Liu Xiaoxiang, Hartwig John F
Department of Chemistry, Yale University, New Haven, Connecticut 06510 USA.
J Am Chem Soc. 2004 Apr 28;126(16):5182-91. doi: 10.1021/ja031544e.
A general procedure for the palladium-catalyzed arylation of trimethylsilyl enolates of esters and imides is reported. In the presence of ZnF2 or Zn(O-t-Bu)2 as an additive, the trimethylsilyl enolates of esters, including those bearing alpha-alkoxy derivatives, underwent arylation in high yield with high functional group tolerance. This arylation chemistry was extended to ester derivatives bearing chiral auxiliaries to form new tertiary stereocenters. The arylation of imides bearing the Evans auxiliary proceeded with selectivities up to 90% de. Further, the arylation of the ketal developed by Ley provided alpha-aryl glycolates with excellent diastereoselectivities (90 to >98% de). This reaction provides a convenient route to the synthesis of enantiopure alpha-aryl-alpha-hydroxy esters. Reactions conducted with Zn(O-t-Bu)2 as an additive occurred at room temperature to give enhanced diastereoselectivities with both chiral reagents. Mechanistic studies showed that the reaction conditions are neutral enough that the observed diastereomeric ratios reflect kinetic selectivities.
报道了一种钯催化酯和酰亚胺的三甲基硅烯醇醚芳基化的通用方法。在ZnF₂ 或Zn(O-t-Bu)₂ 作为添加剂的存在下，酯的三甲基硅烯醇醚，包括那些带有α-烷氧基衍生物的酯，能以高收率和高官能团耐受性进行芳基化反应。这种芳基化化学方法被扩展到带有手性助剂的酯衍生物，以形成新的叔立体中心。带有伊文斯助剂的酰亚胺的芳基化反应的非对映选择性高达90%。此外，Ley开发的缩酮的芳基化反应能以优异的非对映选择性（90%至>98%的非对映体过量）生成α-芳基乙醇酸酯。该反应为合成对映体纯的α-芳基-α-羟基酯提供了一条便捷途径。以Zn(O-t-Bu)₂ 作为添加剂进行的反应在室温下进行，使用两种手性试剂时都能提高非对映选择性。机理研究表明，反应条件足够中性，以至于观察到的非对映体比例反映了动力学选择性。
