ChemInform Abstract: Epoxide‐Initiated Cationic Polyene Cyclizations.
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Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.Keywords:
Polyene
Cationic polymerization
The 9-(Z)-configuration was exclusively obtained in the carotenoid polyene chain irrespective of olefination and disconnection methods for terminal ortho-unsubstituted benzene rings. The 2,6-dimethyl substituents in the terminal rings secure an all-(E)-polyene structure. The single molecular conductance of the pure 9-(Z)-carotene was measured for the first time to be 1.53 × 10–4 ± 6.37 × 10–5G0, whose value was 47% that of the all-(E)-carotene ((3.23 × 10–4) ± (1.23 × 10–4) G0).
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Carotene
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The stereochemical outcome of cationic polyene cyclisations of geranylbenzene derivatives is affected by the different reactivity of hyperconjomer intermediates. The synthesis of (±)-taiwaniaquinone G by a cationic polyene cyclisation is described.
Polyene
Cationic polymerization
Reactivity
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I. M. Heilbron, E. R. H. Jones and R. A. Raphael, J. Chem. Soc., 1944, 136 DOI: 10.1039/JR9440000136
Polyene
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Abstract Some aspects of the formation and propagation of polyene sequences during the thermal degradation of PVC have been discussed. The average polyene sequence length occurring in a suspension polymerized PVC, degraded in nitrogen at 190°C, was determined to ca. 10 units. The results were somewhat dependent on the type of analysis employed. The formation of internal polyene sequences was characterized by three stages. After an initial period, where the number of internal sites remained constant, new sites were rapidly formed. The high rate of formation then gradually decreased with increasing conversion. Degradation mechanisms explaining this behavior were suggested.
Polyene
Degradation
Sequence (biology)
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Polyene
Nystatin
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Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Polyene
Fluorine
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Polyene
Nystatin
Natamycin
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A microwave assisted Wittig reaction allowed the synthesis, in good yields, of the longest polyene so far recorded with 27 conjugated double bonds. The synthesis of this stable, well-soluble polyene represents a noteworthy step in the direction of ultimate λ(max).
Polyene
Wittig reaction
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Abstract π‐Conjugated polyene complexes of the general formula (RuClCp*) n (polyene) [ 2 : n = 1, polyene = 1,4‐diphenylbuta‐1,3‐diene; 3 : n = 1, polyene = 1,6‐diphenylhexa‐1,3,5‐triene; 4 : n = 2, polyene = 1,8‐diphenylocta‐1,3,5,7‐tetraene; 5 : n = 2, polyene = 1,10‐diphenyldeca‐1,3,5,7,9‐pentaene; 6 : n = 3, polyene = 1,12‐diphenyldodeca‐1,3,5,7,9,11‐hexaene], in which each ruthenium(II) atom has Cp* (Cp* = η 5 ‐C 5 Me 5 ) and chlorido ligands, were prepared by treating [Ru(μ 3 ‐Cl)Cp*] 4 ( 1 ) with the corresponding α,ω‐diphenylpolyenes. All diene units of the complexes were fully metalated by the coordination of “RuClCp*” fragments in an η 4 ‐ s ‐ cis conformation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
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Diene
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The Lewis acid (2-propoxy)titanium trichloride is an efficient reagent for epoxide-initiated polyene cyclisations. Thus, 4 underwent tricyclisation to yield tricyclic products 5–7 in 73 % yield. The tetraene epoxide 1 gave pentacycle 15 in 21 % yield. The latter is the first example of a cationic pentacarbocyclisation.
Polyene
Cationic polymerization
Tricyclic
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