Acetylene-free synthesis of vinyloxy pyridine and quinoline
Copper-catalyzed vinylation of 2- and 4-hydroxy pyridine and quinoline affords exclusively N-vinylation products. However, vinyl ethers of 4-hydroxy pyridine and quinoline can be prepared via a three-step sequence involving copper-catalyzed C-O cross coupling reaction of the corresponding N-heteroaryl bromides with ethylene glycol, chlorination of the terminal alcohol, and dehydrohalogenation of the β-chloro ethers. Although not efficient in 2-hydroxy series, this method can be conveniently applied to the preparation of various aza-aryl vinyl ethers in moderate to good overall yields.