Cyclic Ether Synthesis via Palladium-Catalyzed Directed Dehydrogenative Annulation at Unactivated Terminal Positions.

Here, a palladium-catalyzed functionalization of unactivated sp(3) C-H bonds with internal alcohol nucleophiles is described. Directed by an oxime-masked alcohol, annulation chemoselectively occurs at the β position, leading to a range of aliphatic cyclic ethers with four- to seven-membered rings. Tethered primary, secondary, and tertiary free hydroxyl groups can all react to give the corresponding cyclized products. In addition, benzyl and silyl protected alcohols can also be directly coupled. An sp(3) C-H activation/intramolecular SN2 pathway was proposed.