作者:Nour-Eddine Es-Safi、Christine Le Guernevé、Lucien Kerhoas、Paul-Henri Ducrot
DOI:10.1016/j.tet.2005.12.019
日期:2006.3
bond was observed and the corresponding C-4→O→C-3 ether linked procyanidin dimer was isolated in a good yield. In order to avoid the participation of the C-3 hydroxyl group in the dimerization reaction, the two flavanol units were forced into C-4→C-8 coupling by use of an internal link. The structural elucidation of the isolated compounds was achieved through MS and NMR spectroscopy.
研究了在路易斯酸催化的黄烷醇低聚反应中电子吸引取代基的作用。结果表明,在(+)-儿茶素单元的8位上存在的COCF 3强烈影响由4- O-烷氧基保护的儿茶素单元产生的亲电试剂对6个游离亲核试剂黄烷醇位置的攻击。用TiCl 4或TMSOTf作为路易斯酸可以观察到这一点,其中碳-碳键的形成被抑制,相应的二聚体也被少量检测到。相反,观察到碳-氧键的形成,相应的C-4→ O→C-3醚连接的原花青素二聚体以良好的产率被分离。为了避免C-3羟基参与二聚反应,通过使用内部连接将两个黄烷醇单元强制进入C-4→C-8偶联。通过MS和NMR光谱对分离出的化合物进行结构阐明。