Highly Diastereo- and Enantioselective Synthesis of Tetrahydro-5H-Indolo[2,3-b]quinolines through Copper-Catalyzed Propargylic Dearomatization of Indoles.

The first copper-catalyzed intermolecular asymmetric propargylic dearomatization/annulation cascade sequence of indoles via a copper-allenylidene amphiphilic intermediate has been achieved. This protocol provides a direct asymmetric synthetic method for the preparation of tetrahydro-5H-indolo[2,3-b]quinolines, the core structure of indole alkaloids communesins A-H and perophoramidine. This method features excellent yields, high diastereoselectivity (up to >19:1 d.r.) and enantioselectivity (up to 94 % ee), mild conditions and wide substrate scope.