The benzidine rearrangement is claimed to be an example of the quite rare [5,5] sigmatropic migration, which is a ten-electron homologation of the very common [3,3] sigmatropic reaction (e.g. the Cope or Claisen). Some benzidine rearrangements are indeed thought to go through the [3,3] route. The topic has been reviewed here.
- H.J. Shine, K.H. Park, M.L. Brownawell, and J. San Filippo, "Benzidine rearrangements. 19. The concerted nature of the one-proton rearrangement of 2,2'-dimethoxyhydrazobenzene", Journal of the American Chemical Society, vol. 106, pp. 7077-7082, 1984. http://dx.doi.org/10.1021/ja00335a035
- H.J. Shine, L. Kupczyk-Subotkowska, and W. Subotkowski, "Heavy-atom kinetic isotope effects in the acid-catalyzed rearrangement of N-2-naphthyl-N'-phenylhydrazine. Rearrangement is shown to be a concerted process", Journal of the American Chemical Society, vol. 107, pp. 6674-6678, 1985. http://dx.doi.org/10.1021/ja00309a041
- H.J. Shine, "Reflections on the ?-complex theory of benzidine rearrangements", Journal of Physical Organic Chemistry, vol. 2, pp. 491-506, 1989. http://dx.doi.org/10.1002/poc.610020702