摘要:

AbstractUsing extendedHückelwave functions, molecular electrostatic potentials (MEP's) have been calculated for several model clusters representative of zeolites of offretite type. The clusters studied, which are all made of a central unit comprising 2 AlO4and 16 SiO4tetrahedra, differ only by the relative positions of the Al‐atoms occupying the same crystallographic sites (T2) within the zeolite framework. using the MEP values as a color‐coded acidity index for the various clusters, three‐dimensional representations of their molecular surfaces are generated as solid models on a performing computer graphics system. Important differences in acidity are predicted for the clusters which can he classified into two types according to the distribution of Al‐atoms: the first one is characterized by nearly independent acid sites localized around the main channel of zeolite (Figs. 3and6) whereas the second one exhibits interacting acid sites located longitudinally along the channel of the same gmelinite cage (Figs. 4and5). The possible relationship between the structure of the clusters and their catalytic activity towards organic species is d

ISSN:0018-019X    

DOI:10.1002/hlca.19900730112

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractStarting from D‐glutamic acid (5), the bicyclic compounds4aand4bwere synthesizedvia17(Schemes 1and2). The reaction leading to4gand4hwith LiCuPh2was not successful. But treatment of the N‐protected model lactams19,21, and22with Li2Cu(CN)Ph2gave the amino ketones24,26, and27, respectively (Scheme 3). The desired compound23was obtained from20.Conversion of the unprotected lactams28,31, and32gave the phenyl derivative34in excellent yields. Ester35was transformed to the α ‐amino‐γ‐ oxo‐acid derivative36.This conversion opens a novel access to this type

ISSN:0018-019X    

DOI:10.1002/hlca.19900730113

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe 1,2,3,4,4a,5,8,8a‐octahydro‐4β8aα‐dimethylnaphthalen‐4aβ‐ol (= dehydrogeosmin;1) has been identified as the olfactorily dominant compound in the flower scents ofRebutia marsoneriWERD.,Dolichothele longimamma(DC.) BR.etR., andSulcorebutia kruegeri(CARD.) RITT. The structure of1, which might be of importance to the pollination biology of suchCactaceae, is based on spectral data a

ISSN:0018-019X    

DOI:10.1002/hlca.19900730114

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe three ligands 1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetrakis(methylenephosphonic acid) (1), 1,4,7,11‐tetraazacyclotridecane‐1,4,7,11‐tetrakis(methylenephosphonic acid) (2), and 1,4,8,11‐tetraazacyclotetradecane‐1,4,8,1 1‐tetrakis(methylenephosphonic acid) (3) have been synthesized by condensation of the corresponding macrocycles with formaldehyde and phosphorous acid. The protonation and stability constants with the earth‐alkali ions have been determined at 25° andI= 0.1 M (Me4)N(NO3) by potentiometric titrations. Because of the high values of the first two protonation constants,1H‐NMR measurements were necessary to determine them. Titrations in different supporting electrolytes (NaNO3, KNO3, RbNO3, CsNO3, and Me4N(NO3)) show that their choice is of paramount importance, as the above ligands can form complexes with alkali‐metal ions. The potentiometric results for the earth‐alkali ions show that beside mononuclear complexes of different degrees of protonation ([MLHn],n= 0–4), also binuclear species are formed ([M2LHm],m= 0–2). It is interesting that1with the smallest macrocyclic ring has the greatest tendency to form binuclear complexes, which are so stable that they partially prevent the formation of the corresponding mononuclear species. For [ML], [MLH], [M2L], and [M2LH], the stability sequence is Mg2+Ba2+, whereas for [MLH2], [MLH3], and [MLH4], the stability stead

ISSN:0018-019X    

DOI:10.1002/hlca.19900730115

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe Cu2+complex of1, having a non‐coordinating carboxylic group, can be reacted under the typical conditions of peptide formation with amines such as 2‐methylpropylamine or (pyrid‐2‐yl)methylamine to give, after removal of Cu2+with CN−, the amides 4 and 5. The Cu2+ion is of paramount importance since it protects the four amino groups of the macrocycle so that the amide condensation can specifically be done with the exogenous amine It is also shown that the Cu2+complex of1can be covalently attached to bovine serum albumin (BSA), thus opening the possibility to use this compound as a labelling agent for proteins and a

ISSN:0018-019X    

DOI:10.1002/hlca.19900730116

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe title complex crystallises in twoC3v, isomeric forms differing in carbonyl‐ligand arrangement. In solution, the isomer1bwith three edge‐bridging carbonyls on a common face of the metal tetrahedron convertsviaan endothermic equilibrium into the isomer1uwith no bridging carbonyls. The latter was shown by13C‐NMR to be the intermediate of the ‘merry‐go‐round’ process which exchanges the sites of t

ISSN:0018-019X    

DOI:10.1002/hlca.19900730117

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe ‘naked sugar’ (+)‐(1R,2R4R)‐2‐endo‐cyano‐7‐oxabicyclo[2.2.1]hept‐5‐sn‐2‐exo‐yl acetate ((+)‐4) was converted (7 steps, 45% overall) with high stereoselectivity into (−)‐(4R,5S,6R)‐4,5,6‐tris{[(tert‐butyl)dimethylsilyl]oxy}cyclohex‐2‐en‐1‐one ((−)‐11). Reduction of (−)‐1with NaBH4‐ CeCl3· 7 H2O, followed by deprotection of the silyl ether moieties gave (+)‐conduritol F ((+)‐1; 47%) whose characteristics were identical to those of natural (+)‐leucanthemitol. Reduction of (−)‐11with DIBAH, followed by deprotecti

ISSN:0018-019X    

DOI:10.1002/hlca.19900730118

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractAdamantanone‐derived nitrone4and some other keto‐nitrones, when reacted with aromatic and aliphatic aldehydes in refluxing toluene or tetrahydrofuran, formed the corresponding aldonitrones (Z)‐10, the latter arising from the fragmentation of an initially formed1,4,2‐dioxazolidine6to adamantan‐2‐one and an oxaziridine intermediate11, which then rearrange

ISSN:0018-019X    

DOI:10.1002/hlca.19900730119

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractA new vicinal dioxime ligand with two crown‐ether groups, 1,2‐bis[(monoaza[15]crown‐5)‐N‐Yl]‐glyoxime(LH2), has been prepared from cyanogen di‐N‐oxide and monoaza[15]crown‐5. Ni(II), Pd(II), and Pt(IV) complexes of LH2with or without alkali‐metal ions bound to macrocyclic groups have been isolated. The high affinity of [Pd(LH)2] and [Ni(LH)2] for the K+ion is observed in solvent extraction experiments. A single‐crystal X‐ray structure confirms the postulated geometry of [Pd(LH)2]‐ The Pd‐atom of the centro‐symmetric molecule has square‐planar PdN4coordination where Pd–N distances range from 1.978(3) to 1.970(3) Å. The N

ISSN:0018-019X    

DOI:10.1002/hlca.19900730120

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY

摘要:

AbstractThe synthesis of some derivatives of the title compoundVIis described. Bromination of diethyl (cis‐3‐azido‐2‐oxo‐4‐styrylazetidin‐1‐yl)(pyridin‐2‐yl)methylphosphonate (6) in MeOH gave tricyclic β‐lactam7, while similar bromination of diethyl (cis‐3‐azido‐2‐oxo‐4‐vinylazetidin‐1‐yl)(pyridin‐2‐yl)methylphosphonate (9) afforded tri‐cyclic β‐lactam10. Mechanisms for the

ISSN:0018-019X    

DOI:10.1002/hlca.19900730121

出版商:WILEY‐VCH Verlag GmbH    

年代:1990

数据来源: WILEY