Is there any selectivity between the C-2 and C-4 positions of pyridine in SNAr reactions?

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I really dont think its that simple. If you look in the literature (pyridine SNAr is very common in med chem for example), there are examples of both selective C-2 and selective C-4 substitution, and I think it really depends on conditions and exact substrate. See e.g. More

"Pyridines readily undergo SNAr, usually faster at C-4 than C-2/6, but highly dependent on nucleophile and conditions"More