Nucleophilic attacks are classified based on the hybridization of the electrophilic center (tet (sp 3 ), trig (sp 2 ) and dig (sp). And in exo and endo ring closures, depending on whether the bond broken during the closure of the ring is inside (endo) or outside (exo) of the ring that is formed.

baldwin rules 01

Let's see some examples:

baldwin rules 02