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  • 1985-1989  (7)
  • 1970-1974  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Synthese einiger 8-substituierter 2-Methyl-1,2,3,4-tetrahydroisochinoline (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 1828-1834 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Synthesis of Some 8-Substituted 2-Methyl-1,2,3,4-tetrahydroisoquinolinesA general route to 8-substituted tetrahydroisoquinolines is exemplified by the preparation of the 2-methyl-1,2,3,4-tetrahydroisoquinolin-8-ol (11), the -8-carbaldehyde oxime (12) and the -8-carbonitrile (13). It involves the conversion of isoquinoline (1) by partially modified Steps 1, 2, 3, and 5 (see the Scheme) into the 5-bromo-8-nitro derivative 5, reduction of the latter to the 8-amino derivative 8 and replacement of the NH2-group with an appropriate substituent by a Sandmeyer-like reaction. The selective reductions of the N-containing ring in 6 (Steps 5, 6, and 8) and of the NO2-group in 5 (Steps 4 and 7) were also studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680704
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  • 2
    Electronic Resource
    Electronic Resource
    Kurze Totalsynthesen von (±)-Sativen und (±)-cis-Sativendiol (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 788-807 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Short Total Syntheses of (±)-Sativene and (±)-cis-SativenediolOur approach to (±)-sativene (7) and (±)-cis-sdtivenediol (9) involves: (a) reaction of 3-methylbutanoyl chloride with Et3N/cyclopentadiene to give the endo-isopropyl-ketone 1 (here improved to 71%), (b) NBS bromination of 1 to a 5:1 mixture (87%) of the bromo-ketones 2 and 3, (c) NFD-reaction sequence initiated by the attack of 1,2-butadienyl titanate (complex of 15, obtained from 2-butine) on 2/3 to afford 52% of the brexenone derivative 4 (along with 8% of its epimer 16), (d) addition of dibromomethane to 4 forming 63% of the diene-alcohol 5 (along with 13% of the diene-carbaldehyde 38), and (e) carbenoid ring-expansion with MeLi applied to 5 resulting in 41% the diene-ketone 6 (along with 15% of a 1:3 mixture of the diene-ketones 32 and 33). Wolff-Kishner reduction of 6 led to 81% of (±)-sativene (7), when enough O2 was present, but to 97% of the diene 8 in the strict absence of O2. (±)-cis-Sativenediol (9) was obrained (86%) by OsO4 hydroxylation of 8. The brexenone derivatives 4 and 16 (6:1, 50%) were also produced when the NFD-reaction sequence was applied to the isomeric bromo-ketone mixture 13/13 (1:3). The latter was obtained by NBS bromination of 10, which in turn was available by base epimerization of 1, followed by destructive removal of unreacted 1 by repeated gas-flow thermolysis. An analogous (less convenient) route to (±)-sativene (7) passed through a series of dihydro compounds (the ene series) it started with the methylidene-ketone 36, which was the product (97%) of a partial hydrogenation of 4. Addition of dibromomethane to 36 led t 62% of the methylidene-alcohol 39 (along with a little tetracyclic ether 40). Carbenoid ring expansion of 39 with MeLi afforded ca. 42% of the methylidene-ketone 41 (along with 7% of the methylidene-ketone 43 or, under slightly different condition, along with 9% of the methylidene-ketone 42 and 10% of the methylidene-carabaldehyde 44). The methylidene-alcohol 39 and the methylidene-ketone 43 were also obtained by partial hydrogenation of 5 and 33, respectively. Wolff-Kisher reduction converted 41 into (±)-sativene (7 99%); the same conditons applied to 42 afforded only ca. 8% 7 (along with three other hydrocarbons, one of them (ca. 21%) probably being (±)-copacamphene (45)). In the diene series, the two succeeding reactions (4→5 and 5→6) competed with the same side reaction, a rearrangement leading to the brendene-aldehyde 38. In the ene series, the corresponding dihydro-by-product 44 was found in the reacton 39→41, but not during 36→39. These side reactons could largely be suppressed by keeping the reaction temperature low. An explanation is proposed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710414
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  • 3
    Electronic Resource
    Electronic Resource
    Cyclobut-2-enones from Alkynes via Dichlorocyclobut-2-enonesIn part taken from the Ph.D. thesis of A.A.A., University of Zürich, 1986. (1987)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 70 (1987), S. 321-328 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The [2 + 2]-cycloaddition of dichloroketene (prepared in situ from CCl3COCl and Zn(Cu)) with three alkynes 1a-c to form 2,3-dimethyl-(2a), 2,3-diethyl-(2b) and 3-butyl-4,4-dichlorocyclobut-2-enone (2c) proceeds rapidly in the absence of POCl3. The primary products 2a-c rearrange in situ to the 2,4-dichlorocyclobut-2-enones 3a-c under the influence of ZnCL2 produced during the reaction. ZnCl2 converts both 2a and 3a into a 4:6 equilibrium mixture of the two; this isomerization does not occur with LiCl. The Cl-atoms of both 2a, b and 3a, band of 2c may reductively be removed with Zn(Cu) in AcOH/pyridine to afford the alkylcyclobutenones 4a-c. Without pyridine, this reduction gives ca. 1:1 mixtures of the double-bond isomers 4 and 5 in low yields. The cyclobutenones 2c and 4c may be deuterated by CD3COOD in the presence of pyridine. D-Atom is introduced into 2c at C(4) and at C(γ), and into 4c at C(2) and C(4). A mechanism for this deuteration is considered, which does not involve a cyclobutadienolate 7, but rather a cyclobutenolate of type 8. The reductions of 2 and 3 to 4 might also pass through the same type of intermediate 8.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19870700208
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  • 4
    Electronic Resource
    Electronic Resource
    Acid-Catalysed Rearrangements of α-Vinylcyclobutanones (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 439-449 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The BF3 · Et2O- and the CH3SO3H-catalysed rearrangements of 10 α-vinylcyclobutanones have been examined. With little acid, the β,β-dialkyl derivatives 1 were transformed into linear dienones 2 and 3; with more acid, they were converted into cyclopentenones 4 by Nazarov cyclisation of initially formed 2/3. The β-monoalkyl (including the β,γ-dialkyl) derivatives 7 rearranged only with a high acid concentration to afford the cyclopentenones 8 by 1,2-acyl migration. In the case of 7a, the cyclopentenone 8a was accompanied by the unexpected constitutional isomer 9a, which is explained by a reversible interconversion of the cyclobutanone 7a with its isomer 19 via a cyclopropane intermediate like 18. In the case of the β,β-dialkyl derivative 5, which contains an α-isobutenyl (instead of an α-vinyl) group, the acid-catalysed rearrangement product was the bicyclo[3. 1. 0]hexanone derivative 6.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680217
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  • 5
    Electronic Resource
    Electronic Resource
    Solvolysen von 4-Alkylidenbicyclo[3.2.0]hept-2-en-6-olen. Synthese von 1-Vinylfulvenen und 8,8-Diphenylheptafulven (1985)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 68 (1985), S. 930-939 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Solvolysis of 4-Alkydenbicyclo[3.2.0]hept-2-en-6-oles. Synthesis of 1-Vinylfulvenes and 8,8-DiphenylheptafulveneFour 4-alkylidenebicyclo[3.2.0]hept-2-en-6-ones 2-5, obtained via ketene cycloaddition to fulvenes, were reduced to separated mixtures of the ‘endo’ -alcohols ‘endo’-6 to ‘endo’-9 (68-73%) and ‘exo’-6 to ‘exo’-9 (3-20%). Treatment of some of these alcohols with (CF3SO2)2O in CH2Cl2/pyridine caused a spontaneous solvolysis to yield unsaturated 7-membered rings as pyridinium triflates 10-12 or 1-vinylfulvenes 13 and 14, a new class of reactive tetraenes: Both ‘endo’-9 and ‘exo’-9, having two methyl groups at C(7), were converted into the vinylfulvene 13 (≈ 80%). The alcohols with two H-atoms at C(7) exhibited a stereochemically controlled reaction selectivity, inasmuch as ‘endo’-6 to ‘endo’-8 afforded only the corresponding 7-membered-ring pyridinium salts 10-12 (66-79%), while ‘exo’-6 produced only the vinylfulvene 14 (77%). A stereoelectronic control argument explains the C(1), C(5)-bond cleavage with ‘endo’-B and ‘endo’-6-‘endo’-8, as well as the C(1), C(7)-bond cleavage with ‘exo’-B, ‘exo’-6, and with both ‘endo’- and ‘exo’-9. Thermolysis (120°) of the pyridinium triflates 10 and 11 yielded the 3-isopropenyl-cycloheptatrienes 18 and 19, respectively (≈90%); similar conditions (145°) applied to the triflate 12 produced the doubly cyclized fluorene derivative 21 (60%). When the iodide 22 derived from the triflate 12 with Nal was heated in refluxing toluene, 8,8-diphenylheptafulvene (23, 86%) was obtained.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19850680415
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  • 6
    Electronic Resource
    Electronic Resource
    Short Syntheses of (±)-Grandisol and (±) Lineatin via, a common Intermediate (1987)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 70 (1987), S. 1302-1306 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A 6-step synthesis of (±)-grandisol (1) is presented, which involves dichloroketene addition to 3-methyl-3-butenyl acetate (4), reductive dechlorination of the adduct 6 to the ketone 7 and saponification to 8, aldolization of 7 or 8 with acetone and cyclization to the bicyclic ketone 9, Wolff-kishner, reduction to 14, and finally ring opening to 1. Since 9 is a known intermediate of the synthesis of (±)-lineatin (2), the latter can now be obtained in 6 steps.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19870700510
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  • 7
    Electronic Resource
    Electronic Resource
    Synthese von enantiomerenreinen Violaxanthinen und verwandten Verbindungen (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 931-956 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses of Enantiomerically Pure Violaxanthins and Related CompoundsThe epoxides 16 and ent-16, prepared by Sharpless-Katsuki oxidation of 15 in excellent yield and very high enantiomeric purity, were used as synthons for the preparation of (+)-(S)-didehydrovomifoliol (45), (+)-(6S, 7E, 9E)-abscisic ester 46, (+)-(6S, 7E, 9Z)-abscsic ester 47, (-)-(3S, 7E, 9E)-xanthoxin (49), (-)-(3R, 7E, 9E)-xanthoxin (50), (3S, 5R, 6S, 3′S,5′R, 6′S, all-E)-violaxanthin (1) (3R, 5R,6S,3′R,5′R,6′S, all-E)-violaxanthin (55) and their (9Z) (see 53, 57), (13Z) (see 54, 58), and (15Z) (see 60) isomers. The novel violadione (61) was prepared from 1 by oxidation with DMSO/Ac2O. By base treatment, 61 was converted into violadienedione (62), a potential precursor of carotenoids with phenolic end groups.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710502
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  • 8
    Electronic Resource
    Electronic Resource
    The structure of Arteannuin B and its Acid Hydrolysis Product (1974)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 57 (1974), S. 602-615 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Die Struktur des Sesquiterpen-γ-Laktons Arteannuin B (1) wurde röntgenographisch und diejenige seines Hydrolyseproduktes (2) durch eine vollständige Analyse des NMR.-Spektrums ermittelt.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19740570314
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  • 9
    Electronic Resource
    Electronic Resource
    Isomerisierungen und Umlagerungen in Bicyclischen Systemen via cyclopropan-carbaldehyd-enamine (1974)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 57 (1974), S. 734-748 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pyrrolidino-aminal (4) of bicyclo[3.1.0]hex-2-ene-6-endo-carbaldehyde (3) underwent a facile (80°), mildly acid catalyzed isomerization to the corresponding exo-aminal (6), which was characterized by hydrolysis to bicyclo[3.1.0]hex-2-ene-6-exo-carbaldehyde (7).At higher temperatures (140°), the two aminals 4 and 6 were converted smoothly to a 1:1 mixture of syn- and anti-4-(pyrrolidino-methylidene)-bicyclo[3.1.0]hex-2-ene (syn- and anti-7-pyrrolidino-homofulvene1) 8 and 9. The structures of 8 and 9 were derived from spectral data. This corrects a previous interpretation by Cook et al.The endo → exo-aminal isomerization (4 → 6) is considered to occur via the enamine (5) of bicyclo[3.1.0]hex-2-ene-6-carbaldehyde (3 or 7), with which the aminals (4 and 6) are in equilibrium. The same enamine (5), a methylidene cyclopropane derivative, is thought to be the intermediate in the aminal (4 or 6) → amino-homofulvene (8 and 9) conversion, which, therefore, belongs to the vinyl-methylidene-cyclopropane rearrangement type.A cationic mechanism for the endo → exo-aminal isomerization is excluded by the discrepancy in this reaction of the pyrrolidino-aminals (13 and 15) of 6-exo-methyl-bicyclo[3.1.0]hex-2-ene-6-endo-carbaldehyde (12) and of bicyclo[3.1.0]hexane-6-endo-carbaldehyde (14). While the former aminal (13) is stable even under acid catalysis and at higher temperatures, the latter (15) isomerizes readily to the exo-aminal 16.The three endo-aldehydes 3, 12 and 14 were prepared by the alkali catalyzed rearrangement of the three chlorohydrins 7-endo-chloro-bicyclo[3.2.0]hept-2-en-6-endo-ol (20ac), 7-endo-chloro-7-exo-methyl-bicyclo[3.2.0]hept-2-en-6-endo-ol (20ad) and 7-endo-chloro-bicyclo[3.2.0]heptan-6-endo-ol (20bc) according to the method of Brook.The configurations of the unsaturated endo-aldehydes 3 and 12 followed from their equilibria with the corresponding 2-oxa-bicyclo[3.2.1]octa-3,6-diene systems (23) and those of the saturated aldehydes 14 and 17 from oxidations to the corresponding carboxylic acids. The endo- and exo- isomers of the aldehydes and aminals treated in this work were readily distinguished by certain highly characteristic NMR.-signals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19740570327
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