Controlling the Scholl Reaction

Guidelines for the application of the Scholl reaction were developed. Labeling experiments demonstrate
that the Scholl reaction fails in small, unsubstituted oligophenylenes (e.g., o-terphenyl) due to
oligomerization of the products (e.g., triphenylene). Incorporation of suitably placed blocking groups
(e.g., t-butyl) suppresses oligomerization. The well-established directing group effects in electrophilic
aromatic substitution predict the outcome of Scholl reactions of substituted substrates. Activating o,p-directing groups (e.g., MeO) direct bond formation o,p, either intramolecularly or intermolecularly.
Deactivating o,p-directing groups (e.g., Br) also direct bond formation o,p but yields are lower. Deactivating
m-directors (e.g., NO2) suppress reaction. MoCl5 and PhI(OOCCF3)2/BF3·Et2O are general and effective
reagents for the Scholl oxidation. Calculations (B3LYP/6-31G(d)) predict the Scholl reaction in
alkoxyarenes to proceed via arenium cations, not radical cations. Suzuki−Miyaura couplings were used
to generate 12 substituted o-terphenyl derivatives.

本研究确立了肖尔反应（Scholl reaction）的应用规范。标记实验显示，该反应在小型未取代低聚苯（如邻三联苯）中难以顺利进行，原因在于其产物（如三亚苯）发生了寡聚副反应。引入位置适宜的阻聚基团（如叔丁基）可有效抑制寡聚过程。亲电芳香取代反应中已被广泛证实的导向基团效应，可用于预测取代底物参与肖尔反应的结果：活化型邻对位导向基团（如甲氧基（MeO））可通过分子内或分子间路径，引导成键反应发生在邻位或对位；钝化型邻对位导向基团（如溴（Br））同样可引导成键至邻对位，但反应产率更低；而钝化型间位导向基团（如硝基（NO2））则会抑制反应进行。五氯化钼（MoCl5）与三氟乙酸碘苯/三氟化硼乙醚络合物（PhI(OOCCF3)2/BF3·Et2O）是适用于肖尔氧化反应的通用高效试剂。密度泛函计算（B3LYP/6-31G(d)）结果表明，烷氧基芳烃参与的肖尔反应经由芳烃鎓阳离子而非自由基阳离子路径进行。本研究通过铃木-宫浦偶联反应（Suzuki−Miyaura couplings）合成了12种取代邻三联苯衍生物。