Improving Zonisamide Manufacturing: Insights into Stereochemistry and Mechanisms for Continuous Optimization

Zonisamide is a heterocyclic sulfonamide widely employed as anticonvulsant. In this work, we report an efficient process for the preparation of zonisamide, obtained in a six‐step synthesis from phenyl salicylate with an overall 31 % yield. The key step is represented by a base‐promoted intramolecular rearrangement of a β‐ketosultone oxime, leading to the concomitant formation of the benzisoxazole ring and of the exocyclic sulfonic group. This intriguing transformation is investigated with a combination of analytical techniques (NMR, HRMS, PXRD), leading to a preliminary mechanistic proposal.