A detailed mechanistic study of the rhodium-catalyzed carboxylation of aromatic compounds was carried out to clarify the unique characteristics of this reaction.

The Rh‐catalyzed direct carboxylation of alkenyl C−H bonds was achieved by using pyrazole as a removable directing group. In the presence of 5 mol% RhCl3 ⋅ 3H2O, 6 mol% P(Mes)3, and 2 equiv. of AlMe2(OMe), the alkenyl C−H bond of various alkenylpyrazoles was directly carboxylated in good yields under CO2 atmosphere. Furthermore, several useful transformations of the pyrazole moiety of the product were achieved to afford synthetically useful carboxylic acid derivatives in good yields.