The mechanism and the origin of the regioselectivity of the rhodium/diene-catalyzed ring-opening reactions of C1-substituted oxabenzonorbornadienes with arylboronic acids has been examined using hybrid density functional theory (DFT). The overall mechanism for the reaction is considered as a four-step reaction including transmetalation, carborhodation, β-oxygen elimination, and protonolysis. The free energy profiles show that the rate-determining step is involved in the protonolysis step which differs from previous mechanistic studies on metalcatalyzed ring-opening reactions of oxabenzonorbornadienes. Additionally, it is theorized the β-oxygen elimination step is the origin of regioselectivity. DFT calculations predict the formation of the 1,2,4-trisubstituted naphthalene framework is selective over the 1,1,2-trisubstituted product, in agreement with experimental observations.