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The reaction of 2,3-disubstituted-1,1-cyclopropanediesters with nitrones under Lewis acid conditions produces tetrahydro-1,2-oxazines in which the cis/trans relationship of the cyclopropanes is not conserved. Reacting nitrones with 2,3-cis-disubstituted cyclopropanes lead to 5,6-trans-oxazines, and 2,3-trans-disubstituted cyclopropanes lead to 5,6-cis-oxazines. This observed stereochemical inversion provides evidence for a stepwise annulation mechanism in the preparation of tetrahydro-1,2-oxazines. 相似文献
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Jackson SK Karadeolian A Driega AB Kerr MA 《Journal of the American Chemical Society》2008,130(12):4196-4201
The intramolecular reaction of oxime ethers and cyclopropane diesters results in the diastereoselective formation of substituted pyrrolo-isoxazolidines which serve as precursors to the ubiquitous pyrrolidine motif. A simple reversal of addition order of catalyst and substrate results in formation of two discrete diastereomers in a highly selective and predictable manner. The adducts are prepared in excellent yields from either enantiomer of an alkoxyamino-tethered cyclopropanediester, allowing efficient access to highly substituted homochiral pyrrolidines. 相似文献
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