Iridium-Catalyzed Hydrocarboxylation of 1,1-Dimethylallene:  Byproduct-Free Reverse Prenylation of Carboxylic Acids

Exposure of carboxylic acids 1a-12a to commercially available 1,1-dimethylallene in the presence of substoichiometric quantities of an iridium catalyst prepared in situ from [Ir(cod)Cl]2 and BIPHEP provides the corresponding 1,1-dimethylallyl (reverse prenyl) esters 1b-12b in 74-92% isolated yield. This protocol represents the first branch-regioselective allene hydrocarboxylation. Stoichiometric byproducts are not generated in this process and protecting groups are not required for alcohols, phenols, and indolic amines.