摘要:

AbstractTwo general methods for the preparation of β‐silyl‐substituted divinyl ketones have been developed starting from either α, β‐unsaturated aldehydes or simple ketones. Anhydrous FeCl3induces the cyclization to cyclopentenones under mild conditions and in good yields with predictable and complete control over the position of the double bond in the five‐membered ring. The observed effects of substituents on rate can be explained by a rate‐determining cationic electrocyclization. Silyl substitution has been shown to retard

ISSN:0018-019X    

DOI:10.1002/hlca.19830660802

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractThe influence of remote substituents on the stereochemical outcome of electrocyclization in the silicon‐directedNazarovreaction has been examined. While the degree of stereocontrol was modest (ca.3:1) the substituent in the major isomer (4,5 or 7‐substitutedcis‐hexahydroind‐2‐en‐1‐ones) is alwayscisto the protons on the ring fusion. Thorough spectroscopic and conformational analysis revealed that divergent senses of electrocyclization are responsible for the observed products. Additional experiments suggest that steric, rather than stereoelectronic forces control the sense of cyclization. A qualitative description of the nature of reactive intermediates in the silicon‐directedNazarovreaction is proposed as well as an explanation for the remarkable efficacy of FeCl3for induci

ISSN:0018-019X    

DOI:10.1002/hlca.19830660803

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

Isolation and Identification of 8‐C‐Galactosylapigenin from Leaves ofCarlina acanthifolia8‐C‐galactosylapigenin was isolated from the leaves ofCarlina acanthifolia (Compositae). This identification represents only the third report of a mono C‐galactosylapigenin in plants and the first report in theC

ISSN:0018-019X    

DOI:10.1002/hlca.19830660804

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

The rearrangement in trifluoroacetic acid of two indole alkaloids of the echitamine series, desformocorymine(14)and dihydrocorymine(9), has been investigated. Desformocorymine(14)was tranformed into a mixture of carbinolamines17a,b, with the akuammiline skeleton, which were reduced (Et3SiH, CF3CO2H) into an isomer12of cathafoline(6).This sequence constitutes the first example of an interconversion of the corymine skeleton into the akuammiline skeleton(Scheme 2). In the case of dihydrocorymine(9), the rearrangement followed a different pathway owing to the formation of a hemiacetal between the primary alcohol CH2(17)‐OH and a carbonyl formed at C(3). Treatment of this hemiacetal26with aqueous base led to its opening with concomitant formation of a lactam.13C‐NMR seems to indicate that this lactam exists under a hydrated form27.This highly unstable intermediate was cleanly transformed (MeONa‐MeOH) into a 2‐acyl indole30(Scheme 4), the structure of which was determined by X‐ray crystallography. The formation of this acylindole involves the rupture of the C(7)C(16) bond; it is the reverse of the reaction generally postulated as occurring in the biogenesis of the pentacyclic alkaloids. The structure of a by‐product34was established as 17‐hydroxymethylvincoridine by X‐ray crystallography.The acid‐catalyzed rearrangements involve the rupture of the Ph‐NCN chromophore, with formation of a carbonyl at C(3). The reversibility of these steps is used in an easy correlation of dihydrocorymine and of 3‐epidihydrocorymin

ISSN:0018-019X    

DOI:10.1002/hlca.19830660805

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

Thirty‐two sterols are identified in the spongeHyrtios sp. In addition to fourteen monohydroxylated compounds, the sterol fraction contains eight functionalized sidechain sterols, three of them new: 3 β‐hydroxy‐24‐norchol‐5‐en‐23‐al(19), (22‐trans)‐3 β‐hydroxycholest‐5, 22‐dien‐24‐one(20)and (22R, 23R, 24S) or (22S, 23S, 24S)‐ 22,23‐epoxy‐24‐methylchoest‐5‐en‐3 β‐ol(24).The probable biological origin, rather than artifact producti

ISSN:0018-019X    

DOI:10.1002/hlca.19830660806

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractWolff‐Kishnerreduction of the optically active ketomorphinan5afforded the optically active morphinan6differing chromatographically and spectroscopically from the material obtained in aGrewe‐cyclization of the isoquinoline1. A single crystal X‐ray analysis of a hydrobromide salt of a phenolic amine obtained from1and2with refluxing hydrobromic acid showed this compound to be theN‐methylapomor

ISSN:0018-019X    

DOI:10.1002/hlca.19830660807

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractThe deprotonated 2‐phenylpyridine forms a 2:1 chelate with platinum(II) incis‐configuration, which exists as a dimer in a molecular so

ISSN:0018-019X    

DOI:10.1002/hlca.19830660808

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractVolumes of activation for the base hydrolysis of the dichromate anion have been measured at 298.2 K, using high‐pressure stopped‐flow spectrophotometry. The values of ΔV* (cm3· mol−1), − 17.9 ± 0.6, − 19.2 ± 0.9, − 24.9 ± 0.9 and − 26.0 ± 0.7 for OH−, NH3, H2O and 2,6‐lutidine, respectively, are consistent with an interchange mechanism with associati

ISSN:0018-019X    

DOI:10.1002/hlca.19830660809

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractIn view of the significance of steric compression in the base‐catalyzed intramolecular cyclization of polycyclic olefinic alcohols, the standard enthalpies of formation ofanti9,10‐10endo‐hydroxytricyclo [4.2.1.12,5]deca‐3,7‐dien‐9‐one(1)and 9‐oxatetracyclo [5.4.0.03,10.04,8]undec‐5‐en‐2‐one(2)as well as the kinetics of the ether format

ISSN:0018-019X    

DOI:10.1002/hlca.19830660810

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY

摘要:

AbstractMolecular catalysis of ATP‐hydrolysis by a number of protonated macrocyclic polyamines1–9has been investigated by31P‐NMR spectroscopy, and marked rate enhancements have been obtained. The largest acceleration is produced by the [24]‐N6O2macrocycle1, and the process displays the following properties:1. protonated1forms very stable complexes with ATP, as well as with ADP and AMP;2. it enhances the rate of ATP‐hydrolysis by a factor of 103at pH = 8.5; the rate of hydrolysis is constant over a wide pH‐range, from pH = 2.5 to 8.5;3.1is more efficient than acyclic analogues;4. the products of the reaction are orthophosphate (OP) and ADP, which is subsequently hydrolyzed to OP and AMP at a slower rate;5. at pH>6.5, a transient species is detected, which is tentatively identified as a phosphoramidate intermediate, resulting from phosphorylation of the macrocycle1;6. the reaction presents first‐order kinetics and is catalytic. The mechanism of the process is discussed in terms of initial formation of a complex between ATP and protonated1, followed by an intracomplex reaction which may involve a combination of nucleophilic or acid catalysis with electrosta

ISSN:0018-019X    

DOI:10.1002/hlca.19830660811

出版商:WILEY‐VCH Verlag GmbH    

年代:1983

数据来源: WILEY