Site Selectivity Switch in Lewis Acid Catalysis. Mechanism and Kinetic Simulation of Skeletal Rearrangement of Cyclobutene-Fused Homoquinones

We investigated the site selectivity switch in BF3-catalyzed dual skeletal rearrangements of cyclobutene-fused diarylhomobenzoquinones by changing the stoichiometric amount of acid concentration. From the lower to the higher equivalency of BF3·Et2O, the branching product ratios (path A/path B) obeyed nonlinear sigmoid curves against the equivalency of BF3·Et2O. The observed selectivity profiles were simulated to elucidate factors that govern thermodynamic aspects (binding affinity K of each carbonyl function with acid) and kinetic aspects (rate constants k for the cyclobutene-ring cleavage).