Specific <i>Z</i>-Selectivity in the Oxidative Isomerization of Allyl Ethers to Generate Geometrically Defined <i>Z</i>-Enol Ethers Using a Cobalt(II)(salen) Complex Catalyst
Guanxin Huang, Miaolin Ke, Yuan Tao, Fen‐Er Chen
Abstract
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.