Total Syntheses of the Coumarin-Containing Natural Products Pimpinellin and Fraxetin Using Au(I)-Catalyzed Intramolecular Hydroarylation (IMHA) Chemistry

The
title natural products (1 and 2,
respectively) have been synthesized by Au­(I)-catalyzed intramolecular
hydroarylation (IMHA) of the relevant aryl propiolate esters (e.g., 13), which were themselves formed by reaction of the corresponding
phenols with either 3-(trimethylsilyl)­propiolic acid or propiolic
acid and N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride or dicyclohexylcarbodiimide.
(±)-Purpurasol (3) was readily derived from fraxetin
(2) by established procedures.

标题所述的天然产物（分别为化合物1和2），可通过一价金（Au(I)）催化的相关芳基丙炔酸酯（例如化合物13）的分子内氢芳基化（intramolecular hydroarylation, IMHA）反应合成得到。前述芳基丙炔酸酯本身可由相应苯酚与3-(三甲基硅基)丙炔酸或丙炔酸，以及N-(3-二甲氨基丙基)-N'-乙基碳二亚胺盐酸盐（N-(3-dimethylaminopropyl)-N′-ethylcarbodiimide hydrochloride）或二环己基碳二亚胺（dicyclohexylcarbodiimide）反应制得。(±)-紫菜松醇（Purpurasol，化合物3）可通过成熟的实验方法由秦皮素（fraxetin，化合物2）便捷衍生得到。