Regio- and Stereoselective Ring Opening of 2,3-Diaryl Oxiranes by LiBr/Amberlyst 15: A New Stereocontrolled Access to 1,2-Diaryl-2-bromo Alcohols
作者:Arlette Solladié-Cavallo、Paolo Lupattelli、Carlo Bonini
DOI:10.1021/jo048045w
日期:2005.3.1
symmetrical trans-stilbene oxide, the syn- versus anti-bromohydrins ratio ranged between 88/12 and 30/70, by varying the reaction temperature from 20 to −30 °C. In the case of nonsymmetrical para-substituted trans-2,3-diaryloxiranes, the regioselectivity is determined by electronic effects. If one phenyl bears a strong electron-withdrawing group (as NO2 or CF3), the nucleophilic attack is totally on the
对称和不对称的反式-2,3-二芳基环氧乙烷均通过LiBr / Amberlyst 15系统在区域和立体上选择性打开。在对称的反式-二苯乙烯-环氧化合物的情况下,通过将反应温度从20更改为-30°C ,顺式-反式-溴代醇的比例在88/12至30/70之间。在非对称的对位取代的反式-2,3-二芳基环氧乙烷的情况下,区域选择性由电子效应确定。如果一个苯基带有强吸电子基团(如NO 2或CF 3),相对于取代的苯环,亲核攻击完全在β-碳上。在一个带有一个强电子释放基团(OCH 3)的苯基上,区域选择性相反。在质子化的环氧化物结构上进行的DFT / B3LYP / 6-31G *水平的从头算计算支持形成阳离子无环中间体。该方法在邻-甲氧基和邻-硝基2,3-二芳基氧杂环戊烷上的应用通过分别在α-碳或β-碳上的区域和立体选择性开环以优异的产率提供了顺-溴代醇。