Evolution of the Manufacturing Route towards a Key Benzothiophen‐2‐yl‐Boronic Acid Building Block of Rogaratinib

Abstract

The evolution of the synthesis of a benzothiophene‐2‐yl‐boronic acid ‐ a key building block for the anti‐cancer agent Rogaratinib ‑ is reported from multi‐gram scale to industrialization. The pitfalls and learnings during process development are outlined, describing the optimization of the initial research synthesis route, investigation of an alternative approach based on a palladium‐catalyzed Newman‐Kwart rearrangement and finally changing the synthetic strategy from thiophene‐construction to benzene‐ring formation. Although the initial route was utilized to deliver material on kg‐scale, the requirements for market‐supply triggered the decision to pursue a new synthetic route. Catalyst costs, high purity‐requirements, and not the least technical practicality caused the change to a synthesis with indeed higher step‐count. However, this could be mitigated by repeated application of a telescoping approach. The free boronic acid was finally selected and manufactured as a stable isolated intermediate after challenges like proto‐deboronation and trimerization to boroxine upon drying could be solved by an optimized crystallization procedure.