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Dimethylzinc-Mediated Additions of Alkenylzirconocenes to Aldimines. New Methodologies for Allylic Amine and C-Cyclopropylalkylamine Syntheses
Ist Teil von
Journal of the American Chemical Society, 2003-01, Vol.125 (3), p.761-768
Ort / Verlag
Washington, DC: American Chemical Society
Erscheinungsjahr
2003
Link zum Volltext
Quelle
Alma/SFX Local Collection
Beschreibungen/Notizen
Hydrozirconation of alkynes with zirconocene hydrochloride followed by in situ transmetalation to dimethylzinc provides access to reactive alkenyl organometallic reagents from readily available precursors. Upon addition of imines, 1,2-attack leads to synthetically useful allylic amine building blocks. In the presence of CH2I2 or CH2Cl2, the N-metalated allylic amide intermediate is cyclopropanated and C-cyclopropylalkylamines are formed in high yield and excellent diastereoselectivities favoring the anti products. The use of enynes as starting materials for this domino reaction provides conjugated biscyclopropanes and thus allows the stereoselective formation of five new carbon−carbon bonds. A transition state that explains the need for both zirconocene complex and alkyl zinc in the cyclopropanation reaction is proposed.