摘要:

AbstractThe synthesis of five macrobicyclic polyamines1–5is described following a route in which the macrobicycle is formed by the coupling of two tripodal subunits. Such a sequence is appreciably shorter than the stepwise constructionviaa macrocycle, and may give higher yields, as illustrated by the case of bis‐tren3, which has been synthesized following both rou

ISSN:0018-019X    

DOI:10.1002/hlca.19850680202

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractTwo methods for stereoselective β‐glycosylation of digitoxose were developed. The first achieved stereocontrol by a 1,3‐participation of aN‐methylurethane group under acid catalysis. The second utilized mercuric‐ion catalyzed cleavage of thioglycosides and a 1,3‐participation of ap‐methoxybenzoyl group in a neutral medium. The first highly stereoselective and quite efficient synthesis of digitoxin (C7) was achieved by a combination of these methods. The furyl‐substituted precursorIVof digitoxigenin (Scheme 1) was used as aglycone, and the furan group was converted to the unsaturated lactone of digitoxin by our known oxidation procedure (m‐chloroperbenzoic acid/NaBH4) after the assembly of the carbohydrate portion of the molecule and its deblocki

ISSN:0018-019X    

DOI:10.1002/hlca.19850680203

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractA cell‐free extract, which was isolated from the leaves of matureCatharanthus roseusplants by a previously published procedure,does notconvert a mixture of secologanin and radiolabelled tryptamine to vindoline, as was recently claimed. The radioactivity in the purified alkaloid extract determined by earlier workers is certainly due to ‘impurities’ in the presumed ‘vindoline’. This was shown by extensive purification of the alkaloid extract (which contained added unlabelled vindoline as a carrier) followed by chemical conversion of vindoline to two derivatives and subsequent purification, ultimately giving unlabelled deacetyl

ISSN:0018-019X    

DOI:10.1002/hlca.19850680204

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractInduced by a stoichiometric excess of dichloro(diisopropoxy)titanium, 1‐(trimethylsiloxy)cyclohexene andp‐substituted β‐nitrostyrenes (Y = H,CH3,CH3O,CN) combine in CH2Cl2solution at −90° preferentially with relative topicityul– opposite to the corresponding reaction of enolates or enamines. The primary products are the bicyclic nitronates3–5which can be separated, and which are cleaved by KF in MeOH to give the aryl(nitroethyl)‐substituted cyclohexanones1and2(Tables 1and2, two typical procedures are given). The major products (2:1 to 4:1) are the hitherto not readily available diastereoisomers2ofl‐configuration. Instead of being solvolyzed, the bicyclic nitronate5can be used for nitroaldol additions (→6) and for [3 + 2]‐dipolar cycloadditions (→7), diastereoselectively furnishing products with 4 asymmetric C‐atoms (not counting acetal centers). TheMichaeladdition described here is yet another example of anul‐combination of trigonal centers induced byLewisacids, overriding the influence of the configura

ISSN:0018-019X    

DOI:10.1002/hlca.19850680205

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

Reduction of 1,2‐Bis[(Z)‐(2‐nitrophenyl)‐NNO‐azoxy]benzene1: Synthesis of Cyclotrisazobenzene ( = (5E,6aZ,11E,12aZ,17E,18aZ)‐5,6,11,12,17,18‐Hexaazatribenzo[aei][1,3,5,7,9,11]cyclododeca‐hexaene)Na2S reduction of 1,2‐bis[(Z)‐(2‐nitrophenyl)‐NNO‐azoxy]benzene (2) yielded 3 deoxygenated products: the (known) red 2,2′‐((E,E)‐1,2‐phenylenbisazo)dianiline (3, 23%), the orange 2‐[2‐((E)‐2‐aminophenylazo)phenyl]‐2H‐benzotriazol (4, 55%) and the colorless 2,2′‐(1,2‐phenylene)di‐2H‐benzotriazol (5, 13%). The constitutions of3–5and of6, theN‐acetyl derivative of4, were deduced from their1H‐NMR spectra (chemical shifts, couplings, and symmetry properties), and the configurations of3,4, and6at their N,N‐double bonds are assumed to be the same as in2. Oxidation of3with 2 mol‐equiv. of Pb(OAc)4afforded5(47%) and a novel, highly symmetrical macrocycle, called cyclotrisazobenzene (7, 24%). The constitution of7as a tribenzo‐hexaaza[12]annulene and its (E)‐configuration at the N,N‐bonds was confirmed by X‐ray analysis. The molecular symmetry expressed by the1H‐,13C‐ and15N‐NMR spectra of7reveals a rapid torsional motion around the six N,C bonds. This implies that the N,N‐double bonds in the cyclic 12π‐electron syste

ISSN:0018-019X    

DOI:10.1002/hlca.19850680206

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractA short synthesis of the title compound13is reported. The acetal group in13enables one to control the regio‐ and stereoselectivity of the two successiveDiels‐Alderadditions of the tetraene. The first addition is significantly faster than the second one, thus making13a versatile reagent for regio‐ and stereoselective ‘tandem’ cyclo

ISSN:0018-019X    

DOI:10.1002/hlca.19850680207

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractAs a further application of the cyclopentenone formationA→Cviathe thermal α‐alkynone cyclisationB→Cand in order to test the fate of an isolated C,C‐double bond within a molecule under these conditions, we investigated the synthesis of the acorone intermediate3starting from the known carboxylic acid1. The α‐alkynone2was obtained from1viathe acyl chloride6and a Pd(II)‐catalysed route (22%). The thermolysis of2at 550° provided the target molecule3(48%) together with the product9(20%) of a competing intramolecular ene reaction and its dimer10(4%). At a higher thermolysis temperature (650°), the spiro ketone3was found to be unstable, affording theretro‐Diels‐Alderfragments 4‐methylidene‐2‐cyclopentenone (12) (33%) and isoprene (32%). A further example of the influence of an isolated double bond on the yield of the cyclopentenone‐formation sequenceA→Cwas provided by the comparison of the annelation14→20(5% overall with Pd(II)‐catalysed acylation) with that of its non‐olefinic analogue17→21(53%

ISSN:0018-019X    

DOI:10.1002/hlca.19850680208

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractThe title compound (1) is preparedin situfrom 5‐methylenebicyclo[2.2.0]hex‐2‐ene by pyrolysis and subsequent photoionization in a photoelectron spectrometer or by X‐ray irradiation in an Ar matrix where its electronic absorption spectrum is obtained. The results confirm earlier conjectures that the title cation exists as a distinct entity on the C7H8+hypersurface and can be obtained photochemically from other isomeric ions or by aMcLaffertyrearrangement. The enthalpies of formation of1, its precursor and the corresponding radical ions are compared to the most recent data available for other C7H8isomers and their ions. It is shown that the thermodynamic stability of1+is closer to that of toluene cation than concluded on the basis of earlier

ISSN:0018-019X    

DOI:10.1002/hlca.19850680209

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

Rearrangements of (2′‐Propinyl)cyclohexadienols and ‐semibenzenesThe acid‐catalyzed dienol‐benzene rearrangement of 3‐ and 5‐methyl‐substituted (2′‐propinyl)cyclohexadienols has been investigated. Treatment of the dienols with CF3COOH in CCl4yields allenyl‐ and (2′‐propinyl)benzenesvia[3,4]‐ and [1,2]‐sigmatropic rearrangements, respectively. The reaction with H2SO4in Et2O leeds to a mixture of allenyl‐, 2′‐propinyl‐, 3′‐butinyl‐ and (2′,3′‐butadienyl)benzenes (Scheme 3). The latter are products of a thermal semibenzene‐benzene rearrangement(cf. Scheme 9). The corresponding semibenzenes have been prepared by dehydration of the cyclohexadienols with H2SO4or POCl3(Schemes 6and7). Under acidic conditions, the p‐(2′‐propinyl)semibenzenes33–35(Scheme 8)undergo [3,4]‐ and [1,2]‐sigmatropic rearrangements to give again allenyl‐ and (2′‐propinyl)benzenes, whereas the thermal rearrangements to the 3′‐butinyl‐ and (2′,3′‐butadienyl)benzenes(Scheme 9)involves a radical mechanism. In contrast, theo‐(2′‐propinyl)semibenzeneb(Sc

ISSN:0018-019X    

DOI:10.1002/hlca.19850680210

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY

摘要:

AbstractHyperfine coupling constants and g‐factors determined by ESR and ENDOR spectroscopy are given for the radical anions of 21syn‐1,6:8,13‐bridged [14]annulenes. The great majority of these values is reported for the first time. The hyperfine data are consistent with the single occupancy of an orbital which resembles a π‐perimeter‐LUMO of the same nodal properties. The sum of the coupling constants of the protons attached to the π‐perimeter can be used as a planarity criterion for t

ISSN:0018-019X    

DOI:10.1002/hlca.19850680211

出版商:WILEY‐VCH Verlag GmbH    

年代:1985

数据来源: WILEY