Pyrrolizidine Alkaloids. The Synthesis and Absolute Configuration of All Stereoisomers of Monocrotalic Acid
作者:Takashi Matsumoto、Makoto Takahashi、Yutaka Kashihara
DOI:10.1246/bcsj.52.3329
日期:1979.11
All stereoisomers (3a, b–6a, b) of monocrotalic acid have been synthesized. Methylation of (±)-cis-2,3,4-trimethyl-2-pentenedioic acid with diazomethane followed by cis-hydroxylation with potassium permanganate afforded two epimeric γ-lactone esters in a ratio of ca. 1:5. These esters were then hydrolyzed with dilute hydrochloric acid to the corresponding acids, (±)-3 and racemic monocrotalic acid
已合成了百合酸的所有立体异构体(3a、b-6a、b)。(±)-cis-2,3,4-trimethyl-2-pentenedioic 酸用重氮甲烷甲基化,然后用高锰酸钾顺式羟基化,得到两种差向异构 γ-内酯酯,比例约为 1:5。然后用稀盐酸将这些酯水解成相应的酸,(±)-3 和外消旋单巴豆酸 (4)。(±)-3 与 brucine 的光学分辨率提供 3a (2R,3R,4S) 和 3b (2S,3S,4R)。外消旋的单巴豆酸也通过马铃薯碱分解,得到天然的单巴豆酸(4a:2R、3R、4R)及其对映异构体(4b:2S、3S、4S)。随后,(±)-trans-2,3,4-trimethyl-2-pentenedioic acid 用辛可尼丁拆分,得到 8a 和 8b,通过与已知的 (R)-(-)-2-苯基丙酸相关联,其立体化学分别指定为 S- 和 R- 构型。8a 甲基化,然后顺式羟基化和水解得到