Low-valent niobium-mediated double activation of C-F/C-H bonds: fluorene synthesis from o-arylated alpha,alpha,alpha-trifluorotoluene derivatives.

By the treatment of 0.3 molar amount of NbCl5 and LiAlH4, o-arylated alpha,alpha,alpha-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.