摘要:

AbstractAchiral spiroactivated cyclopropanes are isomerized to optically active (R)‐(cycloalk‐2‐enyl)‐Meldrum's acids ( = (R)‐5‐(cycloalk‐2‐enyl)‐2,2‐dimethyl‐1,3‐dioxane‐4,6‐diones) in high yield and ee's up to 86% by catalytic amounts of cob(I)alam

ISSN:0018-019X    

DOI:10.1002/hlca.19940770502

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractKinetic and equilibrium studies show that typical xenicanes such as dictyolactone (1) and 4‐hydroxydictyolactone (3) undergo slow conformation medium‐ring flipping between the predominanttrans‐(1aor3a; Me(20)transto H–C(3)) and the minorcis‐conformers (1bor3b; Me(20)cisto H–C(3); seeScheme 1). The formation of the latter is inhibited in heterocyclic‐ring‐opened congeners such as 18‐acetoxy‐4‐hydroxydictyo‐19‐al (7). Molecular‐mechanics calculations suggest that typical‐xenicanecis‐conformers are disfavoured by mainly C(4)–C(5) torsional strain. This is confirmed by the observation of two sizably populatedcis‐andtrans‐conformers for the unnatural 4‐oxoxenicanes10–12. Unusually facile thermal (E)→(Z) isomerization of xenicanes1,3,10–12, and7is also observed (→13–17and9, resp.;Scheme 3), reflecting great strain relief in the transition state. Conflicting results in the literature now fit into this scheme which provides a basis for unravelling recognition

ISSN:0018-019X    

DOI:10.1002/hlca.19940770503

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractReductive electrocrystallization at a constant current density (11.0–11.5 μA/cm2) of millimolar solutions of [M(bpy)3](PF6)2, where M = Fe, Ru, or Os, and bpy = 2,2′‐bipyridine in acetonitrile containing 0.1MBu4NPF6results in the formation of dark crystals on the Pt cathode. The crystals grow as long, thin, and shiny needles having a hexagonal cross section of 0.1–0.5 mm in diameter. Combustion microanalyses results are consistent with the composition for [Fe(bpy)3], [Ru(bpy)3], and [Os(bpy)3]. In addition, the chromophores are conserved, as confirmed by recording both the electronic and the1H‐NMR spectra after reoxidation of the electrocrystals in humid air. The spectra are identical to those for authentic samples of [Fe(bpy)3]2+, [Ru(bpy)3]2+, and [Os(bpy)3]2+. A ratio of 2.0 ± 0.1 e−/molecule is observed upon completion of the controlled potential electrolysis of a solution of [M(bpy)3]2+, which results in the precipitation of a dark solid and the almost complete fading of the color of the original solution. Unexpectedly, the crystals do not exhibit an ESR signal. These data indicate the formation of novel materials, crystalline [Fe(bpy)3], [Ru(bpy)3], a

ISSN:0018-019X    

DOI:10.1002/hlca.19940770504

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractDuring the examination of extracts fromOncinotis tenuilobaSTAPFa new polyamine,N4‐benzoylsperimidine (8), was isolated. For unambiguous structure elucidation, it was transformed into the diacetyl derivative13, and the three possibleN‐benzoyl‐substituted isomers of spermidine5, 8, and11together with their peracetylated derivatives12–14, respectively, were synthesized and ide

ISSN:0018-019X    

DOI:10.1002/hlca.19940770505

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Abstract(–)‐Carbovir ((–)‐1) was synthesizedviathe cyclic carbonate2in four steps starting from enantiomerically enriched (–)‐(S)‐(cyclopent‐2‐enyl

ISSN:0018-019X    

DOI:10.1002/hlca.19940770506

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractJuvenoids16–30, 32, 36, 38–41, 44–46, and49–56containing carbamate, carbonate, and urea moieties in the molecule were synthesized and subjected to a biological screening (Schemes 2–7, Table 2). Carbamate juvenoids1–4were used as reference compounds for a detailed structure‐activity study of their analogues. A clear relationship between the nature of the side chain functional group and the biological activity was found. Surprisingly, not only the juvenoids1–4but also38–41, the compounds with a reversed carbamateN,O‐substitution pattern, showed very promising biological activity. In contrast, the carbonate and urea derivatives displayed a remarkably low activity. The relationship between the size and substitution at atoms C(2) and C(3) of the saturated ring and the biological activity is very complex and is still not co

ISSN:0018-019X    

DOI:10.1002/hlca.19940770507

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe preparation of an analogue3aof the acetylcholinesterase inhibitor, huperzine A (1), is described in which the pyridinone moiety of the natural product is replaced with a thiazolone moiety. The synthesis started from cyclohexane‐1,4‐dione monoethylene ketal (7) by first annulating the thiazole ring using theGewaldprotocol (→8;Scheme 1) and then constructing the bicyclo[3.3.1]nonane substructure using our previously describedMichaeladdition/aldol condensation methodology (Scheme 3). The central problem was the protection of the thiazolone carbonyl group; only the 2‐unsubstituted thiazole survived the reaction conditions of the first half of the synthesis. Refunctionalization was later effected by lithiation and subsequent chlorination with hexachloroethane (30→31). Compound3awas ineffective in the acetylcholinesterase inhibition assay in concentrations up

ISSN:0018-019X    

DOI:10.1002/hlca.19940770508

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe 2‐(4‐nitrophenyl)ethoxycarbonyl(npeoc) group, introduced 1984 as protecting group for exocyclic amino functions of nucleic‐acid bases, reacts with amines under mild conditions to urea derivatives. Treatment of 2′,5′‐di‐O‐acetyl‐N6‐[2‐(4‐nitrophenyl) ethoxycarbonyl]cordycepin (3) with NH3/MeOH overnight at room temperature affords cordycepin (4) andN6‐carbamoylcordycepin (5). Preliminary investigations towards the elucidation of the reaction mechanism indicate that the aminolysis proceedsviaan addition‐elimination or an isocyanate mechanism, depending on the reaction conditions. The phenoxycarbonyl (phoc) group atN6orN4was chosen to study the mild conversion of carbamates with aromatic amines into ureas of adenosine

ISSN:0018-019X    

DOI:10.1002/hlca.19940770509

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe two‐step alkylation of phenyl prop‐2‐enyl sulfone (1) with protected ω‐bromoalkanols and 1‐iodoalkanes (→3; seeScheme 1) followed by a Pd‐catalyzed desulfonylation with LiBH4affords a 96:4 mixture of vinylbranched, protected alcohols and corresponding ethylidene‐branched isomers (see Scheme 2;4and5, respectively). By utilizing the large difference in reactivity of mono‐ and trisubstituted CC bonds towards singlet oxygen, the ethylidene derivatives are easily removed from the mixture by photo‐oxygenation. The vinyl‐branched compounds are inert to this reaction and can be conveniently isolated in highly pure form (99.5%)

ISSN:0018-019X    

DOI:10.1002/hlca.19940770510

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe reaction of Cu(AcO)2· H2O and tridentate β‐iminoketone ligands yielded four new copper complexes: acetato{4‐{[2‐(dimethylamino)ethyl]amino}pent‐3‐en‐2‐onato}copper(II) (1), triacetato{4‐{[3‐(dimethylamino)‐propyl]amino}pent‐3‐en‐2‐onato}dicopper(II) (2), {4‐{[2‐(dimethylamino)ethyl]amino}‐1,1,1‐trifluoropent‐3‐en‐2‐onato}( trifluoroacetato)copper(II) (3), and pentaacetato{4‐{[3‐(dimethylamino)propyl]amino}‐1,1,1‐trifluoropent‐3‐en‐2‐ onato}tricopper(II) (4). All compounds were coloured and air‐stable solids. The crystal structures of1and the dioxane adduct of3, μ‐(1,4‐dioxane)bis{{4‐{[2‐(dimethylamino)ethyl]amino}‐1,1,1‐trifluoropent‐3‐ en‐2‐onato}(trifluoroacetato)copper(II)} (3a), were determined. Complex1consists of dimeric units [{Cu(AcO)L}2] in the solid state (L = β‐iminoketonato ligand). In3a, two [Cu(CF3COO)L] are linkedviathe O‐atoms of the coordinated solvent 1,4‐dioxane. Compound1crystallized in the monoclinic space groupP21/nwith a formula unit in a cell having the dimensionsa= 11.152(6)Å,b= 10.104(3)Å,c= 11.805(7)Å, and β = 99.02(4)Å, and compound3acrystallized in the triclinic space groupP1with a formula unit in a cell having the dimensionsa= 8.709(3)Å,b= 9.439(4)Å,c= 12.395(3)Å, α = 67.57(3)°, β = 77.01(2)°, and β = 84.17(3)°. Mass spectra (MS), thermal analysis (DTA/TG), and evaporation‐rate measurements are

ISSN:0018-019X    

DOI:10.1002/hlca.19940770511

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY