摘要:

Stability and Reactivity of 3‐Cyclopropylideneprop‐1‐enyl Ethyl Ether3‐Cyclopropylideneprop‐1‐enyl ethyl ether (1) dimerizes to a cyclobutane derivative2which, upon prolonged heating, is converted to a cyclooctadiene (3). The reactivity of1is discussed. The structures of2and3as well as of their derivatives have been determined using1H‐NMR spectroscopy and X‐ray crystal‐s

ISSN:0018-019X    

DOI:10.1002/hlca.19930760112

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractCrystallineN‐hydroxyamino‐acid derivatives4, readily available from non‐chiral acyl chlorides2and sultams1, were treated with aldehydes in the presence of NaBH3CN to giveN‐alkylhydroxylamines5.N,O‐Hydrogenolysis of5and saponification of6furnished (S)‐N‐alkylamino acids7in high optical purity. Similarly, (R)‐N‐alkylamino acids12were obtained from the antip

ISSN:0018-019X    

DOI:10.1002/hlca.19930760113

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe intramolecular addition of unsaturated alkoxycarbenes leads in high yields and diastereoselectively to fused cyclopropanes (Scheme 1). Reaction of the halodiazirines2,10,11, and20with the unsaturated phenolates1,8, and9yielded intermediate alkoxydiazirines, and hence the homobenzofurans5,12–16,22, and26(Scheme 2). The intermediate alkoxydiazirine25was isolated at low temperature (Scheme 3). An equilibrium between the cyclopropane derivatives12and27, and14and28was established at 120°. At 200°,12rearranged to the chromene29, by disrotarory opening of the cyclopropane ring, followed by electrocyclization. Hydrogenation of29gave the (all‐cis)‐chroman32(Scheme 4). The homoindole35was obtained in good yields, presumably by anSRN1 reaction from34and10(Sc

ISSN:0018-019X    

DOI:10.1002/hlca.19930760114

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractAryl‐halo‐diazirines react under basic conditions with 1,3‐cis‐, 1,2‐cisand 1,2‐trans‐diols to give acetals. Yields are high. Diastereoselectivities depend upon the diol and upon the reaction conditions. Thus, reaction of the 1,3‐cis‐diol1(Scheme 1) with2gave3as a single diastereoisomer. The 1,2‐cis‐diols4and7led to theendo‐ andexo‐acetals5/6(93:7) and8/9(ca.10:1), respectively, The 1,2‐trans‐diols10,16, and19reacted with2to afford11/12(90:10),17/18(1:1), and20/21(6:1), respectively. Reaction of the (4‐nitrophenyl)diazirine13with10at higher temperatures yielded14/15(6:4). The uracil moiety, the acetamido group, and the enol‐ether moiety are compatible with the reaction conditions. The diastereoselectivity is rationalized on the basis of a reaction sequence involving alkoxy‐halogen exchange, which is regioselective or not, thermolysis of the ensuing alkoxydiazirine(s), protonation of the alkoxycarbene to form an (E)‐configurated oxycarbenium ion, and attack of the neighboring oxy or hydroxy group, which is only possi

ISSN:0018-019X    

DOI:10.1002/hlca.19930760115

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractTheDiels‐Alderadducts8of furan to 1‐cyanovinyl acetate were converted into (Methyl 3‐chloro)‐5‐O‐(3‐chlorobenzoyl)‐2, 3‐dideoxy‐α‐dl‐arabino‐hexofuranosid)uronic acid ((α)‐18a) and into (methyl 3‐azido‐5‐O‐(3‐chlorobenzoyl_‐2,3‐dideoxy‐α‐dl‐ribo‐hexofuranosid)uronic acid ((α)‐41a). These compounds were condensed to (3S)‐3‐[(1′S)‐1′‐amino‐3′‐methylbutyl]‐3,4‐dihydro‐8‐hydroxyisocoumarin hydrochloride ((−)‐2); the resulting mixtures of diastereoisomeric amides were transfor

ISSN:0018-019X    

DOI:10.1002/hlca.19930760116

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe lanthanide nitrate complexes with 13‐crown‐4(13‐C‐4) have been prepared in AcOEt. These new complexes with the general formula Ln(NO3)3.(13‐c‐4) (Ln = La–Nd, Sm–Lu) have been characterized by means of elemental analysis, IR and1H‐NMR spectra, conductivity measurements, and TG‐DTA techniques. The crystal and molecular structure of Nd(No3)3. (13‐c‐4) has been determined by single crystal X‐ray diffraction. It crystallizes in the monoclinic space groupP21/a with Z = 8. Lattice parameters are a = 15.393(1), b = 12.578(1), c = 19.279(2) Å, β = 113.05(1)°, V = 3435 Å3, Dc= 2.01 g cm−3, μ = 31.0 cm−1(Mok2), F(000) = 2056. The structure was solved byPattersonandFouriertechniques and refined by least‐squares to a final conventionalRvalue of 0.032 for 5218 independent reflections withI ⩽ 3σ(I). There are two independent Nd(No3)3· (13‐C‐4) monomers in one asymmetrical unit. The coordination numbe

ISSN:0018-019X    

DOI:10.1002/hlca.19930760117

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe novel uncharged analog 2 of adenosine 3′,5′ ‐monophosphate (1) was prepared in its racemic form. To increase membrane permeability, the phosphate diester monoanion group of 1 was replaced by a dimethylene sulfone unit ( = methanosulfonylmethano group), and the 2′‐OH group was removed. To decrease lability against acid‐catalyzed depurination, the ring O‐atom was replaced by a CH2group. All three modifications are also expected to increase the stability of analog 2 towards enzymatic degradation. The carbocyclic skeleton of 2 was constructed from trinorbornenecarbaldehyde 3 (see Scheme1–3), and the adenine precursor 6‐chloropurine was introduced in the carbocyclic unit via an SN2 reaction based onMitsunobuchemistry

ISSN:0018-019X    

DOI:10.1002/hlca.19930760118

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Why Pentose‐And Not Hexose‐Nucleic Acids? Part III. Oligo(2′,3′‐dideoxy‐β‐D‐glucopyranosyl)nucleotides. (‘Homo‐DNA’): Base‐Pairing PropertiesSummaryin collaboration with Prof. Dr.C. E. Wintner, Haverford College, Haverford, PA 19041‐1392.The paper presents results of a comprehensive investigation on the pairing properties of homo‐DNA oligonucleotides, the preparation of which has been described inPart IIof this series [2]. The investigation was carried out by using established methods described in the literature for the characterization of oligonucleotides in the natural series, such as determination of melting temperatures of oligonucleotide duplexes by temperature‐dependent of melting temperatures, determination of pairing stoichiometry by ratio‐dependent UV spectroscopy of binary mixtures of pairing partners, temperature‐dependent CD spectroscopy, gel electrophoresis under non‐denaturing conditions, and – in selected cases –1H – and31P‐NMR spectroscopy.The systematic comparison of the paring properties of homo‐DNA oligonucleotides with corresponding DNA nucleotides (up to dodecamers) indicates that homo‐DNA is a highly efficient, autonomous, artificial pairing system with a pairing behavior that is in part similar to, but also, in part, strikingly different from, the pairing behavior of DNA. The pairing properties established so far are listed below in a manner that reflects the sequence of subtitles inChapt.2of the text; they were determined under the conditions: H2O, 0.15MNaCl, 0.01MTris‐HCl buffer, pH 7, oligonucleotide concentrations in the μMrange, 1:1 ratio of single st

ISSN:0018-019X    

DOI:10.1002/hlca.19930760119

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Synthesis of Chiral Cobalt Complexes with Planoid‐Tetradentate Ligand SystemThe synthesis of a series of Cbl‐related, achiral CoIIIcomplexes9a–cas well as enantiomerically pure,C2‐symmetric CoIIIcomplexes15and18, is reported (Schemes 3, 5, and7). The crystal structures of9cand15were determined. Complex18acts as an enantioselective catalyst in the isomerization of 1,4‐epiperoxides to hydroxycyclo

ISSN:0018-019X    

DOI:10.1002/hlca.19930760120

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThepara‐substituted tridentate ligands 2,6‐bis[1‐(3,5‐dimethoxybenzyl)benzimidazol‐2‐yl]‐4′‐X‐phenyl)‐pyridine (X = H: L3; X = NO2: L4; X = NEt2: L5) have been synthesized in six steps using Kröhnke reactions. Spectroscopic results show that the electronic properties of the ligands are strongly influenced by the nature of the substituent bound to the pyridine ring and extendedHückelcalculations performed on 4‐(X‐phenyl)pyridine fragments give a qualitative insight into the factors responsible for the striking differences observed in the absorption spectra. Upon complexation to FeII, the ligands L2–L5give intensely coloured pseudo‐ocatahedral low spin [Fe(Ln)2]2+(n = 2–5) complexes in acetonitrile solution. Electrochemical and spectroscopic measurements show that the particular electronic characteristics associated with each substituent strongly influence the properties of the resulting FeIIcomplexes as demonstrated by the very intense MLCT transition (ϵ>50000M−1cm−1) obs

ISSN:0018-019X    

DOI:10.1002/hlca.19930760121

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY