Activation of 1,1-Difluoro-1-alkenes with a Transition-Metal Complex:  Palladium(II)-Catalyzed Friedel–Crafts-Type Cyclization of 4,4-(Difluorohomoallyl)arenes

Cationic palladium(II) ([Pd(MeCN)₄](BF₄)₂) provides the first transition-metal-catalyzed method for electrophilic activation of electron-deficient 1,1-difluoro-1-alkenes, which allows their Friedel−Crafts-type cyclization with an intramolecular aryl group via a Wacker-type process. By using BF₃·OEt₂, the cyclization was effected by a catalytic amount of the palladium without its reoxidation.