β-Cleavage with concomitant specific transfer of a γ-hydrogen atom in a six-membered transition state in mono-unsaturated systems, irrespective of whether the rearrangement is formulated by a radical or an ionic mechanism, and irrespective of the position of the charge.
Source:
Orange Book, 2nd ed., p. 207 (https://media.iupac.org/publications/analytical_compendium/)