Developing an Asymmetric Transfer Hydrogenation Process for (S)‑5-Fluoro-3-methylisobenzofuran-1(3H)‑one, a Key Intermediate to Lorlatinib

Synthesis of (S)-5-fluoro-3-methylisobenzofuran-1­(3H)-one (6), a key intermediate to lorlatinib, is described. A few synthetic methodologies, that is, boron reduction, enzymatic reduction, asymmetric hydrogenation, and asymmetric transfer hydrogenation, were evaluated for the chiral reduction of the substituted acetophenone intermediate (8). A manufacturing process, on the basis of the asymmetric transfer hydrogenation, was developed. This process was successfully scaled up to prepare 400 kg of 6.