Origins of regioselectivity in radical arylation of aniline: A computational study |
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Authors: | Xiang Zhang |
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Institution: | Department of Applied Chemistry, Zhejiang Gongshang University, Hangzhou, China |
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Abstract: | The radical arylation of the para‐substituted anilines under three different conditions (A: arylhydrazines as the radical precursors and MnO2 as the oxidant in acetonitrile; B: arylhydrazine hydrochlorides as the radical precursors and O2 as the oxidant in aqueous sodium hydroxide solution; C: arenediazonium salts as the radical precursors and TiCl3 as the reductant in aqueous hydrochloric acid solution) has been theoretically studied and the origins of the ortho/meta regioselectivity have been explored. The arylation process is suggested to contain three steps: radical generation, radical addition, and rearomatization. Calculations show that the arylation of the neutral anilines is kinetically controlled under conditions A and B, and the regioselectivity is determined by the radical addition. As a directing group, ? NH2 plays an important role in these cases with the assistance of Mn(OH)2 (the reduced product of MnO2 under condition A) and Na+ (condition B). As for the arylation of the protonated anilines under condition C, the regioselectivity is affected by the substituents in the para‐position of anilines. Electron‐donating groups support meta‐addition and the selectivity is decided by the radical addition. Conversely, electron‐withdrawing groups favor ortho‐addition, and in this situation the arylation process is thermodynamically controlled and the regioselectivity is determined by the radical addition and rearomatization. © 2015 Wiley Periodicals, Inc. |
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Keywords: | radical arylation rearomatization regioselectivity aniline density functional theory (DFT) |
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