RESUMO
A double conjugate addition between the lithium dianion of ethyl 3-nitropropionate and p-benzoquinone dimethyl ketal afforded a mixture of diastereomeric [3.2.1]bicylooctanones. These products were converted into an advanced intermediate previously carried forward to (+/-)-gelsemine by Fukuyama and Liu.
Assuntos
Alcaloides/síntese química , Nitrocompostos/química , Propionatos/química , Alcaloides/química , Benzoquinonas/química , Lítio/química , Estrutura Molecular , EstereoisomerismoRESUMO
[reaction: see text]. A series of quinone monoacetals bearing electron-withdrawing groups was treated with diethyl malonate and other bifunctional nucleophiles in the presence of KO-t-Bu in THF. Reactions of ethyl 3-nitropropionate or diethyl malonate resulted in single conjugate addition adducts. When ethyl acetoacetate was used as a nucleophile, bridged bicyclic products were obtained in good yields. The regiochemistry of conjugate addition was dependent on the quinone monoacetal substitution.
Assuntos
Compostos Bicíclicos Heterocíclicos com Pontes/síntese química , Cicloexanos/química , Cristalografia por Raios X , Cicloexenos , Conformação Molecular , Estrutura Molecular , EstereoisomerismoAssuntos
Catálise , Isoxazóis/síntese química , Rutênio/química , Alcinos/química , Nitrilas/química , Óxidos/química , TemperaturaRESUMO
The Lewis acid-mediated reactions of substituted cyclopropanone acetals with alkyl azides were found to strongly depend on the structure of the ketone component. When cyclopropanone acetal was treated with alkyl azides, N-substituted 2-azetidinones and ethyl carbamate products were obtained, arising from azide addition to the carbonyl, followed by ring expansion or rearrangement, respectively. When 2,2-dimethylcyclopropanone acetals were reacted with azides in the presence of BF3.OEt2, the products obtained were alpha-amino-alpha'-diazomethyl ketones, which arose from C2-C3 bond cleavage of the corresponding cyclopropanone, giving oxyallyl cations that were captured by azides. Aryl-substituted cyclopropanone acetals, when subjected to these conditions, afforded [1,2,3]oxaborazoles exclusively, which were also the result of C2-C3 bond rupture, azide capture, and then loss of nitrogen. In the reactions of n-hexyl-substituted cyclopropanone acetals with alkyl azides, a mixture of 2-azetidinones and regioisomeric [1,2,3]oxaborazoles was obtained. The reasons for the different behavior of the various systems are discussed.