Rh-catalyzed sequential oxidative C-H and N-N bond activation: Conversion of azines into isoquinolines with air at room temperature

Article abstract of DOI:10.1021/ol501483k

A rhodium-catalyzed sequential oxidative C-H annulation reaction between ketazines and internal alkynes has been developed via C-H and N-N bond activation with air as an external oxidant, which led to an efficient approach toward isoquinolines with high atom efficiency at rt. Utilizing the distinctive reactivity of this catalysis, both N-atoms of the azines could be efficiently incorporated to the desired isoquinolines under very robust and mild reaction conditions.

Full text of DOI:10.1021/ol501483k

Letter
pubs.acs.org/OrgLett
Rh-Catalyzed Sequential Oxidative C−H and N−N Bond Activation:
Conversion of Azines into Isoquinolines with Air at Room
Temperature
Wenjia Han,‡,§ Guoying Zhang,†,§ Guangxing Li,*,‡ and Hanmin Huang*,†
†
State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of
Sciences, Lanzhou 730000, China
‡
School of Chemistry and Chemical Engineering, Huazhong University of Science & Technology, Wuhan 430074, China
S
* Supporting Information
ABSTRACT: A rhodium-catalyzed sequential oxidative C−H
annulation reaction between ketazines and internal alkynes has
been developed via C−H and N−N bond activation with air as
an external oxidant, which led to an efficient approach toward
isoquinolines with high atom efficiency at rt. Utilizing the
distinctive reactivity of this catalysis, both N-atoms of the
azines could be efficiently incorporated to the desired
isoquinolines under very robust and mild reaction conditions.
Scheme 1. A New Strategy for Synthesis of Isoquinolines via
C−H and N−N Bond Activation
ransition-metal-catalyzed C−C bond coupling reactions via
direct C−H bond activation under relatively mild reaction
T
conditions compared to traditional synthetic methods1 have
exemplified the construction advantage of heterocyclic com-
pounds. Among many of them, Rh-catalyzed C−H activation/
oxidative coupling reactions are notable for their excellent
catalytic efficiency, good functional group tolerance, and value of
applications.2 However, most approaches require the use of
superstoichiometric amounts of external oxidants, especially
metal salts, to sustain the catalytic turnover, which indisputably
results in lower atom efficiency by producing undesired waste
byproduct and off-cycle side reactions.3 To avoid the use of
external oxidants, a new strategy employing an internal
multifunctional group that acts as both a directing group and
an oxidant to regenerate the catalyst has been developed.4 These
remarkable procedures, while taking a large step toward
eliminating the need for external oxidants, still require
prefunctionalized substrates and suffer from low atom economy
since these oxidizing moieties contained in the substrates have
never been incorporated to the desired products (Scheme 1).
Herein, we report the realization of this goal in the Rh-catalyzed
oxidative C−H annulation with ketazines and internal alkynes for
synthesizing diverse isoquinolines via sequential C−H and N−N
bond activation at rt,5 wherein the N−N bond was reductively
cleaved and both N-atoms of the azines were efficiently
incorporated to the desired isoquinolines under mild reaction
conditions.
possibility of establishing a sequential oxidative catalytic system
for the synthesis of isoquinolines8 by using the N−N bond of
azines as an internal oxidant and molecular oxygen as an external
oxidant, respectively. We postulated that, in the presence of a
catalytic RhIII-complex, a diverse range of ketazines 1, readily
prepared via the reaction of ketone and hydrazine, would first
react with one molecule of internal alkyne 2 to afford one
molecule of isoquinoline along with a Rh-imide complex via C−
H and N−N bond activation. Facile C−H activation and
subsequent alkyne insertion/reductive elimination, which leads
to the sandwich type RhI-bond isoquinoline complex, would
ideally take place.7 Oxygen mediated reoxidation of the RhI-
Among the plentiful N−N bond containing compounds,
azines (R2CN−NCR2) are very useful compounds. The
N−N bond could be reductively cleaved by a redox-active metal
complex via metal−ligand cooperation, in which the N−N bond
acted as an internal oxidant.6 This unique feature, coupled with
our success in Rh-catalyzed C−H activation/annulation with
molecular oxygen as a sole oxidant,7 led us to envision the
Received: May 22, 2014
© XXXX American Chemical Society
A
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Letter
complex in the presence of acid would reconstitute the RhIII-
catalyst and deliver the other molecule of the desired
isoquinoline product. On the basis of this mechanistic
assumption, we recognized that consuming one molecule of
azine would give rise to two molecules of isoquinoline and only
water was produced as the byproduct in this sequential oxidative
C−H and N−N bond activation.
yield, Table 1, entry 6) was obtained using benzoic acid.
Fortunately, the yield was maintained when the dosage of acid
was lowered to 0.5 equiv (Table 1, entry 7).10 A control reaction
in the absence of PhCO2H failed to give the desired product in
high yield (Table 1, entry 8), indicating that the acid is crucial to
promoting the molecular oxygen to oxidize RhI to regenerate
active RhIII.3a,b,7 Another cationic RhIII species Cp*Rh-
(CH3CN)3(OTf)2, an efficient catalyst precursor in the C−H
activation reaction, gave a slightly lower yield (Table 1, entry 9)
under the same reaction conditions. To our great delight, when
we performed the reaction under an air atmosphere instead of
oxygen, a good yield still resulted (Table 1, entry 10). Further
control experimentation demonstrated that only a lower yield of
the desired product 3aa was obtained in the absence of oxygen or
air (Table 1, entry 11) under otherwise identical reaction
conditions, indicating the crucial role of oxygen in the Rh
catalytic cycle and the oxidative efficiency of air. Furthermore,
when the ratio of 2a/1a decreased from 5/2 to 5/3, the yield of
product 3aa slightly increased to 70% (based on the amount of
2a, Table 1, entry 12). Increasing the catalyst loading could not
enhance the reaction efficiency obviously (Table 1, entry 13).
Finally, lowering the concentration of the reaction could improve
the yield to 75% (Table 1, entry 14) owing to the poor solubility
of 1a in methanol.
As an initial attempt, the reaction between ketazine 1a and 1,2-
diphenylethyne 2a in methanol was chosen as the model reaction
for optimization of the reaction conditions (Table 1). Because
a
Table 1. Optimization of the Reaction Conditions
yield
(%)
entry
[Rh]
[O] HX (equiv) t (°C)
b
1
Cp*Rh(H2O)3(OTf)2
Cp*Rh(H2O)3(OTf)2
Cp*Rh(H2O)3(OTf)2
Cp*Rh(H2O)3(OTf)2
Cp*Rh(H2O)3(OTf)2
Cp*Rh(H2O)3(OTf)2
−
HOAc (1.0)
120
120
25
15
66
56
57
17
65
2
3
4
5
6
O2 HOAc (1.0)
O2 HOAc (1.0)
O2 PivOH (1.0)
O2 HOTf (1.0)
25
25
Encouraged by the optimized results, we started to investigate
the substrate scope of this new protocol (Scheme 2). The
O2 PhCO2H
(1.0)
25
7
Cp*Rh(H2O)3(OTf)2
O2 PhCO2H
(0.5)
25
66
a
Scheme 2. Substrate Scope of Ketazines
8
9
Cp*Rh(H2O)3(OTf)2
Cp*Rh(CH3CN)3(OTf)2
O2
−
25
25
27
61
O2 PhCO2H
(0.5)
10
Cp*Rh(H2O)3(OTf)2
Cp*Rh(H2O)3(OTf)2
Cp*Rh(H2O)3(OTf)2
Cp*Rh(H2O)3(OTf)2
Cp*Rh(H2O)3(OTf)2
air PhCO2H
(0.5)
25
25
25
25
25
65
28
70
71
75
b
11
−
PhCO2H
(0.5)
c
12
air PhCO2H
(0.25)
cd
,
13
air PhCO2H
(0.25)
ce
,
14
air PhCO2H
(0.25)
a
Reaction conditions: 1a (0.25 mmol), 2a (0.625 mmol), [Rh] (0.01
mmol), HX based on the amount of 1a, CH3OH (2 mL), O2 (1 atm),
24 h, yield of isolated product and based on the amount of ketimine
b
c
unit. Under vacuum. With 1a (0.3 mmol) and 2a (0.5 mmol), [Rh]
d
(0.01 mmol), HX and yield based on the amount of 2a. [Rh] (0.015
mmol). CH3OH (4 mL).
e
a
General conditions: 1 (0.3 mmol), 2a (0.5 mmol), Cp*Rh-
Cp*Rh(H2O)3(OTf)2 has shown to be highly effective for the
oxidative C−H activation/annulation of phenylpyridines and
alkynes,7 we initially focused on exploring conditions using this
readily available catalyst at 120 °C. The desired 1-methyl-3,4-
diphenylisoquinoline 3aa was obtained in 15% yield (based on
the amount of ketimine unit),9 when the reaction was conducted
in the absence of an external oxidant. This result indicated that
our proposed internal oxidative C−H activation/annulation
between the ketazine 1a and internal alkyne 2a was indeed
possible.
To achieve a higher yield, molecular oxygen was introduced
into the reaction system under the same reaction conditions and
the yield dramatically increased to 66% in the presence of HOAc
(1.0 equiv) (Table 1, entry 2). Temperature screening indicated
that when the reaction was ran at 25 °C instead of 120 °C, the
product was still obtained in 56% yield. We next examined the
optimal acids (Table 1, entries 4−8), and the best result (65%
(H2O)3(OTf)2 (0.01 mmol, 2 mol %), PhCO2H (0.125 mmol, 25
mol %), CH3OH (4 mL), air, 25 °C, 24 h. Yield of isolated product
b
and based on the amount of 2a. CH3OH/CH2Cl2 = 1:1 (4 mL).
optimized reaction conditions were compatible to a broad range
of ketazines derived from substituted acetophenones. For the
reactions of acetophenone azines, having electron-donating
groups at the para position of the phenyl ring (e.g., methyl,
methoxy, isobutyl), with 2a, the desired products were afforded
(3ba, 3da, and 3fa) in good yields (81%−87%). The meta methyl
substituted substrate also gave a regioselective product in good
yield (3ca). However, the ortho methoxy substituted substrate
led to a rather lower yield. This was plausibly ascribed to the
steric hindrance of the ortho position (3ea). Electron-with-
drawing groups (e.g., F, Cl, Br) at the same positions resulted in
lower yields (3ga−3ia), which might result from their poor
B
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Letter
solubility in methanol. In addition to acetophenone derived
ketazines, alkyl aryl ketones such as benzophenone and α-
tetralone derived ketazines (3ja−3ma) also proceeded well to
give the corresponding products in good to excellent yields (75−
91% yields) under the standard reaction conditions.
After investigating the scope of substitution features of the
ketazines, the scope of this sequential oxidative C−H activation/
annulation with respect to the alkynes was also surveyed. As
summarized in Scheme 3, the annulation reaction of 4-
a
Scheme 3. Substrate Scope of Alkynes
Figure 1. Proposed mechanism.
product 3aa. Then the other molecule of 2a coordinates to
complex II followed by insertion into the Rh−C bond of
complex C, affording the seven-membered rhodacycle complex
D. Finally reductive elimination from D gives rise to the sandwich
type RhI-complex E, which is reoxidized by air in the presence of
acid to release the other molecule of 3aa and regenerate the
active catalyst for the next catalytic cycle.
Further strong evidence for supporting the above mechanism
was stemmed from the ESI-MS studies (see Supporting
Information). After stirring the mixture of the ketazine 1a and
Cp*Rh(H2O)3(OTf)2 (10 mol %) in methanol at 60 °C under a
nitrogen atmosphere for 2.5 h, the unreacted ketazine 1a was
removed by filtration and the resulting solution was analyzed by
HRMS analysis. A strong peak at m/z = 473.1463 was observed,
which could be attributed to the corresponding rhodacycle
complex [I−X]. Furthermore, two peaks of m/z = 356.0889 and
534.1678 were successfully detected when alkyne 2a was
introduced into the above reaction mixture at rt under a nitrogen
atmosphere. These two peaks could be assigned as [II+H] and
[D+H] or [E+H], respectively.
In summary, we have successfully developed a novel simple
method for the assembling of ketone, alkyne, and hydrazine via a
Rh-catalyzed C−H and N−N bond activation, which led to
establishing an efficient approach toward isoquinolines. Utilizing
the distinctive reactivity of this catalysis, both N-atoms of the
ketazine could be efficiently incorporated to the desired
isoquinolines under very mild reaction conditions. The method
is very simple and can be efficiently performed in an open vessel
at rt without the addition of external co-oxidants, which is among
the mildest reaction conditions for the reported oxidative C−H
activation reactions.
a
General conditions: 1b (0.3 mmol), 2 (0.5 mmol), Cp*Rh-
(H2O)3(OTf)2 (0.01 mmol, 2 mol %), PhCO2H (0.125 mmol, 25
mol %), CH3OH (4 mL), air, 25 °C, 24 h. Yield of isolated product
and based on the amount of 2. b Cp*Rh(H2O)3(OTf)2 (0.02 mmol, 4
c
mol %), 36 h. CH3OH/CH2Cl2 = 1:1 (4 mL).
methylacetophenone azine with alkynes catalyzed by the
Cp*Rh(H2O)3(OTf)2 was found to be general with diaryl
alkynes bearing a variety of substituents (3bb−3bf). Typical
functional groups, such as methoxy and halide groups, were
compatible with the reaction conditions, which offered an
opportunity for subsequent transformation via transition-metal
catalysis. An aliphatic internal alkyne was also compatible under
the standard reaction conditions, achieving the expected product
3bg in 67% yield. An aryl alkyl alkyne, such as prop-1-
ynylbenzene, was also suitable for this reaction, affording the
expected product 3bh in moderate yield with excellent
regioselectivity. Furthermore, the reactions of unsymmetric
substituted diaryl alkynes were also investigated. Mono 4-methyl
and 4-Br substituted diphenylacetylenes gave the corresponding
isoquinolines in 82% and 80% yields with lower regioselectivities.
A possible mechanism for the present sequential oxidative C−
H and N−N bond activation/annulation is shown in Figure 1.
Initial coordination of ketazine 1a to Cp*Rh(H2O)3(OTf)2 and
ortho arene C−H bond activation take place, generating the five-
membered rhodacycle complex I. After ligand exchange to form
intermediate A, insertion of the alkyne into the Rh−C bond of A
gives the seven-membered rhodacycle intermediate B. Subse-
quent reductive elimination and N−N bond cleavage release a
five-membered rhodacycle complex II and give the desired
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental procedures, spectroscopic data, structural assign-
ment, and NMR spectra for all synthesized compounds. This
material is available free of charge via the Internet at http://pubs.
acs.org.
C
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Organic Letters
Letter
J. R.; Kurti, L. J. Am. Chem. Soc. 2012, 134, 18253. (n) Neely, J. M.;
̈
AUTHOR INFORMATION
Corresponding Authors
■
Rovis, T. J. Am. Chem. Soc. 2013, 135, 66. (o) Presset, M.; Oehlrich, D.;
Rombouts, F.; Molander, G. A. Org. Lett. 2013, 15, 1528. (p) Liu, B.;
Song, C.; Sun, C.; Zhou, S.; Zhu, J. J. Am. Chem. Soc. 2013, 135, 16625.
(q) Jat, J. L.; Paudyal, M. P.; Gao, H.; Xu, Q.-L.; Yousufuddin, M.;
*E-mail: hmhuang@licp.cas.cn.
*E-mail: ligxabc@163.com.
Author Contributions
§These authors contributed equally.
Devarajan, D.; Ess, D. H.; Kurti, L.; Falck, J. R. Science 2014, 343, 61.
̈
(5) (a) Fritsch, P. Ber. Dtsch. Chem. Ges. 1893, 26, 419. (b) Pomeranz,
C. Monatsh. Chem. 1893, 14, 116. (c) Bischler, A.; Napieralski, B. Ber.
Dtsch. Chem. Ges. 1893, 26, 1903. (d) Pictet, A.; Spengler, T. Chem. Ber.
1911, 44, 2030. (e) Herz, W.; Tocker, S. J. Am. Chem. Soc. 1955, 77,
6355. (f) Brown, E. V. J. Org. Chem. 1977, 42, 3208. (g) Ishikawa, T.;
Shimooka, K.; Narioka, T.; Noguchi, S.; Saito, T.; Ishikawa, A.;
Yamazaki, E.; Harayama, T.; Seki, H.; Yamaguchi, K. J. Org. Chem. 2000,
65, 9143. (h) Youn, S. W. J. Org. Chem. 2006, 71, 2521. (i) Xu, X.; Guo,
S.; Dang, Q.; Chen, J.; Bai, X. J. Comb. Chem. 2007, 9, 773.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Chinese Academy of Sciences
and the National Natural Science Foundation of China
(21222203, 21133011, and 21372231).
(6) (a) Ohff, A.; Zippel, T.; Arndt, P.; Spannenberg, A.; Kempe, R.;
Rosenthal, U. Organometallics 1998, 17, 1649. (b) Zippel, T.; Arndt, P.;
Ohff, A.; Spannenberg, A.; Kempe, R.; Rosenthal, U. Organometallics
1998, 17, 4429. (c) Kiplinger, J. L.; Morris, D. E.; Scott, B. L.; Burns, C. J.
Organometallics 2002, 21, 3073. (d) Cohen, R.; Rybtchinski, B.;
Gandelman, M.; Shimon, L. J. W.; Martin, J. M. L.; Milstein, D. Angew.
Chem., Int. Ed. 2003, 115, 1993. (e) Umehara, K.; Kuwata, S.; Ikariya, T.
J. Am. Chem. Soc. 2013, 135, 6754.
(7) (a) Zhang, G.; Yang, L.; Wang, Y.; Xie, Y.; Huang, H. J. Am. Chem.
Soc. 2013, 135, 8850. (b) Yang, L.; Zhang, G.; Huang, H. Adv. Synth.
Catal. 2014, 356, 1509. (c) Zhang, G.; Yu, H.; Qin, G.; Huang, H. Chem.
Commun. 2014, 50, 4331.
(8) For selected examples for synthesis of isoquinolines: (a) Roesch, K.
R.; Larock, R. C. J. Org. Chem. 1998, 63, 5306. (b) Roesch, K. R.; Larock,
R. C. Org. Lett. 1999, 1, 553. (c) Dai, G.; Larock, R. C. Org. Lett. 2002, 4,
193. (d) Huang, Q.; Larock, R. C. J. Org. Chem. 2003, 68, 980.
(e) Konno, T.; Chae, J.; Miyabe, T.; Ishihara, T. J. Org. Chem. 2005, 70,
10172. (f) Korivi, R. P.; Cheng, C.-H. Org. Lett. 2005, 7, 5179.
(g) Fischer, D.; Tomeba, H.; Pahadi, N. K.; Patil, N. T.; Yamamoto, Y.
Angew. Chem., Int. Ed. 2007, 46, 4764. (h) Li, L.; Brennessel, W. W.;
Jones, W. D. J. Am. Chem. Soc. 2008, 130, 12414. (i) Fukutani, T.;
Umeda, N.; Hirano, K.; Satoh, T.; Miura, M. Chem. Commun. 2009,
5141. (j) Hwang, S.; Lee, Y.; Lee, P. H.; Shin, S. Tetrahedron Lett. 2009,
50, 2305. (k) Gao, H.; Zhang, J. Adv. Synth. Catal. 2009, 351, 85.
(l) Jayakumar, J.; Parthasarathy, K.; Cheng, C.-H. Angew. Chem., Int. Ed.
2012, 51, 197. (m) Karthikeyan, J.; Haridharan, R.; Cheng, C.-H. Angew.
Chem., Int. Ed. 2012, 51, 12343. (n) Huang, X.-C.; Yang, X.-H.; Song, R.-
J.; Li, J.-H. J. Org. Chem. 2014, 79, 1025.
REFERENCES
■
(1) For leading reviews on C−H bond activation: (a) Ritleng, V.; Sirlin,
C.; Pfeffer, M. Chem. Rev. 2002, 102, 1731. (b) Kakiuchi, F.; Murai, S.
Acc. Chem, Res. 2002, 35, 826. (c) Alberico, D.; Scott, M. E.; Lautens, M.
Chem. Rev. 2007, 107, 174. (d) Ackermann, L.; Vicente, R.; Kapdi, A. R.
Angew. Chem., Int. Ed. 2009, 48, 9792. (e) Chen, X.; Engle, K. M.; Wang,
D.-H.; Yu, J.-Q. Angew. Chem., Int. Ed. 2009, 48, 5094. (f) Daugulis, O.;
Do, H.-Q.; Shabashov, D. Acc. Chem. Res. 2009, 42, 1074. (g) Lyons, T.
W.; Sanford, M. S. Chem. Rev. 2010, 110, 1147. (h) Willis, M. C. Chem.
Rev. 2010, 110, 725. (i) Cho, S. H.; Kim, J. Y.; Kwak, J.; Chang, S. Chem.
Soc. Rev. 2011, 40, 5068. (j) Sun, C.-L.; Li, B.-J.; Shi, Z.-J. Chem. Rev.
2011, 111, 1293. (k) Ackermann, L. Chem. Rev. 2011, 111, 1315.
(l) Arockiam, P. B.; Bruneau, C.; Dixneuf, P. H. Chem. Rev. 2012, 112,
5879. (m) Yang, L.; Huang, H. Catal. Sci. Technol. 2012, 2, 1099.
(n) Yamaguchi, J.; Yamaguchi, A. D.; Itami, K. Angew. Chem., Int. Ed.
2012, 51, 8960. (o) Neufeldt, S. R.; Sanford, M. S. Acc. Chem. Res. 2012,
45, 936. (p) Wencel-Delord, J.; Glorius, F. Nat. Chem. 2013, 5, 369.
(2) For reviews on Rh-catalyzed C−H activation: (a) Lewis, J. C.;
Bergman, R. G.; Ellman, J. A. Acc. Chem. Res. 2008, 41, 1013. (b) Colby,
D. A.; Bergman, R. G.; Ellman, J. A. Chem. Rev. 2010, 110, 624.
(c) Bouffard, J.; Itami, K. Top. Curr. Chem. 2010, 292, 231. (d) Satoh, T.;
Miura, M. Chem.Eur. J. 2010, 16, 11212. (e) Colby, D. A.; Tsai, A. S.;
Bergman, R. G.; Ellman, J. A. Acc. Chem. Res. 2012, 45, 814. (f) Song, G.;
Wang, F.; Li, X. Chem. Soc. Rev. 2012, 41, 3651. (g) Patureau, F. W.;
Wencel-Delord, J.; Glorius, F. Aldrichimica Acta 2012, 45, 31.
(3) For some examples on Rh-catalyzed oxidative C−H activation with
a stoichiometric extenal oxidant: (a) Umeda, N.; Tsurugi, H.; Satoh, T.;
Miura, M. Angew. Chem., Int. Ed. 2008, 47, 4019. (b) Stuart, D. R.;
Alsabeh, P.; Kuhn, M.; Fagnou, K. J. Am. Chem. Soc. 2010, 132, 18326.
(c) Mochida, S.; Hirano, K.; Satoh, T.; Miura, M. J. Org. Chem. 2011, 76,
3024. (d) Li, X.; Zhao, M. J. Org. Chem. 2011, 76, 8530. (e) Park, S. H.;
Kim, J. Y.; Chang, S. Org. Lett. 2011, 13, 2372. (f) Tsai, A. S.; Brasse, M.;
Bergman, R. G.; Ellman, J. A. Org. Lett. 2011, 13, 540. (g) Umeda, N.;
Hirano, K.; Satoh, T.; Shibata, N.; Sato, H.; Miura, M. J. Org. Chem.
2011, 76, 13. (h) Fukuyani, T.; Hirano, K.; Satoh, T.; Miura, M. J. Org.
Chem. 2011, 76, 2867. (i) Wang, C.; Sun, H.; Fang, Y.; Huang, Y. Angew.
Chem., Int. Ed. 2013, 52, 5795. (j) Shang, Y.; Jie, X.; Zhao, H.; Hu, P.; Su,
W. Org. Lett. 2014, 16, 416.
(9) CCDC 979252 (3aa) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
(10) The oxidative coupling reaction between benzonic acid and
alkynes was not observed under the present conditions. For the
oxidative coupling of benzonic acid with alkynes at 110 to 120 °C, see:
(a) Ueura, K.; Satoh, T.; Miura, M. Org. Lett. 2007, 9, 1407. (b) Ueura,
K.; Satoh, T.; Miura, M. J. Org. Chem. 2007, 72, 5362.
(4) For selected examples of the oxidizing group used in Rh-catalyzed
C−H activation: (a) Guimond, N.; Fagnou, K. J. Am. Chem. Soc. 2009,
131, 12050. (b) Guimond, N.; Gouliaras, C.; Fagnou, K. J. Am. Chem.
Soc. 2010, 132, 6908. (c) Too, P. C.; Wang, Y.-F.; Chiba, S. Org. Lett.
2010, 12, 5688. (d) Rakshit, S.; Grohmann, C.; Besset, T.; Glorius, F. J.
Am. Chem. Soc. 2011, 133, 2350. (e) Patureau, F. W.; Glorius, F. Angew.
Chem., Int. Ed. 2011, 50, 1977. (f) Wang, Y.-F.; Toh, K. K.; Lee, J.-Y.;
Chiba, S. Angew. Chem., Int. Ed. 2011, 50, 5927. (g) Hyster, T. K.; Rovis,
T. Chem. Commun. 2011, 47, 11846. (h) Xu, X.; Liu, Y.; Park, C.-M.
Angew. Chem., Int. Ed. 2012, 51, 9506. (i) Wang, H.; Glorius, F. Angew.
Chem., Int. Ed. 2012, 51, 7318. (j) Wang, H.; Grohmann, C.; Nimphius,
C.; Glorius, F. J. Am. Chem. Soc. 2012, 134, 19592. (k) Hyster, T. K.;
Kncrr, L.; Ward, T. R.; Rovis, T. Science 2012, 338, 500. (l) Ye, B.;
Cramer, N. Science 2012, 338, 504. (m) Zhu, C.; Li, G.; Ess, D. H.; Falck,
D
dx.doi.org/10.1021/ol501483k | Org. Lett. XXXX, XXX, XXX−XXX