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.