Mitigating the Risk of Coprecipitation of Pinacol during Isolation from Telescoped Miyaura Borylation and Suzuki Couplings Utilizing Boron Pinacol Esters: Use of Modeling for Process Design

Process definition and optimization of a telescoped Miyaura borylation and Suzuki coupling reaction employing bis(pinacolato)diboron (BisPin), used in the developmental synthesis of an intermediate for Abemaciclib, led to the unexpected coprecipitation of pinacol during the isolation. Thermodynamic phase separation, distillation, and pinacol phase diagram models were used to guide the design of a modified process to maintain pinacol fully soluble. A Quality by Design (QbD) approach was used to illustrate the control strategy and provide a maximally flexible process for manufacturing to maintain high purity of the intermediate. Different possible representations of the design space to mitigate pinacol precipitation are discussed and compared. The risk of pinacol precipitation may not be unique to the system of study and could have broad implication to the development of this class of reactions.