Palbociclib Commercial Manufacturing Process Development. Part I: Control of Regioselectivity in a Grignard-Mediated SNAr Coupling

This is the first in a series of three papers describing commercial manufacturing process development for palbociclib (1). This manuscript focuses on the SNAr coupling between aminopyridine 3 and chloropyrimidine 7. The regioselectivity of the SNAr coupling was studied from a synthetic and mechanistic perspective. Grignard bases were identified as the preferred class of bases for this reaction, allowing for a simplified process and reduced usage factor for aminopyridine 3. The development of this SNAr reaction into a scalable commercial manufacturing process is also described.