1,6-Dihydro-3(2H)-pyridinones. VII. Stereoselective total synthesis of a monoterpene alkaloid, (.+-.)-tecomanine.
作者:TAKESHI IMANISHI、NORIYUKI YAGI、MIYOJI HANAOKA
DOI:10.1248/cpb.31.1243
日期:——
The first total and stereoselective synthesis of (±)-tecomanine (1), one of the monoterpene alkaloids, was accomplished starting from ethyl 1, 6-dihydro-3 (2H)-oxopyridine-1-carboxylate (2a). The allylic alcohol (8), obtained as a major product on treatment of 2a with methylmagnesium iodide, was subjected to the Claisen rearrangement using ethyl (1-propenyl) ether to afford the aldehyde (30) which was converted to the methyl ketone (32). The acetal (33) was stereoselectively hydrated by a hydroboration-oxidation process to give the alcohol (34) in an excellent yield. To prevent formation of the furan (38), the product (34) was initially hydrolyzed and then oxidized to afford the diketone (36). Although 36 is a mixture of two diastereoisomers due to the configuration of the side-chain methyl group, each isomer, 36a and 36b, provided solely the desired product (40) upon base-catalyzed intramolecular aldol reaction. The urethane (40) was easily converted into (±)-tecomanine (1) by LiAIH4 reduction and subsequent PCC oxidation.
从 1,6-二氢-3 (2H) -氧代吡啶-1-甲酸乙酯 (2a) 开始,首次完成了单萜生物碱之一 (±)-tecomanine (1) 的全合成和立体选择性合成。用甲基碘化镁处理 2a 时得到的主要产物烯丙基醇(8),用(1-丙烯基)乙醚进行克莱森重排,得到醛(30),并转化为甲基酮(32)。缩醛(33)通过氢硼氧化过程进行立体选择性水合,得到醇(34),收率极高。为了防止形成呋喃 (38),产物 (34) 首先被水解,然后被氧化,得到二酮 (36)。虽然由于侧链甲基的构型,36 是两种非对映异构体的混合物,但在碱催化的分子内醛醇反应中,36a 和 36b 这两种异构体都能提供所需的产物(40)。通过 LiAIH4 还原和随后的 PCC 氧化,氨基甲酸酯 (40) 很容易转化为 (±)-tecomanine (1)。