Pd(II) acts simultaneously as a Lewis acid and as a transition-metal catalyst: synthesis of cyclic alkenyl ethers from acetylenic aldehydes.
The reaction of carbon-tethered acetylenic aldehydes with alcohols in the presence of a catalytic amount of Pd(OAc)2 in 1,4-dioxane at room temperature gave the 5- or 6-membered acetal products in high yields. The 13C NMR studies suggested that a Pd(II) catalyst exhibited dual roles in the present reaction; the attack of ROH to aldehyde is catalyzed by Lewis acidic Pd(OAc)2, and the nucleophilic oxygen of the resulting hemiacetal reacts with alkyne complexed by Pd(II), giving the alkenyl ethers.
Asao
Naoki
N
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan.
Nogami
Tsutomu
T
Takahashi
Kumiko
K
Yamamoto
Yoshinori
Y