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1.
Amadej Juranovi?Krištof Kranjc Franc PerdihSlovenko Polanc Marijan Ko?evar 《Tetrahedron》2011,67(19):3490-3500
A comparative study of the reaction pathway of the cycloaddition of various vinyl-containing dienophiles on a set of substituted 3-acylamino-2H-pyran-2-ones under microwave-assisted and high-pressure conditions is presented. In the course of the reaction both the intermediate products, i.e., the 2-oxabicyclo[2.2.2]oct-5-ene (the exo/endo selectivity depended upon the dienophile) and the alkoxycyclohexadiene systems, were isolated and comprehensively characterized; this included X-ray diffraction analyses. The role of the base (DABCO) as an organocatalyst was further elucidated. 相似文献
2.
Krištof Kranjc Amadej Juranovič Marijan Kočevar Franc Perdih 《Journal of chemical crystallography》2012,42(5):443-449
Abstract
The compounds methyl 3-(benzoylamino)-6-methyl-2-oxo-2H-pyran-5-carboxylate (1), C15H13NO5, and N-[5-(3,4-dimethoxyphenyl)-6-methyl-2-oxo-2H-pyran-3-yl]benzamide (2), C21H19NO5, crystallize as a centrosymmetric hydrogen-bonded dimer facilitated by N–H···O interactions involving the amide and carbonyl moiety of the lactone group of adjacent molecules. Supramolecular aggregation in 1 is controlled by a combination of π–π interactions [centroid–centroid distance = 4.0745(11) ?] and weak C–H···O hydrogen bonding between the phenyl ring of the benzoylamino group and the carbonyl atom of the methoxycarbonyl group and in 2 by a combination of π–π interactions [centroid–centroid distance = 4.0699(8) and 4.1556(10) ?], weak C–H···O interactions between the methoxy substituents of the adjacent dimethoxyphenyl group and weak C–H··· π interactions. 相似文献3.
HPTLC silica gel plates without and with fluorescence indicator F254 in combination with n-hexane–ethyl acetate–formic acid (20:19:1, v/v/v) as a developing solvent were explored for the HPTLC–densitometric and HPTLC–MS/(MSn) analyses of flavonoids. Pre-development of the plates with chloroform–methanol (1:1, v/v) was needed for reliable HPTLC–densitometric analyses of flavonoid aglycones in the whole RF range, while 2-step pre-development (1st methanol–formic acid (10:1, v/v), 2nd methanol), that decreased background signals of formic acid adducts, was required for HPTLC–MS analyses. Optimization with conditioning of the adsorbent layer with water before development and saturation of the twin trough chamber resulted in required decrease of the RF values of studied flavonoids (flavone, apigenin, luteolin, chrysin, quercetin dihydrate, myricetin, kaempferide, kaempferol, naringenin, pinocembrin).Detection was performed based on fluorescence quenching (on the plates with F254), natural fluorescence and after post-chromatographic derivatization with natural product reagent without or with further enhancement and stabilization of fluorescent zones with polyethylene glycol (PEG 400 or PEG 4000) or paraffin–n-hexane reagents. For all three reagents, drying temperature and time passed after drying influenced the intensity, which was increasing the first 20?min, and the stability (less than 2?h for PEGs and at least 24?h for paraffin–n-hexane) of the standards’ zones.Optimal wavelengths for densitometric evaluation were selected based on in-situ absorption spectra scanned before and after derivatization and after stabilization. The developed method was tested via analyses of propolis, roasted coffee, rose hip, hibiscus, rosemary and sage crude extracts. To further increase the reliability of the obtained densitometric results HPTLC–MS/(MSn) analyses of all crude extracts were performed. Several phenolic and non-phenolic compounds were tentatively identified.Some possible interferences with phenolic acids (chlorogenic acid, rosmarinic acid, protocatechuic acid, gallic acid, syringic acid, ellagic acid, trans-cinnamic acid, o-coumaric acid, m-coumaric acid, p-coumaric acid, caffeic acid, ferulic acid, sinapic acid) that are often present in the extracts together with flavonoids were also examined. 相似文献
4.
Dolenec T Lojen S Lambasa Z Dolenec M 《Isotopes in environmental and health studies》2006,42(1):77-85
Analyses of nitrogen stable isotopes in the marine sea grass Posidonia oceanica were used to investigate the influence of fish farming on the coastal ecosystem of Vrgada Island in the Murter Sea, Central Adriatic. The results show a statistically significant 15N enrichment (up to 4.7 per thousand at p < 0.005) in P. oceanica leaf and shoot tissues from fish cage sites with respect to the unaffected offshore reference site of Lumbarda Reef Flat (Kornati Islands). Heavy nitrogen enrichment was also detected in other benthic organisms analysed during this study and is attributed to the absorption and assimilation of 15N-enriched fish farm derived nitrogen waste. 相似文献
5.
Krištof Kranjc 《Tetrahedron》2008,64(1):45-52
The cycloaddition of (Z)-1-methoxybut-1-en-3-yne (2) with 5,6-disubstituted 3-acylamino-2H-pyran-2-ones 1 under microwave-irradiation conditions, with classical heating or at high-pressures (13-15 kbar) affords the benzene derivatives 3 with a strategically positioned 2-methoxyethenyl moiety. In some cases, at high-pressures after long reaction times, 2,2-dimethoxyethyl products 4 were obtained. Adducts 3 and 4 can be cyclized under mild conditions into 1,5,6-trisubstituted indole derivatives 5. 相似文献
6.
Nitrogen-rich heterocycles are increasingly used in energetic chemistry with the aim to achieve superior performance of the new energetic materials. Combining such building blocks into biheterocycles increases energy output while at the same time retains low sensitivity. Herein, we report the synthesis and characterization of a compound containing a 5-amino-1,2,4-triazole moiety connected with a 1,2,4-oxadiazole ring. The trichloromethyl group attached to the oxadiazole ring offers an attractive point for further transformations into potentially energetic compounds. 相似文献
7.
Tadej Dolenec Sbreveivana Lambasbrevea Matej Dolenec 《Isotopes in environmental and health studies》2013,49(1):77-85
Analyses of nitrogen stable isotopes in the marine sea grass Posidonia oceanica were used to investigate the influence of fish farming on the coastal ecosystem of Vrgada Island in the Murter Sea, Central Adriatic. The results show a statistically significant 15N enrichment (up to 4.7‰ at p?<?0.005) in P. oceanica leaf and shoot tissues from fish cage sites with respect to the unaffected offshore reference site of Lumbarda Reef Flat (Kornati Islands). Heavy nitrogen enrichment was also detected in other benthic organisms analysed during this study and is attributed to the absorption and assimilation of 15N-enriched fish farm derived nitrogen waste. 相似文献
8.
Ga?per Jakli? Tadej Kandu? Selena Praprotnik Emil ?agar 《Journal of Optimization Theory and Applications》2012,155(2):680-693
In this article, an optimal mountain ascent is studied as a particular problem of a human walking over a rugged terrain. First, an approximation of the terrain is constructed using particular smooth splines??macro-elements. Then a functional measuring the energy consumption along boundary curves of a macro-element is defined. Finally, the corresponding discrete problem of finding the optimal path on a mesh of curves is applied. Numerical results on real-life data indicate that computed paths are a good approximation of hiking paths in nature. 相似文献
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10.
Krivec M Gazvoda M Kranjc K Polanc S Kočevar M 《The Journal of organic chemistry》2012,77(6):2857-2864
The application of activated carbon (Darco KB) for the acceleration and direction of the transformation of various 2H-pyran-2-ones with N-substituted maleimides toward isoindole derivatives through the reaction sequence cycloaddition/elimination/dehydrogenation is described. In this reaction, the catalyst mainly influences the dehydrogenation step, which is essential to avoid the formation of bicyclo[2.2.2]octenes as the other possible products. We found that the combination of Darco KB, as the metal-free catalyst, and decalin, as the solvent in a closed vessel, represents the most successful conditions. A comparison of the effect of various dehydrogenation catalysts and reaction conditions is also presented. In addition, we have proven that the aromatization occurs via a hydrogen transfer from the cyclohexadiene intermediate to the maleimide derivative (therefore producing succinimides). This transfer is facilitated by the active surface of the heterogeneous carbon-based catalyst. 相似文献