MeOH) and increasing chemical shifts (10.97 → 11.42→11.71 DMSO-d6). We conclude that the paradoxical decrease in CO stretching frequencies by the 3-positoin EW groups is explained by an ‘assistive’ electron-withdrawing effect, whereby the 3-position EW group assists the electronegative oxygen atom in recruiting more electron density, and – as a result – attaining more oxyanion character (decreased the
我们报告了通过亲电
溴化(Br 2)或自由基三
氟甲基化(NaSO 2 CF 3 / t BuOOH)在3位的
吡啶酮和
吡喃酮的区域选择性功能化。违反直觉的是,3位EW基团使羰基的拉伸能降低了6-23 cm -1。然而,与3-Br
吡啶酮相比,3,5-二
溴化使C O频率增加了10-22 cm -1。X射线晶体学显示
吡啶酮互变异构体具有收缩的C O键度量。3-H→Br→CF 3系列的p K a值和1 H NMR位移揭示了酸度增加的预期趋势(p K a = 8.85→8.33→6.78,MeOH)和增加的
化学位移(10.97→11.42→11.71
DMSO- d 6)。我们得出的结论是,“ 3-positoin” EW基团通过“辅助”吸电子效应解释了CO延伸频率的反常下降,其中3-位EW基团协助负电性氧原子募集更多的电子密度,并且-结果–获得更多的
氧阴离子特性(降低了C O键强度)。