Selectfluor promoted NHC–oxazoline gold(i) complex catalyzed cycloaddition/oxidation reaction of enynones with alkenes

The ortho- and meta-substituted NHC–oxazoline ligands based on a phenyl scaffold have been synthesized in a six-step pathway, and their coordination with Au(Me2S)Cl gave the corresponding NHC–gold(I) complexes in good yields. Resulting from restricted rotation between the phenyl ring and the benzimidazole ring, the ortho-substituted NHC–oxazoline gold(I) complexes exhibited as a pair of diastereomers, and their structures have been further confirmed by X-ray diffraction analysis. Moreover, combination of these gold(I) complexes with Selectfluor in situ was used to catalyze the reaction of enynone with alkenes using air as an oxidant to give naphthalene derivatives in moderate to excellent yields. Some controlled experiments were carried out to reveal the active species as a chelated NHC–oxazoline gold(I) species and the role Selecfluor played in this reaction.