Quinolizidines. XVIII. Syntheses of (-)- and (+)-ankorines through a lactim ether route.
作者:TOZO FUJII、MASASHI OHBA、KAORU YONEYAMA、HIROKO KIZU、SHIGEYUKI YOSHIFUJI
DOI:10.1248/cpb.34.669
日期:——
A formal chiral synthesis of the Alangium alkaloid (-)-ankorine [(-)-6] has been accomplished in the form of the synthesis of the lactam phenol (+)-14 from the (+)-trans-lactim ether (+)-5 and 2-benzyloxy-3, 4-dimethoxyphenacyl bromide through the intermediates (+)-10 and 11. A parallel sequence of conversions starting from the (-)-trans-lactim ether (-)-5 and proceeding through the intermediates (-)-10, 24, (-)-14, (-)-15, 26, (+)-27, and (+)-28 produced the enantiomer [(+)-6] of natural ankorine. For an alternative chial synthesis of (-)-6, ethyl cincholoiponate [(+)-19] was acetylated and the resulting N-acetyl derivative (+)-20-was oxidized with RuO4 to give the 6-piperidone (+)-21, and 2-piperidone (-)-23 in 55% and 27% yields, respectively. The (-)-cis-lactim ether (-)-16, obtained by ethylation of (+)-21 with triethyl-oxonium fluoroborate, was then converted into (-)-13, a known precursor for the synthesis of (-)-ankorine [(-)-6], in good overall yield by a "lactim ether route, " which proceeded through (+)-15 and 12.
通过中间体(+)-10和11,从(+)-反式-亚内酯醚(+)-5和2-苄氧基-3, 4-二甲氧基苯乙酮溴化物合成内酰胺苯酚(+)-14的形式,完成了阿兰生物碱(-)-安考林[(-)-6]的正式手性合成。从(-)-反式-内酰亚胺醚(-)-5开始,通过中间体(-)-10、24、(-)-14、(-)-15、26、(+)-27和(+)-28进行平行的一系列转化,产生了天然安考林的对映体[(+)-6]。在合成(-)-6的另一种方法中,将[(+)-19]乙酰化,得到的N-乙酰衍生物(+)-20-用RuO4氧化,得到6-哌啶酮(+)-21和2-哌啶酮(-)-23,收率分别为55%和27%。(+)-21用三乙酮氧鎓氟硼酸盐乙氧基化后得到(-)-顺式-内脂醚(-)-16,然后通过 "内脂醚路线",经过(+)-15和12,以良好的总收率转化成(-)-13,这是合成(-)-安康岭[(-)-6]的已知前体。