96.
A simple and efficient nitrile-directed
meta-C−H olefination, acetoxylation, and iodination of biaryl compounds is reported. Compared to the previous approach of installing a complex U-shaped template to achieve a molecular U-turn and assemble the large-sized cyclophane transition state for the remote C−H activation, a synthetically useful phenyl nitrile functional group could also direct remote
meta-C−H activation. This reaction provides a useful method for the modification of biaryl compounds because the nitrile group can be readily converted to amines, acids, amides, or other heterocycles. Notably, the remote
meta-selectivity of biphenylnitriles could not be expected from previous results with a macrocyclophane nitrile template. DFT computational studies show that a ligand-containing Pd–Ag heterodimeric transition state (TS) favors the desired remote
meta-selectivity. Control experiments demonstrate the directing effect of the nitrile group and exclude the possibility of non-directed
meta-C−H activation. Substituted 2-pyridone ligands were found to be key in assisting the cleavage of the
meta-C−H bond in the concerted metalation–deprotonation (CMD) process.
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