Synthesis of (E)-α,β-Unsaturated Esters and (Z)-Vinyl Halides with Total or High Diastereoselectivity by Using Samarium Metal
作者:José M. Concellón、Humberto Rodríguez-Solla、Mónica Huerta、Juan A. Pérez-Andrés
DOI:10.1002/1099-0690(200206)2002:11<1839::aid-ejoc1839>3.0.co;2-r
日期:2002.6
2-halo-3-hydroxy esters 1 or O-acetylated 1,1-dihaloalkan-2-ols 4 is achieved with samarium in the presence of diiodomethane, yielding α,β-unsaturated esters 2 or vinyl halides 5, respectively. The β-elimination reaction was promoted by samarium diiodide, which was generated in situ. The starting halohydrins 1 or 4 are easily prepared by reaction of the corresponding lithium enolates of α-halo esters or dihalomethyllithium
在二碘甲烷存在下用钐实现 2-halo-3-羟基酯 1 或 O-乙酰化 1,1-dihaloalkan-2-ols 4 的高度非对映选择性 β-消除,产生 α,β-不饱和酯 2 或乙烯基分别是卤化物 5。β-消除反应由原位生成的二碘化钐促进。起始卤代醇 1 或 4 很容易通过相应的 α-卤代酯或二卤甲基锂的烯醇锂与醛在 -78 °C 下反应制备。讨论了反应条件和起始化合物的结构对β-消除反应的非对映选择性的影响。还进行了与预先形成的 SmI2 和金属钐的 β-消除反应的比较研究。这些消除反应可以通过提出的机制来解释。