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. 2016 Nov 23;138(46):15278-15284.
doi: 10.1021/jacs.6b10220. Epub 2016 Nov 14.

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

Sarah Yunmi Lee  1 , John F Hartwig  1
Affiliations

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

Sarah Yunmi Lee et al. J Am Chem Soc. .

Abstract

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.

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Figures

Figure 1
Figure 1
ORTEP diagram of complex 6. Bonds and angles: O1–Pd1 2.117(14) Å; P1–Pd1 2.332(6) Å; C1–Pd1 2.094(2) Å; C2–Pd1 2.145(2) Å; C3–Pd1 2.259(2) Å; C3–C2–C1 118.8(2)°; C15-P1-Pd1 109.0(7)°; C10-O1-Pd1 112.1(13)°. Ellipsoids are shown at 50% probability, and hydrogen atoms are omitted for clarity.
Figure 2
Figure 2
ORTEP diagram of L-ligated silver pivalate (7). Bonds and angles: P1–Ag1 2.349(12) Å; O1–Ag1 2.135(3) Å; O2–Ag1 2.714(4) Å; P2–Ag2 2.346(1) Å; O5–Ag2 2.305(4) Å; O4–Ag2 2.447(5) Å; O1–Ag1–P1 171.4(10)°; O2–Ag1–P1 136.5(9)°; O1–Ag1–O2 52.0(1)°; O5–Ag2–P2 148.4(1)°. O4–Ag2–P2 156.0(1)°; O5–Ag2–O4 55.0(1)°. Ellipsoids are shown at 50% probability, and hydrogen atoms are omitted for clarity.
Figure 3
Figure 3
ORTEP diagram of the P(2-anisyl)3-ligated silver-aryl complex. Bonds and angles: P1–Ag1 2.378(9) Å; C1–Ag1 2.123(3) Å; P1–Ag1–C1 178.5(1)°. Ellipsoids are shown at 50% probability, and hydrogen atoms are omitted for clarity.
Figure 4
Figure 4
Outline of a possible mechanism for Pd-catalyzed and Ag-mediated direct allylation of arenes with allylic pivalates.
Figure 5
Figure 5
ORTEP diagram of dimeric palladacycle 12. Bonds and angles: Pd1–Pd2 3.248(6) Å; C1–Pd1 1.984(3) Å; P1–Pd1 2.237(9) Å; O2–Pd1 2.130(2) Å; O4–Pd1 2.105(2) Å; P1–Pd1–C1 69.3(9)°; Pd1–C1–C6 108.2(2)°; C1–C6–P1 97.1(2)°; C6–P1–Pd1 85.4(1)°; O4–Pd1–O2 90.8(8)°. Ellipsoids are shown at 50% probability, and hydrogen atoms are omitted for clarity.
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