名称:
Total synthesis of montanine-type Amaryllidaceae alkaloids, which possess a 5,11-methanomorphanthridine ring system, through cyclization with sodium bis(2-methoxyethoxy)aluminum hydride (SMEAH): the first stereoselective total syntheses of (.+-.)-montanine, (.+-.)-coccinine, (.+-.)-O-acetylmontanine, (.+-.)-pancracine, and (.+-.)-brunsvigine
摘要:
The stereoselective total syntheses of the title alkaloids 1-5 from allylic chloride 31 are described. The key steps in the reaction sequences are as follows: (1) stereoselective hydroboration-oxidation of 12 by means of an intramolecular charge-transfer complex to afford alcohol 13 as a single isomer; (2) cyclization of tosylamide alcohol 21 with sodium bis(2-methoxyethoxy)aluminum hydride (SMEAH) to afford functionalized 5,11-methanomorphanthridine 22, which possesses the basic skeleton of montanine-type alkaloids; and (3) conversion of 30a to allylic chloride 31 by treatment with PhSeCl in MeOH under ultrasonication followed by NaIO4 oxidation. A formal total synthesis of (+/-)-manthine (6) was also accomplished.