6(R)-(2-(8'-acyloxy-2'-methyl-6'-methyl (or hydrogen)-polyhydronaphthyl-1')-ethyl)-4(R)-hydroxy-3,4,5,6-tetrahydro-2H-pyran-2-ones, the hydroxy acid form of said pyranones, the pharmaceutically acceptable salts of said hydroxy acids, and the lower alkyl, and phenyl, dimethylamino or acetylamino substituted lower alkyl esters of said hydroxy acid, processes for preparing the same, and a pharmaceutical antihypercholesterolemic composition containing the same.

6(R)-(2-(8'-acyloxy-2'-methyl-6'-methyl (or hydrogen) -polyhydronaphthyl-1')-ethyl]-4(R) -hydroxy-3,4,5,6-tetrahydro-2H-pyran-2-ones are prepared by acylation of the corresponding 8'-hydroxy compounds. The products are strong inhibitors of the biosynthesis of cholesterol. The 8'-hydroxy compounds are prepared by hydrolysis of the corresponding, naturally occurring 8'-(2(S)-methylbutyryloxy) compounds with a strong base at elevated temperatures to remove the acyl group.