Alkylidenation of ester carbonyl groups by means of a reagent derived from RCHBr2, Zn, TiCl4, and TMEDA. Stereoselective preparation of (Z)-alkenyl ethers
Sir: Though alkenyl ethers have considerable synthetic utility,l the preparation of the ethers is limited to methods which use as starting materials either acetals2 or acety- lene ~ . ~ ~ ~ It is usually difficult to prepare the alkenyl ethers, especially trisubstituted ones, in a regie and stereoselective manner by these methods. The most promising direct approach to solve these problems is the alkylidenation of ester carbonyl groups, which has remained a persistent challenge in ...