Palladium-Catalyzed Heteroannulation Route to Indoles and Benzofurans

Significance

Reported is the synthesis of indoles and benzofurans via a direct arylation-isomerization strategy. Starting from N- and O-aryl-2-­haloallylic amines and ethers 1, standard cross-­coupling conditions, for example, Pd(OAc)₂/XPhos as a catalytic system, afforded the corresponding indoles and benzofurans in good to high yields in most of the cases. In the case of indoles, the isomerization occurs during the arylation step, whereas an acid-catalyzed aromatization step is required to lead to the benzofurans. In the latter case, the possible isolation of the non-aromatic exo-alkene isomers opens the door to further chemistry, for example, dihydroxylation/acetate formation or epoxidation, as demonstrated. A variety of aryl substituents proved to be compatible with the reaction.