NBS-Promoted Reactions of Symmetrically Hindered Methylphenols via <i>p</i>-Benzoquinone Methide
作者:Woonphil Baik、Hyun Joo Lee、Jung Min Jang、Sangho Koo、Byeong Hyo Kim
DOI:10.1021/jo9911185
日期:2000.1.1
Symmetrically hindered methylphenols 1 react smoothly with NBS to form transient intermediates, p-benzoquinone methides (BM), which can be further processed to give hydroxybenzaldehydes in the presence of DMSO. This reaction is initiated by the formation of the phenoxy radical, followed by disproportionation to afford BM. None of the side-chain-brominated product is observed. The existence of BM is
受对称对称的甲基苯酚1与NBS平稳反应,形成瞬态中间体对苯醌甲基化物(BM),可以在DMSO存在下将其进一步加工成羟基苯甲醛。该反应通过苯氧基的形成而引发,然后歧化得到BM。没有观察到侧链溴化产物。以下观察结果支持了BM的存在:溶液中BM的形成可以通过GC和GC-MS进行监测;亲电子次甲基部分通过苯甲醚参与亲电子芳香族取代,得到羟基苄基化产物15;外环次甲基的双键特性在与二烯的[4 + 2]环加成中发挥作用,以提供Diels-Alder加合物。相反,与NBS不对称受阻或简单的甲基苯酚(对甲酚)照常提供核溴化产物。使用密度泛函理论计算了对称受阻BM,非对称受阻BM和简单BM的能量。对于等位受阻的BM,通过等渗方程在B3LYP / 6-31G // B3LYP / 6-31G水平计算的相对稳定能提高了3-6 kcal / mol。