124183-01-3Relevant academic research and scientific papers
Some 6,6-disubstituted 2,4-cyclohexadien-1-ones and the facial selectivity in their Diels-Alder reactions with dimethyl acetylenedicarboxylate
Yates, Peter,Gomes, Anabela,Burnell, Jean D.,Cong, Dong Dao,Sawyer, Jeffery F.
, p. 37 - 47 (2007/10/02)
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)bicycloocta-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 crystallograpfy and chemical correlation that the endo-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.Key words: Diels-Alder reactions, substituted 2,4-cyclohexadien-1-ones, facial selectivity, dimethyl acetylenedicarboxylate.
