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Catalytic activation of carbon–carbon bonds in cyclopentanones
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Catalytic activation of carbon–carbon bonds in cyclopentanones
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Journal Article
Catalytic activation of carbon–carbon bonds in cyclopentanones
2016
Overview
In the chemical industry, it is often necessary to activate carbon–carbon bonds in order to synthesize complex organic molecules, but this is challenging when starting with simple five- or six-membered carbon rings; a new method uses a rhodium pre-catalyst and an amino-pyridine co-catalyst, enabling an overall energetically favourable reaction that involves activation of carbon–carbon bonds plus activation of carbon–hydrogen bonds.
Access to tetralones
Most molecules of interest to organic chemists are primarily made up of carbon skeletons, so carbon–carbon bond activation is of prime importance in making and modifying such molecules. Transition-metal-mediated carbon–carbon bond activation of cyclic carbon species is a versatile approach, but challenging for five- and six-membered rings because the lack of ring strain provides an insufficient driving force for the reaction. Now, Guangbin Dong and co-workers demonstrate a rhodium-catalysed activation of phenyl-functionalized unstrained cyclopentanones, giving rapid access to tetralones.
In the chemical industry, molecules of interest are based primarily on carbon skeletons. When synthesizing such molecules, the activation of carbon–carbon single bonds (C–C bonds) in simple substrates is strategically important: it offers a way of disconnecting such inert bonds, forming more active linkages (for example, between carbon and a transition metal) and eventually producing more versatile scaffolds
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. The challenge in achieving such activation is the kinetic inertness of C–C bonds and the relative weakness of newly formed carbon–metal bonds
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. The most common tactic starts with a three- or four-membered carbon-ring system
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, in which strain release provides a crucial thermodynamic driving force. However, broadly useful methods that are based on catalytic activation of unstrained C–C bonds have proven elusive, because the cleavage process is much less energetically favourable. Here we report a general approach to the catalytic activation of C–C bonds in simple cyclopentanones and some cyclohexanones. The key to our success is the combination of a rhodium pre-catalyst, an
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-heterocyclic carbene ligand and an amino-pyridine co-catalyst. When an aryl group is present in the C3 position of cyclopentanone, the less strained C–C bond can be activated; this is followed by activation of a carbon–hydrogen bond in the aryl group, leading to efficient synthesis of functionalized α-tetralones—a common structural motif and versatile building block in organic synthesis. Furthermore, this method can substantially enhance the efficiency of the enantioselective synthesis of some natural products of terpenoids. Density functional theory calculations reveal a mechanism involving an intriguing rhodium-bridged bicyclic intermediate.
Publisher
Nature Publishing Group UK,Nature Publishing Group
