Abstract
Total synthesis of (±)-dendrobine has been completed. The ketol (19) was derived to the keto-nitrile (21). Hydrogenation of (21) gave the compound (5). Treatment of (5) with Br2, followed by dehydrobromination provided the enone (6). After ketalization, the compound (5) was hydrolyzed and deketalization of the product gave the keto-lactone (8). The compound (8) was derived to the keto-lactam (9) which was successively treated with iso-PrMgBr, KHSO4, I2-AcOAg-AcOH-H2O, KOH-MeOH-H2O, and CrO3-pyridine to afford the enone (10) and (55). Hydrocyanation of (10) with Et2AlCN gave three isomeric cyano-ketones (11), (56), and (57). Hydrolysis of the cyano-ketone (11) with H2SO4-AcOH, followed by methylation afforded the keto-ester (60). Reduction of (60) with NaBH4 gave the hydroxy-ester (61). Hydrolysis of (61) with KOH, followed by acidification yielded (±)-oxodendrobine (13). Reduction of (13) by the Borch's method gave (±)-dendrobine (1).
