摘要:

AbstractThe bridged bis(dihydrooxazole) compound (−)‐2and its silylated derivative (−)‐3have been synthesised as building blocks for chiral ligands. The complex of (−)‐3with CuIIhas been obtained, and its crystal structure has been determined. The CuIIion is bound to two deprotonated ligands in a twisted tetracoordinat

ISSN:0018-019X    

DOI:10.1002/hlca.19910740103

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractA series of new 2′–5′‐oligonucleotide trimers carrying a 9‐(2′,3′‐anhydro‐β‐D‐ribofuranosyl)‐(59), 9‐(3′‐deoxy‐β‐D‐glycero‐pent‐3‐enofuranosyl)‐(63), 9‐(3′‐azido‐3′‐deoxy‐β‐D‐xylofuranosyl)‐(62), and 9‐(3′‐halo‐3′‐deoxy‐β‐D‐xylofuranosyl)adenine (60and61) moiety at the 2′‐terminal end have been synthesizedviathe phosphotriester method. The properly protected, modified monomeric building blocks (6,9,16,19,27,33,36,37, and43) were obtained, in general, by a sequence of reactions, introducing the protecting groups into the right positions. Their condensations with the intermediary dimeric 2′‐terminal phosphodiesters48and49led to the fully protected 2′–5′‐trimers50–58which were deblocked to form the free 2′–5′‐trimers59–63. Easy elimination of HBr on deprotection did not allow to form the trimeric (3′‐bromo‐3′‐deoxy‐β‐D‐xylofuranosyl)adenine analogue but only63carrying an unsaturated su

ISSN:0018-019X    

DOI:10.1002/hlca.19910740104

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractHydrosilation of methylenecyclohexane and hex‐1‐ene by octa(hydridosilsesquioxane) catalysed by hexachloroplatinic acid is a new route to polyhedral organylsilsesquioxanes. Quantitative yield of octa(cyclohexylmethylsilsesquioxane) is reached. This reaction opens a vast field of yet unknown polyhedral silsesquioxa

ISSN:0018-019X    

DOI:10.1002/hlca.19910740105

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe substituted 2,2‐dialkyl‐2,3‐dihydro‐4H‐pyran‐4‐ones of typeIIandIIIhave been prepared by acid‐catalyzed cyclization of the corresponding substituted acetylenic ketonesIin good to excellent yields (Scheme 1). These 2,2‐dialkyl‐2,3‐dihydro‐4H‐pyran‐4‐onesIIandIIIhave been used for thein situpreparation of highly reactive dienes of typeIV–VI(Scheme 2) in carbonyl‐alkyne exchange reactions with electron‐poor alkynesVIIto yield the highly substituted aromatic compoundsVIIIandIX.These reactions proceed in good yields and with excellent degree of regioselectivity. Aryl‐substituted 2,2‐dialkyl‐2,3‐dihydro‐4H‐pyran‐4‐onesIII(R1= Ar) subsequently yield highly substituted biaryls. Reaction mechanisms are presented for the formation of the 2,2‐dialkyl‐2,3‐dihydro‐4H‐pyran‐4‐ones as well as for the

ISSN:0018-019X    

DOI:10.1002/hlca.19910740106

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractIt is shown here that the red seaweedLaurencia microcladia, collected off the torrent II Rogiolo, south of Livorno, contains rogiolenyne A (=(−)‐(1R*,2S*,3R*,5S*,7S*)‐2‐(bromomethyl)‐5‐[(Z)‐1‐chlorohex‐3‐en‐5‐ynyl]‐3‐ethyl‐4,8‐dioxabicyclo[5.1.0]octane; (−)‐1) while the spongeSpongia zimocca, which grows in the same small area, contains rogiolenyne B (=(−)‐(2R*3R*,4R*,5R*,7S*)‐3‐(bromomethyl)‐5‐chloro‐7‐[(Z)‐1‐chlorohex‐3‐en‐5‐ynyl]‐2‐ethyloxepan‐4‐ol; (−)‐4a) and its acetate, rogiolenyne C((−)‐4b). These structures, which are based on extensive NMR and MS data and on chemical transformation, are the first examples of branched marine C15acetogenins. Biogenesis of (−)‐1inL. microcladiais thought to involve C(12) extrusion form a C15linear tetraen‐1‐yne precursorviaH+‐induced cyclopropane ring closure, followed by Br+‐induced cyclopropane ring opening, aided by C–O−attack (Scheme 2). It is also proposed that transfer of (−)‐

ISSN:0018-019X    

DOI:10.1002/hlca.19910740107

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractIn presence of crown ether, 2‐alkoxy‐1,1‐dichlorocyclopropanes react witht‐BuOK/THF preferentiallyviaring opening to 2‐chloroalk‐2‐en‐1‐ones and alkynones or to chlorocyclopropenes. The latter may be intercepted with 1,3‐diphenylisobenzofuran, but in the absence of trapping agent, the rearrangement to vinylcarb

ISSN:0018-019X    

DOI:10.1002/hlca.19910740108

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe crystal and molecular structure ofbis[dinitrato‐(2,4,8,15,18,21‐hexaoxatricyclo[20.4.0.09,14]hexacosane)europium(III)]pentakis(nitrato)europiate(III) [Eu(NO3)2LB]2([Eu(NO3)5]), has been determined at 170 K from single‐crystal X‐ray diffraction. The complex crystallizes in the monoclinic space groupP21/n(ITCNo. 14):a= 16.338(3) Å,b= 15.704(3) Å,c= 24.474(4) Å, β = 97.73(1)°,Z= 4. The structure was refined to a finalRvalue of 0.058 (Rw= 0.060). The asymmetric unit contains three independent ions lying on general positions: [Eu(NO3)5]2−and two distinct [Eu(NO3)2LB]+cations with the macrocyclic ligand in thecis‐anti‐cisconformation (B‐isomer). The EuIIIions are 10‐coordinate with the following mean bond lengths: Eu–O(nitrate) = 2.48(2) Å in the anion and 2.45(2) Å in the two cations, Eu–O(ether) = 2.56(8) and 2.55(5) Å. Small but significant differences are observed between the two complex cations, especially with respect to the positions of the cyclohexyl substituent. A conformational analysis performed on the six O‐atoms of the complex cations confirms the predictions of a simple model. The metal ion sites of the complex have been probed by high‐resolution excitation and emission spectra at 296 and 77 K. The5D0←7F0excitation spectrum displays two main bands along with several other minor components. A detailed analysis of the corresponding and selectively excited emission spectra leads to the observation of three types of spectra corresponding to the three crystallographically different EuIIIions. Moreover, three minor sites are identified, one anionic and two cationic, with a population equal to ca. 10% of the population of the main sites. We interpret this finding as reflecting the presence of molecules wi

ISSN:0018-019X    

DOI:10.1002/hlca.19910740109

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractThe efficiency of aromatic ketones as singlet‐oxygen (1O2(1Δg)) sensitizers can vary considerably with the electronic configuration of their lowest triplet state and the solvent used. Near‐infrared measurements of tie luminescence of singlet oxygen have shown that the quantum yield of singlet‐oxygen production (ΦΔ) by 1H‐phenalen‐1‐one (1) is close to unity in both polar (ΦΔ= 0.97±0.03 in methanol) and non‐polar solvents (ΦΔ= 0.93±0.04 in benzene). Analysis of the absorption spectra of the ground state and phosphorescence measurements show that the lowest singlet and triplet states have dominant π, π* electronic configurations. The quantum yield of intersystem crossing (ΦISC) of1, determined by laser flash photolysis (partial‐saturation method), is equal to unity. In comparison with other aromatic ketones, these parameters are important for the discussion of the surprisingly high ΦISCof1and the efficient energy transfer from its triplet state to molecular oxygen. The 1H‐phenalen‐1‐one (1), being one of the most efficient singlet‐oxygen sensitizers in both polar and non‐polar media, could be used as a reference sensitizer, in particular in the area of

ISSN:0018-019X    

DOI:10.1002/hlca.19910740110

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractTo obtain stable derivatives of α‐unsubstituted pyrroles, the reaction of the test pyrrole9with a series of chalcones14a–hwere studied.Michaeladducts16b–hcould be isolated. In order to synthesize coloured derivatives, the reaction of different pyrroles9, 21, 23, and25with diphenylpropynone19was investigated. In these cases, too,Michael‐addition products were formed. The intense absorption band around 400 nm makes the identification of these derivati

ISSN:0018-019X    

DOI:10.1002/hlca.19910740111

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY

摘要:

AbstractTheC2‐symmetrical chiral pyrrolidines2and3are of opposite helicity. The correspondingN‐acylnitroso dienophiles6and7react in good yield with cyclohexadiene, leading thereby with excellent diastereoisomeric excess to the expectedDiels‐Aldercycloadducts (seeScheme). The [2.2.2] bicyclic moieties of the major diastereoisomers9and11proved to be of opposite configuration, as expected. Their configuration is best explained by assuming the acylnitroso dienophile to be in the s‐cisconformation in the transition state, the approach of the diene beingendo(s

ISSN:0018-019X    

DOI:10.1002/hlca.19910740112

出版商:WILEY‐VCH Verlag GmbH    

年代:1991

数据来源: WILEY