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Photochemie von in 4-Stellung substituierten 5-Methyl-3-phenyl-isoxazole


Dietliker, Kurt; Gilgen, Paul; Heimgartner, Heinz; Schmid, Hans (1976). Photochemie von in 4-Stellung substituierten 5-Methyl-3-phenyl-isoxazole. Helvetica Chimica Acta, 59(6):2074-2099.

Abstract

4-Trideuterioacetyl-5-methyl-3-phenyl-isoxazole ([CD3CO]-27), upon irradiation with 254 nm light, was converted into a 1:1 mixture of oxazoles [CD3CO]-35 and [CD3]-35 (Scheme 13). This isomerization is accompagnied by a slower transformation of [CD3CO]-27 into [CD3]-27. Irradiation of the isoxazole derivatives 28, 29, 30 and (E)-31 yielded only oxazoles 36, 37, 38 and (E),(Z)-39; no 4-acetyl-5-alkoxy-2-phenyl-oxazole, 2-acetyl-3-methyl-5-phenyl-pyrrole or 2-acetyl-4-methoxycarbonyl-3-methyl-5-phenyl-pyrrole, respectively, were formed (Scheme 9 and 10). Similarly (E)-32gave a mixture of (E),(Z)-40 only (Scheme17). Upon shorter irradiation, the intermediate 2H-azirines (E),(Z)-41 could be isolated (Scheme 11). Photochemical (E)/(Z)-isomerization of the 2-(trifluoro-ethoxycarbonyl)-1-methyl-vinyl side chain in all the compounds 32, 40 and 41 is fast. At 230° the isoxazoles (E)- and (Z)-32 are converted into oxazoles (E)(Z)-40. The same compounds are also obtained by thermal isomerization of the 2H-azirines (E),(Z)-41. The most probable mechanism for the photochemical transformations of the isoxazoles, as exemplified in the case of the isoxazole 27, is shown in Scheme 13. A benzonitrile-methylide intermediate is postulated for the photochemical conversion of the 2H-azirines into oxazoles. 2H-Azirines are also intermediates in the thermal isoxazole-oxazole rearrangement. It is however not yet clear, if the thermal 2H-azirine-oxazole transformation involves the same transient species as the photochemical reaction. A mechanism for the photochemical isomerization of the 2H-azirine 11 to the oxazole 15 is proposed (Scheme 3)

4-Trideuterioacetyl-5-methyl-3-phenyl-isoxazole ([CD3CO]-27), upon irradiation with 254 nm light, was converted into a 1:1 mixture of oxazoles [CD3CO]-35 and [CD3]-35 (Scheme 13). This isomerization is accompagnied by a slower transformation of [CD3CO]-27 into [CD3]-27. Irradiation of the isoxazole derivatives 28, 29, 30 and (E)-31 yielded only oxazoles 36, 37, 38 and (E),(Z)-39; no 4-acetyl-5-alkoxy-2-phenyl-oxazole, 2-acetyl-3-methyl-5-phenyl-pyrrole or 2-acetyl-4-methoxycarbonyl-3-methyl-5-phenyl-pyrrole, respectively, were formed (Scheme 9 and 10). Similarly (E)-32gave a mixture of (E),(Z)-40 only (Scheme17). Upon shorter irradiation, the intermediate 2H-azirines (E),(Z)-41 could be isolated (Scheme 11). Photochemical (E)/(Z)-isomerization of the 2-(trifluoro-ethoxycarbonyl)-1-methyl-vinyl side chain in all the compounds 32, 40 and 41 is fast. At 230° the isoxazoles (E)- and (Z)-32 are converted into oxazoles (E)(Z)-40. The same compounds are also obtained by thermal isomerization of the 2H-azirines (E),(Z)-41. The most probable mechanism for the photochemical transformations of the isoxazoles, as exemplified in the case of the isoxazole 27, is shown in Scheme 13. A benzonitrile-methylide intermediate is postulated for the photochemical conversion of the 2H-azirines into oxazoles. 2H-Azirines are also intermediates in the thermal isoxazole-oxazole rearrangement. It is however not yet clear, if the thermal 2H-azirine-oxazole transformation involves the same transient species as the photochemical reaction. A mechanism for the photochemical isomerization of the 2H-azirine 11 to the oxazole 15 is proposed (Scheme 3)

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Additional indexing

Other titles:Photochemistry of 4-substituted 5-Methyl-3-phenyl-isoxazoles
Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:German
Date:1976
Deposited On:05 Nov 2014 11:33
Last Modified:05 Apr 2016 18:28
Publisher:Wiley-Blackwell Publishing, Inc.
ISSN:0018-019X
Funders:Schweizerischer Nationalfonds zur Förderung der wissenschaftlichen Forschung
Publisher DOI:https://doi.org/10.1002/hlca.19760590621
Permanent URL: https://doi.org/10.5167/uzh-100185

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