Ligand-Controlled Regiodivergent Palladium-Catalyzed Hydrogermylation of Ynamides.

ABSTRACT

Ynamides are fascinating small molecules with complementary reactivities under radical, ionic, and metal-catalyzed conditions. We report herein synthetic and DFT investigations of palladium-catalyzed ligand-controlled regiodivergent hydrometalation reactions of ynamides. Germylated and stannylated enamides are obtained with excellent α,E- or ß,E-selectivities and a broad functional group tolerance. Such a regiodivergent palladium-catalyzed process is unique in ynamide chemistry and allows for the elaboration of metalated enamides that are useful building blocks for cross-coupling reactions or heterocyclic chemistry. DFT calculations fully support the experimental data and demonstrate the crucial roles of the trans-geometry of the [H-Pd(L)-Ge] complex, as well as of the steric requirements of the phosphine ligand. In addition, these calculations support the prevalence of a hydro-palladation pathway over a metal palladation of the π system of the ynamide.