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

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.