I'm specifically interested in the pathway from pyridine N-oxide, where there is some kind of reaction and rearrangement with acetic anhydride.
I'm assuming there is first a substitution (by the negative oxygen) at the carbonyl. The -OAc group can then attack at the alpha-position on the ring.
We could continue and say that the loss of H and the -OAc group on nitrogen happens next to restore aromaticity, but then we're stuck with that OAc group instead of the carbonyl.
From what I could find, it doesn't seem that there's a radical mechanism here, but if there is some intramolecular rearrangement, I cannot seem to find it.