抄録
We have developed the first highly stereoselective synthesis of tetrasubstituted, functionalized (E)-enol ethers via olefination of esters with ynolates, which are generated from α,α-dibromo esters. Lithium ynolates easily react with esters at room temperature to give β-alkoxy- α,β-unsaturated carboxylates with good to excellent (E)-selectivity and in good yield. The E/Z selectivity is controlled by the torquoselectivity in the ring-opening of β-lactone enolate intermediates. In contrast to esters, thiol esters were found to provide β-keto thiol esters via the reaction with ynolates. This homologation can be regarded as the C-S insertion of ynolates. The α-keto ketene intermediates, which would be generated by elimination of the thiolates from the initial adducts, would be attacked by the thiolates to afford β-keto thiol esters.
