Highly regioselective synthesis of cyclic enol silyl ethers using ring-closing metathesis

We developed the first highly regioselective synthesis of cyclic enol ethers from readily accessible acyclic alkenyl ketones or acyclic alkenyl silyl esters using ring-closing metathesis (RCM). The RCM of acyclic enol silyl ethers was examined using Tebbe reagent 5 or Grubbs catalyst 6 or 7 and successfully proceeded using the second generation Grubbs catalyst 7 to afford the corresponding cyclic enol ethers in high yield (up to 99%, two steps from alkenyl kenone). This process can be applied to syntheses of a variety of cyclic enol ethers in a highly regioselective manner.