sulfur as chelation groups in CÀH activation,8 possibly
due to its strong coordination ability. Herein, we describe
thefirst exampleofthe useofthioetherastheonlydirecting
group for the Pd-catalyzed olefination of arenes. The
thioethers can be easily removed or engaged in a variety
of useful transformations.9,10 This result established that
sulfur can be used as chelation group in CÀH activation,
which may lead to the creation of economical synthetic
methods for sulfur containing compounds.
Thioether is an important structural motif in a wide
range of molecules with numerous and important appli-
cations.11 It has been widely used as coordination groups
with various metals in many useful complexes.12 The
important applications of thioether derivatives in drug
discovery and natural product synthesis11 prompted us to
develop a Pd-catalyzed ortho-alkenylation of aryl thioethers
(Figure 1).13 Initially, we examined a variety of S-involving
groups as directing group for the palladium catalyzed direct
alkenylation of aromatic CÀH bond with methyl acrylate 2a.
It was found that the length of the tether group between arene
and sulfur exerted a drastic effect on the reaction, and the
benzyl thioethers showed the best efficiency. Smaller groups
in thioether facilitate the transformation as shown when
benzyl was replaced by methyl group, possibly due to the
more efficient coordination. Arylthio presented better reac-
tivity, although dialkenylated product was formed. Notably,
the reaction of other S-containing groups such as sulfoxide,
sulfone, and thioesters are sluggish, indicating that the
properties of the sulfur play crucial role on the chelation with
palladium. Analogous O-based groups such as phenylether
had proven to be totally inactive.
Figure 1. S-containing Directing Groups for Aromatic C-H
Alkenylation. Reaction conditions: arenes (0.3 mmol), 2a
(51.6 mg, 0.6 mmol), Pd(OAc)2 (6.7 mg, 0.03 mmol), and AgOAc
(100.2 mg, 0.6 mmol) in DCE (2 mL) under air at 120 °C for 12 h.
a AgOTFA was used instead of AgOAc.
this Pd(II)-catalyzed alkenylation of (2-methylbenzyl)-
(phenyl)sulfane 1f with butyl acrylate under 100 °C for
12 h in DCE (see the Supporting Information for details).
The substrate scope of the reaction is summarized in Figure 2.
Various acrylic esters had proven to be reliable sub-
strates in the reaction, and the yields increased from 55
to 72% with the elevation of the boiling point of the acrylic
ester (3aa, 3ab, and 3ac). When phenylthio 1b and
p-tolylthio 1c were used as directing groups, dialkenylation
product was observed (3ba and 3ca). The electron-rich
arenes were readily alkenylated to give the antici-
pated products fast in good yields (3dcÀ3fc). Notably,
the reaction presented excellent regioselectivity with
the alkenylation at the ortho-position of the less steric
side of the arenes (3dcÀ3ec, 3ga, 3gc, and 3jc). The
ortho-substituent arylthioethers participated in the reac-
tion smoothly to afford the desired alkenylated products in
good yields (3faÀ3fc). The electronic-deficient arenes
furnished the alkenylated products in good yields as well,
but longer reaction time was required (3gaÀ3ia). The
arenes bearing a strong electron-withdrawing group such
as CN showed lower reactivity to give low yield even after
prolongation of reaction time (3jc).
After extensive screening the reaction conditions, we
discovered that 2 equiv of Ag(OTFA) promoted efficiently
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Arenes bearing double electron-donating groups were
also subjected to the reaction. It was surprising that
no expected product was observed. After switching the
oxidant to AgOAc, the reaction was smooth, with mono-
alkenylation occurring on the less steric side of the arenes
(3ka and 3lc). In contrast, double electron-withdrawing
group substituted arenes such as 3m were compatible with
AgOTFA, giving the regioselective alkenylaion product
3mc in a 37% yield.
It should be pointed out that dialkenylation product was
not detected in the reactions involving meta- and ortho-
substituted arenes. However, in the case of unsubstituted
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