Chromium-Catalyzed Selective Cross-Electrophile Coupling between Unactivated C(aryl)–F and C(aryl)–O Bonds
Fan Fei, Lixing Zhao, Meiming Luo, Xiaoming Zeng
Abstract
Chemically inert C(aryl)–F bonds have rarely been used to couple with other unactivated bonds, and this remains a challenge because of the difficulty of the successive cleavage of two unactivated bonds by metal catalysis. We report here the chromium-catalyzed cleavage of chemically inert C(aryl)–F bonds for coupling with unactivated C(aryl)–O bonds, allowing cross-electrophile coupling between unreactive aryl fluorides and aryl esters to be achieved in high regio- and chemoselectivity. The reactive Cr, which was formed in situ by reducing CrCl2, enables cleavage of the o-C(aryl)–F bonds to afford monovalent and quartet cyclochromate; subsequent bipyridyl-enabled insertion into the ester C(aryl)–O bond followed by reductive elimination allowed the orthogonal coupling of these two different and unactivated bonds. Mechanistic studies indicate that the bipyridyl ligand greatly enhances the reactivity of Cr in the cleavage of C(aryl)–O bonds, and the second oxidative addition may occur sluggishly compared with the reductive elimination in the catalytic cycle.