10.1021/jo035830k.s010 Takuya Koizumi Takuya Koizumi Eiko Mochizuki Eiko Mochizuki Ken Kokubo Ken Kokubo Takumi Oshima Takumi Oshima Mechanism of Novel Consecutive Rearrangements of Cyclobutene-Fused Diphenylhomobenzoquinones Catalyzed by Lewis Acids American Chemical Society 2004 BF tricyclic diones 5 α proton transfer stereoselective proton transfer PM 3 calculations Lewis Acids Lewis acid rearrangement Novel Consecutive Rearrangements TiCl 4 bicyclic diones 4 2004-07-09 00:00:00 Dataset https://acs.figshare.com/articles/dataset/Mechanism_of_Novel_Consecutive_Rearrangements_of_Cyclobutene_Fused_Diphenylhomobenzoquinones_Catalyzed_by_Lewis_Acids/3332779 Lewis acid catalyzed rearrangements of highly strained [2 + 2] photoadducts <b>1a</b>−<b>d</b> of diphenylhomobenzoquinone with various acetylenes were investigated under the influence of AlCl<sub>3</sub>, SnCl<sub>4</sub>, BF<sub>3</sub>, and TiCl<sub>4</sub>. With the relief of steric strain, these tricyclo[5.2.0.0<sup>3,5</sup>]non-8-ene-2,6-diones underwent the three steps of consecutive skeletal transformations. The first step was the two-way cyclobutene ring-cleavage reaction with a Wagner−Meerwein vinyl migration to either Lewis acid activated carbonyl function. This process virtually occurred under the anchimeric assistance of the <i>endo</i>-phenyl ring to give, after proton transfer, the phenylene-bridged tetracyclic keto alcohols <b>2</b> and <b>3</b>, respectively. The next step was the acid-induced cyclopropane ring cleavage of only <b>3</b> to lead to bicyclic diones <b>4 </b>via a following stereoselective proton transfer. The last one involved a Michael-type intramolecular cyclization of <b>4</b> accompanied by a proton transfer to afford thermodynamically less stable tricyclic diones <b>5</b>α which epimerized to <b>5</b>β only by TiCl<sub>4</sub>. The factors that control the selectivity and the reactivity of these tandem reactions were addressed on the basis of the X-ray crystal analyses as well as the PM3 calculations. It was found the present Lewis acid-catalyzed rearrangements were very dependent on the substituents of <b>1a</b>−<b>d</b> and the nature of the Lewis acids.