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  • 1
    Electronic Resource
    Electronic Resource
    Thermische Umwandlung von Phenyl-penta-2,4-dienyläthern in 4-[Penta-2,4-dienyl]-phenole als Beispiel für [5,5]-sigmatropische Umlagerungen. Vorläufige MitteilungEine ausführliche Mitteilung soll in dieser Zeitschrift erscheinen. (1968)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 51 (1968), S. 190-193 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction between phenol and trans penta-2,4-dienyl chloride gave trans penta-2,4-dienyl Phenyl ether (I), whereas with a mixture of sorbyl chloride and 1-methylpenta-2,4-dienyl chloride, pure trans, trans hexa-2,4-dienyl phenyl ether (IV) and trans 1-methylpenta-2,4-dienyl phenyl ether (V) were obtained. The ether I gave, on heating in dilute solution at 185°, 4-(penta-2,4-dienyl)-phenol (III) as the main product, and also some 2-(2-vinylallyl)-phenol (II). The ether IV provided, on heating at 165°, in addition to the ortho CLAISEN rearrangement product VI, mainly a mixture consisting of 94% 4-(1-methylpenta-2,4-dienyl)-phenol (VIII) and only 6% 4-(hexa-2,4-dineyl)-phenol(IX). The latter product (IX) was the only para isomer produced on heating ether V, but in addition 22% of the ortho rearrangement product VII was formed.The migrations I → III, IV → VIII, and V → IX, proceeding through a ten membered transition state, are the first [5,5] sigmatropic rearrangements described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19680510120
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  • 2
    Electronic Resource
    Electronic Resource
    Eine neue 2-Allylphenol-Cumaran-Umlagerung (1972)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 55 (1972), S. 1625-1674 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2-(1′-Arylallyl)-phenols (9, 10, 11, 12, 13, 14, 15, 16) are transformed on heating in N, N-diethylaniline at 225° into trans-2-aryl-3-methyl-coumarans (26, 29, 32, 34, 36, 38, 40, 42) in excellent yields. The corresponding cis-coumarans are minor products. Similar thermal behaviour is shown by 2-(1′-vinylallyl)-phenols (7, 8) which are thermally converted into trans-3-methyl-2-vinyl-coumarans (24, 19) and 5-methyl-2,5-dihydro-(1-benzoxepins) (25, 18). The latter compounds are thermally unstable and rearrange to give approximatively 3:1 mixtures of trans- and cis-3-methyl-2-vinyl-coumarans (24, 19). Reaction mechanisms for these new thermal rearrangements are discussed in schemes 2, 3 and 4.The 2-(1′-arylallyl)-phenols 9, 12 and 14 yield under acidic conditions (HBr/HOAc) the expected 3-aryl-2-methyl-coumarans 28, 35, 39 along with 2-aryl-3-methyl-coumarans 26, 34, 38 and 2-aryl-2-methyl-coumarans 44, 45, 46. The intervention of phenonium ions is discussed for these reactions (cf. scheme 5).When the 2-(1′-arylallyl)-phenols 12 and 14 were irradiated in benzene solution with a mercury high pressure lamp, the main products obtained were 3-aryl-2-methyl-coumarans 35 and 39 which were formed rapidly. 2-Aryl-3-methyl-coumarans yield also 3-aryl-2-methyl-coumarans, when irradiated in benzene solution.
    Additional Material: 11 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19720550526
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  • 3
    Electronic Resource
    Electronic Resource
    Zur Stereochemie der aromatischen CLAISEN-Umlagerung (1969)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 52 (1969), S. 335-361 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The possible transition state conformations (chair (S), boat (W), and twist (T), respectively cross (K) forms) and methods for their determination in the thermal ortho-CLAISEN rearrangement of allyl aryl ethers are discussed.Crotyl 3,5-dimethylphenyl ether (11) gives a mixture of 2-(α-methylallyl)-3,5-dimethyl-phenol (12) and 4-crotyl-3,5-dimethyl-phenol (13) on heating in N, N-diethylaniline. Values of 3 and 31 were obtained for the ratio of 12/13 for trans-11 and cis-11, respectively. It therefore follows that both ethers rearrange steroselectively ( 〉 90%) by the S or W forms of the activated complex.αMethylallyl 6-alkylphenyl ethers rearrange on heating in various solvents to a mixture of trans-and cis-2-crotyl-6-alkyl-phenols. The amount of the cis-phenols in the rearrangement products decreases with the increasing bulk of the 6-alkyl substituent. This result is only obvious if the chair form of the transition state during the rearrangement of these ethers is highly favoured.trans-Crotyl 2,6-dimethylphenyl ether (trans-33) rearranges highly steroselectively (94%) on heating to trans-4-crotyl-2,6-dimethyl-phenol (trans-34). In the case of the corresponding cis ether 33, the rapid cis → trans isomerisation of this ether and the cis/trans ratio of the phenol 34 indicate that the reverse rearrangement of the intermediate ortho-dienone to the ether 33 and the further rearrangement to 4-crotyl-2,6-dimethyl-phenol (34) has little stereoselective character.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19690520141
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  • 4
    Electronic Resource
    Electronic Resource
    Thermische Umwandlung von Penta-2, 4-dienyl-phenyläthern in 4-(Penta-2, 4-dienyl)-phenole; [5s, 5s]-sigmatropische Umlagerungen (1970)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 53 (1970), S. 269-290 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: trans-Penta-2, 4-dienyl phenyl ether (trans-1), on heating at 186° in a five-fold excess of N, N-diethylaniline, gave via a [3s, 3s] rearrangement 23% of 2-(1-vinyl-allyl)-phenol (2) and via a [5s, 5s] rearrangement 37% of trans-4-(penta-2, 4-dienyl)-phenol (trans-3). The dimeric residue was formed from trans-1 by diene synthesis. By working at high dilution, the formation of dimeric products was kept to a minimum. The inversion of the migrating pentadienyl residue during the rearrangement of trans-1 to trans-3 was proved by rearrangement of the methyl labelled ether trans, trans-4 to the p-dienyl-phenol 8 (93%) (accompanied by only 7% of 9). trans-5 gave the p-phenol 9 quantitatively.cis-Penta-2, 4-dienyl phenyl ether (cis-1) was converted to 10 on heating, by a fast [1, 5s] H-migration.The above mentioned reactions of the type trans-1 → trans-3 show first order kinetics and are the first examples of [5s, 5s] sigmatropic rearrangements shown to go through a ten-membered transition state. The conformation of the activated complex is discussed in the light of the stereochemistry of the migrating penta-2, 4-dienyl group.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19700530208
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  • 5
    Electronic Resource
    Electronic Resource
    Thermisches Verhalten von Cyclopropa[c]chromenenHerrn Prof. Dr. H. H. Inhoffen zum 65. Geburtstag gewidmet (1971)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 54 (1971), S. 306-327 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Cyclopropa[c]chromenes 14, trans-and cis-15, trans-and cis-16 and 17 rearrange on heating 〉 200° in N, N-diethylaniline to give 2-alkyl-2H-chromenes 7, 8, 21, 22. The rate determining step of this rearrangement is the ‘homoelectrocyclic’ ring opening of the cyclopro-pa[c]chromenes to give ω-allyl-quinomethanes of type 4. These intermediates show fast [1,5s] and [1,7a] H-shifts, followed by electrocyclic ring closure. Deuterium labelling experiments are in agreement with this mechanism. The remarkable dependence of the rates of rearrangement with respect to the stereochemistry of the cyclopropa[c]chromenes (cf. table 2) suggests that in the first step only one of the two possible disrotatory modes of ring opening is involved.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19710540130
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  • 6
    Electronic Resource
    Electronic Resource
    Intramolekulare Diels-Alder-Additionen in 6-Methyl-6-(penta-2,4-dienyl)-cyclohexa-2,4-dien-1-on-Systemen. Vorläufige MitteilungEine ausführliche Mitteilung soll in dieser Zeitschrift erscheinen.Herrn Prof. Dr. A. Wettstein zum 65. Geburtstag gewidmet (1972)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 55 (1972), S. 526-531 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Thermal rearrangement of trans-penta-2,4-dienyl mesityl ether (trans-1) gave, besides trans, cis-2 and trans, trans-2, the homotwistanone derivative 1,3,10-trimethyl-tricyclo[5.4.0.03,9]undeca-5,10-dien-2-one (3) as well as its isomer 1,3,9-trimethyl-tricyclo[5.3.1.03,8]undeca-5, 9-dien-2-one (4). The tricyclic ketones 3 und 4 were shown to be products of intramolecular Diels-Alder addition in the intermediate 2,4,6-trimethyl-6-(penta-2,4-dienyl)cyclohexa-2,4-dien-1-one (5). Preparation of 2,6-methyl-6-(3-methyl-penta-2,4-dienyl)-cyclohexa2,4-dien-1-one (6) and subsequent heating of 6 in benzene gave the homotwistanone derivative 1,3-6-trimethyl-tricyclo5.4.0.03,9]undeca-5,10-dien-2-one (7) together with its isomer 1,3,6-trimethyl-tricyclo[5.3.1.03,8]undeca-5,9-dien-2-one (8) in good yield.
    Additional Material: 7 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19720550224
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  • 7
    Electronic Resource
    Electronic Resource
    Über die photochemische Cyclisierung von 2-Allylphenolen7. Mitteilung über Photoreaktionen von Heterocyclen. 6. Mitteilung siehe [1]. (1967)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 50 (1967), S. 255-262 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of 2-allyl-phenols and 2-but-3′-enyl-phenol were photochemically rearranged to the corresponding cyclic ethers. The isomer distribution was shown to be similar to that observed for the acid catalysed cyclisation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19670500132
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