Abstract
A catalytic meta selective C-H alkylation of arenes is described using a wide range of α-halo carbonyls as coupling partners. Previously unreported primary alkylations with high meta selectivity have been enabled by this methodology whereas using straight chain alkyl halides affords ortho substituted products. Mechanistic analysis reveals an activation pathway whereby cyclometalation with a ruthenium(ii) complex activates the substrate molecule and is responsible for the meta selectivity observed. A distinct second activation of the coupling partner allows site selective reaction between both components.
Highlights
The direct functionalization of C–H bonds is an attractive methodology for the atom economic and streamlined synthesis of organic molecules
Given our previous work where reaction with a tertiary α-halo carbonyl could readily furnish meta substituted products,[42] we believed that ethyl bromoacetate 2a would be a suitably activated coupling partner to achieve this
We previously proposed a dual role of ruthenium in tertiary alkylation reactions; activation of the substrate by cyclometalation, and a single electron redox catalyst to generate an alkyl radical
Summary
The direct functionalization of C–H bonds is an attractive methodology for the atom economic and streamlined synthesis of organic molecules. There are a number of strategies to overcome these challenges and research into this area has received great attention in the last decade.[1,2] One of the prevailing methods is the directing group approach. This method utilizes existing functionality within a molecule to coordinate a transition metal catalyst and position it in the vicinity of a C–H bond. A number of alternative strategies have been devised (Scheme 1).[10,11]
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