Solvent Controlled NBS‐Driven Divergent Bromo‐Lactonization of <i>Ortho</i> ‐Styryl Benzamides

We developed a metal‐free and solvent‐controlled protocol for the bromo‐lactonization of ( E )‐ N ‐substituted ortho ‐styryl benzamides using N ‐bromosuccinimide (NBS) as the sole reagent under ambient conditions. The reaction proceeded through an NBS‐derived bromine radical that evolved into a bromonium‐ion intermediate, enabling a trans ‐selective intramolecular cyclization exclusively through the amide oxygen. The reaction outcome depended strongly on the solvent: acetonitrile furnished bromo‐imino‐lactones, whereas wet methanol promoted oxime hydrolysis in the final step to afford 3,4‐dihydroisocoumarins. This NBS‐driven and solvent‐directed strategy therefore expanded the synthetic utility of prefunctionalized amides and provided a sustainable approach to oxygen‐containing heterocycles.