AlCl3‑Catalyzed Ring Expansion Cascades of Bicyclic Cyclobutenamides Involving Highly Strained Cis,Trans-Cycloheptadienone Intermediates

We report the first experimental
evidence for the generation of
highly strained cis,trans-cycloheptadienones
by electrocyclic ring opening of 4,5-fused cyclobutenamides. In the
presence of AlCl3, the cyclobutenamides rearrange to [2.2.1]-bicyclic
ketones; DFT calculations provide evidence for a mechanism involving
torquoselective 4π-electrocyclic ring opening to a cis,trans-cycloheptadienone followed by a Nazarov-like
recyclization and a 1,2-alkyl shift. Similarly, 4,6-fused cyclobutenamides
undergo AlCl3-catalyzed rearrangements to [3.2.1]-bicyclic
ketones through cis,trans-cyclooctadienone
intermediates. The products can be further elaborated via facile cascade
reactions to give complex tri- and tetracyclic molecules.

本研究首次报告了通过电环反应开环4,5-并环苯甲酰胺生成高度应变cis,trans-环庚二烯酮的实验证据。在AlCl3的存在下，苯甲酰胺发生重排生成[2.2.1]-双环酮；密度泛函理论计算证实了涉及扭曲选择性4π-电环反应开环至cis,trans-环庚二烯酮，随后通过类似Nazarov环化反应和1,2-烷基位移的机制。类似地，4,6-并环苯甲酰胺在AlCl3催化下通过cis,trans-环辛二烯酮中间体重排生成[3.2.1]-双环酮。所得产物可通过简单的级联反应进一步加工，形成复杂的三角环和四环分子。