Computational and Further Experimental Explorations of the Competing Cascades following Claisen Rearrangements of Aryl Propargyl Ethers: Substituent Effects on Reactivity and Regioselectivity

We report a computational investigation of two reaction cascades occurring following the Claisen rearrangements of aryl propargyl ethers to the alternate ortho positions in unsymmetrical reactants. Our computations explain how substituents influence reactivity and regioselectivity. Rearrangement to the substituted ortho carbon leads to a tricyclo[3.2.1.0]octane core, while rearrangement to an unsubstituted ortho carbon leads to a benzopyran. Density functional theory with ωB97X-D indicates that these reactions involve rate-determining Claisen rearrangements followed by subsequent reaction cascades of the Claisen rearrangement products depending on the presence or absence of a substituent at the ortho carbon.