively, were optimised. The activation q for salicylic acid was increased to obtain reliable detection of both salicylic acid and its product ion. The maximum ion injection time for the time segment containing phenylbutazone was decreased since there were not enough scans across the chromatographic peak of this compound. The multi-residue method was able to detect the different analytes below or at the maximum residue limit (MRL) or minimum required performance limit (MRPL) or, in the case of phenylbutazone and ketoprofen, at 100 and 20 microg kg(-1), respectively. 相似文献