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

Here,
a palladium-catalyzed functionalization of unactivated sp3 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 sp3 C–H activation/intramolecular
SN2 pathway was proposed.