Mechanistic Insights into the Chemo- and Regio-selective B(C6F5)3 Catalyzed C−H Functionalization of Phenols with Diazoesters

The Lewis acidic B(C6F5)3 was recently demonstrated to be effective for the C−H alkylation of phenols with diazoesters. The method avoids the general hydroxyl activation in transition metal catalysis. Ortho-selective C−H alkylation occurs regardless of potential para-selective C−H alkylation and O−H alkylation. In the present study, a theoretical calculation was carried out to elucidate the reaction mechanism and the origin of chemo- and regio-selectivity. It is found that the previously-proposed B(C6F5)3/N or B(C6F5)3/C bonding-involved mechanisms are not favorable, and a more favored one involves the B(C6F5)3/C=O bonding, rate-determining N2 elimination, selectivity-determining electrophilic attack and proton transfer steps. Meanwhile, the new mechanism is consistent with KIE and competition experiments. The facility of the mechanism is attributed from two factors: First, the B(C6F5)3/C=O bonding reduces the steric hindrance during electrophilic attack. Second, the bonding forms the conjugated system by...