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.