Stereoselective E-Carbofunctionalization of Alkynes to Vinyl-Triflates via Gold Redox Catalysis

Carbofunctionalization of alkynes with trifluoromethylsulfonate nucleophiles is a powerful strategy for the synthesis of vinyl triflates with diverse molecular complexity. However, stereoselective protocols are challenging to realize, and the development of novel strategies for controlling the selectivity is highly desirable. In this work, we show that gold complexes bearing the hemilabile MeDalPhos ligand (MeDalPhos = di(1-adamantyl)-2-dimethylamino-phenylphosphine) catalyze the E-stereoselective carbofunctionalization of internal alkynes using aryl/vinyl iodides and AgOTf as simple starting reagents. Based on the outer-sphere nature of this reaction and the beneficial effect of the MeDalPhos ligand, the Z-selective attack is practically suppressed, leading to an ideal kinetic selectivity. Mechanistic studies, both experimental and theoretical, revealed that the interplay between kinetics and thermodynamics is crucial in determining the final E/Z ratios for each substrate.