Cyclisatioh de diarylalcanes en milieu superacide : synthese de cetones tricycliques a methyle angulaire et mecanisme de leur isomerisation

Cyclisation of readily available diary1-1,2 ethanes $\text{1→4}$ proceeds in SbF₅,-HF at 0°C to yield tricyclic phenanthrenones $\text{5}$, $\text{6}$, $\text{7}$ and $\text{11}$ bearing an angular methyl group. This process implies the electrophilic attack of the more basic aromatic ring, reacting through its diprotonated form (on the oxygen and the meta carbon atom) on the second aromatic ring. Isomerization of these primary products may be observed to give ketones $\text{8}$, $\text{9}$, $\text{10}$ from $\text{3}$ and $\text{12}$ from $\text{4}$) and it has been demonstrated by the use of specifically deuterated $\text{3d}$ that it involves stereospecific 1,2 hydride (or deuteride) shifts, without exchange.