Acetic Acid-Promoted Rhodium(III)-Catalyzed Hydroarylation of Terminal Alkynes

Article abstract of DOI:10.1055/s-0037-1611780

Rhodium(III)-catalyzed hydroarylation of terminal alkynes has not previously been achieved because of the inevitable oligomerization and other side reactions. Here, we report a novel Cp?Rh(III)-catalyzed hydroarylation of terminal alkynes in acetic acid as solvent to facilitate the C-H bond activation and subsequent transformations. This reaction proceeds under mild conditions, providing an effective approach to the synthesis of alkenylated heterocycles in high to excellent yields (31-99%) with a broad substrate scope (37 examples) and good functional-group compatibility. In this transformation, the loading of the alkyne can be reduced to 1.2 equivalents, which indicates the significant role of HOAc in lowering the reaction temperature and suppressing the oligomerization of the terminal alkyne. Preliminary mechanistic studies are also presented.

Full text of DOI:10.1055/s-0037-1611780

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© Georg Thieme Verlag Stuttgart · New York
2019, 30, A–G
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A
en
C.-L. Duan et al.
Letter
Synlett
Acetic Acid-Promoted Rhodium(III)-Catalyzed Hydroarylation of
Terminal Alkynes
Chang-Lin Duan◊a,b
broad
substrate scope
excellent
regioselectivity
Xing-Yu Liu◊b,d
Yun-Xuan Tanb
Rui Dingc
DG
H
DG
Ar
R = aryl, alkyl
[Cp∗RhCl2]2 (2.5 mol%)
R
H
H
R
+
Shiping Yang*a
AgSbF6 (15 mol%)
HOAc, rt, 12 h
Ar
(1.2 equiv)
Ping Tian*b,c
0
0
0
0-
0
0
0
2-5
6
1
2-0
6
6
4
37 examples
up to 99% yield
Guo-Qiang Lin*b,c
low
mild
alkyne loading
reaction conditions
a Department of Chemistry, Shanghai Normal University, 100
Guilin Road, Shanghai 200234, P. R. of China
shipingy@shnu.edu.cn
DG = directing group
Cp* = pentamethylcyclopentadienyl
b CAS Key Laboratory of Synthetic Chemistry of Natural Sub-
stances,Center for Excellence in Molecular Synthesis, Shanghai
Institute of Organic Chemistry, University of Chinese Academy
of Sciences, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, P. R. of China
tianping@sioc.ac.cn
lingq@sioc.ac.cn
c Innovation Research Institute of Traditional Chinese Medicine, Shanghai University of Traditional Chinese Medicine, 1200 Cailun Road, Shanghai 201203, P. R. of China
tianping@shutcm.edu.cn
d School of Physical Science and Technology, ShanghaiTech University, 100 Haike Road, Shanghai 201210, P. R. of China
◊Both authors contributed equally to this work
Received: 18.02.2019
Accepted after revision: 13.03.2019
Published online: 26.03.2019
In 2010, Fagnou and co-workers reported the first ex-
ample of a Cp*Rh(III)-catalyzed intermolecular hydroaryla-
tion of alkynes with indole by using an acetanilide directing
group (Scheme 1).4a In 2014, the Miura group realized a C–
H alkenylation of a benzene ring by using sulfoxide4b and
phenylphosphine sulfide4c as directing groups. The same C–
H functionalization was then extended to chromones,4d
tetrazole,4f and 1-(2H)-phthalazinone4e by other groups
(Scheme 1); these reactions might have considerable po-
tential for use in organic synthesis and pharmaceutical
chemistry.5 Also, similar ortho-alkenylations of benzene
with internal alkynes have been reported by the groups of
Wang,4g Loh,4h and Nicholls.4i Moreover, the Shi group
demonstrated that pyridines with strong coordination of
nitrogen atom were well tolerated in this reaction.4j More
recently, Miura and co-workers reported the C–H alkenyla-
tion of benzothiophenes without the aid of any directing
group.4k
DOI: 10.1055/s-0037-1611780; Art ID: st-2019-u0095-l
Abstract Rhodium(III)-catalyzed hydroarylation of terminal alkynes
has not previously been achieved because of the inevitable oligomeriza-
tion and other side reactions. Here, we report a novel Cp*Rh(III)-cata-
lyzed hydroarylation of terminal alkynes in acetic acid as solvent to facil-
itate the C–H bond activation and subsequent transformations. This
reaction proceeds under mild conditions, providing an effective ap-
proach to the synthesis of alkenylated heterocycles in high to excellent
yields (31–99%) with a broad substrate scope (37 examples) and good
functional-group compatibility. In this transformation, the loading of
the alkyne can be reduced to 1.2 equivalents, which indicates the signif-
icant role of HOAc in lowering the reaction temperature and suppress-
ing the oligomerization of the terminal alkyne. Preliminary mechanistic
studies are also presented.
Key words acetic acid, rhodium catalysis, hydroarylation, alkynes
◊These authors contributed equally to this work.
Transition-metal-catalyzed C–H bond activation has re-
ceived considerable attention because it avoids the need for
prior functionalization of substrates and provides an atom-
economical method for organic synthesis.1 Among transi-
tion-metal catalysts, the Cp*Rh(III) complex (Cp* = pentam-
ethylcyclopentadienyl) has proven to be one of the most
powerful catalysts because of its high reactivity, tolerance
to robust reaction conditions, and broad substrate compati-
bility.2 Because of the wide utility of alkynes as coupling
partners,3 the Cp*Rh(III)-catalyzed hydroarylation of
alkynes through C–H bond activation has made significant
progress in the past decade.
However, all these cases required high reaction tem-
peratures and were limited to internal alkyne substrates. To
our surprise, the Cp*Rh(III)-catalyzed hydroarylation of ter-
minal alkynes had not been realized, due to their incidental
oligomerization and other side reactions.6–8 It was therefore
necessary to develop a more general method for this reac-
tion under mild conditions that could be applied to termi-
nal alkynes. Here, we report the results of our researches on
Cp*Rh(III)-catalyzed hydroarylations of terminal alkynes
promoted by acetic acid as the solvent.
Inspired by Huang’s elegant work on Brønsted acid-en-
hanced Cp*Rh(III)-catalyzed conjugate addition of aryl C–H
bonds to ,-unsaturated ketones,9 we surmised that the
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–G

B
C.-L. Duan et al.
Letter
Synlett
Table 1 Selected optimization studiesa
Previous work
DG
[Cp∗RhCl2]2
DG
R1
Cp*Rh(III)
H
H
R1
R2
AgSbF6
Solvent (1 ml)
Temp (°C)
+
+
Ph
R2
R1, R2 ≠ H
N
N
O
H
O
H
P
1a
2a
3aa
H
S
N
R1
S
Entry
1a/2a
Solvent
Temp (°C)
Yieldb (%)
NMe2
Cy
Cy
H
O
O
1
2:1
HOAc
100
100
60
40
rt
67
47
99
99
88
92
99
0
Fagnou, 2010
Miura, 2014
Miura, 2014
N
Hong, 2014
2c
3
2:1
HOAc
N
N
2:1
HOAc
H
O
N
N
NRR,
4
2:1
HOAc
H
NH
N
H
H
S
5
2:1
HOAc
H
O
6
1:2
HOAc
rt
Huestis, 2016
Shi, 2016
Miura, 2018
Yu, 2015
Limitations:
7
1:1.2
1:1.2
1:1.2
1:1.2
1:1.2
1:1.2
1:1.2
HOAc
rt
high temperature: 70–150 °C
limited in internal alkynes
8
MeOH
F3CCH2OH
(F3C)2CHOH
H2O
rt
9
rt
0
10
11
12d
13e
rt
0
This work
DG
rt
0
broad
excellent
regioselectivity
substrate scope
HOAc
rt
33
99 (94)f
DG
H
Cp*Rh(III)
HOAc
rt
H
R
H
R
+
a Reaction conditions: 1a (0.2 mmol), 2a, [Cp*RhCl2]2 (5 mol%), AgSbF6 (30
mol%), solvent (1 mL), under argon.
HOAc, rt
R = aryl, alkyl
b Determined by 1H NMR analysis with CH2Br2 as an internal standard.
c In the presence of Cu(OAc)2 (40 mol%) as additive.
d Without AgSbF6.
Advantages:
room temperature
terminal alkynes
e [Cp*RhCl2]2 (2.5 mol%) and AgSbF6 (15 mol%) were used.
f Isolated yield.
Scheme 1 Cp*Rh(III)-catalyzed hydroarylations of alkynes. DG = di-
recting group; Cp* = pentamethylcyclopentadienyl.
On adjusting the ratio of 1a to 2a (Table 1, entries 6–7),
the yield increased to 99% and 1.2 equivalents of the alkyne
were found to be sufficient for this reaction, confirming
that HOAc is effective in suppressing undesired oligomeri-
zation. Other protic solvents [MeOH, F3CCH2OH,
(F3C)2CHOH, or H2O] failed to give the desired product (en-
tries 8–11). A control experiment showed that a poor yield
(33%) was obtained in the absence of AgSbF6 (entry 12). Fi-
nally, reducing the catalyst loading to 2.5 mol% did not in-
fluence the catalytic efficiency (entry 13).
With the optimized conditions in hand, we first ex-
plored the scope for the alkyne (Scheme 2). Neither elec-
tron-donating nor electron-withdrawing groups had any
obvious effect on the formation of the hydroarylation prod-
ucts 3aa–ae. It was noteworthy that halogen atoms F, Cl,
and Br remained intact after the reaction (3af–ah). Alkynes
with ortho- or meta-substituents on the benzene also gave
the corresponding products smoothly (3ai–aj).
use of HOAc as a solvent might promote aryl C–H bond acti-
vation and suppress oligomerization of terminal alkynes.
Thus, in an initial experiment, we treated 2-phenylpyridine
(1a) with ethynylbenzene (2a) in the presence of [Cp*RhCl2]2
(5 mol %) in HOAc at 100 °C. We were pleased to find that
the desired hydroarylation product 3aa was obtained in
67% yield (Table 1, entry 1). The addition of Cu(OAc)2 was
detrimental to the reaction (entry 2) due to the oxidative
character of Cu(II). On lowering the reaction temperature to
60 or 40 °C, quantitative yields were obtained (entries 3
and 4). To our delight, the reaction proceeded smoothly
even at the room temperature, albeit with a slight decrease
in yield to 88% (entry 5).
Next, other aromatic rings were tested under our condi-
tions. 2-Ethynylthiophene (2k), containing a hetaromatic
ring, and 2-ethynylnaphthalene (2l) or 1-ethynylpyrene
(2m), bearing larger extended conjugate systems, were also
converted into the desired products (Scheme 2; 3ak–am).
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–G

C
C.-L. Duan et al.
Letter
Synlett
R1
[Cp∗RhCl2]2 (2.5 mol %)
AgSbF6 (15 mol %)
H
R1
H
H
+
N
N
HOAc, rt, Ar
1a
2
3
3aa, R2 = H, 94%
3ab, R2 = Me, 90%
3ac, R2 = OMe, 93%
3ad, R2 = CHO, 92%
3ae, R2 = CO2Me, 93%
3af, R2 = F, 92%
3ag, R2 = Cl, 98%
3ah, R2 = Br, 94%
Me
N
R2
N
3ai, 97%
Me
S
N
N
N
3aj, 95%
3ak, 92%
3al, 79%
O
O
N
N
N
3am, 91%
3an, 86%a
3ao, 84%a
Cl
N
N
4 Cl
4
Si(i-Pr)3
N
N
Si(i-Pr)3
3aq + 3aq'= 2.9:1, 31%a,b
3ap + 3ap'= 17:1, 96%a,b
N
COOEt
Ph
Ph
N
N
3aa' = 55%c,d
3ar, trace
3as, trace
Scheme 2 Substrate scope of alkynes. Reaction conditions: 1a (0.2 mmol, 1.0 equiv), 2 (0.24 mmol, 1.2 equiv), [Cp*RhCl2]2 (2.5 mol %), AgSbF6 (15 mol %),
HOAc (1.0 mL), rt, under argon, 12 h. Yields of the isolated products are reported. a 1a (0.4 mmol, 2 equiv) and 2 (0.2 mmol, 1 equiv) were used.
b The ratio of the regioisomers was determined by 1H NMR analysis. c At 80 °C. d 2a (0.48 mmol, 2.4 equiv) was used.
Most importantly, various other aliphatic alkynes were
equally suitable for this protocol, which showed excellent
regioselectivity (Scheme 2; 3an–ap). As for ethynyl(triiso-
propyl)silane (2q), the hydroarylation reaction also pro-
ceeded well to give product 3aq, albeit with a slightly lower
yield and regioselectivity. Furthermore, a dialkenylated
product 3aa′ was obtained by increasing both the loading of
2a and the reaction temperature. However, an ester-substi-
tuted alkyne [ethyl propiolate (2r)] and an internal alkyne
[diphenylacetylene (2s)], failed to give the corresponding
hydroarylation products 3ar and 3as.
Next, we examined the scope of the arylpyridine under
our optimized conditions. Phenylpyridines with various
functional groups at the para-position of the benzene ring,
including an aldehyde group, gave the corresponding hy-
droarylation products in high yields (Scheme 3; 3ba–ha).
Next, the effects of substituents on the directing pyridine
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–G

D
C.-L. Duan et al.
Letter
Synlett
ring were investigated. 3-Methyl-2-phenylpyridine needed
a higher temperature (80 °C) to complete this transforma-
tion due to the increased steric effect during C–H bond acti-
vation (Scheme 3; 3ia).
ed under our conditions.10 We were pleased to find that
various N-9 substituents, including isopropyl, cyclopropyl,
and allyl groups, did not affect the high efficiency of this re-
action (Scheme 3; 3sa–ua).
Substitutions at other positions of the pyridine ring had
no influences on the formation of the product under the
standard conditions (Scheme 3, 3ja–la). Moreover, replace-
ment of the phenyl ring with a thiophene or indole moiety
was also tolerated, and the corresponding alkenylation
products 3ma–oa were obtained in high yields. Next, other
directing groups were tested. The more-hindered isoquino-
line remained reactive at 80 °C (Scheme 3; 3pa). Pyrazole
also served as a directing group to afford the desired prod-
uct (Scheme 3, 3qa). By controlling the amount of 2a, we
were able to prepare the mono- or dialkenylated 2-phen-
ylpyrimidines 3ra and 3ra′ selectively. Finally, to highlight
the utility of this method, various 6-arylpurines were test-
Several experiments were conducted to gain further in-
sight into this hydroarylation reaction. First, the rhodacyclic
complex 4 was used in the reaction, and the product 3aa
was obtained in high yield [Scheme 4(a)], indicating that 4
is probably the catalytically active species. Then, the penta-
deuterated 2-phenylpyridine (1a-d5) was treated under
standard conditions in the absence of an alkyne, and 2-
phenylpyridine was recovered with only 2% of D remaining
[Scheme 4(b)], showing that a reversible C–H activation
process had occurred. Two deuterium-labeling experiments
were carried out in the presence of CH3COOD, and signifi-
cant deuteration was observed at the olefinic C–H position
[Scheme 4(c)], confirming that the solvent participates in
R4
R4
[Cp∗RhCl2]2 (2.5 mol %)
AgSbF6 (15 mol %)
Ph
+
N
N
R3
R3
AcOH, rt, Ar
Ph
H
1
2a
3
R5
3ba, R5 = Me, 95%
3ca, R5 = OMe, 89%
3da, R5 = F, 99%
3iaa, R6 = 3-Me, 92%
3ja, R6 = 4-Me, 89%
3ka, R6 = 4-Ph, 91%
3la, R6 = 5-Me, 97%
3ea, R5 = Cl, 91%
3fa, R5 = Br, 93%
3ga, R5 = CF3, 98%
3ha, R5 = CHO, 83%
3
R6
4
N
N
5
S
N
N
N
X
N
3pa, 91%a
3ma, 96%
3na, X = CH, 94%
3oa, X = N, 83%
N
N
N
N
N
N
3qa, 65%
3ra, 50%
3ra', 95%b
N
N
N
N
N
N
N
N
N
N
N
N
3sa, 96%
3ta, 96%
3ua, 93%
Scheme 3 Substrate scope of arylpyridines. Reaction conditions: 1 (0.2 mmol, 1.0 equiv), 2a (0.24 mmol, 1.2 equiv), [Cp*RhCl2]2 (2.5 mol %), AgSbF6
(15 mol %), HOAc (1.0 mL), rt, under argon, 12 h. Yields of isolated products are reported. a At 80 °C. b 2a (0.48 mmol, 2.4 equiv) was used.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–G

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C.-L. Duan et al.
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the protonolysis and that the C–H bond cleavage in the ter-
minal alkyne is reversible. Also, the low deuterium incorpo-
ration on the ortho C–H bond demonstrated inhibition of a
second C–H bond activation. In addition, when the deuter-
ated 2p-d1 (95%) was treated with 1a in HOAc, obvious H–D
exchange occurred on the terminal hydrogen of the alkyne,
further confirming the reversibility of C–H bond cleavage in
the terminal alkyne [Scheme 4(c)]. Next, a kinetic isotope
effect (KIE) study was performed through an intermolecu-
lar competition reaction [Scheme 4(d)]. The result of this
experiment (kH/kD = 2.0) showed that C–H bond activation
might be involved in the turnover-limiting step.
a) Cp*Rh(III)-Complex as catalyst
Rh
N
Cl
4
H
+
Ph
(5 mol %)
N
N
AgSbF6 (6 mol %)
AcOH, rt, Ar
1a
2a
D
3aa
88%
b) H/D exchange experiment
D
D
D
D
D
D
D
Standard conditions
N
N
2% D
2% D
1a–d5 (99% D)
c) Deuterium labeling experiment
60% D
H/D
H
[RhCp*Cl2]2 (2.5 mol %)
Cl
Cl
D/H
+
AgSbF6 (15 mol %)
CH3COOD, rt, 5 h
4
4
H/D
10% D
N
N
81% D
1a
2p
3ap–dn
95% D
[RhCp*Cl2]2 (2.5mol %)
D
Cl
Cl
+
4
AgSbF6 (15 mol %)
AcOH, rt, 5 h
H/D
4
N
N
18% D
2p–d1
3ap–d1
1a
d) KIE determined from intermolecular competition
Cl
4
N
N
[RhCp*Cl2]2 (2.5mol %)
AgSbF6 (15 mol %)
Cl
1a
D
3ap
+
4
+
AcOH, rt, 10 min
D
2p
kH/D = 2.0
D
D
D
D
D
D
D
Total yield 12%
Cl
4
N
N
1a–d5
3ap–d4
Scheme 4 Mechanistic studies
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–G

F
C.-L. Duan et al.
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In conclusion, we have developed a novel Cp*Rh(III)-cat-
alyzed alkenylation of arenes with terminal alkynes under
mild conditions.11 This reaction offers a convenient method
for the construction of alkenylated heterocycles with excel-
lent regioselectivity, broad substrate scope, and good func-
tional-group compatibility. Furthermore, the low alkyne
loading (1.2 equivalents) indicated that incidental oligom-
erization was effectively suppressed by the use of HOAc as
solvent. AcOH as solvent also suppressed the inherent sub-
strate-inhibition effect in this type of reaction. Studies on
other Cp*Rh(III)-catalyzed C–H bond-activation reactions
are in progress in our laboratory.
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Chem. Rev. 2013, 113, 6864. (d) Boyarskiy, V. P.; Ryabukhin, S.
D.; Bokach, A. N.; Vasilyev, V. A. Chem. Rev. 2016, 116, 5894.
(4) (a) Schipper, D. J.; Hutchinson, M.; Fagnou, K. J. Am. Chem. Soc.
2010, 132, 6910. (b) Nobushige, K.; Hirano, K.; Satoh, T.; Miura,
M. Org. Lett. 2014, 16, 1188. (c) Yokoyama, Y.; Unoh, Y.; Hirano,
K.; Satoh, T.; Miura, M. J. Org. Chem. 2014, 79, 7649. (d) Min, M.;
Kim, D.; Hong, S. Chem. Commun. 2014, 50, 8028. (e) Huestis, M.
P. J. Org. Chem. 2016, 81, 12545. (f) Chen, B.; Jiang, Y.; Cheng, J.;
Yu, J.-T. Org. Biomol. Chem. 2015, 13, 2901. (g) Li, B.; Ma, J.;
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2013, 1950. (h) Wang, C.-Q.; Feng, C.; Loh, T.-P. Asian J. Org.
Chem. 2016, 5, 1002. (i) Kathiravan, S.; Nicholls, I. A. Tetrahedron
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Org. Biomol. Chem. 2014, 12, 3594. (k) Morita, T.; Morisaka, H.;
Satoh, T.; Miura, M. Asian J. Org. Chem. 2018, 7, 1330.
(5) (a) Wu, E. S. C.; Loch, J. T. III; Toder, B. H.; Borrelli, A. R.; Gawlak,
D.; Radov, L. A.; Gensmantel, N. P. J. Med. Chem. 1992, 35, 3519.
(b) Michael, J. P. Nat. Prod. Rep. 2008, 25, 166. (c) Moon, Y.;
Kwon, D.; Hong, S. Angew. Chem. Int. Ed. 2012, 51, 11333.
(d) Fernández-Bachiller, M. I.; Pérez, C.; Monjas, L.; Rademann,
J.; Rodríguez-Franco, M. I. J. Med. Chem. 2012, 55, 1303. (e) Kim,
J. H.; Lee, J. H.; Paik, S. H.; Kim, J. H.; Chi, Y. H. Arch. Pharmacal
Res. 2012, 35, 1123. (f) Vila, N.; Besada, P.; Costas, T.; Costas-
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Funding Information
Financial support was generously provided by the NSFC (Nos.
21572251, 21572253, and 21871184), the SMEC (No. 2019-01-07-00-
10-E00072), the STCSM (No. 18401933500), the 973 Program (No.
2015CB856600), and the CAS (Nos. XDB 20020100 and QYZDY-SSW-
SLH026).
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Supporting Information
Supporting information for this article is available online at
(6) For selected alkenylation reaction with terminal alkynes cata-
lyzed by other metals, see: (a) Cheng, K.; Yao, B.; Zhao, J.; Zhang,
Y. Org. Lett. 2008, 10, 5309. (b) Xie, M.; Wang, M.; Wu, C.-D.
Inorg. Chem. 2009, 48, 10477. (c) Zhou, B.; Chen, H.; Wang, C.
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Emayavaramban, B.; Premkumar, J. R.; Sundararaju, B. Chem.
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(7) For Rh(I)-catalyzed alkenylation reactions of terminal alkynes,
see: Katagiri, T.; Mukai, T.; Satoh, T.; Hirano, K.; Miura, M. Chem.
Lett. 2009, 38, 118.
(8) (a) Trost, B. M.; Toste, F. D.; Pinkerton, A. B. Chem. Rev. 2001,
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(c) Dominguez, G.; Pérez-Castells, J. Chem. Soc. Rev. 2011, 40,
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References and Notes
(1) For selected recent reviews on transition-metal-catalyzed C–H
functionalizations, see: (a) Gandeepan, P.; Ackermann, L. Chem.
2018, 4, 199. (b) Sambiagio, C.; Schönbauer, D.; Blieck, R.; Dao-
Huy, T.; Pototschnig, G.; Schaaf, P.; Wiesinger, T.; Zia, M. F.;
Wencel-Delord, J.; Besset, T.; Maes, B. U. W.; Schnürch, M. Chem.
Soc. Rev. 2018, 47, 6603. (c) Ping, L.; Chung, D. S.; Bouffard, J.;
Lee, S.-g. Chem. Soc. Rev. 2017, 46, 4299. (d) Dong, Z.; Ren, Z.;
Thompson, S. J.; Xu, Y.; Dong, G. Chem. Rev. 2017, 117, 9333.
(e) Park, Y.; Kim, Y.; Chang, S. Chem. Rev. 2017, 117, 9247.
(f) Hummel, J. R.; Boerth, J. A.; Ellman, J. A. Chem. Rev. 2017, 117,
9163. (g) He, J.; Wasa, M.; Chan, K. S. L.; Shao, Q.; Yu, J.-Q. Chem.
Rev. 2017, 117, 8754. (h) Wang, F.; Yu, S.; Li, X. Chem. Soc. Rev.
2016, 45, 6462. (i) Gensch, T. M.; Hopkinson, N.; Glorius, F.;
Wencel-Delord, J. Chem. Soc. Rev. 2016, 45, 2900. (j) Yang, L.;
Huang, H. Chem. Rev. 2015, 115, 3468. (k) Huang, H.; Ji, X.; Wu,
W.; Jiang, H. Chem. Soc. Rev. 2015, 44, 1155. (l) Shin, K.; Kim, H.;
Chang, S. Acc. Chem. Res. 2015, 48, 1040. (m) Zhang, F.; Spring,
D. R. Chem. Soc. Rev. 2014, 43, 6906. (n) Lyons, T. W.; Sanford, M.
S. Chem. Rev. 2010, 110, 1147. (o) Ackermann, L.; Vicente, R.;
Kapdi, A. R. Angew. Chem. Int. Ed. 2009, 48, 9792. (p) Chen, X.;
Engle, K. M.; Wang, D.-H.; Yu, J.-Q. Angew. Chem. Int. Ed. 2009,
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(11) 2-{2-[(E)-2-Phenylvinyl]phenyl}pyridine (3aa); Typical Pro-
cedure
A dried Schlenk tube equipped with a magnetic stirrer bar was
charged sequentially with [Cp*RhCl2]2 (3.1 mg, 0.005 mmol, 2.5
mol%), AgSbF6 (10.3 mg, 0.03 mmol, 15 mol%), substrate 1a (0.2
mmol), HOAc (1 mL), and ethynylbenzene (2a; 0.24 mmol)
under argon. The mixture was then stirred at rt for 12 h. When
the reaction as complete, the mixture was diluted with EtOAc
(10 mL), filtered through a short pad of silica gel that was
washed with EtOAc (30 mL). The filtrate was adsorbed on silica
gel and concentrated by rotary evaporation. The crude product
(2) For selected recent reviews on Cp*Rh(III)-catalyzed C–H func-
tionalizations, see: (a) Yang, Y.; Li, K.; Cheng, Y.; Wan, D.; Li, M.;
You, J. Chem. Commun. 2016, 52, 2872. (b) Wencel-Delord, J.;
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(c) Ye, B.; Cramer, N. Acc. Chem. Res. 2015, 48, 1308. (d) Song, G.;
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© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–G

G
C.-L. Duan et al.
Letter
Synlett
was purified by flash chromatography [silica gel (300–400
mesh); PE/EA (9:1)] to give a yellow oil; yield: 48.3 mg (94%).1H
NMR (400 MHz, CDCl3):  = 8.76 (d, J = 4.4 Hz, 1 H), 7.80–7.71
(m, 2 H), 7.56 (d, J = 6.5 Hz, 1 H), 7.48–7.36 (m, 5 H), 7.34–7.19
(m, 5 H), 7.06 (d, J = 16.2 Hz, 1 H). 13C NMR (100 MHz, CDCl3):
 = 158.8, 149.4, 139.4, 137.6, 136.2, 135.7, 130.3, 130.2, 128.7,
128.6, 127.7, 127.6, 127.5, 126.6, 126.3, 125.1, 121.9.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2019, 30, A–G