Abstract Acetylation of d-glucono-1,5-lactone and subsequent treatment with triethylamine gave 2,4,6-tri- O-acetyl- d- erythro-hex-2-enono-1,5-lactone. Hydrogenation of the latter in the presence of palladium on carbon yielded 2,4,6-tri- O-acetyl-3-deoxy- d- arabino-hexono-1,5-lactone ( 5) in almost quantitative yield calculated from gluconolactone. Catalytic hydrogenation of 5 with platinum on carbon in the presence of triethylamine gave 2,4,6-tri- O-acetyl-3-deoxy- d- arabino-hexopyranose in quantitative yield. Deacetylation of 5 gave 3-deoxy- d- arabino-hexono-1,4-lactone, which was converted into 3-deoxy-5,6- O-isopropylidene-2- O-methanesulfonyl- d- arabino-hexono-1,4-lactone ( 10). The latter was converted into 2-acetamido-2,3-dideoxy- d- erythro-hex-2-enono-1,4-lactone ( Leptosphaerin). When 10 was boiled in water in the presence of acid, it gave a high yield of 2,5-anhydro-3-deoxy- d- ribo-hexonic acid.