Regioselectivity of Direct Arylations

Regioselective direct arylations are difficult to achieve because the arene reagents often contain several inequivalent C-H bonds that can react with the metal center at similar rates. Several approaches have been investigated to address tliis challenge. In some cases the reactions have been conducted intramolecularly, while in other cases the reactions have 

CHAPTER 19 TRANSITION METAL-CATALYZED COUPLING REACTIONS 

Intramolecular reactions of the two arene components linked by a tether can occur regioselectively because of the geometric constraints. An example of an intramolecular direct arylation controlled by a temporary tether is shown in Equation 19.148. In this synthesis of dioncophylline C, two important features of intramolecular direct arylation are illustrated. First, intramolecular arylation reactions are typically used for the construction of five-, six- (as shown in Equation 19.148), and seven-membered rings. Second, direct arylation tends to occur at the less-hindered aryl C-H bond. 

DG = directing group ketone, aldehyde, amide, phenol, imine, oxazoles, imidazoles, etc. 

Regioselectivity for direct arylation of electron-rich heteroarenes  

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