Symmetrical vicinal diuloses were prepared from 2,3:4,5‐di‐O‐isopropylidene‐D‐arabinose and ‐L‐arabinose by using methyltriphenylphosphonium bromide to convert both enantiomers into the corresponding 1,2‐dideoxy‐3,4:5,6‐di‐O‐isopropylidene‐arabino‐hex‐1‐enitols D‐5 and L‐5. The metathesis reactions of D‐5 with itself and with L‐5, respectively, by using the Hoveyda–Grubbs catalyst gave diastereomeric dec‐5‐enitols DD‐6 and DL‐6, which were dihydroxylated with osmium tetroxide to give 1,2:3,4:7,8:9,10‐tetra‐O‐isopropylidene‐protected decitols DD‐7 and DL‐7. Swern oxidation of the decitols afforded isopropylidene‐protected deco‐5,6‐diuloses DD‐8 and DL‐8, which gave unprotected deco‐5,6‐diuloses DD‐9 and DL‐9 upon acidic cleavage of the isopropylidene groups. The structures of both diastereomers were confirmed by NMR spectroscopy and X‐ray crystal structure analysis.