摘要:

AbstractA synthesis of the isosteric mono‐phosphonate analogues2aand19of the β‐and α‐D‐fructose 2,6‐bisphosphate, respectively, is described. Chain elongation of the 1‐deoxy‐1‐nitro‐D‐arabinose3(Scheme 1) by aHenryreaction with paraformaldehyde followed by protection of the resulting alcohol (methoxymethyl ether) and a radical‐chain substitution by nitromethane anion gave the key intermediates, thegluco‐anhydroalditol6and themanno‐anhydroalditol7. These products equilibrated under basic conditions. Conversion of7to the aldehyde9,Abramovreaction of9with diphenyl phosphite followed by deoxygenation according toBartongave the phosphonate11(Scheme 2). Selective hydrogenolysis of11, phosphorylation and deprotection gave2which was converted to the tetrasodium salt2a. Similarly,6was transformed into the isosteric phosphonate analogue19of the α‐D‐fruc

ISSN:0018-019X    

DOI:10.1002/hlca.19860690402

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractThe photo‐oxidation of [2.2.2]hericene (6) gave successively the endoperoxides11(9,10,11,12‐tetramethylidene‐4,5‐dioxatricyclo[6.2.2.02,7]dodec‐2(7)‐ene), the bis‐endoperoxide16(15,16‐dimethylidene‐4,5,11,12‐tetraoxatetracyclo[6.6.2.02,7.o9,14]hexadeca‐2(7),9(14)‐diene), and the tris‐endoperoxide19(4,5,11,12,17,18‐hexaoxapentacyclo[6.6.6.02,7.09,14.015,20]icosa‐2(7),9(14),15(20)‐triene). The endoperoxides11, 16, and19were formed in the presence or in the absence of a dye sensitizer. The sensitized photo‐oxidations of 2,3,5,6‐tetramethylidenebicyclo[2.2.2]octane (4), 5,6,7,8‐tetramethylidenebicyclo[2.2.2]oct‐2‐ene (5), 2,3,5,6‐tetramethylidenebicyclo[2.2.1]‐heptane (7), and 2,3,5,6‐tetramethylidene‐7‐oxabicyclo[2.2.1]heptane (8) gave successively the corresponding mono‐endoperoxides9, 10, 12, and13and the bis‐endoperoxides14, 15, 17, and18, respectively. Low‐temperature NMR spectra of the bis‐endoperoxides14and16indicated that theirC2andCsconformers have the same stability. Similarly, there was no difference in the enthalpy of theD3andC2conformers of the tris‐endoperoxide19. The following reactivity sequence was observed for the sensitized photo‐oxidations of6–8and 5,6‐dimethylidene‐7‐oxabicyclo[2.2.1]hept‐2‐ene (23):6+1O2→11>7+1O2→12>8+1O2→13>23+1O2→24, a trend parallel with that reported for the ethylenetetracarbonitrile (TCNE) cycloadditions to the same polyenes. The rate‐constant ratiosk1/k2andk2/k3for the three successive photo‐oxidations of [2.2.2]hericene (6) did not differ significantly from unity, in contrast with theDiels‐Alderadditions of6. Similarly, the rate‐constant ratiosk1/k2for the two successive photo‐oxidations of tetraenes7and8were significantly smaller than those reported for the successive TCNE cycloadditions to7to8. The endoperoxide formations are not sensitive to the change in the exothermicit

ISSN:0018-019X    

DOI:10.1002/hlca.19860690403

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Reactions of 1,3‐Thiazole‐5(4H)‐thiones withGrignard‐ and Organolithium Compounds: Carbophilic and Thiophilic AdditionsOrganolithium compounds and 1,3‐thiazole‐5(4H)‐thiones9reactedviathiophilic addition on the exocyclic S‐atom. The intermediate anionEhas been trapped by protonation to give12and by alkylation to yield16, respectively (Schemes 5and6). In competition with protonation ofE, a fragmentation to benzonitrile and a dithioester14was observed(Scheme 5). In some cases, the alkylation ofEled to the formation of dithioacetals17instead of16(Scheme 6). Methyl, ethyl, and isopropylGrignardreagents and9in THF underwent again a thiophilic addition yielding 4,5‐dihydro‐1,3‐thiazoles of type12(Scheme 3). In contrast to this result, MeMgI reacted with9ain Et2Oviacarbophilic addition to11. Again a carbophilic attack at C(5) of9was observed with allylmagnesium and 2‐propynylmagnesium bromide

ISSN:0018-019X    

DOI:10.1002/hlca.19860690404

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractThe conformational properties of Aib‐containing oligopeptides having the propensity to adopt amphiphilic helical conformations were investigated by CD spectroscopy in solution. The peptides CF3COOH.H‐Pro‐Glu‐[Ala‐Aib‐Glu‐Aib‐]4Gly‐OH (I), HCl.H‐Pro‐Ala‐Aib‐[Gul‐Ala‐Ala‐Aib‐]2Glu‐Ala‐Aib‐Gly‐PEGM (II), and CF3COOH.H‐Ala‐Aib‐[Glu‐Glu‐Ala‐Aib‐]3PEGM (III) were synthesized according to the general principles of the liquid‐phase method for peptide synthesis. PeptidesI‐IIIexhibit helical conformations in CF3CH2OH, MeOH, and in H2O at acidic pH; however, at pH 7, onlyIIforms a stable helix, whereasIandIIIare predominantly in an unordered conformation. Some general features for the construction of amphiphilic

ISSN:0018-019X    

DOI:10.1002/hlca.19860690405

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

2‐Aza‐1,3‐dienes. A New Approach to Substituted 2‐AminopyrazinesTreatment of enamines by tosylated isonitrosomalono derivatives gives access to 5‐dialkylamino‐1, 1‐dicyano 2‐aza‐1,3‐dienes (or 1‐methoxycarbonyl analogous) which are precursors of various regiospecific 5,6‐substituted 2‐amino‐3‐cyano (or methoxycarbonyl) pyrazines. Some examples of utilisation of these intermediates for synthesis of lumazines, pteridines, and other bic

ISSN:0018-019X    

DOI:10.1002/hlca.19860690406

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractThe reduction of δ‐hydroxy‐β‐ketoesters1was investigated with three different reducing agents. In several instances, high selectivity in favor ofsyn‐1,3‐diols w

ISSN:0018-019X    

DOI:10.1002/hlca.19860690407

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractA stereospecific and regioselectiveSN2 mechanism (Waldeninversion) is observed during studies involving modified terpenoid epimeric diols in a high‐pressure ion source using ammonia as a reagent ga

ISSN:0018-019X    

DOI:10.1002/hlca.19860690408

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Optically Active 4,5‐Epoxy‐4,5‐dihydro‐α‐ionones; Synthesis of the Stereoisomeric 4,5:4′,5′‐Diepoxy‐4,5,4′,5′‐tetrahydro‐ϵ,ϵ‐carotenes and the Steric Course of their HydrolysisWe prove that epoxidation with peracid of α‐ionone, contrary to a recently published statement, predominantly leads to thecis‐epoxide. Acid hydrolysis affords a single 4,5‐glycol whose structure, established by an X‐ray analysis, shows that oxirane opening occurred with inversion at the least substituted position (C(4)). Stablecis‐andtrans‐epoxides are prepared by epoxidation of the C15‐phosphonates derived from α‐ionone. Both the racemic and optically active form are used for the synthesis of the 4,5:4′,5′‐diepoxy‐4,5,4′,5′‐tetrahydro‐ϵ,ϵ‐carotenes having the following configuration in the end groups:meso‐cis/cis,meso‐trans/trans,rac‐cis/trans,rac‐ and (6R, 6′R)‐cis/cis,rac‐ and (6R, 6′R)‐trans/trans,rac‐ and (6R, 6′R)‐cis/trans, and (6R, 6′R)‐cis/ϵ. Acid hydrolysis of thecis/cis‐epoxycarotenoids under relatively strong conditions occurs again with inversion at C(4)/C(4′) in case of thecis/cis‐epoxycarotenoids, but at C(5)/C(5′) in case of thetrans/trans‐epoxycarotenoids. An independent synthesis of this 4,5,4′,5′‐tetrahydro‐ϵ,ϵ‐carotene‐4,5,4′,5′‐tetrol is presented. The irregular results of the oxirane hydrolysis are explained by assumption of neighbouring effects of the lateral chain. 400‐Mz‐1H‐NMR data are given for each of the stereoisomeric sets. In the visible

ISSN:0018-019X    

DOI:10.1002/hlca.19860690409

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

Synthesis of Triafulvene Precursors forRetro‐Diels‐AlderReactionsTriafulvene precursorsexo−15andendo−15have been prepared by addition of dibromocarbene to benzobarrelene12followed by a lithium‐halogen exchange, methylation, and elimination of HBr (12→13→14→15),(Scheme 2). Gas‐phase pyrolysis ofexo/endo‐mixtures of15above 400° gave minor amounts of naphthalene (16), traces of a hydrocarbon C4H4identified by MS (presumably triafulvene1) and predominantly (36%) the isomerization product17(Scheme 3). In a second synthetic approach the well‐known cycloheptatriene‐norcaradiene equilibrium of type26⇆27has been utilised to prepare variousendo‐trans‐3‐(X‐methyl) tricyclo[3.2.2.02,4]nona‐6,8‐dienes31(Scheme 5). However, numerous elimination experiments31→9failed so far. The structure of two rearrangement prod

ISSN:0018-019X    

DOI:10.1002/hlca.19860690410

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY

摘要:

AbstractLipophilic Co(III) and Mn(III) complexes of 5,10,15,20‐tetrakis[4‐(hexyloxycarbonyl)phenyl]porphyrin act as positively charged carriers for anions and induce anion selectivities in membranes clearly deviating from the sequence of classical anion exchangers. Different anion selectivities are observed for the Co(III) and Mn(III) porphyr

ISSN:0018-019X    

DOI:10.1002/hlca.19860690411

出版商:WILEY‐VCH Verlag GmbH    

年代:1986

数据来源: WILEY