Manganese(I) Catalyzed ortho C−H Allylation of Benzoic Acids

The 3d-metal catalyst Mn(CO)₅Br was found to efficiently promote ortho C−H allylations of arenecarboxylates in the presence of neocuproine as the ligand. Despite the simplicity of directing group and catalyst system, the selectivity goes well beyond the state-of-the-art in that mono-allylated products are obtained exclusively with high selectivities for the least hindered ortho-position. The directing group can optionally be removed by in situ decarboxylation, opening up a regioselective entry to allyl arenes. The preparative utility of the process and its othogonality to other approaches was demonstrated by 44 products with otherwise hard-to-access substitution patterns, including 3-bromo-allylbenzene, 3-allylbenzofuran, or 5-allyl-2-methylnitrobenzene.