The diastereoselective synthesis of (−)-denticulatin A (1a) was achieved for the first time in 9 steps (41% yield) based on a novel group-selective aldolization of a meso dialdehyde as a key step. The inherent chirality present in bornanesultam 4 was thus transmitted to the five stereocenters spanning C4–C8 in key intermediate 8. In addition, denticulatin B (1b) was obtained from the common intermediate 8 en route to denticulatin A in 10 steps and 35% overall yield.