Cyclization zirconium-promoted

Alternately, CpjZr can also be prepared by the reaction of Cp2ZrCl2with two equivalents of n-BuLi at —78°C E.-I Negishi, F. K. Cederbaum and T. Takahashi, Reaction of zirconocene dichloride with alkyl lithiums or alkyl Grignard reagents as a convenient method for generating a zirconocene equivalent and its use in zirconium promoted cyclization of alkenes, alkynes dienes, eneynes and diynes, Tetrahedron Lett. 27 2829 (1986). 

Uesaka N, Saitoh F, Mori M, Shibasaki M, Okamura K, Date T (1994) Formal Total Synthesis of (—)-Dendrobine Using Zirconium-Promoted Reductive Cyclization. J Org Chem 59 5633... 

Mori et al. have shown that asymmetric alkylation with an allylic tosyl amide followed by a zirconium-promoted cyclization provides an efficient route to mesembrine and mesembrane alkaloids [107]. The best ee was obtained with BINAPO as the ligand. Scheme 28. The product was obtained in 86% ee and following recrystallization the sulfonamide was obtained in 99% ee. 

Total syntheses of (-)-mesembrane and (-)-mesembrinef ° were based on zirconium-promoted diene, diyne, and enyne cyclizations. This procedure was very useful... 

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