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Palladium-Catalyzed, Site-Selective Direct Allylation of Aryl C–H Bonds by Silver-Mediated C–H Activation: A Synthetic and Mechanistic Investigation

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posted on 31.10.2016, 00:00 by Sarah Yunmi Lee, John F. Hartwig
We describe a method for the site-selective construction of a C­(aryl)–C­(sp3) bond by the palladium-catalyzed direct allylation of arenes with allylic pivalates in the presence of AgOPiv to afford the linear (E)-allylated arene with excellent regio­selectivity; this reaction occurs with arenes that have not undergone site-selective and stereo­selective direct allylation previously, such as monofluoro­benzenes and non-fluorinated arenes. Mechanistic studies indicate that AgOPiv ligated by a phosphine reacts with the arene to form an arylsilver­(I) species, presumably through a concerted metalation–deprotonation pathway. The activated aryl moiety is then transferred to an allylpalladium­(II) intermediate formed by oxidative addition of the allylic pivalate to the Pd(0) complex. Subsequent reductive elimination furnishes the allyl–aryl coupled product. The aforementioned proposed intermediates, including an arylsilver complex, have been isolated, structurally characterized, and determined to be chemically and kinetically competent to undergo the proposed elementary steps of the catalytic cycle.