Palladium-Catalyzed Cycloaddition of Alkynyl Aryl Ethers with Internal Alkynes via Selective Ortho C–H Activation

Alkynyl aryl ethers react with internal alkynes through
selective
ortho C–H activation by a palladium(0) catalyst to give substituted
2-methylidene-2H-chromenes. The alkynoxy group acts
as a directing group to promote ortho C–H functionalization.
Deuterium-labeling experiments indicated that the arylpalladium hydride
complex is a key intermediate via oxidative addition. Various functional
groups tolerate the present transformation to give the corresponding
products.