The Influence of Nucleophile Substituents on the Orientation in the Reaction between 2,4-Difluoronitrobenzene and Lithium Phenoxides in Liquid Ammonia
作者:Larisa Politanskaya、Evgenij Malykhin、Vitalij Shteingarts
DOI:10.1002/1099-0690(200101)2001:2<405::aid-ejoc405>3.0.co;2-6
日期:2001.1
dependence of the orientation of aryloxydefluorination of 2,4-difluoronitrobenzene (1) (o/p ratio) by the action of X-substituted lithium phenoxides 2 (X = p-OMe, p-Me, p-Et, p-iPr, p-tBu, m-Me, H, p-F) in liquid ammonia in the temperature range from −55 to −35 °C has been investigated. The enthalpic preference for ortho-fluorine substitution decreases with weakening substituent electron-donating capability
2,4-二氟硝基苯 (1) 芳氧基脱氟取向的依赖性 (o/p 比) 通过 X 取代的苯酚锂 2 (X = p-OMe, p-Me, p-Et, p-iPr , p-tBu, m-Me, H, pF) 在液氨中在 -55 到 -35 °C 的温度范围内进行了研究。邻氟取代的焓偏好随着取代基给电子能力的减弱而降低:p-OMe > p-Me ≈ p-Et > m-Me > H ⩾ pF。当 X = p-iPr 时,X = p-Me、p-Et 在邻位的主要氟取代变成了对位取代的偏好,并且这在 X = p-tBu 时进一步增加。PM3、AM1 和 MNDO MO 计算表明,在对位亲核试剂加成时形成的中间阴离子 σ-配合物具有更高的稳定性,因此表明 X = p-OMe、m-Me、H、pF 和 p-Alk = Me、Et 的主要邻位取代是由于基板中电荷分布对取向的控制。作为控制因素的底物电子结构可能会因中间阴离子