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Site-selective arene C-H amination via photoredox catalysis

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Science  18 Sep 2015:
Vol. 349, Issue 6254, pp. 1326-1330
DOI: 10.1126/science.aac9895

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Lighting the way to aryl C-N bonding

Medicinal chemists like to add N bonds to the C atoms of aromatic rings to make bioactive compounds. By harnessing the energy in visible light, Romero et al. made these links and transformed C-H into C-N bonds. They used a blue-absorbing acridinium ion to activate a ring C for an incoming N partner. A nitroxyl radical co-catalyst (TEMPO) then choreographed the transfer of the H atom to O. The reaction worked for a broad range of substrates, including ammonium as a N source.

Science, this issue p. 1326

Abstract

Over the past several decades, organometallic cross-coupling chemistry has developed into one of the most reliable approaches to assemble complex aromatic compounds from preoxidized starting materials. More recently, transition metal–catalyzed carbon-hydrogen activation has circumvented the need for preoxidized starting materials, but this approach is limited by a lack of practical amination protocols. Here, we present a blueprint for aromatic carbon-hydrogen functionalization via photoredox catalysis and describe the utility of this strategy for arene amination. An organic photoredox-based catalyst system, consisting of an acridinium photooxidant and a nitroxyl radical, promotes site-selective amination of a variety of simple and complex aromatics with heteroaromatic azoles of interest in pharmaceutical research. We also describe the atom-economical use of ammonia to form anilines, without the need for prefunctionalization of the aromatic component.

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