Stereospecific Synthesis Of Allylic And Homoallylic Alcohols From Functionalized Propargylic Alcohols

1-Substituted 4,4,5,5-tetraethoxy-2-pentyn-1-ols undergo stereospecific reduction to allylic and homoallylic alcohols under the right conditions. Hydrogenation over Lindlar's catalyst gave the corresponding (Z)-allylic alcohols in excellent yield provided potassium carbonate was added. Reduction was also achieved with lithium aluminum hydride, but the product appeared to be solvent and temperature dependent. In THF at -15 degrees C the corresponding (E)-allylic alcohols were formed, in better than 70% yield from secondary propargylic alcohols, but below 60% from tertiary ones; in refluxing diethyl ether the products were the corresponding 1-substituted derivatives of homoallylic alcohol (E)-4,5,5-triethoxypent-3-en-1-ol, obtained in 93% yield in the best case.