Biaryl compounds are extremely important structural motifs in natural products, biologically active components and pharmaceuticals. Selective synthesis of biaryls by distinguishing the subtle reactivity difference of distal arene C-H bonds are significantly challenging. Herein, we describe para-selective C-H arylation, which is acheived by a unique combination of a meta-directing group and norbornene as a transient mediator. Upon direct meta-C-H palladation, one-bond relay palladation occurs in presence of norbornene and subsequently para-C-H arylation is achieved for sulfonates, phosphonates and phenols bearing 2,6-disubstitution patterns. The protocol is amenable to electron-deficient aryl iodides. Multisubstituted arenes and phenols are obtained by postsynthetic modification of the products. The protocol allows the synthesis of hexa-substituted benzene by sequential selective distal C-H functionalization.
Keywords: Catellani reaction; C−H activation; arylation; palladation; relay reactions.
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