Controlled chlorination of 2, 6-diaminopyridine (1) affords 2, 6-diamino-3, 5-dichloropyridine (2a) which is then bis (diazotised) to give 2, 3, 5, 6-tetrachloropyridine (3a); similarly prepared are other 2, 3, 5, 6-tetra (chloro/bromo) pyridines and 2, 6-dichloro-3, 5-bis (thiocyanato) pyridine (3h), from which 3, 5-bis (alkylthio) pyridines are easily obtained.
[Barlow, Michael G.; Sibous, Lakhdar; Suliman, Nadia N. E.; Tipping, Anthony E. Journal of the Chemical Society - Perkin Transactions 1, 1996 , # 6 p. 519 - 524]