Hypervalent Iodine-mediated Aryl-aryl Coupling And Rearrangement: A New Method For The Synthesis Of Biaryls

Biaryl is a class of important structural motif, and has been found in a number ofnatural products with pharmacological activity. Besides, it has also been foundimportant applications in organic chemistry. In recent years, the method involving thedirect cross-dehydrogenative coupling of two unfunctionalized aromatic rings hasbecame a new strategy to synthesize biaryls. Due to its atom economy as well asenvironmental benignity, it has drawn a great attention by chemists. Most of theexisting methods require the participation of a transition metal as catalyst. Limitationsof the existing methods include the limisted scope of substrates and the requirementof high temperature.Herein, we disclosed a dehydrogenative coupling reaction concomitant withrearrangement mediated by hypervalent iodine reagent. Features of this reactioninclude:1) oxidative aromatic C(sp2) C(sp2) aryl-aryl bond formation;2) cleavage ofa C(sp2) C(O) bond;3) lactamization or lactonization.We chose2-acylamino-N-phenyl-benzamides119as substrates, PIDA as oxidant,and21biaryls121with potential pharmacological activity have been synthesized inacetonitrile under reflux. In the presence of PIFA/BF3·OEt2, a series of2-hydroxy-N-phenylbenzamides132have been converted to novel biaryls133inone-pot manner. All the compounds have been well characterized by1H NMR,13CNMR, IR and HRMS. In addition, compound121a was also confirmed by its X-raycrystallography.A plausible mechanism of the reaction process has been proposed. The isolationand characterization of intermediate134as well as some experimental facts provesthe rationality of the mechanism. In addition, we also explored the application of thebiaryl products. The unsymmetric biaryls with amino group or hydroxyl group havebeen obtained via the hydrolysis of the biaryl products.