Current methods for Zincke ring-opening chemistry cannot enable the general process for pyridine halogenation described in Figure 1B . The pyridine N-activation step requires forcing conditions and often fails when 2-position substituents are present. This limitation excludes many classes of substituted pyridines. To address these restrictions, we focused on ring-opening of NTf-pyridinium salts. These reactive intermediates are readily formed from the pyridine and Tf2O at low temperatures and encompass most substitution patterns, except 2,6-disubstitution. Toscano reported a ring-opening with Tf2O but did not extend this process beyond pyridine and observed mixtures of ring-opened products . With 2-phenylpyridine (1), we surveyed a series of aliphatic amines as nucleophiles (Figure ). Pyrrolidine, piperidine, and morpholine gave moderate yields of ring-opened products, as did diisobutylamine (2a-2d). However, dibenzylamine proved optimal with 2e formed in high yield (conditions A). Figs. and show further examples of pyridine ring-openings using this protocol. For the next stage of reaction development, we tested Zincke imine 2e with halogen electrophiles (Figure ). At the outset, we did not anticipate C-Hal bond formation would be selective because there is no clear electronic bias between the two dsites at C3 and C5 (vide infra) in 2e . However, using NIS resulted in 3-I in 92% yield and exclusive 3-selectivity within five minutes at room temperature. Using NBS, we observed a 4.4:1 ratio of 3-Br and 4-Br at room temperature and a 92:1 ratio at -78 ºC in CH2Cl2. Chlorinating with NCS is lower-yielding, less selective (3-Cl and 4-Cl), and decomposes 2e. Figure shows that halogenating 3-substituted imines require a different procedure. Ring-opening of 3-phenylpyridine produced Zincke imine 2f in 82% yield, but NIS did not react with 2f at room temperature and decomposed to unidentified byproducts when heated to 50 ºC. However, when we included two equivalents of TFA, iodopyridine 6-I formed in high yield . We attribute this unexpected rearomatization to steric interactions between the 3-and 5-substituents in the s-trans conformation of 5-I promote ringclosure. Gratifyingly, the same outcome occurs when brominating using NBS and TFA (6-Br), and a modified procedure using NCS with HCl in CH2Cl2 chlorinates 2f effectively to form 6-Cl.