摘要:

Abstract(±)‐4,5,5‐Trimethyl‐1‐pyrroline‐1‐oxide reacted readily with ethyl 4,5,6,7‐tetra‐O‐acetyl‐trans‐2,3‐dehydro‐2,3‐dideoxy‐L(−)‐arabinoheptenoate in anhydrous benzene to give a mixture of two diastereomeric isoxazolidines, [2α,3β,3aα,5α]‐ and [2α,3β,3aα,5β]‐ethyl hexahydro‐2‐(1,2,3,4‐ tetraacetoxybutyl)‐5,6,6‐trimethylpyrrolo[1,2‐b] isoxazole‐3‐carboxylate. The structures and configurations of both diastereomers were determined through the

ISSN:0749-1581    

DOI:10.1002/mrc.1260290702

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractTwo new β‐dihydroagarofuran sesquiterpene polyesters were isolated fromCelastrus paniculatus. The structures were deduced using various 2D NMR techniques (HH COSY, CH COSY, COLOC, NOESY), NOE difference spectra and mass spectra. The positions of the ester moieties were located by 2D heteronuclear correlated spectra via long‐range coupling, or combined with NOE experiments. Their stereochemical structures were studied and the complete assignments of the1H and13C chemical shifts w

ISSN:0749-1581    

DOI:10.1002/mrc.1260290703

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe structural changes during the complexation of benzo‐crown ethers with Cs+, K+and Na+were studied by NOESY and variable‐temperature13C NMR spectroscopy. It was found that, on complexation, the distance between the CH‐α and 1‐CH2is reduced in dibenzo‐24‐crown‐8 (DB24C8), dibenzo‐18‐crown‐6 and benzo‐15‐crown‐5. Two mechanisms have been proposed for the distance reduction, the fluttering motion of the benzo group and the elongation of the crown moiety. However, it is concluded that both of these mechanisms seem to play a role in the distance reduction. In the complexed state of DB24C8 with Cs+, Cs+is predicted to be slightly above the plane of the crown oxyg

ISSN:0749-1581    

DOI:10.1002/mrc.1260290704

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe13C chemical shifts of elaiophylin and 21 of its derivatives are described and discussed.

ISSN:0749-1581    

DOI:10.1002/mrc.1260290705

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractCarbon‐13 NMR chemical shifts (CDCl3and C6D6solvents) and relaxation times (T1) were determined for carbons in a series of allenic esters [RR1CCCHCO2Et; (1) R = R1= H; (2) R = H, R1= CH3; (3) R = H, R1= CH3CH2; (4) R = R1= CH3; (5) R = CH3, R1= CH3CH2]. A comparison of the experimental δ13C values with those obtained by semi‐empirical additivity relationships revealed the inadequacy of these relationships to explain the obtained results. A rationalization of δ13C and relaxation time data is offered,inter alia, in terms of rotameric conformational preferences of the ester

ISSN:0749-1581    

DOI:10.1002/mrc.1260290706

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractNOE andT1proton measurements were carried out in order to determine unambiguously theZandEconfigurations of some CF3‐trisubstituted vinylic compounds (HCRCR′CF3). The β‐ethylenic carbon in olefins, enol ethers and enamines is always more strongly coupled to CF3in theciscompound (CF3and the vinylic protoncisto each other): |3J(CF)|cis>|3J(CF)|trans. This observation, in addition to the already known higher shielding of19F NMR signal in thecisisomer, allows the safe assignments ofZandEisomers even when only one is obtained, regardless of the nature of

ISSN:0749-1581    

DOI:10.1002/mrc.1260290707

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

Abstract39K NMR spectroscopy was used to study a blue potassium solution in tetraglyme containing 18‐crown‐6 and in a solution without the crown ether. Direct proof of the existence of potassium anions and complexed potassium cations in both solutions has been presen

ISSN:0749-1581    

DOI:10.1002/mrc.1260290708

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe1H and13C NMR spectra of heptakis(2,6‐di‐O‐pentyl)‐β‐cyclodextrin in deuteriochloroform have been fully and unambiguously assigned. Several methods, including homo‐ and heteronuclear spin decoupling, two‐dimensional homo‐ and hetero‐nuclear correlation NMR spectroscopy, spectral simulation and the measurement of relaxation times were used for chemical

ISSN:0749-1581    

DOI:10.1002/mrc.1260290709

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

Abstract2 + 2‐Cycloaddition reactions ofcis‐ andtrans‐cyclopenta‐, ‐cyclohexa‐ and ‐cyclohepta‐ andtrans‐cycloocta [e]‐2‐phenyl‐4H‐1,3‐thiazines gave new types of hydrated tricyclic 1,3‐thiazino‐β‐lactam derivatives having the 2‐phenyl substituent and H‐9 incispositions. The configurations and conformations of the new compounds were determined by1H and13C NMR spectroscopy, including double r

ISSN:0749-1581    

DOI:10.1002/mrc.1260290710

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

Abstract1H NMR shifts and13C spin–lattice relaxation rates were measured for various aromatic π‐acceptors (S) in solutions containing paramagnetic cobalt(II) and iron(III) porphyrins (P). The stability constants of P · S molecular complexes and limiting values of substrate chemical shifts in the complexes were determined from the concentration dependence of chemical shifts. The abilities of different substituents to promote complexation of aromatics with metalloporphyrins are discussed. The preferred substrate orientation in molecular complexes were derived using relative values of chemical shifts and relaxation rates induced by metalloporphyrins. Both monocyclic (benzene and pyridine derivatives) and bicyclic (naphthalene derivative) substrates tend to form ‘axially symmetric’ adducts with parallel π‐planes and the centre of the aromatic system situated in the vicinity of the por

ISSN:0749-1581    

DOI:10.1002/mrc.1260290711

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY