Regioselective Heck Reactions of Indene: A Switch of Regioselectivity by the Phenolate Ligand

Substituted indenes are common motifs in some drugs and bioactive natural products. Regioselective Heck reactions of indene remain difficult to achieve to date due to slow aryl insertion, low regioselectivity, and competing side reactions of aryl halides. We report two efficient Heck methods for both α- and β-selective arylation of indene by using a single palladium complex of bulky dialkylphosphine XPhos. Importantly, KOPh completely switched the regioselectivity from the β- to the α-arylation of indene. We found that trans-complexes of phenolate XPhosP(Ar)(OPh) were the active species for selective α-arylation, and they were stabilized by weak π–π interactions between the phenoxide and migrating aryl ligands, according to experiments using isolated complexes and DFT calculations.