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)/(BF3Et2O)-Et-center dot 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.