AlCl<sub>3</sub>‑Catalyzed Ring Expansion Cascades of Bicyclic Cyclobutenamides Involving Highly Strained <i>Cis</i>,<i>Trans</i>-Cycloheptadienone Intermediates
2015-04-29T00:00:00Z (GMT) by
We report the first experimental evidence for the generation of highly strained <i>cis</i>,<i>trans</i>-cycloheptadienones by electrocyclic ring opening of 4,5-fused cyclobutenamides. In the presence of AlCl<sub>3</sub>, the cyclobutenamides rearrange to [2.2.1]-bicyclic ketones; DFT calculations provide evidence for a mechanism involving torquoselective 4π-electrocyclic ring opening to a <i>cis</i>,<i>trans</i>-cycloheptadienone followed by a Nazarov-like recyclization and a 1,2-alkyl shift. Similarly, 4,6-fused cyclobutenamides undergo AlCl<sub>3</sub>-catalyzed rearrangements to [3.2.1]-bicyclic ketones through <i>cis</i>,<i>trans</i>-cyclooctadienone intermediates. The products can be further elaborated via facile cascade reactions to give complex tri- and tetracyclic molecules.