How is Abemaciclib Impurity 1 (CAS: 1231930-33-8) typically synthesized?

Abemaciclib Impurity 1 is typically synthesized via a multi-step process involving the protection of a carboxylic acid, followed by amide formation, esterification, and subsequent deprotection. Common catalysts include acids like hydrochloric acid, and the process yields a high purity product with good selectivity. The exact steps and conditions vary depending on the starting materials and specific impurity profile.