Directing group
Molecular substituent that facilitates reactions by interacting with a reagent
In organic chemistry, a directing group (DG) is a substituent on a molecule or ion that facilitates reactions by interacting with a reagent. The term is usually applied to C-H activation of hydrocarbons, where it is defined as a "coordinating moiety (an 'internal ligand'), which directs a metal catalyst into the proximity of a certain C-H bond." In a well known example, the ketone group (C=O) in acetophenone is the DG in the Murai reaction.
The Murai reaction is related to directed ortho metalation, a reaction is typically applied to the lithiation of substituted aromatic rings.
A wide variety of functional groups can serve as directing groups.
01Transient directing groups
Since directing groups are ligands, their effectiveness correlates with their affinities for metals. Common functional groups such as ketones usually are only weak ligands and thus often are poor DGs. This problem is solved by the use of a transient directing group. Transient DGs reversibly convert weak DGs (e.g., ketones) into strong DG's (e.g., imines) via a Schiff base condensation. Subsequent to serving their role as DGs, the imine can hydrolyze, regenerating the ketone and amine.
Sources and credits
This article is adapted from the Wikipedia article “Directing group”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
Images, from Wikimedia Commons:
- Figure 1. General scheme of a Murai reaction.png by Codswalloper, CC BY-SA 4.0
- Directedorthometalation.png by V8rik at English Wikipedia, CC BY-SA 3.0
- JunTDG.png by Smokefoot, Public domain
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