The conjugate addition of (E)-1,2-diphenylethenylboronic acid to 2-cyclohexenone in the presence of a diene/rhodium catalyst leads to a rearranged product incorporating a 2-((E)-2-phenylethenyl)phenyl group. The catalytic cycle involves a 1,4-Rh shift from the 1,2-diphenylethenylrhodium intermediate to form a new 2-((E)-2-phenylethenyl)phenylrhodium intermediate. DFT calculations demonstrate that the 1,4-Rh shift occurs via C–H oxidative addition and reductive elimination to/from a distorted square-pyramidal Rh(III)-hydride intermediate. The relative ΔG^≠ of the 1,4-shift and carborhodation transition states are in good agreement with the experimentally observed selectivity.