Sulfoxide complexes nomenclature

The interrelation among homovalent and ambivalent reactions on the five-atom pericycles (equations 3 and 4) was described and given a similar but more complex nomenclature reflecting their lower symmetry. Homovalent pericycles include the amine oxide eliminations in Scheme 1 and the sulfoxide-sulfenate rearrangement in Scheme 2, with the shells in boldface as in Figure 1. For the ambivalent reactions of equation (4) the ambivalent atom X is often not carbon, as seen in Scheme 3 for a metal reduction of vicinal dihalides (which may not be pericyclic) Scheme 3 has an unchanging shell of only one bond. The cycloaddition of sulfur dioxide to dienes in Scheme 4 is another with a three-bond shell. Numerous examples were quoted, again many not confirmed as pericyclic. ... 

---