Evans P Andrew, Uraguchi Daisuke
Department of Chemistry, Indiana University, Bloomington, Indiana 47405, USA.
J Am Chem Soc. 2003 Jun 18;125(24):7158-9. doi: 10.1021/ja035216q.
The transition metal-catalyzed allylic substitution with unstabilized carbon nucleophiles represents an important cross-coupling reaction for the construction of ternary carbon stereogenic centers. We have developed a new regio- and enantiospecific rhodium-catalyzed allylic alkylation of acyclic unsymmetrical chiral nonracemic allylic alcohol derivatives with aryl zinc bromides. This study demonstrates that the hydrotris(pyrazolyl)borate rhodium catalyst and zinc(II) halide salt are crucial for efficiency, while the addition of lithium bromide to the catalyst is necessary for obtaining optimal regiospecificity. The stereochemical course of this reaction was established through the synthesis of (S)-ibuprofen, which demonstrated that the alkylation proceeds with net inversion of absolute configuration consistent with direct addition of the nucleophile to the metal center followed by reductive elimination.
过渡金属催化的、使用未稳定化碳亲核试剂的烯丙基取代反应，是构建三元碳立体中心的重要交叉偶联反应。我们开发了一种新的区域和对映体特异性铑催化的、无环不对称手性非外消旋烯丙醇衍生物与芳基溴化锌的烯丙基烷基化反应。这项研究表明，三（吡唑基）硼酸铑氢化物催化剂和卤化锌盐对反应效率至关重要，而向催化剂中添加溴化锂对于获得最佳区域特异性是必要的。通过合成（S）-布洛芬确定了该反应的立体化学过程，这表明烷基化反应的绝对构型发生净反转，这与亲核试剂直接加成到金属中心随后进行还原消除一致。
