Rhodium(III)-Catalyzed Oxidative C–H Alkylation of Aniline Derivatives with Allylic Alcohols To Produce β‑Aryl Ketones

The Rh­(III)-catalyzed C–H oxidative alkylation of aniline derivatives with readily available secondary allyl alcohols using a pyrimidine-directing group, leading to the production of β-aryl ketones, is described. A wide variety of functional groups are tolerated in the reaction. In the reaction with an allyl alcohol bearing a methyl group at the α-hydroxy carbon, such as but-3-en-2-ol (2a), a metal oxidant is not required. In sharp contrast, no reaction occurs when the methyl group in 2a is replaced with ethyl, propyl, pentyl, and phenyl groups. In these cases, the addition of Ag2CO3 is necessary for the reaction to proceed successfully. Mechanistic experiments suggest that 2a acts as an alkylating reagent as well as an oxidant through β-hydroxy elimination to regenerate an active Rh­(III) species. In contrast, Ag2CO3 is required to regenerate an active Rh­(III) species in the reaction with allyl alcohols for reactants other than 2a. Thus, the catalyst regeneration step is different depending on the structure of the allyl alcohol.本研究报道了以嘧啶为导向基团，在铑(III)催化下，苯胺衍生物与易得的二级烯丙基醇发生C–H氧化烷基化反应，进而生成β-芳基酮类化合物。该反应对多种官能团均具有良好的兼容性。当烯丙基醇的α-羟基碳上连有甲基时（如丁-3-烯-2-醇，2a），反应无需金属氧化剂。与之形成鲜明对比的是，若将2a中的甲基替换为乙基、丙基、戊基或苯基，则无反应发生。此类场景下，需添加碳酸银（Ag₂CO₃）以确保反应顺利进行。机理实验结果表明，2a可通过β-羟基消除步骤同时充当烷基化试剂与氧化剂，再生出活性铑(III)物种。与之相反，对于以2a以外的烯丙基醇为底物的反应，则需依靠Ag₂CO₃来再生活性铑(III)物种。由此可见，催化剂的再生步骤因烯丙基醇的结构差异而有所不同。