作者:Philip Garner、James T. Anderson、Philip B. Cox、Stephen J. Klippenstein、Ray Leslie、Noemi Scardovi
DOI:10.1021/jo010880f
日期:2002.8.1
development of an effective chiral auxiliary for hydroxyalkyl radicals is delineated. Both the 2-tetrahydropyranyl (THP) and tri-O-benzyl-2-deoxy-alpha-D-glucopyranosyl (GLU) auxiliaries resulted in diastereoselective radical additions to methyl acrylate at -78 degrees C (ds = 6/1 and 11/1, respectively). The developing stereochemistry at the radical center was completely under auxiliary control. Correlation
描绘了对于羟烷基自由基的有效手性助剂的开发。2-四氢吡喃基(THP)和三-O-苄基-2-脱氧-α-D-吡喃葡萄糖基(GLU)助剂在-78摄氏度下导致丙烯酸酯的非对映选择性自由基加成(ds = 6/1和11 / 1)。在自由基中心发展的立体化学完全处于辅助控制之下。相关实验表明,D-GLU助剂会导致对基硅面的侵蚀。当使用反应性更高的2-硝基丙烯捕集器时,这些自由基加成物的选择性大大降低。计算研究表明,观察到的面部选择性主要归因于过渡状态中的熵因素,但还涉及较小的温度依赖性焓贡献。假设在C-6处结合四元中心(THP编号)将通过限制进入的烯烃可用的方向来恢复具有更多反应性自由基陷阱的面部选择性。在这种情况下,反式-6-叔丁基四氢吡喃基(tBu-THP)助剂与2-硝基丙烯(ds = 35/1在-78摄氏度,15/1在0摄氏度,和8 /在向α-三氟乙酰氧基丙烯酸乙酯中添加时(在0℃时ds = 10/1),在三-O-苄基-6