Remote site-selective C-H activation directed by a catalytic bifunctional template
A method is described for selectively activating remote C-H bonds in heterocycles by using a catalytic template that binds by reversible coordination instead of a covalent linkage, removing the need for specific functional groups on which to attach the template.
In chemical syntheses, the activation of carbon-hydrogen (C-H) bonds converts them directly into carbon-carbon or carbon-heteroatom bonds without requiring any prior functionalization. C-H activation can thus substantially reduce the number of steps involved in a synthesis. A single specific C-H bond in a substrate can be activated by using a ‘directing' (usually a functional) group to obtain the desired product selectively1,2,3,4,5. The applicability of such a C-H activation reaction can be severely curtailed by the distance of the C-H bond in question from the directing group, and by the shape of the substrate, but several approaches have been developed to overcome these limitations6,7,8,9,10,11,12. In one such approach, an understanding of the distal and geometric relationships between the functional groups and C-H bonds of a substrate has been exploited to achievemeta-selective C-H activation by using a covalently attached, U-shaped template13,14,15,16,17. However, stoichiometric installation of this template has not been feasible in the absence of an appropriate functional group on which to attach it. Here we report the design of a catalytic, bifunctional nitrile template that binds a heterocyclic substrate via a reversible coordination instead of a covalent linkage. The two metal centres coordinated to this template have different roles: one reversibly anchors substrates near the catalyst, and the other cleaves remote C-H bonds. Using this strategy, we demonstrate remote, site-selective C-H olefination of heterocyclic substrates that do not have the necessary functional groups for covalently attaching templates.