摘要:

AbstractNitroalkenes3–5react with ynamines (1‐aminoacetylenes)6to yield four‐membered cyclic nitrones (2,3‐dihydroazete 1‐oxides) 7–13. The nitroalkenes3and5cgive thecisfourmembered cyclic nitrones7–11, whereas4and5byield thetransfour‐membered cyclic nitrones 12–13 upon reaction with6. Nitroalkene4ireacts with6cto give a 1:1 mixture of thecisandtransfour‐membered cyclic nitrones9gand13i. Thetransstereochemistry oftrans‐N,N‐diethyl‐2, 3‐dihydro‐3‐(2‐methoxynaphthalenyl)‐2‐methyl‐4‐phenyl‐2‐azetecarboxamide 1‐oxide (13k) was elucidated by means of X‐ray analysis. Only from the reaction of 1‐nitrocyclopentene (5a) with6c, the initially formed (4 + 2) cycloadduct, the nitronic ester17has been isolated. The thermal ring contraction of17yields 3a, 4, 5, 6‐tetrahydro‐N,N‐dimethyl‐3‐phenyl‐3H‐cyclopent[c]isoxazole‐3‐ carboxamide (19), the structure of which was established by X‐ray analysis. Thetransfour‐membered cyclic nitrones are thermally relatively stable compared with thecisnitrones. The mechanism of the stereoselective formation of the nitrones is related to the conformation of the (4 + 2) c

ISSN:0165-0513    

DOI:10.1002/recl.19881070202

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractA series of 4‐nitro‐1‐cyclobuten‐l‐amines3was isolated from the thermal (2 + 2) cycloaddition of nitro(cyclo)alkenes1and ynamines2. Heating of3a‐dyielded products corresponding with disrotatory ring openingviz.the 1,3‐dienes6a‐d. Heating of3e,fat 60°C gave the dienes7a,b, as the result of aconrotatoryring opening reaction, together with thetrans‐2‐nitrocyclobutenes8a,b, as the result of a hydrogen shift in the cyclobutene ring. Upon prolonged heating at 80°C8bwas converted into the diene7b. Treatment of3ewith acid yielded the 2‐nitrocyclobutenes9aand9b. The structures of3a, 3f, 6aand7bwere elucidated by X‐ray analysis. The formation of6a‐dis attributed toE/Zisomerization of the product, initially formed by

ISSN:0165-0513    

DOI:10.1002/recl.19881070203

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractReactions of the four‐membered cyclic nitrones1with acetyl chloride differ strongly from those of other (cyclic) nitrones. In the presence of water, the nitrones1yield the 2‐[(acetyloxy)‐amino]‐N,N‐diethylalkanamides4. The structure of4bwas confirmed by X‐ray analysis. In the absence of water, theN,N‐diethyl‐4‐methylene‐2‐azetidinecarboxamides5or theN,N‐diethyl‐2,3‐dihydro‐2‐azetecarboxamides6were obtained. X‐ray analysis elucidated the structure of5a. Under acidic conditions, compounds5ayielded the 2‐oxa‐5‐azabicyclo[2.1.1]hexan‐3‐one derivative13. Acid hydrolysis of6agave the α‐chloroketone der

ISSN:0165-0513    

DOI:10.1002/recl.19881070204

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe four‐membered cyclic nitrones (2,3‐dihydroazete l‐oxides)1a‐dand2a‐creact with a variety of nucleophiles by stereoselective addition to the nitrone moiety. Reaction of the nitrones1and2with alkyl‐, allyl‐, benzyl‐, and arylmagnesium halides yields the l‐hydroxyazetidines3, 4, 5, and6, with the nucleophile adding from the less hindered side of the molecule. The keto nitrone1breacts with potassium cyanide to give the l‐hydroxyazetidine4f. Reduction of nitrone1bto give the l‐hydroxyazetidines7and8is achieved by reaction with lithium aluminum hydride at 0°C and at room temperature, respectively. In contrast, nitrone1dreacts with lithium aluminum hydride only at 45°C to give the l‐hydroxyazetidine11. The differences in the reactivity of the nitrones1and2towards nucleophilic reagents are explained in terms of steric hindrance in the addition step. Oxidation of the l‐hydroxyazetidine3bwith lead(IV) oxide affords the 2,3‐dihydroazete l‐oxide15. Reduction of nitrone15with sodium borohydride affords the 1‐hydroxyazetidine16, the epimer of compound3b. Reaction of l‐hydroxyazetidine3dwith PbO2yields the dimeric structure17. Nitrone1areacts with the sodium salt of nitromethane to yield the l‐hydroxyazetidine12. Keto nitrone1breacts with 4‐nitrobenzaldehyde in the presence of a catalytic amount of potassium hydroxide to give the 4‐benzylidene‐2,3‐dihydroazete l‐oxide13. Upon prolonged reaction, nitrone13isomerizes to oxime14, probably by an electrocyclic ring openin

ISSN:0165-0513    

DOI:10.1002/recl.19881070205

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractIn this paper, we report the preparation of three isotopomers of L‐tryptophan on a gram scale, specifically labelled with 99%15N (position 1) and 99%13C (position 2) in the indole ring; for position 3, the incorporation was 90%13C. The isotopically enriched indoles were synthesized from H15NO3, K13CN and13CH3CN and then converted, with L‐serine, into the correspondingly labelled L‐tryptophans using genetic manipulatedE. colibacteria, which contain high amounts of the enzyme tryptophan synthetase. The13C‐13C,13C‐1H,13C‐15N and15N‐1H coupling constants of the indoles and the tryptophans were determined from the1H NMR and13

ISSN:0165-0513    

DOI:10.1002/recl.19881070206

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractA number of epimeric pairs of 3‐X‐3‐oxo‐trans‐2, 4, 7‐trioxa‐3‐phosphabicyclo[4.3.0]‐nonanes [5, X  OCH3; X  OPh;7, X  Cl;8, X  N(CH3)2;9, X  S−;10, X  O−] have been prepared as no‐base analogues of 3′,5′‐cyclic nucleotides.1H NMR analysis shows the phosphate ring of thecisdiastereomers (relationship of singly bonded substituent on phosphorus and proton H1)5a–7a, 9aand10and thetransdiastereomers8band9bto be in the chair conformation 15. The phosphate rings of the epimers5b–7band8aexist as an equilibrium between chair conformation15and twist conformation16. The mole fraction of twist depends on the nature of the singly bonded substituent and varies from about 0.3 for5bto 0.8 for7b. The close similarity in coupling constants of the tetrahydrofuran ring of the phosphates5–10indicates that the population of a twist conformer has little effect on the conformation of this ring, which is close to4E‐4T3. The results obtained for5–10are compared with those of conformational studies on corresponding

ISSN:0165-0513    

DOI:10.1002/recl.19881070207

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractCalculations are reported on the conformational energies of the dichloro‐bis(pyridine) complexes of zinc, copper, nickel and cobalt. Results based on experimental geometries show that the tetrahedral conformer of the zinc complex is favoured over the corresponding square‐planar structure in line with experimental data, but the latter is preferred for the copper complex though the energy differences between both conformers is small. Square‐planar conformations are predicted for the nickel and cobalt comp

ISSN:0165-0513    

DOI:10.1002/recl.19881070208

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThe synthesis of 5,5′‐di‐tert‐butyl‐3‐(carboxymethyl)biphenyl crown ethers and several lariat ethers with pendant carboxylic acid groups, together with the determinations of the pKavalues of these crown ether carboxylic acids, are described. In addition, the complexation of urea by these crown ethers has been investigated. Both the larger‐ring biphenyl crown ethers (≥ 29 ring atoms) and lariat ethers (≥ 27 ring atoms) solubilized urea in chloroform. The data for urea complexation by the lariat ethers show that, for assistance in urea complexation, it is important for the carboxylic acid group to be located close to the macrocyclic ring. When the carboxylic acid group of the lariat ethers is located in an appropriate position, urea is complexed by 21–27% of these macrocyclic ligands, as is also the case with the biphenyl crown‐ether carboxylic acids. These results demonstrate that a pendant carboxylic acid group can assist in the complexation

ISSN:0165-0513    

DOI:10.1002/recl.19881070209

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

摘要:

AbstractThis paper describes the possibility of using 2D‐NMR spectroscopy in the study of the morphology of micelles. In aqueous solution, the monomeric surfactant 1‐methyl‐4‐dodecylpyridinium iodideexhibits positive NOE's whereas negative NOE's are observed for the micellar aggregate. 1‐Methyl‐4‐n‐butylpyridinium iodide, which does not form micelles, only shows positive NOE's. It is argued that the observation of negative NOE's for micelles is reconcilable with quantitative data for the dynamics of these surfac

ISSN:0165-0513    

DOI:10.1002/recl.19881070210

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19881070211

出版商:WILEY‐VCH Verlag    

年代:1988

数据来源: WILEY