摘要:

AbstractFrom the reactions of 3‐endo‐benzoyl‐6‐exo‐phenylbicyclo[2.2.1] heptane‐2‐endo‐carboxylic acid (2) and α,ω‐diamines oro‐aminophenol/thiophenol, different tri‐, tetra‐ and pentacyclic phenyl‐substituted norbornane‐condensed heterocycles were prepared. With ethylenediamine, 2 furnished two isomeric imidazolo[2,1‐a]isoindolones. In the formation of one of them, anend→oexoisomerizaton was observed. The stereostructures (configurations and conformations) of the compounds were elucidated by1H and13C NMR spectroscopy, with the aid of routine spectra and also DR, DNOE, DE

ISSN:0749-1581    

DOI:10.1002/mrc.1260321202

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractTen substituted 5,5‐dimethyl‐1‐pyrroline‐N‐oxides as well as the parent nitrene spin trap (DMPO) were prepared: 5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2,5,5‐trimethyl‐1‐pyrroline‐N‐oxide, 2‐tert‐butyl‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐phenyl‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐d5‐phenyl‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐phenyl‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide‐nitronyl‐13C, 2‐(4‐fluorophenyl)‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐(4‐chlorophenyl)‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐(4‐tert‐butylphenyl)‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide, 2‐(4‐methylphenyl‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide) and 2‐(2‐ methylphenyl)‐5,5‐dimethyl‐1‐pyrroline‐N‐oxide. Analytical (i.e. EPR‐grade) samples of these novel cyclic nitrones were obtained and characterized by (among other methods)1H NMR spectroscopy. Reduction of DMPO and these various 2‐substituted cyclic nitrones gave the corresponding cyclicN,N‐dialkylhydroxylamines, whose structures and conformations were also analyzed by1H NMR spectroscopy. Air oxidation of these cyclicN,N‐dialkylhydroxylamines provided access to the EPR spectra of the hydrogen, methyl,tert‐butyl, phenyl,d5‐phenyl,nitronyl‐13C‐phenyl, 4‐fluorophenyl, 4‐chlorophenyl, 4‐tert‐butylphenyl, 4‐methylphenyl and 2‐methylphenyl cyclic aminoxyl (pyrrolidineN‐oxyl nitroxide) radical spin adducts of DMPO. The14N,13C (where applicable) and1H hyperfine splitting constants of these aminoxyl adducts in ten solvents of widely different polarities (e.g., hexane to water) were measured and the solvent effect on these parameters was evaluated. It was found that for the various 2‐substituted DMPO‐type spin adducts both the nitrogen and β‐hydrogen EPR hyperfine

ISSN:0749-1581    

DOI:10.1002/mrc.1260321203

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractInvestigations of intermediates generated in the course of lithiation of four 2‐alkylbenzotriazoles revealed largescale temperature‐dependent changes in their ESR spectra. A cautionary observation was that the ESR spectra obtained under synthesis conditions exhibited lineshapes that were assignable to a monoradical, while additional, lower temperature measurements clearly showed the species to be a biradical. The electron–electron dipolar couplings yield an average distance between the two unpaired electrons in the biradical,Rav, of about 5.3 ± 0.16 Å. TheseRavvalues are consistent with the unpaired electrons being localized on the nitrogen atoms of the two benzotriazole moieties in the biradical fragment. This conclusion is supported by oxygen trapping (nitroxide radical formation) studies. The biradicals are shown to have triplets as the ground state with a single‐triplet separation of about 26±

ISSN:0749-1581    

DOI:10.1002/mrc.1260321204

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe discrimination of enantiomeric cyclic hemiacetals and methyl acetals derived from hydroxamic acids and lactams with the 2H‐1,4‐benzoxazin‐3(4H)‐one and 2H‐1,4‐benzothiazin‐3(4H)‐one skeleton was investigated using (S)‐(−)‐phenylethylamine, (−)‐quinine, β‐cyclodextrin and, for the first time, (5R,11R)‐(+)‐2,8‐dimethyl‐6H,12H‐5,11‐ methanodibezo [b,f] [1,5]diazocine, a Troeger's base enantiomer, as chiral solvating agents (CSA). Conditions for the enantiomeric discrimination of six configurationally stable methyl acetals are reported. 2,4‐Dihydroxy‐2H‐1,4‐benzoxazin‐3(4H)‐one and its 7‐methoxy derivative, bioactive aglucones from Gramineae species, are the first cyclic hemiacetals that could be differentiated into enantiomers by means of1H NMR, despite their oxo–cyclo tautomerization that prevented enantioseparation by chromatography or capillary electrophoresis. However, 2‐hydroxy‐2H‐1,4‐benzothiazin‐3(4H)‐ones (thiohemiacetals) could not be differentiated by the use of these CSA. The influence of the structure of the enantiomers, CSA, temperature and conc

ISSN:0749-1581    

DOI:10.1002/mrc.1260321205

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractFully assigned13C NMR chemical shifts for 4,5‐epoxy‐3‐keto‐, ‐3‐hydroxy‐, and ‐3‐acetoxydecalins and ‐10‐methyldecalins, Δ4‐octalins and 10‐methyl‐Δ4‐octalins are reported together with epoxide‐ and methyl‐induced shifts. The 4,5α‐ and 4,5β‐epoxydecalins present epoxide γ shielding in the A ring consistent in general with thesyn‐axial hydrogen rule. The 4,5α‐ and 4,5β‐epoxy‐10‐methyldecalins present only slightly different shielding effects at γ‐carbons C‐1, C‐2, C‐7, C‐9 and C‐11. Methyl‐induced shifts in 4,5α‐ and 4,5β‐epoxy‐10‐methyldecalins are similar at all carbons to those fortrans‐ andcis‐decalins (low temperature in the case of the latter), respectively, suggesting the predominance of the transoid and cisoid A ring conformations, respectively, in these epoxides. The methyl‐induced shifts in the A ring of octalin analogues are intermediate between those of the two epoxide configurational isomers. Epoxide γ‐antideshielding and γ‐synshielding (analogous to those in 5‐hydroxydecalins) are evident when comparison is made with13C shifts from analogous decalins,

ISSN:0749-1581    

DOI:10.1002/mrc.1260321206

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

Abstract17O NMR relaxation rate measurements were made on aqueous perchlorate solutions of the light lanthanide ions Nd3+and Pr3+, with the aim of measuring the kinetics of water exchange on these ennea aqua ions. Variable‐temperature results at three magnetic fields show that the ‘kinetic’ effect is not the only contribution to the difference between the transverse and longitudinal relaxation rates. The results at high magnetic field allow lower limits,k ex298⩾ 5 × 108S−1andk ex298⩾ 4 × 108s−1, to be determined for water exchange rates at 298.15 K on [Nd(H2O)9]3+and [Pr(H2O)9]3+, respectively. These limits are consistent with our current understanding of water exchange on the lanthanide aqua ions, based on the change of relative stability of the ennea and octa aqua ion

ISSN:0749-1581    

DOI:10.1002/mrc.1260321207

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

Abstract13C and15N NMR measurements are reported from a study of five mesoionic compounds containing either the 2,3‐diphenyl‐ or 1,3‐diphenyltetrazolium ring, and either the 2,3‐diphenyltetrazolium ring or its linear analogue as an exocyclic group. Three15N‐labelled compounds were synthesized for signal assignment purposes. Some15N13C and15N15N coupling constants were determined. A proton was found to be located on the exocyclic groups of two of

ISSN:0749-1581    

DOI:10.1002/mrc.1260321208

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractA series of nine diethyl phosphonates were prepared and an analysis of their1H NMR spectra was undertaken. Some erroneous literature assignments of signals were revised.

ISSN:0749-1581    

DOI:10.1002/mrc.1260321209

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe characteristic13C NMR chemical shift ranges as a guide for the establishment of the parent skeletons of various categories and subcategories of lignoids (lignans, neolignans and oxyneolignans) and for the determination of the substitution pattern of the side‐chain are tabulate

ISSN:0749-1581    

DOI:10.1002/mrc.1260321210

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

Abstract13C NMR spectral assignments for a number of naturally occurring and hemi‐synthetic abieta‐8,11,13‐triene diterpe‐noids are reported. The most significant effects caused by common structural variations for this kind of compound are di

ISSN:0749-1581    

DOI:10.1002/mrc.1260321211

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY