..to overcome would be the synth of 4-bromopyridine. Simple bromination of pyridine won't work, since pyridine is deactivated (in regard of electrophilic aromatic substitution, of course) in the 2-, 4-, and 6-position, S
AE reaction is possible only in 3- and 5-position. Nucleophilic substitution can be achieved on 2-, 4-, and 6-position, the 2-position is clearly preferred. Cicibabin reaction (the reaction of pyridine with sodium amide) yields almost exclusively 2-aminopyridine.
Back to the 4-bromopyridine, how do you want to synthesize that compound?
I'd say forget it, go straight for the 4-aminopyridine by oxidising pyridine to pyridine-N-oxide (activating the aromat), nitrating it with strong mixed acid (HNO
3 + H
2SO
4) to get 4-nitropyridine-N-oxide and reducing the latter compound to 4-aminopyridine with hydrogen/Raney-Ni in acetic acid/acetic acid anhydride.
Now to the Sandmeyer...should work if a diazonium compound forms. Diazonium compounds can be formed even from aromats with strong deactivating groups (e.g. a nitrated or sulfonated aminobenzene), so the Sandmeyer should work, at least theoretically....(never did it myself on pyridines)...
[Edit: Ooops, misunderstood...you already want to go
that route:
pyridine -> pyridine-N-oxide -> 4-nitropyridine-N-oxide -> 4-aminopyridine -> 4-bromopyridine (via Sandmeyer)
Answer is still the same, should work...]
Quidquid agis, prudenter agas et respice finem!