Enol
ether structural motifs exist in many highly oxygenated biologically
active natural products and pharmaceuticals. The synthesis of the
geometrically less stable Z-enol ethers is challenging.
An efficient Z-selective oxidative isomerization
process of allyl ethers catalyzed by a cobalt(II) (salen) complex
using N-fluoro-2,4,6-trimethylpyridinium trifluoromethanesulfonate
(Me3NFPY•OTf) as an oxidant has been developed.
Thermodynamically less stable Z-enol ethers were
prepared in excellent yields with high geometric control. This methodology
also demonstrates the effectiveness in controlling the Z-selective isomerization reaction of diallyl ethers at room temperature.
This catalytic system provides an alternative pathway to extend the
traditional reductive isomerization of allyl ethers.