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Photochemistry of 2,3-benzo-2,4-cyclooctadienones: Isolation and chemistry of Δ4,5-trans isomers
Year:
1977
Authors :
Dunkelblum, Ezra
;
.
Volume :
99
Co-Authors:
Suzuki, M., Department of Chemistry, Michigan State University, East Lansing, MI 48824, United States
Hart, H., Department of Chemistry, Michigan State University, East Lansing, MI 48824, United States
Dunkelblum, E., Department of Chemistry, Michigan State University, East Lansing, MI 48824, United States
Li, W., Department of Chemistry, Michigan State University, East Lansing, MI 48824, United States
Facilitators :
From page:
5083
To page:
5090
(
Total pages:
8
)
Abstract:
Irradiation of the two 2,3-benzo-2,4-cyclooctadienones 8 and 20 gave the corresponding Δ4,5-trans isomers, whose physical properties (IR, NMR, UV) were determined. The IR spectrum of 8t suggests transannular conjugation between the carbonyl and carbon-carbon double bonds, and chemical evidence (for example, stereoselective transannular methanol addition) supports the view that the trans double bond is polarized δ+ at C(4), δ- at C(5), opposite to that in the cis isomer. Thus methanol adds to 8t at room temperature to give 10, and 20t similarly gives 21. The trans ketones 8t and 20t were reduced stereospecifically with lithium aluminum hydride to give only one of the two possible diastereomeric alcohols, 12t (crystalline) and 22t, respectively. Chromatography of 8t on silica gel caused stereoselective transannular addition of water to give the diol 9. Irradiation of 8 absorbed on silica gel (cyclohexane) gave the unsaturated alcohol 13. Irradiation of 14 in methanol also gave a stereoselective methanol adduct 18 (analogous to 10 and 21). However, in this case the intermediate trans ketone 14t could not be detected physically. Presumably the methyl groups are located in such a position as to sharply increase the strain and reactivity of 14t as compared with 8t or 20t. Irradiation of 14 in ether caused both isomerization of the Δ4,5 double bond (to give 15) and α-cleavage (to give 16 and 17). The synthesis of 8, which proceeded via the hemiketal 24 (Scheme V) required critical control of reaction conditions to avoid the undesired transannular products 25 and 26.
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Database:
Scopus
Publication Type:
article
;
.
Language:
English
Editors' remarks:
ID:
29163
Last updated date:
02/03/2022 17:27
Creation date:
17/04/2018 00:44
Scientific Publication
Photochemistry of 2,3-benzo-2,4-cyclooctadienones: Isolation and chemistry of Δ4,5-trans isomers
99
Suzuki, M., Department of Chemistry, Michigan State University, East Lansing, MI 48824, United States
Hart, H., Department of Chemistry, Michigan State University, East Lansing, MI 48824, United States
Dunkelblum, E., Department of Chemistry, Michigan State University, East Lansing, MI 48824, United States
Li, W., Department of Chemistry, Michigan State University, East Lansing, MI 48824, United States
Photochemistry of 2,3-benzo-2,4-cyclooctadienones: Isolation and chemistry of Δ4,5-trans isomers
Irradiation of the two 2,3-benzo-2,4-cyclooctadienones 8 and 20 gave the corresponding Δ4,5-trans isomers, whose physical properties (IR, NMR, UV) were determined. The IR spectrum of 8t suggests transannular conjugation between the carbonyl and carbon-carbon double bonds, and chemical evidence (for example, stereoselective transannular methanol addition) supports the view that the trans double bond is polarized δ+ at C(4), δ- at C(5), opposite to that in the cis isomer. Thus methanol adds to 8t at room temperature to give 10, and 20t similarly gives 21. The trans ketones 8t and 20t were reduced stereospecifically with lithium aluminum hydride to give only one of the two possible diastereomeric alcohols, 12t (crystalline) and 22t, respectively. Chromatography of 8t on silica gel caused stereoselective transannular addition of water to give the diol 9. Irradiation of 8 absorbed on silica gel (cyclohexane) gave the unsaturated alcohol 13. Irradiation of 14 in methanol also gave a stereoselective methanol adduct 18 (analogous to 10 and 21). However, in this case the intermediate trans ketone 14t could not be detected physically. Presumably the methyl groups are located in such a position as to sharply increase the strain and reactivity of 14t as compared with 8t or 20t. Irradiation of 14 in ether caused both isomerization of the Δ4,5 double bond (to give 15) and α-cleavage (to give 16 and 17). The synthesis of 8, which proceeded via the hemiketal 24 (Scheme V) required critical control of reaction conditions to avoid the undesired transannular products 25 and 26.
Scientific Publication
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