Nishizawa, Mugio Iwamoto, Yoshihiro Takao, Hiroko Imagawa, Hiroshi Sugihara, Takumichi The C-Ring Problem of Sterol Biosynthesis:  TiCl<sub>4</sub>-Induced Rearrangement into the Anti-Markovnikov Cation Corresponding to the C-Ring Cation <b>9</b>, generated by the reaction of diol <b>8</b> and BF<sub>3</sub>·Et<sub>2</sub>O, SnCl<sub>4</sub>, Sc(OTf)<sub>3</sub>, FeCl<sub>3</sub>, TiF<sub>4</sub>, or CF<sub>3</sub>SO<sub>3</sub>H, leads to a hydride shift, providing cation <b>11</b>, which corresponds to the initiation of backbone rearrangement. On the other hand, TiCl<sub>4</sub> selectively induces rearrangement to secondary cation<b> 13 </b>by ring expansion, which corresponds to the C-ring formation of sterol biosynthesis. AlCl<sub>3</sub> and ZrCl<sub>4</sub> induce further rearrangement into six-membered ring <i>tert</i>-cation <b>16</b>. BF;ZrCl 4;TiF 4;FeCl 3;hydride shift;SnCl 4;cation 11;TiCl 4;CF 3;AlCl 3;backbone rearrangement;Induced Rearrangement;cation 16;3 H;ring expansion;Cation;diol 8;cation 13;sterol biosynthesis 2000-05-18
    https://acs.figshare.com/articles/journal_contribution/The_C-Ring_Problem_of_Sterol_Biosynthesis_TiCl_sub_4_sub_-Induced_Rearrangement_into_the_Anti-Markovnikov_Cation_Corresponding_to_the_C-Ring/3735948
10.1021/ol0057582.s002