directing group

{{Short description|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."{{cite journal |author=Sambiagio, C. |author2=D. Schönbauer |author3=R. Blieck |author4=T. Dao-Huy |author5=G. Pototschnig |author6=P. Schaaf |author7=T. Wiesinger |author8=M. F. Zia |author9=J. Wencel-Delord |author10=T. Besset |author11=B. U. W. Maes |author12=M. Schnürch |year=2018|title=A Comprehensive Overview of Directing Groups Applied in Metal-Catalysed C–H functionalisation chemistry|journal=Chem. Soc. Rev.|volume=47|issue=17|pages=6603–6743|doi=10.1039/C8CS00201K|pmid=30033454|pmc=6113863}} In a well known example, the ketone group ({{chem2|C\dO}}) in acetophenone is the DG in the Murai reaction.

File:Figure_1._General_scheme_of_a_Murai_reaction.png. X = directing group.]]

The Murai reaction is related to directed ortho metalation, a reaction is typically applied to the lithiation of substituted aromatic rings.Snieckus, Victor (1990). [https://pubs.acs.org/doi/pdf/10.1021/cr00104a001 "Directed ortho metalation. Tertiary amide and O-carbamate directors in synthetic strategies for polysubstituted aromatics"] Chem. Rev.; 90 (6): 879–933.

File:Directedorthometalation.png]]

A wide variety of functional groups can serve as directing groups.{{cite journal |doi=10.1021/acs.chemrev.6b00622|title=Palladium-Catalyzed Transformations of Alkyl C–H Bonds |year=2017 |last1=He |first1=Jian |last2=Wasa |first2=Masayuki |last3=Chan |first3=Kelvin S. L. |last4=Shao |first4=Qian |last5=Yu |first5=Jin-Quan |journal=Chemical Reviews |volume=117 |issue=13 |pages=8754–8786 |pmid=28697604 |pmc=5516964 }}