Palladium-Catalyzed Ortho-Arylation of O-Phenylcarbamates with Simple Arenes and Sodium Persulfate

By palladium catalysis, the C−H bond functionalization of O-phenylcarbamates with simple arenes has been achieved using sodium persulfate (Na2S2O8), an inexpensive, easy-to-handle, and environmentally friendly oxidant. This oxidative cross-coupling involves two aromatic C−H bonds undergoing concomitant oxidation to furnish a new biaryl C−C linkage. Excellent reaction efficiencies and regioselectivities were observed with a range of electron-rich, electron-neutral, and electron-deficient arenes; minimal homocoupling of either component was observed. When two reactive C−H bonds are present on the O-phenylcarbamate, selective diarylation can be achieved via quadruple C−H bond functionalization. This work represents a rare example of using O-carbamates as directing groups for catalytic C−H bond activation. Additionally, a palladacycle obtained from an O-phenylcarbamate was prepared and fully characterized. This trifluoroacetate-bridged bimetallic Pd complex exhibits clean conversion to the ortho-arylation product upon treatment with simple arenes. The addition of trifluoroacetic acid (TFA) was found to be critical for successful cyclopalladation of O-phenylcarbamates. We propose this oxidative arene cross-coupling occurs via two discrete C−H bond activations, namely cyclopalladation and electrophilic metalation, within a Pd(0/II) catalytic cycle.