(-)-Monoterpenylmagnolol (3) was synthesized in eight steps from (+)-3,9-dibromocamphor (4) and the bis(methoxymethyl) ether (22) of 3-(4-hydroxyphenyl)-1-propanol. Fragmentation of an endo-3-aryl-9-bromocamphor (27) provided the correct absolute stereochemistry. In this total synthesis, dissolving metal conditions were developed to reduce enol phosphate and isopropenyl functions without concomitant reduction of an attached phenol. Palladium(O)-catalyzed cross-coupling of an arylzinc chloride with 4-allyl-2-iodophenyl methoxymethyl ether (34) provided the desired tricyclic 1,2,3,5-tetrasubstituted biaryl 41 in fair yield without optimization and with little isomerization of the allyl group. Magnolol (1) was also synthesized by aryl coupling of 34 and the methoxymethyl ether of 4-allyl-2-lithiophenol via the zinc chloride method as above, as well as from 5,5'-dibromo-2,2'-dimethoxybiphenyl (37) by allylation with allyltributylstannane followed by ether cleavage.
(-)-单萜烯基黄素醇 (3) 由 (+)-3,9-二
溴化
樟脑 (4) 和
3-(4-羟基苯基)-1-丙醇的双(羟甲基)醚 (22) 经过八步合成。 内-3-取代苯基-9-
溴化
樟脑 (27) 的断裂提供了正确的绝对构型。 在此全合成中,开发了可溶
金属还原条件,用于分别还原烯醇
磷酸盐和异
丙烯基功能,而不会同时还原连接的
酚羟基。 通过
钯 (0) 催化的芳基
氯化锌与 4-烯丙基-2-
碘苯基羟甲基醚 (34) 的交叉偶联,得到了预期的
三环 1,2,3,5-四取代
联苯 41,产率尚可,未经优化且烯丙基异构化很少。 另外,还通过
锌氯化物法将 34 和 4-烯丙基-2-
锂代
苯酚的羟甲基醚进行偶联,以及由 5,5’-二
溴-
2,2’-二甲氧基联苯 (37) 通过与
烯丙基三丁基锡进行烯丙基化反应后再进行醚键裂解,合成了黄素醇 (1)。