Niobium-Mediated Double Activation of C-F/C-H Bonds: Fluorene Synthesis

Significance

This is a simple method for the preparation of fluorenes from 2-trifluoro-methylbiphenyls, readily available by a cross-coupling method. Usually, the C-F bond is very resistant toward the activation and only few of such reactions are known. Mechanistically, this process is a rare case of double C-F and C-H activation in a ‘one-pot’ reaction. With toluene as a solvent, the products of the attack on the aryl ring are formed, unfortunately, as a mixture of regioisomers. A number of functionalized fluorenes were prepared by this method, showing a broad synthetic scope for this new reaction.