A Base-Mediated Rearrangement of the Benzylic 1,5-Hexadipyridynyl Moiety

A previously unrecognized base-mediated rearrangement of a benzylic 1,5-hexadipyridynyl moiety is reported. Upon exposure to base, this structural motif rearranges into a constrained vinyl-pyridine substituted cyclobutene. Computational modeling indicates that the rearrangement takes place following a route involving stepwise deprotonation, shifted reprotonation, and 4π-electrocyclization. The reaction rate and the stereochemical outcome is consistent with the experimental observations. Furthermore, nonbase mediates rearrangements, through well-known Cope-like [3,3]-sigmatropic shifts, are found to be high in energy, and therefore, take a backseat to the base-mediated pathway. This rearrangement may provide a novel reactivity pathway of conjugated systems for synthetic methodology development.