Pd(II) Acts Simultaneously as a Lewis Acid and as a Transition-Metal Catalyst: Synthesis of Cyclic Alkenyl Ethers from Acetylenic Aldehydes

Abstract

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.