Iridium-Catalyzed C–H Borylation-Based Synthesis of Natural Indolequinones

An iridium-catalyzed C–H borylation provides the key step in a short synthesis of two indolequinone natural products. This regioselective C–H functionalization strategy delivers 7-borylindoles that undergo facile oxidation–hydrolysis to 7-hydroxyindoles and subsequent oxidation to the desired indolequinones, thereby demonstrating a powerful application of the iridium-catalyzed C–H borylation reaction. A significant result has arisen from the iridium-catalyzed borylation of <i>N</i>-diethylhydrosilyl-6-methoxyindole; even in the presence of a substituent at C6, the <i>N</i>-hydrosilyl group still directs borylation exclusively into the more sterically hindered C7 position in preference to C2