Simvastatin is produced from lovastatin in high yield and in pharmaceutical purity by forming an amide of lovastatin and protecting the free hydroxyl groups of the lovastatin amide with hexamethyidisilazane (HMDS) to form a protected lovastatin amide. The .alpha.-carbon of the 2-methylbutyrate secondary chain of the protected lovastatin amide may be methylated to form a protected simvastatin amide. The protecting groups may be removed therefrom by quenching the methylation reaction with water. The simvastatin amide which is obtained may be hydrolyzed to form simvastatin acid, followed by forming a simvastatin ammonium salt, lactonizing the salt to form simvastatin, and recrystallizing the thus formed crude Simvastatin to a high degree of purity. The HMDS protecting agent for the lactone hydroxyl groups of Lovastatin is selected so as to result in a reaction that does not produce acid so that a base, such as imidazole, is not required to neutralize the acidity of the reaction medium. Another advantage of using HMDS as a protecting agent is that the removal of the protecting agent after the methylation reaction is carried out simply, for example, by water quenching. The lactonization reaction of the present invention may be carried out using a low boiling point solvent, such as methylene chloride, in the presence of inorganic acids such as sulfuric, hydrochloric, methanesulfonic or phosphoric acid as catalyst.