Direct and highly enantioselective iso-Pictet-Spengler reactions with α-ketoamides: access to underexplored indole core structures.

Direct, one-pot, operationally simple, and highly enantioselective iso-Pictet-Spengler reactions are reported. The reactions involve the condensation of either (1H-indol-4-yl)methanamine or 2-(1H-Indol-1-yl)ethanamine with a variety of α-ketoamides, followed by the addition of a simple and commercially available chiral silicon Lewis acid. These reactions are the first asymmetric examples of these cyclization modes and provide access to 3,3-disubstituted-1,3,4,5-tetrahydropyrrolo[4,3,2-de]isoquinolines and 1,1-disubstituted-1,2,3,4-tetrahydropyrazino[1,2-a]indoles, respectively, two relatively underexplored indole-based core structure motifs in medicinal chemistry.