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Regioselective Introduction of Heteroatoms at the C‑8 Position of Quinoline N‑Oxides: Remote C–H Activation Using N‑Oxide as a Stepping Stone

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posted on 2014-07-30, 00:00 authored by Heejun Hwang, Jinwoo Kim, Jisu Jeong, Sukbok Chang
Reported herein is the metal-catalyzed regioselective C–H functionalization of quinoline N-oxides at the 8-position: direct iodination and amidation were developed using rhodium and iridium catalytic systems, respectively. Mechanistic study of the amidation revealed that the unique regioselectivity is achieved through the smooth formation of N-oxide-chelated iridacycle and that an acid additive plays a key role in the rate-determining protodemetalation step. While this approach of remote C–H activation using N-oxide as a directing group could readily be applied to a wide range of heterocyclic substrates under mild conditions with high functional group tolerance, an efficient synthesis of zinquin ester (a fluorescent zinc indicator) was demonstrated.