Zirconium enolates 2,3 -Wittig rearrangement

As noted previously, the [2.3] Wittig rearrangement of zirconium ester enolates demonstrates a strong preference for Z-oleftn formation. For secondary allylic ethers 16, the preferential formation of Z-i v -products suggests that rearrangement occurs through an Ra transition stale conformation in order to minimize the RA-G steric interaction62,6a. 

Scheme 6.15. [2,3]-Wittig rearrangements of chiral propargyloxy acetates (a) Zirconium ester enolates [81,82]. (b) Lithium endiolates, S = solvent [81-83].

Scheme 6.22. [2,3]-Wittig rearrangement of amide zirconium enolates using Katsuki s pyrrolidine auxiliary [90].

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