In order to determine the absolute configuration of product from a reaction of sugar lactone and lithiated heterocycles, and X-ray crystal structural analysis of 1-(1, 3-dithian-2-yl)-2, 3 : 5, 6-di-O-isopropylidene-β-L-gulofuranose was carried out. This compound was prepared from 2, 3 : 5, 6-di-O-isopropylidene-L-gulono-1, 4-lactone and lithiated 1, 3-dithiane. The crystals are monoclinic with space group P2₁ and unit cell dimensions of a=18.566 (7) Å, b=9.544 (2) Å, c=6.462 (1) Å, β=91.68 (3)°, z=2. The X-ray analysis was carried out with the heavy-atom method and refined by the block-diagonal least-squares method including anisotropic thermal parameters, and the final R value was 0.071. In conclusion, the absolute configuration of the anomeric position was determined to be R chirality.