Remote C6-Selective Ruthenium-Catalyzed C-H Alkylation of Indole Derivatives via sigma-Activation

摘要

The site-selective functionalization of an indole template offers exciting possibilities for the derivatization of molecules with useful biological properties. Herein, we report the remote C6-selective C-H alkylation of indole derivatives enabled by dual cyclometalation/redox ruthenium catalysis. Remote alkylation was achieved using N-pyrimidinyl indoles with an ancillary ester directing group at the C3 position. This ancillary directing group proved pivotal to reactivity at C6, with yields up to 92% achieved. A one-pot procedure to install this directing group followed by remote C6 functionalization has also been reported; both processes are shown to proceed via ruthenium redox catalysis. Computationally calculated Fukui indices elucidated that the C6 position was the most reactive vacant C-H site toward potential functionalization. When this investigation was coupled with deuterium incorporation studies, a C2-cyclometalation/remote a-activation pathway was deduced.