Gold-Catalyzed [5+2]- and [5+1]-Annulations between Ynamides and 1,2-Benzisoxazoles with Ligand-Controlled Chemoselectivity

This work describes two distinct annulations between ynamides and 1,2-benzisoxazoles with chemoselectivity controlled by ligands. With IPrAuCl/AgNTf₂, aryl-substituted ynamides undergo [5+2]-annulation reactions, whereas P­(t-Bu)₂(o-biphenyl)­AuCl/AgNTf₂ alters the chemoselectivity of the same ynamides to implement [5+1]-annulation reactions. ¹³C-Labeling experiments confirm that a 1,2-sulfonamide shift is involved in the [5+1]-annulation process. A plausible mechanism is postulated to rationalize the mechanisms of the two annulations.