Stereoselective\nSynthesis of Spirolactone Analogues\nof Pyrrolomorpholine Alkaloids

The synthesis of a spirolactone analogue of xylapyrraside\nB<sub>1</sub>, a potent antioxidant agent, is described. The key step\nis\nthe stereoselective formation of the spirolactone skeleton via the\nformal [3+2] annulation of the isopropylidene-protected glyceraldehyde\nand δ-methylene lactone, mediated by trifluoroborane etherate.\nThis study addresses the stereoselective synthesis of pyrrolomorpholine\nspiroketal alkaloids, enabling the production of these bioactive compounds\nand their analogues.