AbstractThe relative and absolute configuration of (+)‐3,12‐dihydroxypalmitic acid, a constituent of the Ipomea operculata M. resin, has been determined by synthesis. Dimethyl L‐malate was converted via (S)‐(+)‐1 into the oxirane (S)‐(‐)‐2. Reaction of (‐)‐2 with the Grignard reagent of 8‐benzyloxybromooctane provided (S)‐(+)‐3 in 84% yield, and this was converted into the aldehyde (S)‐(‐)‐6 via (S)‐(‐)‐4 and (S)‐(‐)‐5. Reaction with the lithium enolate of methyl acetate gave 7 and 8, which could be converted via 9 and 10, 11 and 12, 13 and 14 into the lactones (4S,13S)‐(+)‐15 and (4R,13S)‐(+)‐16 and finally into the methyl esters (3S,12S)‐(+)‐17 and (3R,12S)‐(+)‐18 and acids (‐)‐19 and (+)‐20. The erythro configuration of (+)‐17 was established by a stereoselective synthesis starting from (S)‐(‐)‐2 via (S)‐(+)‐21, (+)‐22, (+)‐23, the Grignard reagent of (+)‐24 and (R)‐(+)‐2‐(2‐benzyloxyethyl)oxirane to give (3S,12S)‐(‐)‐25, (‐)‐26, (+)‐27 and (+)‐28, which could be oxidized to the diacetoxy acid (3S,12S)‐(+)‐29. Saponification and esterification gave (3S,12S)‐(‐)‐19 and (3S,12S)‐(+)‐17, with properties identical to those of (+)‐17 obtained from the resin glycoside.