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.
Authors: Nathan A. Romero, Kaila A. Margrey, Nicholas E. Tay, David A. Nicewicz
The fight over the name of a mountain or the treatment of a figure from history rests in large part on competing ownership of histories, peppered with contemporary political context.
Since 2011, August 12 has been set aside as World Elephant Day. Supported by numerous conservation agencies, it’s a day to “spread awareness, share knowledge, and provide solutions for better care and management of both captive and wild elephants,” according to the organizer’s website. Elephants face numerous challenges, including poaching, habitat loss, exploitation, abuse, and proximity to human conflict and poverty. The International Union for Conservation of Nature lists African elephants as “vulnerable” and Asian elephants as “endangered.” On this World Elephant Day, I present a collection of images of these amazing animals.
Melbourne Zoo's newest Asian elephant receives a nudge from her mother after going on display to the public for the first time on February 10, 2010.
(William West / AFP / Getty)
Directing groups in a substrate are frequently used to direct the regioselectivity of C–H activation reactions. Now it has been shown that regioselectivity can be directed by a ligand, which binds to both the catalysing metal centre and a distal hydrogen-bond acceptor in the substrate. This secondary interaction places the metal in close proximity to the reacting C–H bond.
