[see reaction]. The Still-Wittig rearrangement gave opposite selectivities for (Z:E)-alkenes in THF (3:1) vs toluene (1:3) in the synthesis of serine-proline dipeptide amide isosteres. Four transition states leading to (Z)-and (E)-alkenes with THF and without (representing toluene) were identified by ab initio calculations at the 3-21G* level. The calculated (Z:E)-ratios with THF (4.7:1) and without
[请参阅反应]。在合成
丝氨酸-脯
氨酸二肽酰胺等排体时,Still-Wittig重排在THF(3:1)对
甲苯(1:3)中对(Z:E)烯烃具有相反的选择性。通过从头算计算在3-21G *
水平下鉴定出导致具有THF且不具有(代表
甲苯)的(Z)-和(E)-烯烃的四个过渡态。使用THF(4.7:1)和不使用THF(1:3.2)的计算的(Z:E)比值表明过渡态的几何形状和能量可以通过计算很好地表示。