Highly Enantioselective Intermolecular Cu(I)-Catalyzed Cyclopropanation of Cyclic Enol Ethers. Asymmetric Total Synthesis of (+)-Quebrachamine
作者:Oliver Temme、Shabbir-Ali Taj、Pher G. Andersson
DOI:10.1021/jo9807417
日期:1998.8.1
structures 34c-h, the reaction was used as a key step in the asymmetric synthesis of (+)-quebrachamine 7, an indole alkaloid of the Aspidosperma family. After acid-induced ring opening of bicyclic compound 34f to lactone 40 followed by LiAlH(4) reduction to the masked aldehyde 41, a reaction with tryptamine gave intermediate 42. This alcohol was efficiently converted into the indole alkaloid (+)-quebrachamine
合成了一组衍生自在烯烃体系上具有不同取代方式的2,3-二氢呋喃35和3,4-二氢吡喃8的环状烯醇醚。发现具有Cu(I)OTf的Evans配体5是环状烯醇醚14、19、28-31和33与重氮乙酸乙酯6的环丙烷化反应的有效催化剂,其非对映选择性高达exo / endo = 95:5几乎所有情况下对映选择性都高于95%。由于选择性地建立了一个四级碳中心,并且在形成双环结构34c-h中具有良好的收率,该反应被用作非对称合成(+)-quebrachamine 7(曲霉属的吲哚生物碱)的关键步骤。 。酸诱导双环化合物34f开环成内酯40,然后LiAlH(4)还原成掩蔽的醛41后,与色胺的反应得到中间体42。从手性合成子34f开始,将该醇有效地转化为吲哚生物碱(+)-quebrachamine 7,总产率为37%。此外,它揭示了环丙烷化产物34f的四元中心的绝对构型为S。