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-hydroyindoles 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 N-diethylhydrosilyl-6-methoxyindole; even in the presence of a substituent at C6, the N-hydrosilyl group still directs borylation exclusively into the more sterically hindered C7 position in preference to C2.