the two alkenes, to form (2) the sandaracopimarenyl cation. (b) This cation then undergoes an internal cyclization to stabilize the carbocation in the ring by proton transfer to form (3) intermediate. (c) By doing this, the molecule sets itself up for a methyl migration to stabilize that secondary cation and generate that tertiary carbocation at (4). (d) This induces a loss of proton to get (5) levopimaradiene. (e) With oxidation, a loss of a proton to form an aromatic ring generates (6) abietatriene. (g) This newly formed abietatriene undergoes a 1,2-alkyl shift to break the 6-membered ring into (7) with a five-membered ring (more favorable). (h) Another 1,2-alkyl shift takes place at the same time a ring cleavage takes place to generate (8). (i) Oxidation at all the positions with alkenes generates (9) intermediate which then undergoes ring closures featuring one hemiacetal and all three lactones to get ginkgolide B at (10). See also Bilobalide References Gamma-lactones Diterpenes Glycine receptor antagonists Tert-butyl compounds Cyclopentanes