Identification and Elimination of an Unexpected Catalyst Poison in Suzuki Coupling

A Suzuki coupling reaction gave an uncharacteristically low conversion in a GMP campaign. Initial investigation revealed a palladium catalyst poison in the starting material. A temporary solution was developed along with contingency plans to enable successful material delivery. Further systematic studies led to the identification of elemental sulfur as the culprit. A "sulfur-free" synthesis of the starting material was developed for the next round of manufacturing.