Stable benzopyrylium tetrafluoroborates, prepared by palladium-catalyzed annulation of aryl triisopropylsilylethynyl ethers with internal alkynes followed by BF3·OEt2 treatment, exhibited solid-state luminescence upon UV irradiation.
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