摘要:

Synthesis of Sulfonylsubstituted Heterocycles by Cyclocondensation of Sulfones with Bifunctionalised Compounds2‐Sulfonylketendithioacetales (1), alkyl‐sulfonylacetates (6), 2‐sulfonyl‐acetophenones (9) and ‐nitriles (12) react by cyclocondensation with bifunctionalised compounds2, 4, 7, 10and13yielding the sulfonylsubstituted chinoline‐3, chinolone‐5, barbituric acid‐8, pyrane‐11and couma

ISSN:0941-1216    

DOI:10.1002/prac.19943360102

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Influence of Aryl‐bonded Substituents on Complex Formation of Benzocrown Ethers with Alkali Metal Ions in Methanol and Acetone SolutionsThe influence of aryl‐bonded substituents upon the complex formation of monobenzocrown ethers towards alkali metal ions in methanol and acetone solutions are investigated by using calorimetric and potentiometric titration. A different complexation behaviour of the ligands in acetone and methanol was found. In the case of the 1:1 complexation of Na+a correlation between substiuent effects and stability constants in acetone was noticed, however, the influence of substituents upon complex stability is weak. In methanol solutions no similar correlation could be established. During sandwich complexation of K+in methanol, no significant substituent influences on K1and K2were observed. On the other hand, a considerable increase of ΔH2for both the electron accepting and electron releasing substituents was found, probably caused by changes in ligand‐cation solvation due to the substi

ISSN:0941-1216    

DOI:10.1002/prac.19943360103

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Fluorescence Detection System for the Multielement Determination of Cations after Separation by HPLCFluorescence determination of cations after HPLC separation requires an unselective detection principle to achieve multielement capability. Following the principle of the photometric Zn‐EDTA‐PAR‐system, 2, 2′‐pyridylbenzimidazole (PBI) is used as a fluorescent indicator. Cations are separated on a Nucleosil 5SA column using tartaric acid as eluent. Zn is replaced by the eluent traces in a post column reactor and determined as the fluorescent Zn‐PBI‐chelate. Detection limits for Mn, Mg, Ca, Cu, Cd are 7–92 ng in 20 μL

ISSN:0941-1216    

DOI:10.1002/prac.19943360104

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Abstract23, 24‐Dihydrocucurbitacin‐F has been isolated fromhemsleya amabilis. Its structure was studied in detail by1H‐ and13C‐,1H,1H COSY,1H,13C HETCOR,1H,13C LOCOR, and 1D NOE NMR spectroscopy. All1H‐ and13C‐spectral data for this compound have been assigned, and some assignments of1H and13C signals have been revised based on the 2D NMR spectra. In particular, previously unassigned methyl and hydroxy signals have been completely assigned via NOE and1H,13C‐LOCO

ISSN:0941-1216    

DOI:10.1002/prac.19943360105

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractAn improved synthesis of CTMC is described. This cyclobutene is thermally stable towards electrocyclic ring opening. Its reactivity is explored and a number of radical adducts are described. A more complicated picture is observed with various nucleophiles. The strong dienophilic character of CTMC is illustrated by numerous examples. CTMC reacts well as a dipolarophile with diphenylnitrone, diphenylnitrilimine and diazoalkanes. The high reactivity of this cyclobutene is due to its inherent polarity and strain.

ISSN:0941-1216    

DOI:10.1002/prac.19943360106

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe reaction of diethyl [(1‐isocyano‐2,2‐dichloro)‐ethenyl]phosphonate (1) with mono‐ and bifunctional aliphatic and aromatic amines and thiols has been studied. Because1is a push‐pull olefine, a nucleophilic attack can take place at the halide‐substituted carbon atom. On the other hand,1possesses with the isocyano group a further reactive centre, which is able to undergo typical isocyanide reactions. With secondary and ethylene‐bridged bifunctional nucleophiles the substitution of the chloro atoms of1furnishes ketene N,N‐, N,S‐ and S,S‐acetals (8, 12, 14). By treating1with primary amines imidazoles6are obtained, an α‐addition of an amino function to an isocyano group under mild conditions being involved. The isocyano‐substituted cyclic ketene N,N‐acetal12 ainserts acceptor‐substituted isocyanides forming the fused pyrazines18. The structure of18 ais corroborated by X

ISSN:0941-1216    

DOI:10.1002/prac.19943360107

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Multi‐Step Redox Systems. LXI. Synthesis of 1,4‐Bis(2‐methyl‐indolizin‐1‐yl‐methyl)‐benzene and Related Model CompoundsThe synthesis of1a, in which two 1‐indolizine units are connected by a p‐xylylene bridge is preformed from its 3,3′bis‐acetyl derivative1bvia the precursors8–11. This route was first tested by the synthesis of benzyl indolizines2band2avia the pyridyl‐aminopropanol3a. 2acan be oxidatively dimerized to the 3,3′‐bis‐indolizine6which forms a perfectly reversible two step

ISSN:0941-1216    

DOI:10.1002/prac.19943360108

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractEight defined primary and secondary alkylhydroperoxides were decomposed in n‐alkanes as the solvent, mostly in the presence of manganese stearate. In all cases the corresponding alcohols and carbonyl compounds were formed as the main products with yields of 60–90%. Besides, difunctional products were formed by an intramolecular H‐transfer in the alkoxy radicals corresponding to the starting hydroperoxides. Products possibly formed by an intramolecular H‐transfer in the corresponding alkylperoxy radical could be found only in the case of 4‐methyl‐2‐hydroperoxy pentane. The amount of products formed by intramolecular H‐transfer depended on the nature of the C‐H bond in δ‐position to the original hydroperoxy group and lay between 4% (primary C‐H in the case of 4‐hydroperoxy heptane) and 13% (tertiary C‐H in the case of 2‐hydroperoxy‐5‐methyl hexane) with respect to the starting hydroperoxide.The amount of products formed by oxidative attack of the alkoxy and alkylperoxy radicals at the normal paraffins used as the solvents was unexpectedly low (always less than 10% with respect to the starting hydroperoxide).An increment system is proposed for the calculation of13C‐

ISSN:0941-1216    

DOI:10.1002/prac.19943360109

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Silver(I) Complexes of 3‐Substituted 1‐Methyl‐perhydro‐1,2,4‐triazine‐5,6‐dithionesHeterocyclic triazine compounds such as 1‐methyl‐perhydro‐1,2,4‐triazin‐5,6‐dithiones react with silver salts forming complex species [AgL2]+(L = triazinedithione). In water the complexes are unstable owing to ligand hydrolysis. Stable solid complex [AgL2]Br(L = 1,3,3‐trimethyl‐perhydro‐1,2,4‐triazine‐5,6‐dithione) can be obtained by the digestion of AgBr‐microcrystals with the triazinedithione in methanol. As shown by X‐ray crystal structure analysis the silver ion in this complex is coordinated trig

ISSN:0941-1216    

DOI:10.1002/prac.19943360110

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Equilibriums of Ethene Adsorption on 4A ZeolitesFrom the isotherms of ethene, measured on the zeolites NaA, K0,085Na0,915A and Me0,22+Na0,8(Me = Mg, Ca, Zn, Ba) in the temperature range of 298 K to 353 K, the isosteric heats of adsorption and the partial molar entropies were calculated. All three quantities show a specific dependence on the loading. The exchanged univalent and divalent cations as adsorption centres have an essential influence on the shape of isotherms. The sequence of cations ordered according to highest adsorption heats depends also on the loading, caused by the different influence of the nonloaded and loaded divalent cations on the mobility and ionizity and therefore on the adsorption strength of the blocking Na+cations.

ISSN:0941-1216    

DOI:10.1002/prac.19943360111

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY