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991.
Caterina Arnone Giovanni Gottarelli Gian Piero Spada Domenico Spinelli
Otto Exner
《Journal of Molecular Structure》1986,147(3-4):307-314The conformation of chiral 2,2′-dinitro-3,3′-bithienyl-4,4′-dicarboxylic acid (Ia), its dimethylester (Ib), and analogous selenium derivatives Ic and Id was investigated by means of induced cholesteric mesophases. A parallel investigation on the diester (Ib) and on other model 3,3′-bithienyls was carried out with dipole moment measurements. The conclusions reached with the two independent methods for derivative Ib are in excellent agreement and indicate, if a single conformation is assumed, a preferred cisoid conformation with a dihedral angle somewhat smaller than 90°. Alternatively, if the existence of both cisoid and transoid conformations having supplementary dihedral angles is assumed, the data indicate a higher population for the cisoid form. 相似文献
992.
Giovanni Meazza Giampaolo Zanardi Paolo Piccardi 《Journal of heterocyclic chemistry》1993,30(2):365-371
Trifluoromethyl-substituted pyrazoles were synthesized via 1,3-dipolar cycloaddition from sydnones 2a-j and 1-aryl-3,3,3-trifluoro-propynes 5a-f. The regioselectivity of the reaction and the spectroscopic characteristics of the products are discussed. 相似文献
993.
Rassu G Auzzas L Pinna L Zambrano V Zanardi F Battistini L Gaetani E Curti C Casiraghi G 《The Journal of organic chemistry》2003,68(15):5881-5885
The feasibility of sequential vinylogous aldol (intermolecular)/silylative aldol (intramolecular) addition reactions involving furan- and pyrrole-based dienoxysilanes, 6 and 12, in the synthesis of carbasugar frameworks is illustrated by the preparation of the scantily investigated carbaseptanose and carbaoctanose representatives of this class of compounds. The target compounds, 1, 2, 3, ent-2, ent-3, and 4, were obtained from readily available carbohydrate precursors (5 and 19) in yields of 21-30% over 8-12 steps. The irreversible silylative ring-closing aldolisation of gamma-substituted dihydro-5H-furan-2-one and pyrrolidin-2-one aldehydes (9, 16, ent-16, and 22) driven by the TBSOTf/Pr(i)(2)EtN Lewis acid-Lewis base couple was shown to be a practical, diastereoselective maneuver to forge the densely functionalized, medium-sized core carbocycles. 相似文献
994.
M. Baubillier I. J. Bloodworth A. J. Burns J. N. Carney G. F. Cox U. Dore J. B. Kinson K. Knudson F. Lévy P. J. Negus B. Y. Oh E. Quercigh J. M. Scarr G. A. Smith O. Villalobos Baillie M. F. Votruba J. Whitmore R. Zitoun 《Zeitschrift fur Physik C Particles and Fields》1984,26(1):37-41
The production ofK * resonances has been studied in the reaction \(K^ - p \to \bar K^0 \pi ^ - p\) at 8.25 GeV/c. The data comes from a high statistics bubble chamber experiment (180 events/μb). Masses, widths and production cross-sections have been determined for the first threeK *'s. The contributions from natural and unnatural parity exchange have been obtained for theK *(890) and theK *(1420). A partial wave analysis of theK π system from threshold to 1.9 GeV provides evidence for a 0+ enhancement near 1.4 GeV which could be interpreted as the κ(1350). 相似文献
995.
Detailed analysis and group-type separation of natural fats and oils using comprehensive two-dimensional gas chromatography 总被引:1,自引:0,他引:1
Mondello L Casilli A Tranchida PQ Dugo P Dugo G 《Journal of chromatography. A》2003,1019(1-2):187-196
Comprehensive gas chromatography (GC x GC) is an adequate methodology for the separation and identification of very complex samples. It is based on the coupling of two capillary columns that each give a different but substantial contribution to the unprecedented resolving power of this technique. The 2D space chromatograms that derive from GC x GC analysis have great potential for identification. This is due to the fact that the contour plot positions, pinpointed by two retention time coordinates, give characteristic patterns for specific families of compounds that can be mathematically translated. This investigation concerned the application of this principle to fatty acid methyl esters that were grouped on an equal double bond number basis. The ester samples were derived from various lipids and all underwent bidimensional analysis on two sets of columns. Peak attribution was supported by mass spectra, linear retention indices and information reported in the literature. 相似文献
996.
Valgimigli L Brigati G Pedulli GF DiLabio GA Mastragostino M Arbizzani C Pratt DA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(20):4997-5010
Six substituted 5-pyrimidinols were synthesized, and the thermochemistry and kinetics of their reactions with free radicals were studied and compared to those of equivalently substituted phenols. To assess their potential as hydrogen-atom donors to free radicals, we measured their O-H bond dissociation enthalpies (BDEs) using the radical equilibration electron paramagnetic resonance technique. This revealed that the O-H BDEs in 5-pyrimidinols are, on average, about 2.5 kcal mol(-1) higher than those in equivalently substituted phenols. The results are in good agreement with theoretical predictions, and confirm that substituent effects on the O-H BDE of 5-pyrimidinol are essentially the same as those on the Obond;H BDE in phenol. The kinetics of the reactions of these compounds with peroxyl radicals has been studied by their inhibition of the AIBN-initiated autoxidation of styrene, and with alkyl and alkoxyl radicals by competition kinetics. Despite their larger O-H BDEs, 5-pyrimidinols appear to transfer their phenolic hydrogen-atom to peroxyl radicals as quickly as equivalently substituted phenols, while their reactivity toward alkyl radicals far exceeds that of the corresponding phenols. We suggest that this rate enhancement, which is large in the case of alkyl radical reactions, small in the case of peroxyl radical reactions, and nonexistent in the case of alkoxyl radical reactions, is due to polar effects in the transition states of these atom-transfer reactions. This hypothesis is supported by additional experimental and theoretical results. Despite this higher reactivity of 5-pyrimidinols towards radicals compared to phenols, electrochemical measurements indicate that they are more stable to one-electron oxidation than equivalently substituted phenols. For example, the 5-pyrimidinol analogues of 2,4,6-trimethylphenol and butylated hydroxytoluene (BHT) were found to have oxidation potentials approximately 400 mV higher than their phenolic counterparts, but reacted roughly one order of magnitude faster with alkyl radicals and at about the same rate with peroxyl radicals. The 5-pyrimidinol structure should, therefore, serve as a useful template for the rational design of novel air-stable radical scavengers and chain-breaking antioxidants that are more effective than phenols. 相似文献
997.
Giovanni Casini Francesco Claudi Mario Grifantini Sante Martelli 《Journal of heterocyclic chemistry》1974,11(3):377-386
The course of the hydriodic acid-catalysed and iodide-catalysed isomerization of various 2-amino-3-substituted-aziridino-1,4-naphthoquinones (I) to 1,2,3,4,5,10-hexahydrobenzo[g]-quinoxaline-5,10-diones (III) is investigated, and steric aspects of the reaction are also considered. Only in the case of the phenylaziridino derivative (Ie) does hydriodic acid afford direct cyclization to the corresponding benzoquinoxalinedione (IIIe); in all other cases the hydriodides (V) of the cleavage products (II) are obtained, and liberation of the free bases (II) results in cyclization to the corresponding benzoquinoxalinediones (III) when the aziridine ring is monosubstituted or trans disubstituted, with retention of configuration in the latter case. In contrast, the free bases (II) obtained from cis disubstituted (I) are relatively stable and cyclize with excess iodide yielding trans disubstituted (III). Correspondingly, monosubstituted and trans disubstituted I undergo iodide-catalysed isomerization to III whereas cis disubstituted I do not react. 相似文献
998.
Giovanni Minghetti Angelino Doppiu Antonio Zucca Sergio Stoccoro Maria Agostina Cinellu Mario Manassero Mirella Sansoni 《Chemistry of Heterocyclic Compounds》1999,35(8):992-1000
Reaction of Pd(OAc)2 with HL1 and HL2 (HL1=6-iso-propyl-2,2-bipyridine; HL2=6-neo-pentyl-2,2-bipyridine), followed by treatment with LiCl or KI, gives [PdCl(L1)]2, (1), [PdCl(L2)]2 (2), and [PdI(L2)]2 (3), respectively. The chloride bridge in complexes1 and2 is split by PPh3 to give the mononuclear species PdCl(L1)(PPh3) (4) and PdCl(L2)(PPh3) (5). Spectroscopic data provide evidence for coordination of the deprotonated ligands through a nitrogen and the C(3) atom of the 6-substituted pyridine. An analogous platinum complex PtCl(L3)(SMe2) (6) (HL3=6-tert-butyl-2,2-bipyridine) was obtained from trans-PtClMe(SMe2)2 and HL3. The crystal structures of compounds1 and6 have been solved by X-ray diffraction analysis.Dipartimento di Chimica, Universita di Sassari, via Vienna 2, I-07100 Sassari, Italy; Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Universita di Milano, Centro CNR, I-20133 Milano, Italy; Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1127–1137, August, 1999. 相似文献
999.
Patrizia Scafato Stefania Labano Giovanni Cunsolo Carlo Rosini 《Tetrahedron: Asymmetry》2003,14(24):3873-3877
New diastereoisomeric phosphites based on either (R)- or (S)-2,2′-dihydroxy-1,1′-binaphthyl (BINOL) and having the chiral alcoholic moiety derived from the monobenzyl ether of (R,R)-1,2-diphenylethane-1,2-diol have been prepared and used as chiral ligands in the enantioselective copper-catalyzed 1,4-addition of diethylzinc to chalcone and 2-cyclohexen-1-one (enantiomeric excesses up to 48%). With the (aR,R,R) ligand dimethylzinc adds enantioselectively to (E)-cyclopentadecen-2-en-1-one to give (R)-(−)-muscone (68% yield, 78% ee). This provides an efficient access to a valuable ingredient of the perfume industry. However, with the (aS,R,R) ligand, (S)-(+)-muscone is obtained with longer reaction times (37% yield and 10% ee) with a very high double diastereoselection effect being observed. 相似文献
1000.
Silvio Aime Eliana Gianolio Davide Corpillo Camilla Cavallotti Giovanni Palmisano Massimo Sisti GiovanniB. Giovenzana Roberto Pagliarin 《Helvetica chimica acta》2003,86(3):615-632
The three novel pyridine‐containing 12‐membered macrocyclic ligands 1 – 3 were synthesized. The coordinating arms are represented by three acetate moieties in 1 and 3 and by one acetate and two phosphonate moieties in 2 . In all three ligands, the acetate arm in the distal position is substituted, with a benzyl group in 1 and 2 and with an arylmethyl moiety in 3 . The relaxivities r1p (20 MHz, 25°) of GdIII complexes are: GD?1 , r1p=8.3 mM ?1 s?1; GD?2 , r1p8.1 mM ?1 s?1; Gd?3 , r1p10.5 mM ?1 s?1. 1H‐NMRD and 17O‐NMR T2 data show that Gd?1 and Gd?3 contain two H2O molecules in the inner sphere, whereas the presence of two phosphonate arms allows the coordination of only one H2O molecule in Gd?2 . Interestingly, the exchange lifetime of coordinated H2O in the three complexes is similar in spite of the difference in the coordination number of the GdIII ion (i.e., 9 in Gd?1 and Gd?3 , and 8 in Gd?2 ). 1H‐Relaxometric measurements at different pH and in the presence of lactate and oxalate were carried out to get some insight into the formation of ternary complexes from Gd?1 and Gd?3 . Finally, it was found that binding to human‐serum albumin (HSA) of Gd?1 and Gd?2 , though weak, yields limited relaxivity enhancements, likely as a consequence of effects on the hydration sphere caused by donor atoms on the surface of the protein. 相似文献