[trinitrotoluene]

My professor gave us the following examples for applying Baldwin's rules for nucleophilic
alkenes. The first scheme I understand that the oxygen is acting as the nucleophile and not the alekene...


The first one I would have guessed to be 5-exo-tet. The second I would have guessed to be 6-exo-tet. Can anyone explain how the labels in the figure are correct?  Thanks a ton!