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).