p-TsOH Promoted Au(I)-Catalyzed Consecutive Endo Cyclization of Yne-Tethered Ynamide: Access to Benzofused Dihydroisoquinolones.

A novel synthetic route to benzo[f]dihydroisoquinolone through a p-TsOH promoted cascade cyclization of easily accessible diyne-tethered ynamides in the presence of a Au(I)-catalyst is described. This reaction unveils a broad substrate scope, constructing a wide range of benzo[f]dihydroisoquinolones in good yields. The diyne-tethered ynamides are synthesized from inexpensive o-iodoaniline through Sonogashira couplings and the Cu-mediated C-N bond formation. The role of p-TsOH is examined, and the reaction pathway is also deduced. The benzo[f]isoquinoline scaffold is constructed from benzo[f]dihydroisoquinolones.