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Some 6,6-disubstituted 2,4-cyclohexadien-1-ones and the facial selectivity in their Die...
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Some 6,6-disubstituted 2,4-cyclohexadien-1-ones and the facial selectivity in their Diels–Alder reactions with dimethyl acetylenedicarboxylate
作者:
Peter Yates,
Anabela Gomes,
D. Jean Burnell,
Dong Dao Cong,
Jeffery F. Sawyer,
期刊:
Canadian Journal of Chemistry
(NRC Available online 1989)
卷期:
Volume 67,
issue 1
页码: 37-47
ISSN:0008-4042
年代: 1989
DOI:10.1139/v89-007
出版商: NRC Research Press
数据来源: NRC
摘要:
6,6-Disubstituted 2,4-cyclohexadien-1-ones can be prepared by dibromination–bisdehydrobromination of the corresponding 6,6-disubstituted 2,2-dibromocyclohexanones. Such dienes undergo Diels–Alder reactions with dimethyl acetylenedicarboxylate to give 3,3-disubstituted 5,6-di(methoxycarbonyl)bicyclo[2.2.2]octa-5,7-dien-2-ones; when the substituents at C-6 in the dienones are different, two diastereomers of the adducts are formed in a ratio dependent on the "facial selectivity" in the Diels–Alder reactions. For the cases where one of the 6-substituents is methyl and the other is methoxycarbonyl, acetoxymethyl, dibromomethyl, or dichloromethyl it has been established via X-ray crystallography and chemical correlation that theendo-3-methyl/exo-3-methyl product ratio is 3.0, 0.9, 8, and 6, respectively. The origin of these differences is discussed briefly and a spectroscopic method for the assignment of structures to the individual diastereomers is proposed.Keywords: Diels–Alderreactions, substituted 2,4-cyclohexadien-1-ones, facial selectivity, dimethyl acetylenedicarboxylate.
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