Rearrangement reactions are useful ways to make substituted aromatic molecules, but most of the methods that shift a substituent around an arene ring leave a functional group behind at the vacated carbon. A rare exception is the “halogen dance” reaction, in which a halogen atom hops to a neighboring carbon, while a hydrogen atom takes its original place.
Junichiro Yamaguchi and a team of chemical choreographers at Waseda University have now developed an analogous “ester dance” reaction, the first carbonyl group rearrangement of its kind (Sci. Adv. 2020, DOI: 10.1126/sciadv.aba7614). The reaction uses a palladium catalyst with a diphosphine-thiophene ligand and a base, and works on more than 30 different arenes, including naphthalenes (example shown) and pyridines. The discovery was a happy accident. “I’ve never seen such a reaction before,” says Yamaguchi.
The researchers think the palladium catalyst inserts itself into the ester before forming a palladium-arene intermediate. This subsequently reforms the ester at a thermodynamically favored position on an adjacent carbon.
They also teamed the ester dance with a decarbonylative coupling reaction, offering a one-pot route to a range of high-value molecules. Yamaguchi says the dance could be used to create ester and carboxylic acid intermediates for pharmaceuticals and agrochemicals.