Switchable C-H Alkylation of Aromatic Acids with Maleimides in Water: Carboxyl as a Diverse Directing Group

A ruthenium-catalyzed protocol to access conjugate addition or decarboxylative conjugate addition of aromatic acids with maleimides has been developed. The reaction shows interesting chemoselectivity with different substituted benzoic acids. The reaction pathway of C-H alkylation is controlled by the intrinsic property of aromatic acids but not reaction conditions. Under almost the same reaction conditions, carboxyl can act as either a classical directing group or a traceless directing group, thereby generating two kinds of products, i.e., 2-alkyl substituted benzoic acids and alkyl substituted benzenes. These two reactions proceeded under mild and redox-neutral conditions in neat water under the atmosphere of air, and could be easily scaled up to grams. The decarboxylative conjugate addition, where carboxyl acts as a traceless directing group, can be realized without the addition of any ligand, silver or copper salt.