摘要:

AbstractThe title compounds4are obtained by photolysis of simpleN‐alkylpyridinium salts in H2O or alcohol. On reaction with [Fe2(CO)9] in THF,4gives bicyclic tricarbonyliron complexes13a–d, which on oxidative decomplexation with ceric ammonium nitrate affordcis‐fused cyclopenteno‐β‐la

ISSN:0018-019X    

DOI:10.1002/hlca.19970800112

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe treatment of bromo‐substituted 1,6‐methano[10]annulenes with sodium thiolates in DMF provides easy access to alkylthio‐ and arylthio‐substituted 1,6‐methano[10]annulenes (Schemes 2‐4). These compounds are then brominated withN‐bromosuccinimide (NBS) to study their reactivity in electrophilic substitution reactions (Schemes 5and6). The resulting brominated thio‐1,6‐methano[10]annulenes are, in a subsequent reaction, subjected toHeckcoupling with (4‐nitrophenyl)acetylene (13) to produce the alkynylated derivatives14in reasonab

ISSN:0018-019X    

DOI:10.1002/hlca.19970800113

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractKhusimone (1), one of the main odor‐donating compounds of vetiver oil is subject of the following study on structure/odor relationship. The omittance of the ethano bridge of the tricyclic khusimone leads to a bicyclic system. The stereoselective approach to this degraded structure is described, and the olfactory properties are studied. The key step of the synthesis of the hydrindane nucleus is based on a highly diastereoselective conjugate addition to a chiral oxo‐cyclopentene‐2‐carb

ISSN:0018-019X    

DOI:10.1002/hlca.19970800114

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractComparative semi‐empirical PM3 andab initioSTO 3‐21G calculations on bornanesultam‐derived dienophiles containing the structural moiety SO2NC(O)X(α) = Y(β) suggest that, among the conformers of low energy, the thermodynamically less stable SO2/C(O)‐syn,C(O)/X=Y‐s‐cisconformation is also reactive in terms of LUMO level and atomic coefficients. Furthermore, the X(α), Y(β) LUMO atomic coefficients are nonequivalent with respect to both X(α)‐re and X(α)‐sifaces, and thus have, depending on the conformation, a matching or mismatching stereoelectronic influence with the co‐operative steric effect. This dissymmetry is believed to result from the generalized anemone effect of the N lone pair, itself anomerically stabilized and directed, in the absence of crucial steric interactions, by the pseudo‐axialanti‐periplanar SO bond. FiveN‐acyl‐substituted bornanesultams arc discussed ((–)‐1a:N‐acryloyl, XCH, YCH2; (–)‐1b;N‐crotonoyl, XCH, YCHMe; (–)‐1c:N‐N′‐fumaroyl, XCH, YCH(C(O)‐bornanesultam);2a:N‐glyoxyloyl, XCH, YO;2b:N‐acylnitroso, XN, YO). In this context, differences with toluenesultams3are pointed out. A previous report onN‐(acylnitroso)‐bornanesultam2bis rev

ISSN:0018-019X    

DOI:10.1002/hlca.19970800115

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe solid‐state structures of three stereoisomer,1–3, of the cyclic tetramer of 3‐aminobutanoic acid are presented. These cyclo‐β‐peptides were found to be highly insoluble materials, and it proved to be impossible to grow crystals of sufficient quality for X‐ray single‐crystal analysis. The samples of 1–3 were, however, suitable candidates for structure determination from powder diffraction data (Fig. 1), and the application of this method is described. All three isomers have been found to adopt tubular structures (Figs. 2–4) in a fashion similar to those already observed for certain cyclo‐α‐peptides. The stacks of 16‐membered rings are held together by four nonlinear CO…︁HN H‐bonds

ISSN:0018-019X    

DOI:10.1002/hlca.19970800116

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractSimple recommendations for the configurational description of chiral fullerenes and fullerene derivatives with a chiral functionalization pattern are presented in detail and illustrated with examples for different types of compounds. The descriptor system is based on the fact that the numbering schemes proposed for fullerenes are chiral (helical) and, thus, constitute an ideal reference for differentiating between enantiomers of chiral carbon cages and of fullerene derivatives with a chiral functionalization pattern. A single descriptor is sufficient to specify the configuration of the chiral spheroids, regardless of their functionalization degree. According to the helicity of the numbering scheme to be used, the descriptors arefC(clockwise) orfA(anticlockwise). The proposed configurational description can also be extended to related classes of compounds such as chiral bowl‐shaped condensed ring systems and their derivatives with a chiral functionalization patter

ISSN:0018-019X    

DOI:10.1002/hlca.19970800117

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThe (2‐dansylethoxy)carbonyl (= {2‐{[5‐(dimethylamino)naphthalen‐l‐yl]sulfonyl}ethoxy}carbonyl; dnseoc) group was employed for protection of the amino functions of the aglycone residues. The lactam function of 2′‐deoxyguanosine was on the one hand unprotected and on the other hand alkylated atO6of the aglycone with the 2‐(4‐nitrophenyl)ethyl (npe) and 2‐(phenylsulfonyl)ethyl (pse) group, respectively. The syntheses of monomeric building blocks, both phosphoramidites and nucleoside‐ functionalized supports, are described for the three common 2′‐deoxynucleosides (2′‐deoxycytidine, 2′‐deoxyadenosine, 2′‐deoxyguanosine). As kinetic studies with the tritylated nucleosides showed, the dnseoc group is more labile towards DBU cleavage than the corresponding 2‐(4‐nitrophenyl)ethyl‐(npe) and [2‐(4‐nitrophenyl)ethoxy]carbonyl(npeoc)‐protected analogues (see Table 2). These results were confirmed by the very fast deprotection r

ISSN:0018-019X    

DOI:10.1002/hlca.19970800118

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

AbstractThree binuclear copper(II) complexes, [Cu2(μ‐L)(μ‐N3)](ClO4)2′ 1‐5 EtOH (1), [Cu2(μ‐L)(μ‐MeO)(ClO4)]‐ClO4‐ EtOH (2) and [Cu2(μ‐L)(μ‐C3H3N2)](ClO4)2· 2H2O, (3) where L is the pentadentale bridging ligand derived from 5‐(tert‐butyl)‐2‐hydroxybenzene‐1, 3‐dicarbaldehyde bis(benzoylhydrazone) (HL) were synthesized and characterized. The crystal‐structure determination of complex 2 provided the following crystal data: monoclinic, space groupP21}/a, a= 11.412(2), b = 24.509(4), c = 14.833(4) Å, β = 104.41(2)°, K = 4018(3) Å3,Z= 4. The structure shows that the CuIIions are bridged by the endogenous phenolato O‐atom and by an exogenous bridge CH3O−. The analysis of variable‐temperature magnetic susceptibility data (4‐300 K.) indicates that there is an antiferromagnetic interaction between the CuIIions in these complexes with an exchange parameter (2J) of −119.1 cm−1for complex 1 and −361.8 cm−1for complex3. The effect of some exogenous bridging ligand

ISSN:0018-019X    

DOI:10.1002/hlca.19970800119

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

Abstractβ‐Cryptoxanthin (1) was acetylated and then epoxidized with monoperoxyphthalic acid. After hydrolysis, repeated chromatography, and crystallization, (3S,5R,6S)‐5,6‐epoxy‐β‐cryptoxanthin (3), (3S,5S,6R)‐5,6‐epoxy‐β‐cryptoxanthin (4), (3R,5′R,6′R)‐5′,6′‐epoxy‐β‐cryptoxanthin (5), (3S,5R,6S,5′R,6′S)‐5,6:5′,6′‐diepoxy‐β‐cryp‐toxanthin (6), and (3S,5S,6R,5′S,6′R)‐5,6:5′,6′‐diepoxy‐β‐cryptoxanthin (7) were isolated as main products and characterized by their UV/VIS, CD,1H‐ and13C‐NMR, and mass spectra. The comparison of the carotenoid isolated from yellow, tomato‐shaped paprika (Capsicum annuum var. lycopersiciform

ISSN:0018-019X    

DOI:10.1002/hlca.19970800120

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY

摘要:

Ring Opening of Sterically Crowded Spirocyclic 2, 5‐Dihydro‐l, 3, 4‐thiadiazoles by Cycloaliphatic Secondary AminesAt room temperature, the spirocyclic 2, 5‐dihydro‐l, 3, 4‐thiadiazole3reacted with cyclic secondary amines6viaring opening to giveN‐alkylidene‐hydrazones of type7(Scheme 2). A reaction mechanismviaa base‐catalyzed transformation of the dihydrothiadiazole ring to the corresponding thiolate19and the intermediate thioaldehyde21is proposed inScheme 6.An analogous reaction occurred with the mixture of the dispiro compounds4/5and morpholine (6a) or azetidine (6d), leading to a mixture of isomeric dihydrazones8and9(Scheme 3). The structure of the symmetrical isomer8awas established by X‐ray crystallography. In addition to8aand9a, the thiiranelOa(Scheme 3) was isolated

ISSN:0018-019X    

DOI:10.1002/hlca.19970800121

出版商:WILEY‐VCH Verlag GmbH    

年代:1997

数据来源: WILEY