Gold versus Palladium: A Regioselective Cycloisomerization of Aromatic Enynes
Résumé
Aromatic enynes can be transformed into arylnaphthalenes or benzofulvenes depending on the reaction conditions. Under gold(I) catalysis, exclusive or major 6-endo-dig cyclization took place leading to arylnaphthalenes. However, a catalytic system based on palladium iodide/1,3-Bis(diphenylphosphino)propane, in the presence of cesium carbonate as a base was necessary to furnish exclusively 5-exo-dig cyclization pattern, regardless to the electronic effects of the substituents. In the latter transformation, a mechanistic study (Kinetic Isotopic Effect, Density Functional Theory) involving a C-H activation is suggested for the exclusive benzofulvenes formation.
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