C-H functionalization of phenols using combined ruthenium and photoredox catalysis: In situ generation of the oxidant

Article abstract of DOI:10.1002/anie.201408891

A combination of ruthenium and photoredox catalysis allowed the ortho olefination of phenols. Using visible light, the direct C-H functionalization of o-(2-pyridyl) phenols occurred, and diverse phenol ethers were obtained in good yields. The regeneration of the ruthenium catalyst was accomplished by a photoredox-catalyzed oxidative process.

Full text of DOI:10.1002/anie.201408891

Angewandte
Chemie
DOI: 10.1002/anie.201408891
Dual Catalysis
À
C H Functionalization of Phenols using Combined Ruthenium and
Photoredox Catalysis: In Situ Generation of the Oxidant**
David C. Fabry, Meria A. Ronge, Jochen Zoller, and Magnus Rueping*
Abstract: A combination of ruthenium and photoredox
catalysis allowed the ortho olefination of phenols. Using
groups in such transformations. Wang und Jeganmohan could
show that not only carbamates, but also azoxybenzenes[7] and
simple aromatic ketones,[8] esters,[9] or amides[10] are suitable
directing groups for the olefination of a broad range of
aromatic and heteroaromatic compounds.
À
visible light, the direct C H functionalization of o-(2-pyri-
dyl)phenols occurred, and diverse phenol ethers were obtained
in good yields. The regeneration of the ruthenium catalyst was
accomplished by a photoredox-catalyzed oxidative process.
Quite recently, the group of Ackermann extended the
substrate scope to protected phenols.[11] Using a 2-pyridyl
protecting group (Pyr), the selective ortho olefination of
a variety of aromatic and heteroaromatic compounds could
be achieved. This procedure made use of over-stoichiometric
amounts of CuII salts. Eager to make these reactions more
environmentally friendly, Wang and co-workers developed
P
henols represent a common structural motif in natural
products and organic materials. Therefore, it is not surprising
that the number of publications on the formation or
modification of phenols or phenol ethers has been increasing
for the past years. In the area of material science, the phenol
motif plays a crucial role for the construction of poly(phenol
ethers) or their modification to adjust their macroscopic
properties, such as their melting or glass-transition temper-
atures, for specific applications.[1]
a
procedure that makes use of internal oxidants.[12]
N-Methoxybenzamides were suitable substrates for the
ortho olefination as the Ru complex was subsequently
reoxidized by cleavage of the methoxy group. Although the
use of copper salts could be prevented, this approach
possesses a considerable limitation regarding the scope of
the reaction as the previously extended scope of directing
groups is reduced again.
As the regeneration of the metal complex is an electron-
transfer process, we were wondering whether the necessary
reoxidation could be facilitated by a photoredox-controlled
process using visible light (Scheme 1). Herein, we report the
first olefination of phenol ethers by metal and photoredox
In the field of natural products or bioactive compounds,
elegant total syntheses incorporating phenols or phenol
ethers as structural motifs have been developed, which were
[2]
À
usually centered in the area of C H activation.
À
Evidently, C H functionalization plays a more and more
important role in method development as disadvantages, such
as prefunctionalization with halogens or reactivity problems
with lighter halogens, have been overcome. Aside from initial
[3]
À
oxidative C H functionalizations using palladium or rho-
dium[4] catalysts in the Fujiwara–Moritani reaction, first
examples with ruthenium were presented. The group of
Satoh and Miura showed that pyrazole is a suitable directing
group (DG) for the ortho olefination of 1-phenylpyrazoles.[5]
The catalytic system, consisting of [{Ru(p-cymene)Cl2}2]
(5 mol%) and Cu(OAc)2 (2 equiv) as the co-oxidant enabled
the efficient coupling of the biaryl moiety with common
acrylates. The use of large amounts of copper salts is a general
feature of these types of reactions as the in situ generated
metal complex needs to be reoxidized first before the next
catalytic cycle can be started.
catalysis using a combination of [{Ru(p-cymene)Cl2}2]/
AgSbF6 und [Ir(ppy)2(bpy)]PF6.[13–15]
Over the last years, the development of many different
variants has enabled the use of various olefins and directing
Scheme 1. Combination of photoredox and RuII catalysis for an ortho
olefination process.
[*] M. Sc. D. C. Fabry, B. Sc. M. A. Ronge, Dipl.-Chem. J. Zoller,
Prof. Dr. M. Rueping
Based on the work of Ackermann, first experiments
replacing the stoichiometric amounts of Cu(OAc)2 with
1 mol% of the photoredox catalyst were conducted. We
were pleased to see that under these conditions, conversion of
substrate 1a could be observed. During a broad solvent
screen with the common photoredox catalysts [Ru(bpy)3]-
(PF6)2 and [Ir(bpy)(ppy)2]PF6, the best yield of 60% for
product 3a was achieved with the Ir-based catalyst in
dimethylacetamide. Interestingly, no clear correlation
between solvent properties and yield was observed. Gener-
Institute of Organic Chemistry, RWTH Aachen
Landoltweg 1, 52074 Aachen (Germany)
E-mail: magnus.rueping@rwth-aachen.de
[**] The research leading to these results has received funding from the
European Research Council under the European Union’s Seventh
Framework Programme (FP/2007-2013)/ERC Grant Agreement
617044 (SunCatChem).
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201408891.
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Table 2: Screening of the reaction conditions for the olefination reaction.
ally, higher yields were obtained for the Ir-based catalyst than
with [Ru(bpy)3](PF6)2; however, this was the case for both
polar aprotic as well as apolar aprotic solvents (Table 1).
À
Table 1: Screening of the reaction conditions for the combined C H
activation.[a]
Entry[a] Catalyst
Photocatalyst
Conditions
Yield [%][b]
1
2
3
4
5
6
7
8
9
10
[Ru]/AgSbF6 [Ir(bpy)(ppy)2]PF6 air
60
0
0
4
0
AgSbF6
[Ru]
[Ir(bpy)(ppy)2]PF6 air
[Ir(bpy)(ppy)2]PF6 air
[Ru]/AgSbF6
–
–
air
[Ir(bpy)(ppy)2]PF6 air
Entry[a]
Photocatalyst
Solvent
Yield [%][b]
[Ru]/AgSbF6 [Ir(bpy)(ppy)2]PF6 O2
[Ru]/AgSbF6 O2
64
6
–
1
2
3
4
5
6
7
8
[Ru(bpy)3](PF6)2
[Ru(bpy)3](PF6)2
[Ru(bpy)3](PF6)2
[Ru(bpy)3](PF6)2
[Ru(bpy)3](PF6)2
[Ru(bpy)3](PF6)2
[Ru(bpy)3](PF6)2
[Ir(bpy)(ppy)2]PF6
[Ir(bpy)(ppy)2]PF6
[Ir(bpy)(ppy)2]PF6
[Ir(bpy)(ppy)2]PF6
[Ir(bpy)(ppy)2]PF6
[Ir(bpy)(ppy)2]PF6
[Ir(bpy)(ppy)2]PF6
DMF
PhCl
DCE
MeCN
DMPU
DMA
TMU
DMF
PhCl
11
35
0
0
0
56
0
49
42
0
[Ru]/AgSbF6 [Ir(bpy)(ppy)2]PF6 argon
[Ru]/AgSbF6 [Ir(bpy)(ppy)2]PF6 argon
0
38[c]
39
[Ru]/AgSbF6
–
KO2 (1 equiv)/
argon
11
12
[Ru]/AgSbF6 [Ir(bpy)(ppy)2]PF6 air
[Ru]/AgSbF6 [Ir(bpy)(ppy)2]PF6 O2
65[d]
65[d]
[a] 1a (0.1 mmol), acrylate (2 equiv), photoredox catalyst (1 mol%),
AgSbF6 (0.2 equiv), and the Ru catalyst (5 mol%) in DMA at 1208C using
a 11 W CFL bulb. [b] Yield of isolated product after column chromatog-
raphy. [c] Photoredox catalyst (100 mol%). [d] Photoredox catalyst
(3 mol%). [Ru]=[{Ru(p-cymene)Cl2}2].
9
10
11
12
13
14
DCE
MeCN
DMPU
DMA
TMU
0
0
60
0
[a] 1a (0.1 mmol), acrylate (2 equiv), photoredox catalyst (1 mol%),
AgSbF6 (0.2 equiv), and Ru catalyst (5 mol%) in the indicated solvent at
1208C under irradiation with a 11 W CFL bulb. [b] Yield of isolated
product after column chromatography. DCE=1,2-dichloroethane,
DMA=dimethylacetamide, DMPU=1,3-dimethyl-3,4,5,6-tetrahydro-2-
pyrimidinone, Pyr=pyridyl, TMU=tetramethylurea.
To evaluate the influence of each component on the
process, the reaction was performed without the ruthenium
dimer (Table 2, entry 2). In this experiment, no conversion
was detected, suggesting that the silver salt is not capable of
À
activating the C H bond of the aryl compound and is
therefore responsible for the precipitation of the chloride
ligands only. To prove this hypothesis, the Ru dimer was used
in the reaction without the silver salt (Table 2, entry 3); as
expected, no conversion was observed.
Next, the role of the photoredox catalyst was analyzed. In
the absence of the photoredox catalyst, only traces of the
desired product 3a were isolated (Table 2, entry 4). This
confirmed that no other oxidant is present in the reaction and
that no oxidant is formed during the reaction in the absence of
À
the photoredox catalyst. To exclude a potential C H activa-
tion through the photoredox catalyst, the reaction was
performed without the Ru/Ag components, which again
gave no conversion (Table 2, entry 5). As it was previously
reported that oxo or peroxo species, which can be formed by
photoredox processes,[16] can be used for the oxidation of
metal complexes, the olefination reaction was conducted
under an oxygen atmosphere. No significant improvement of
the yield could be observed (Table 2, entry 6). When the
photoredox catalyst was omitted, no reoxidation occurred,
and therefore, stoichiometric conversion with respect to the
Ru/Ag components occurred (Table 2, entry 7). This illus-
trates that molecular oxygen cannot be used as a reoxidant
and cannot be converted into an active species in the absence
of the photoredox catalyst. Therefore, peroxo species pre-
sumably take part in this reaction.
To analyze this particular circumstance, the standard
reaction was performed in the presence of 1 and 100 mol% of
the photoredox catalyst under an argon atmosphere (Table 2,
entries 8 and 9, respectively). The fact that no conversion
2
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could be observed when 1 mol% of the photoredox catalyst
was used confirms that the photoredox catalyst itself cannot
function as an oxidant in the absence of oxygen because no
regeneration can take place. In contrast, using 100 mol% of
the photoredox catalyst, the desired product was obtained in
38% (Table 2, entry 9). As in one photoredox cycle, only one
electron can be transferred, this reaction shows that the
photoredox catalyst itself can also function as an oxidant. As
a final confirmation of our hypothesis, KO2 was directly used
as an inorganic superoxide anion instead of the photoredox
catalyst in the reaction under argon atmosphere (Table 2,
entry 10). The desired product was isolated in 39% yield as
the catalytic cycle can be closed, and the peroxo species was
identified as a suitable active oxidant. The reduced yields
obtained with KO2 are due to the instability of the inorganic
salt, which most probably leads to partial decomposition at
the reaction temperature of 1208C before full reoxidation of
the metal complex has been achieved. This finding also
illustrates the user friendliness of the photoredox process, as
oxidizing and potentially explosive reagents can be avoided
while higher yields are obtained.
amounts of the highly reactive superoxide anions are formed
by the photoredox process, which are then rapidly consumed
and therefore not present in excess amounts. In contrast,
when larger amounts are present, side and consecutive
reactions will cause lower yields of the desired product.
Using the obtained data, the following reaction mecha-
nism can be postulated (Scheme 2): After the active RuII
When the catalyst loading of [Ir(bpy)(ppy)2]PF6 was
increased to 3 mol%, the desired product 3a could be
obtained in 65% yield (Table 2, entry 11), which lies in the
same range as yields obtained with copper-based methods.
To gain deeper insight into the individual regeneration
processes mediated by the superoxide anion and the photo-
redox catalyst, the dependence of the yield on the reaction
time was determined for both oxidants (Figure 1). The
Scheme 2. Proposed mechanism for the combined olefination reac-
tion.
catalyst A has been formed by precipitation of the chloride
À
ligands attached to the Ru dimer, ortho C H activation of
substrate 1 to intermediate B occurs with the help of the
directing pyridine moiety. After insertion of the olefinic
compound, which yields intermediate C, and reductive
elimination of product 3, ruthenium complex D is obtained.
Photoredox catalyst IrIII*, which has been excited with visible
light, is now capable of oxidation by electron transfer, thus
regenerating the catalytically active Ru species A. The
resulting IrII complex is now reoxidized to IrIII by molecular
oxygen, and a superoxide anion is generated. The superoxide
anion itself may then oxidize Ru complex D by accepting an
electron.
Figure 1. Yield–time correlation of the olefination reaction.
Subsequently, we began to investigate the substrate scope
of this newly developed method. The acrylate component was
varied first. It was apparent that substituents on this substrate
only had a small influence on the reaction, and the products
were isolated with comparable, good yields (Table 3, rows 1
and 2). Electron-donating substituents in the ortho position
even increased the yield up to 75% for a methoxy group (3e).
The electron-poor substrates 3g–i could also be successfully
used in the olefination reaction. Furthermore, the applicabil-
ity of the reaction was underlined by its tolerance towards
aldehydes, ketones, and esters. Subsequently, also meta-
substituted substrates as well as substrates with more complex
substitution patterns were successfully olefinated (Table 3,
rows 5–8). Independent from the electronic or steric character
of the substrates, partial hydrogenation of the double bond
individual regeneration processes for hydride oxidation
were analyzed individually, either with KO2 (2 equiv) or
with the photoredox catalyst (2 equiv) under an argon
atmosphere; both processes proceeded much slower than
under the standard reaction conditions (3 mol% photoredox
catalyst, air) and therefore led to lower yields after 24 hours.
However, when both processes were combined under the
standard reaction conditions, where both the photoredox
processes as well as the steps involving the superoxide anion
generated in situ can be executed simultaneously, an increase
in the reactivity was observed, and higher yields were
obtained. This can be explained by the fact that only small
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Table 3: Substrate scope of the olefination reaction.[a]
suppressed any consecutive hydrogenation. When the strong
acid para-toluenesulfonic acid (TsOH) was used, the olefin/
alkane ratio was only 6:1 with an overall yield of 46%.
Different weak acids, such as a benzoic acid derivatives or
diphenyl phosphate, indeed led to a 100% selectivity in favor
of the olefin, but to lower yields than acetic acid. The addition
of water as a co-solvent led to lower yields (23%) with an
olefin/alkane ratio of 2:1. Acetic acid also proved to be an
effective additive for other representative substrates, includ-
ing 3b and 3h, for the suppression of consecutive hydro-
genation processes while giving the desired products in
similar yields.
In summary, we have reported a new combination of
photoredox and metal catalysis for the olefination reaction of
À
phenols by C H activation. The unique interplay of metal and
photoredox catalysis allowed the direct reoxidation of the
metal hydride intermediate for the catalytic regeneration of
the catalyst. Mechanistic studies revealed that the regener-
ation reaction can be maximized with small amounts of
superoxide anions, which are formed by photoredox processes
and could also function as the oxidant. As only small amounts
of oxidant are generated, side reactions of substrate and
product could not be observed, and oxidant-sensitive mole-
cules can be employed. Based on mechanistic studies, we
could show that with acid additives, olefinated phenol
derivatives may be synthesized in good yields. As the yields
are comparable with those of similar transformations that
employ stoichiometric amounts of copper, an extension to
À
other C H functionalizations should be possible and feasible.
Furthermore, the combined use of metal and photoredox
À
catalysts should be transferable to other C H functionaliza-
tions.
Received: September 8, 2014
Published online: && &&, &&&&
À
Keywords: alkenylation · C H functionalization ·
photoredox catalysis · superoxide · visible light
.
[a] 1 (0.2 mmol), AcOH (1 equiv), olefin (2 equiv), [Ir(bpy)(ppy)2]PF6
(3 mol%), and the Ru catalyst (5 mol%)/AgSbF6 (20 mol%) in DMA at
1208C using a CFL bulb. Yields of isolated products after column
chromatography; the olefin/alkane ratios are also given.
[1] For overviews on phenols in polymer chemistry, see: a) S. R.
Marder, B. Kippelen, A. K. Y. Jen, N. Peyghambarian, Nature
1997, 388, 845 – 851; b) A. Kraft, A. C. Grimsdale, A. B. Holmes,
Angew. Chem. 1998, 37, 402 – 428; Angew. Chem. 1998, 110, 416 –
443; c) Y. M. Syah, N. S. Aminah, E. H. Hakim, N. Aimi, M.
Kitajima, H. Takayama, S. A. Achmad, Phytochemistry 2003, 63,
913 – 917; d) A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G.
Jokisz, A. B. Holmes, Chem. Rev. 2009, 109, 897 – 1091.
[2] For examples of phenols as bioactive compounds or in total
synthesis, see: a) W. Kurosawa, A. T. Kan, T. Fukuyama, J. Am.
Chem. Soc. 2003, 125, 8112 – 8113; b) T. Yoshinari, K. Ohmori,
M. G. Schrems, A. Pfaltz, K. Suzuki, Angew. Chem. Int. Ed. 2010,
49, 881 – 885; Angew. Chem. 2010, 122, 893 – 897; c) L. Acker-
mann, J. Pospech, Org. Lett. 2011, 13, 4153 – 4155; d) B. Xiao, T.-
J. Gong, Z.-J. Liu, J.-H. Liu, D.-F. Luo, J. Xu, L. Liu, J. Am.
was observed. This consecutive hydrogenation catalyzed by
the ruthenium hydride complex then led to a mixture of the
olefinic and hydrogenated products. This reactivity of ruthe-
nium complexes has previously been described by other
groups in different contexts.[17]
To determine whether the obtained ratio of the olefin and
alkane components can be controlled, naphthyl derivative 1o
was chosen as a model substrate, and different additives were
tested under the standard reaction conditions. As the
consecutive reaction involves the participation of a hydride,
we decided to test a variety of acids with different acidities as
additives. We were pleased to see that with medium-strong
acetic acid (Table S1), we not only observed comparable
yields for product 3o, but also that the addition of the acid
Chem. Soc. 2011, 133, 9250 – 9253.
[3] For selected publications on oxidative Pd -catalyzed C H
II
À
activation, see: a) I. Moritani, Y. Fujiwara, Tetrahedron Lett.
1967, 8, 1119 – 1121; b) Y. Fujiwara, I. Moritani, S. Danno, R.
Asano, S. Teranishi, J. Am. Chem. Soc. 1969, 91, 7166 – 7169;
c) K. Mikami, M. Hatano, M. Terada, Chem. Lett. 1999, 55 – 56;
d) H. M. Zhang, E. M. Ferreira, B. M. Stoltz, Angew. Chem. Int.
4
www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
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Angewandte
Chemie
Ed. 2004, 43, 6144 – 6148; Angew. Chem. 2004, 116, 6270 – 6274;
e) W. Rauf, J. M. Brown, Angew. Chem. Int. Ed. 2008, 47, 4228 –
4230; Angew. Chem. 2008, 120, 4296 – 4298; f) J. A. Schiffner,
T. H. Wçste, M. Oestreich, Eur. J. Org. Chem. 2010, 174 – 182;
g) D. H. Wang, K. M. Engle, B.-F. Shi, J.-Q. Yu, Science 2010,
327, 315 – 319; h) K. M. Engle, D.-H. Wang, J.-Q. Yu, J. Am.
Chem. Soc. 2010, 132, 14137 – 14151; i) D. Mc Cartney, P. J.
Guiry, Chem. Soc. Rev. 2011, 40, 5122 – 5150; j) W. Jianquan, Y.
Zhiqin, Z. Guofu, Prog. Chem. 2012, 24, 523 – 544; k) R. D.
Baxter, D. Sale, K. M. Engle, J.-Q. Yu, D. G. Blackmond, J. Am.
Chem. Soc. 2012, 134, 4600 – 4606.
Venturi, ChemSusChem 2008, 1, 26 – 58; c) M. Fagnoni, D.
Dondi, D. Ravelli, A. Albini, Chem. Rev. 2007, 107, 2725 – 2756;
d) D. Ravelli, D. Dondi, M. Fagnoni, A. Albini, Chem. Soc. Rev.
2009, 38, 1999 – 2011; e) Handbook of Synthetic Photochemistry
(Eds.: A. Albini, M. Fagnoni), Wiley-VCH, Weinheim, 2010;
f) CRC Handbook of Organic Photochemistry and Photobiology,
(Eds.: A. Griesbeck, M. Oelgemçller, F. Ghetti), CRC Press,
Boca Raton, FL, 2012; g) D. Ravelli, M. Fagnoni, A. Albini,
Chem. Soc. Rev. 2013, 42, 97 – 113; h) Chemical Photocatalysis
(Ed.: B. Kçnig), de Gruyter, Berlin, 2013; i) M. Reckenthꢀler, A.
Griesbeck, Adv. Synth. Catal. 2013, 355, 2727 – 2744.
À
[4] For selected publications on Rh-catalyzed arene ortho C H
[15] For recent examples of combined transition-metal and photo-
redox catalysis, see: a) Y. Ye, M. S. Sanford, J. Am. Chem. Soc.
2012, 134, 9034 – 9037; b) S. R. Neufeldt, M. S. Sanford, Adv.
Synth. Catal. 2012, 354, 3517 – 3522; c) M. Rueping, R. M.
Koenigs, K. Poscharny, D. C. Fabry, D. Leonori, C. Vila, Chem.
Eur. J. 2012, 18, 5170 – 5174; d) B. Sahoo, M. N. Hopkinson, F.
Glorius, J. Am. Chem. Soc. 2013, 135, 5505 – 5508; e) D. C. Fabry,
J. Zoller, S. Raja, M. Rueping, Angew. Chem. Int. Ed. 2014, 53,
10228 – 10231; Angew. Chem. 2014, 126, 10392 – 10396; f) J. Du,
K. L. Skubi, D. M. Schultz, T. P. Yoon, Science 2014, 344, 392 –
396; g) Z. Zho, D. T. Ahneman, L. Chu, J. A. Terett, A. G. Doyle,
D. W. C. MacMillan, Science 2014, 345, 437 – 440; h) J. C. Tellis,
D. N. Primer, G. A. Molander, Science 2014, 345, 433 – 436; i) J.
Zoller, D. C. Fabry, M. A. Ronge, M. Rueping, Angew. Chem.
Int. Ed. 2014, 53, 13264 – 13268; Angew. Chem. 2014, 126, 13480 –
13484.
[16] For selected publications on photoredox-generated peroxo
species, see: a) Y. Pan, C. W. Kee, L. Chen, C.-H. Tan, Green
Chem. 2011, 13, 2682 – 2685; b) S. Zhu, M. Rueping, Chem.
Commun. 2012, 48, 11960 – 11962; c) Y. Q. Zou, J. R. Chen, X. P.
Liu, L. Q. Lu, R. L. Davis, K. A. Jørgensen, W.-J. Xiao, Angew.
Chem. Int. Ed. 2012, 51, 784 – 788; Angew. Chem. 2012, 124, 808 –
812; d) S. Zhu, A. Das, L. Bui, H. Zhou, D. P. Curran, M.
Rueping, J. Am. Chem. Soc. 2013, 135, 1823 – 1829; e) S. P. Pitre,
C. D. McTiernan, H. Ismaili, J. C. Scaiano, J. Am. Chem. Soc.
2013, 135, 13286 – 13289.
activation/olefination, see: a) F. W. Patureau, F. Glorius, J. Am.
Chem. Soc. 2010, 132, 9982 – 9983; b) F. W. Patureau, T. Besset,
F. Glorius, Angew. Chem. Int. Ed. 2011, 50, 1064 – 1067; Angew.
Chem. 2011, 123, 1096 – 1099; c) T.-J. Gong, B. Xiao, Z.-J. Liu, J.
Wan, J. Xu, D.-F. Luo, Y. Fu, L. Liu, Org. Lett. 2011, 13, 3235 –
3237; d) C. Feng, T.-P. Loh, Chem. Commun. 2011, 47, 10458 –
10460; e) S. H. Park, J. Y. Kim, S. Chang, Org. Lett. 2011, 13,
2372 – 2375; f) N. Schrçder, T. Besset, F. Glorius, Adv. Synth.
Catal. 2012, 354, 579 – 583; g) C. Wang, H. Chen, Z. Wang, J.
Chen, Y. Huang, Angew. Chem. Int. Ed. 2012, 51, 7242 – 7245;
Angew. Chem. 2012, 124, 7354 – 7357; h) B. Liu, Y. Fan, Y. Gao,
C. Sun, C. Xu, J. Zhu, J. Am. Chem. Soc. 2013, 135, 468 – 473.
[5] Y. Hashimoto, T. Ueyama, T. Fukutani, K. Hirano, T. Satoh, M.
Miura, Chem. Lett. 2011, 40, 1165 – 1166.
[6] a) M. C. Reddy, M. Jeganmohan, Eur. J. Org. Chem. 2013, 1150 –
1157; b) B. Li, J. Ma, Y. Liang, N. Wang, S. Xu, H. Song, B. Wang,
Eur. J. Org. Chem. 2013, 1950 – 1962.
[7] H. Li, X. Xie, L. Wang, Chem. Commun. 2014, 50, 4218 – 4221.
[8] K. Padala, M. Jeganmohan, Org. Lett. 2011, 13, 6144 – 6147.
[9] a) K. Graczyk, W. Ma, L. Ackermann, Org. Lett. 2012, 14, 4110 –
4113; b) K. Padala, S. Pimparkar, P. Madasamy, M. Jeganmohan,
Chem. Commun. 2012, 48, 7140 – 7142.
[10] a) K.-H. Kwon, D. W. Lee, C. S. Yi, Organometallics 2010, 29,
5748 – 5750; b) P. Zhao, R. Niu, F. Wang, K. Han, X. Li, Org.
Lett. 2012, 14, 4166 – 4169; c) J. Qi, L. Huang, Z. Wang, H. Jiang,
Org. Biomol. Chem. 2013, 11, 8009 – 8013.
[11] W. Ma, L. Ackermann, Chem. Eur. J. 2013, 19, 13925 – 13928.
[12] B. Li, J. Ma, N. Wang, H. Feng, S. Xu, B. Wang, Org. Lett. 2012,
14, 736 – 739.
[17] For examples of ruthenium-catalyzed olefin hydrogenations,
see: a) S. E. Clapham, A. Hadzovic, R. H. Morris, Coord. Chem.
Rev. 2004, 248, 2201 – 2237; b) C. S. Yi, D. W. Lee, Organo-
metallics 1999, 18, 5152 – 5156; c) J. P. Lee, Z. Ke, M. A.
Ramꢁrez, T. B. Gunnoe, T. R. Cundari, P. D. Boyle, J. L.
Petersen, Organometallics 2009, 28, 1758 – 1775.
[13] For a review on combined photoredox and metal catalysis, see:
N. Hoffmann, ChemSusChem 2012, 5, 352 – 371.
[14] For selected reviews on photocatalysis, see: a) N. Hoffmann,
Chem. Rev. 2008, 108, 1052 – 1103; b) V. Balzani, A. Credi, M.
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
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.
Angewandte
Communications
Communications
Dual Catalysis
D. C. Fabry, M. A. Ronge, J. Zoller,
M. Rueping*
&&& — &&&
À
C H Functionalization of Phenols using
Combined Ruthenium and Photoredox
Catalysis: In Situ Generation of the
Oxidant
À
Air and light: The direct ortho C H
nium catalyst is regenerated through
oxidation by a photoredox catalyst under
visible-light irradiation.
functionalization of o-(2-pyridyl)phenols
provides various olefinated phenol ethers
in good yields (see Scheme). The ruthe-
6
www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 1 – 6
These are not the final page numbers!