Diastereomeric purification of rosuvastatin

A one pot process for preparing rosuvastatin or a pharmaceutically acceptable salt thereof comprising:

• a) combining MeO-9-BBN with an organic solvent and a source of hydride ions;
• b) adding to said combination a solution of a rosuvastatin intermediate keto-ester in an organic solvent, wherein the rosuvastatin intermediate keto-ester has the following formula:
• wherein X is hydrogen or forms a double bond to provide a ketone, with the proviso that at least one X forms a double bond, and R1 is a carboxy protecting group, to obtain a reaction mixture;
• c) maintaining the reaction mixture to reduce the intermediate;
• and
• d) hydrolyzing the reduced intermediate to rosuvastatin or a pharmaceutically acceptable salt thereof.