Low-Valent Niobium-Mediated Double Activation of C−F/C−H Bonds:  Fluorene Synthesis from o-Arylated α,α,α-Trifluorotoluene Derivatives

By the treatment of 0.3 molar amount of NbCl5 and LiAlH4, o-arylated α,α,α-trifluorotoluenes afforded fluorene derivatives in good yields. C−F bonds of the CF3 group and the neighboring ortho C−H bond were doubly activated to give the coupling products.