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

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.