Gold-Catalyzed cis-Hydroarylation reactions of Ynamides with Indoles: Regio- and Stereoselective synthesis of a new class of 2-vinylindoles

In the last years, among unsatured compounds, ynamides have emerged a versatile building block, becoming a widely exploited starting material in organic synthesis. This class of molecules is characterized by the presence of a nitrogen atom directly connected to a C-sp of an alkyne. As consequence, a strong polarization of the triple bond is observed, enabling a reactivity characterized by high level of regio- and/or steroselection. Recently, gold-catalysts have been employed in reactions involving ynamides in particular for the synthesis of heterocycles. In fact, after activation of the triple bond by the gold species, nucleophilic attack, usually on the Cα, is favored with the formation of a vinyl-gold intermediate that can evolve in other transformations. Thus, in accordance to our interest in gold-catalyzed functionalization on indole ring, we decided to test the possibility of using a simple 3-substituted indole as nucleophile in the reaction with an ynamide. The reaction, conducted in the presence of a gold(I) catalyst led to (Z)-(3-methyl-indol-2-yl)-2-vinyl benzensulfonamide as product.