NOVELTY - Tert.-butyl(3R,5S)-6-oxo-3,5-dihydroxy-3,5-O-isopropylidene-hexanoate compound is synthesized from (S)-tert.-butyl-6-chloro-5-hydroxy-3-oxohexanoate by reducing (S)-tert.-butyl-6-chloro-5-hydroxy-3-oxohexanoate with sodium borohydride to yield (3R,5S)-tert.-butyl-6-chloro-3,5-dihydroxyhexanoate having greater than or equal to 80% de in aqueous micellar aggregate at 0-5 degrees C, and converting (3R,5S)-tert.-butyl-6-chloro-3,5-dihydroxyhexanoate to tert.-butyl-2-((4R,6S)-6-(chloromethyl)-2,2-dimethyl-1,3-dioxan-4-yl)acetate through reaction of 2,2-dimethoxy propane in presence of D-10-camphor sulfonic acid in acetone.    USE - Synthesis of tert.-butyl(3R,5S)-6-oxo-3,5-dihydroxy-3,5-O-isopropylidene-hexanoate for preparation of statins.    ADVANTAGE - The processes are friendly to the environment and are cost effective.    DETAILED DESCRIPTION - Tert.-butyl(3R,5S)-6-oxo-3,5-dihydroxy-3,5-O-isopropylidene-hexanoate of formula (I) is synthesized from (S)-tert.-butyl-6-chloro-5-hydroxy-3-oxohexanoate of formula (VI) by reducing compound (VI) with sodium borohydride to yield (3R,5S)-tert.-butyl-6-chloro-3,5-dihydroxyhexanoate (VIII) having greater than or equal to 80% de in aqueous micellar aggregate at 0-5 degrees C, converting compound (VIII) to tert.-butyl-2-((4R,6S)-6-(chloromethyl)-2,2-dimethyl-1,3-dioxan-4-yl)acetate (XII) through reaction of 2,2-dimethoxy propane in presence of D-10-camphor sulfonic acid in acetone, converting compound (XII) to optically pure tert.-butyl-2-((4R,6S)-6-(acetoxymethyl)-2,2-dimethyl-1,3-dioxan-4-yl)acetate (XI) in the presence of tetra n-butyl ammonium acetate in presence of polar aprotic solvent at 95 degrees C and crystallization from n-heptane, converting compound (XI) to tert.-butyl 2-((4R,6S)-6-(hydroxymethyl)-2,2-dimethyl- 1,3-dioxan-4-yl)acetate (II) in presence of base in methanol as solvent, and converting compound (II) to optically pure compound (I) in presence of copper (salt)/diimine ligand/(2,2,6,6-tetramethylpiperidin-1-yl)oxy (TEMPO)/oxygen as oxidization system in organic solvent at 30-50 degrees C. INDEPENDENT CLAIMS are included for:    (1) synthesis of tert.-butyl(3R,5S)-6-oxo-3,5-dihydroxy-3,5-O-isopropylidene-hexanoate of formula (I) from 4-chloro-3-((alkylsilyl)oxy)butanal of formula (V) which involves reacting compound (V) with Reformatsky reagent of bromo/iodo acetic acid alkyl ester (IV) in solvent to obtain (5S)-tert.-butyl-6-chloro-3,5-dihydroxyhexanoate (VII), treating compound (VII) with tetra-butyl ammonium fluoride in tetrahydrofuran (THF) to obtain compound (VIII), converting diastereomeric excess compound (VIII) to diastereomeric excess compound (XII) through reaction of 2,2-dimethoxy propane in presence of D10-camphor sulfonic acid in acetone, and converting compound (XII) to optically pure tert.-butyl 2-((4R,6S)-6-(chloromethyl)-2,2-dimethyl-1,3-dioxan-4-yl)acetate (IX) having greater than or equal to 98% de through selective hydrolysis of undesired isomer in biphasic mixture of 2 N aqueous hydrochloric acid and dichloromethane at 25 degrees C, followed by separation of compound (IX) through selective extraction with n-hexane from crude product (IX);    (2) synthesis of compound (I) from diasteromeric excess tert.-butyl-2-((4R,6S)-6-(acetoxymethyl)-2,2-dimethyl-1,3-dioxan-4-yl)acetate (XIII) which involves converting compound (XIII) to optically pure compound (XI) having greater than or equal to 98 % de through selective hydrolysis of undesired isomer in biphasic mixture of 2 N aqueous hydrochloric acid and dichloromethane at 25 degrees C, followed by separation of compound (XI), converting compound (XI) to compound (II) in presence of base in methanol as solvent, and converting compound (II) to optically pure compound (I) in presence of Cu (salt)/diimine ligand/TEMPO/oxygen as oxidization system in organic solvent at 30-50 degrees C; and    (3) synthesis of compound (I) from diasteromeric excess tert.-butyl 2-((4R,6S)-6-(hydroxymethyl)-2,2-dimethyl-1,3-dioxan-4-yl)acetate of formula (II) which involves converting compound (II) to optically pure compound (I) in presence of Cu (salt)/diimine ligand/TEMPO/oxygen as oxidization system in organic solvent at 30-50 degrees C.