Dual Ligand-Enabled Nondirected C?H Olefination of Arenes

Article abstract of DOI:10.1002/anie.201712235

The application of the Pd-catalyzed oxidative C?H olefination of arenes, also known as the Fujiwara–Moritani reaction, has traditionally been limited by the requirement for directing groups on the substrate or the need to use the arene in large excess, ty

Full text of DOI:10.1002/anie.201712235

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: Dual Ligand-Enabled Non-Directed C-H Olefination of Arenes
Authors: Hao Chen, Philipp Wedi, Tim Meyer, Ghazal Tavakoli, and
Manuel van Gemmeren
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201712235
Angew. Chem. 10.1002/ange.201712235
Link to VoR: http://dx.doi.org/10.1002/anie.201712235
http://dx.doi.org/10.1002/ange.201712235

10.1002/anie.201712235
Angewandte Chemie International Edition
COMMUNICATION
Dual Ligand-Enabled Non-Directed C–H Olefination of Arenes
Hao Chen+, Philipp Wedi+, Tim Meyer, Ghazal Tavakoli, and Manuel van Gemmeren*
This work is dedicated to Prof. Benjamin List on the occasion of his 50th birthday
Abstract: The applicability of the Pd-catalyzed oxidative C–H
olefination of arenes, also known as the Fujiwara–Moritani reaction,
has traditionally been limited by the requirement for directing groups
on the substrate or the need to use the arene in large excess, typically
as (co)solvent. Herein we report the development of a catalytic system
that, through the combined action of two complementary ligands,
enables the use of directing group free arenes as limiting reagents for
the first time. The reactions proceed under a combination of both
steric and electronic control and enable the application of this powerful
reaction to valuable arenes, which cannot be utilized in excess.
deprotonation (CMD) mechanism for the key C–H activation step,
with the acetate ligand acting as the intramolecular base.[7]
Substantial improvements have been achieved by the use of
pyridine ligands (Approach 2), where an analogous acetate-
based CMD is proposed.[7c] In these systems, the catalytic
efficiency is substantially improved, although the arene is still
required in substantial excess.[8] Alternatively to the use of
pyridine ligands, the use of directing groups on the substrate has
been pursued as a strategy towards more efficient Fujiwara-
Moritani reactions (Approach 3).[9] Such systems profit from an
acceleration through the complex induced proximity effect,[2a]
which enables high catalytic efficiencies with the arene as the
limiting reagent. In the context of these systems, it has also been
found that N-acetyl amino acids can be utilized as ligands to
modulate the activity and selectivity of the catalyst.[10] In such
system, the acetate is replaced by the N-acetyl group, which acts
as an internal base taking up the proton during the CMD step.[10c,
The C–H functionalization of arenes constitutes a highly important
strategy for the development of novel transformations, which bear
great potential in the context of natural product and
pharmaceutical synthesis.[1] Numerous approaches have been
pursued in order to enable such reactions to occur selectively
using various transition metals, with many of these strategies
relying on directing groups on the substrate in order to enable the
desired reactivity and to control the regiochemistry of the
reactions.[2] In parallel to the development of directed arene C–H
functionalization reactions, the use of non-directed reactions has
10d]
However, these systems face obvious drawbacks resulting
from the use of directing groups, most importantly the limitation to
substrates bearing such groups. Furthermore, in this approach
the regioselectivity is dictated by the directing group, although
specialized directing groups, often called templates, have been
developed that enable regioselectivities other than ortho
selectivity.[11] Despite these advances, no method has been
reported to date, that achieves the non-directed Pd-catalyzed C–
H functionalization of arenes as limiting reagents.[12] Such a
system would be highly attractive, since it would pave the way for
applying the plethora of Pd-catalyzed C–H functionalizations that
hitherto require directing groups to the non-directed
functionalization of arene substrates, including valuable
substrates that cannot be utilized in excess.
Herein we report the development of a Pd-catalyzed non-directed
Fujiwara-Moritani reaction, based on the use of two
complementary ligands (Approach 4). We reasoned that by
combining an amino acid-derived ligand and a pyridine ligand, we
might generate a catalyst species that can undergo a CMD
through a species that resembles the ones involved in Approach
3, albeit without the linkage between the donor (DG vs. pyridine
ligand) and the substrate. We expected that this could result in a
catalytic system with the same advantages but without the
disadvantages resulting from the use of directing groups.
Furthermore, we hypothesized that such a system might even be
capable of overriding weak coordinating effects that have
previously been utilized to direct arene C–H activation, thereby
leading to a complementary selectivity pattern.
been identified as
development, since
a
highly attractive target for method
such methods inherently offer
complementary regioselectivity patterns and are potentially
applicable to a wider range of substrates, since the respective
methods would not be limited to substrates containing directing
groups, which has for example been demonstrated through the
development of Ir-catalyzed arene C–H borylations.[3-5] In this
context, Pd-catalyzed reactions have been of particular interest,
but the development of efficient catalyst systems has proven to
be highly challenging.[3] This is for example reflected by the
evolution of approaches for the Fujiwara-Moritani reaction, which
enables the oxidative olefination of arenes and can thus be
considered a prototypical example of a cross-dehydrogenative
coupling reaction (Figure 1).[6] Originally, these reactions were
catalyzed by Pd(OAc)2 without the use of additional ligands or
directing groups, resulting in low catalytic efficiencies and the
need for utilizing the arene coupling partner in a large excess,
typically as (co)solvent (Approach 1). These reactions are
proposed to proceed through
a
concerted metalation
[*]
Hao Chen,[+] Philipp Wedi,[+] Dr. M. van Gemmeren
Max Planck Institute for Chemical Energy Conversion
Stiftstraße 34-36, 45470 Mülheim an der Ruhr (Germany)
Tim Meyer, Dr. Ghazal Tavakoli, Dr. M. van Gemmeren
Organisch-Chemisches Institut
Westfälische Wilhelms-Universität Münster
Corrensstraße 40, 48149 Münster (Germany)
E-mail: mvangemmeren@uni-muenster.de
We chose phenylacetic acid ester (1a) as the model substrate for
our studies, since this compound is known to react with poor
efficiency and virtually no regioselectivity when subjected to the
Fujiwara-Moritani reaction using N-acetyl glycine (Ac-Gly-OH) as
the ligand.[11e] Using this compound we conducted an extensive
optimization of the reaction conditions, leading us to develop the
reaction conditions presented in Table 1 (Entry 1).[13]
[+]
These authors contributed equally to this work
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201712235
Angewandte Chemie International Edition
COMMUNICATION
Figure 1. Approaches to the Pd-catalyzed C–H functionalization of arenes such as the Fujiwara–Moritani reaction. Proposed transition state models are shown.
Table 1. Control experiments confirming the necessity of all elements of the
catalytic system.
Deviation from Standard
Entry[a]
GC-Yield (%)[b]
o:m:p[b]
Conditions
None
No Ac-Gly-OH
No ligand 2
No Pd(OAc)2
1
2
3
4
74 (75)[c]
7:58:35
9:56:35
27:45:27
-
16
29
0
[a] The reactions in this table were conducted on a 0.1 mmol scale. [b] GC-
yields and the o:m:p ratios were determined by GC-FID using 1,3,5-
trimethoxybenzene as internal standard [c] The isolated yield on a 0.2 mmol
scale is given in parentheses. HFIP = 1,1,1,3,3,3-hexafluoroisopropanol.
Under the optimized conditions, we could obtain our model
product 3a in 75% yield with an ortho:meta:para (o:m:p)-ratio of
7:58:35, which indicates that the reaction proceeds under a
combination of both steric and electronic control by the
substrate.[14] A control experiment in the absence of N-acetyl
glycine revealed that this ligand is essential for catalytic activity,
but has little influence on the regiochemistry of the reaction (Entry
2). An analogous experiment without the pyridine ligand showed
that this ligand is both required for an efficient catalysis and has a
substantial influence on the regioselectivity of the process,
presumably by increasing the influence of steric factors relative to
electronic effects and/or by suppressing a weak directing effect
by the electron poor ester functionality (Entry 3). Finally, we
confirmed the central role of palladium in the process by
demonstrating that no product formation occurs in the absence of
Pd(OAc)2 (Entry 4).
Having confirmed the unique performance of our dual ligand-
based catalytic protocol, we proceeded to study the generality of
the reaction towards various arene substrates (Scheme 1). First,
alkyl substituted substrates were tested and the products 3b and
3c were both obtained in 53% yield, with the meta-isomer being
the major product. Substrates bearing deactivating electron-
withdrawing substituents gave the respective products 3d–g in
moderate to good yields and with
Scheme 1. Scope of arene substrates. The structures of the respective starting
materials are shown for simplicity.
increased meta selectivity, presumably resulting from the
combined effects of both steric and electronic control. Our
protocol was also found to be suitable for electron-rich substrates.
This article is protected by copyright. All rights reserved.

10.1002/anie.201712235
Angewandte Chemie International Edition
COMMUNICATION
For example, the benzyl alcohol derivatives 3h and 3i were both
obtained in good yields and the meta isomer as major product.
The phenol-derived product 3j was obtained as an almost even
mixture of the meta and para isomers. The formation of the ortho
product was not observed, presumably due to steric control, while
the ratio between the meta and para product can be rationalized
by a superimposition of the statistical factor in favor of the meta
position and electronic effects favoring the para position.
Remarkably, phthaloyl protected aniline could be converted to
product 3k in 48% yield delivering the meta product as the major
isomer, a regioselectivity that clearly differs from what one would
predict based on electronic considerations. We next turned our
attention to phenylacetic acid and phenylpropionic acid
derivatives. We were interested in probing the reactivity of these
substrates under our conditions, since such substrates have
previously been employed as weak directing groups to induce
ortho selectivity.[15] The resulting products 3l–o were all obtained
in good yields and selectivities in favor of the meta product.
Notably, while the amount remained low, the products 3l–n
contained a somewhat increased quantity of the respective ortho
isomers when compared to the less electron-rich model product
3a. This effect was not observed for product 3o, thus indicating
that with these substrates a small amount of the product may be
Scheme 2. Scope of the olefin coupling partners.
(61%, β:α = 95:5) and 9p (74%, β:α = 94:6) in good yields and
with high β-selectivities. Finally, when phenyl vinyl sulfone and
diethyl vinylphosphonate were utilized as olefins, the respective
products 10p (51%) and 11p (74%) were obtained in near
complete β-regioselectivity. Overall, our studies on the scope of
the protocol reported herein show a broad applicability both with
respect to the arene component used as the limiting reagent and
to the olefinic coupling partner.
In Summary, we have developed a catalytic method that enables
the oxidative C–H olefination of arenes known as the Fujiwara–
Moritani reaction to proceed with directing group-free substrates
as limiting reagents for the first time. The reaction relies on the
combination of N-acetyl glycine with a pyridine ligand and was
shown to be applicable to a wide range of arenes and olefins. We
expect that the synthetic method reported herein will prove to be
a valuable tool for the late-stage functionalization of arenes.
Furthermore, in light of the many Pd-catalyzed reactions that are
currently limited by their need for directing groups, this approach
will likely be applicable to the development of further valuable
transformations under a non-directed regime.
formed through
a directed pathway. We continued our
investigation into the substrate scope of this protocol by studying
di- and tri-substituted arene substrates. The electron-rich
substrates ortho-xylene and veratrole delivered the respective β-
isomers as the sole products in good yields (3p: 65% and 3q:
74%). In contrast, when 1,2-dichlorobenzene was utilized, the α-
isomer of product 3r was predominantly formed, albeit again in
good yield (74%). The 1,3-dialkylated product 3s was obtained in
76% yield and with an almost exclusive formation of the β-isomer.
When 1,3-dichlorobenzene was employed as starting material,
the ortho-directing ability of chlorine already found for product 3r
was again observed, leading to the formation of 3t in 54% yield
as a β:α:α′ = 10:84:6 mixture of isomers. Similarly, when 4-
chlorotoluene was employed as a starting material, product 3u
was obtained in 61% yield (β:α >95:5). The product derived from
4-methyl anisole 3v (49%) was formed with a regioselectivity
favoring the position ortho to the more electron donating and
sterically less hindered MeO-group (89:11). The tri-substituted
products 3w (62%) and 3x (71%) were both obtained with the
expected regioselectivity in favor of the less hindered position.
Finally, in order to demonstrate the synthetic potential of our
protocol, we applied the optimized reaction conditions to
protected forms of phenylalanine and tyrosine, leading to the
formation of the products 3y (67%, m:p = 50:50) and 3z (58%,
β-isomer exclusively) in good yields and the regioselectivities
expected from the previously studied scope.[16]
Having shown the applicability of our protocol to a wide range of
arene substrates as limiting reagents, we were interested in
probing the generality with respect to the olefinic reaction partner
using ortho-xylene as a representative yet analytically convenient
arene coupling partner (Scheme 2).
The n-butyl and 2,2,2-trifluoroethyl esters of acrylic acid delivered
the respective products 4p (85%, β:α = 90:10) and 5p (63%, β:α
= 97:3) with the β-isomer as the major product. When methyl vinyl
ketone or acrolein were employed as olefins, the β-isomers were
formed exclusively and the products 6p and 7p were isolated in
60% and 70% yield respectively. Similarly, acrylamide and N,N-
dimethylacrylamide as olefins resulted in the formation of 8p
Experimental Section
General procedure for the non-directed, arene-limited Fujiwara-Moritani
reaction: An oven dried 10 mL Schlenk tube was charged with Pd(OAc)2
(4.5 mg, 0.020 mmol, 10 mol %), ligand 2 (9.4 mg, 0.040 mmol, 20 mol %),
N-acetyl-glycine (7.0 mg, 0.060 mmol, 30 mol %), AgOAc (100.2 mg,
0.6000 mmol, 3 equiv), arene (0.200 mmol, 1 equiv), olefin (0.600 mmol,
3 equiv), and HFIP (2 mL). The reaction vessel was tightly sealed and
placed into an aluminum block with a tightly fitting recess on a magnetic
stirrer. The reaction mixture was stirred at room temperature for 2 minutes.
The aluminum block was heated to 90 °C and the reaction mixture was
stirred at this temperature for 24 h. The reaction mixture was allowed to
cool to room temperature, transferred into 50 mL round-bottom flask, and
concentrated under reduced pressure. The product was purified by silica
gel column chromatography using a gradient of pentane:ethyl acetate =
500:1 to 1:1 as the eluent.
This article is protected by copyright. All rights reserved.

10.1002/anie.201712235
Angewandte Chemie International Edition
COMMUNICATION
[8]
[9]
a) Y.-H. Zhang, B.-F. Shi, J.-Q. Yu, J. Am. Chem. Soc. 2009, 131, 5072-
5074; b) A. Kubota, M. H. Emmert, M. S. Sanford, Org. Lett. 2012, 14,
1760-1763; c) C.-H. Ying, S.-B. Yan, W.-L. Duan, Org. Lett. 2014, 16,
500-503. For a recent example employing an S,O-ligand to enable a
related reactivity profile, see: d) K. Naksomboon, C. Valderas, M.
Gómez-Martínez, Y. Álvarez-Casao, M. À. Fernández-Ibáñez, ACS
Catal. 2017, 7, 6342-6346.
Acknowledgements
The authors gratefully acknowledge financial support from the
Max Planck Society (Otto Hahn Award to M.v.G.), the FCI (Liebig
Fellowship to M.v.G.), the Alexander von Humboldt Foundation
(Return Fellowship to M.v.G.), and the WWU Münster. We thank
the members of our NMR and MS departments for their excellent
service. Furthermore, we are indebted to Prof. F. Glorius for his
generous support.
For a discussion of directed arene C–H olefinations, see for example
Refs 2c, 2f, 2i, 2k, 2m, 2o, and 2p.
[10] a) B.-F. Shi, N. Maugel, Y.-H. Zhang, J.-Q. Yu, Angew. Chem. 2008, 120,
4960-4964; Angew. Chem. Int. Ed. 2008, 47, 4882-4886; b) D.-H. Wang,
K. M. Engle, B.-F. Shi, J.-Q. Yu, Science 2010, 327, 315-319; c) G.-J.
Cheng, Y.-F. Yang, P. Liu, P. Chen, T.-Y. Sun, G. Li, X. Zhang, K. N.
Houk, J.-Q. Yu, Y.-D. Wu, J. Am. Chem. Soc. 2014, 136, 894-897; d) Y.-
F. Yang, X. Hong, J.-Q. Yu, K. N. Houk, Acc. Chem. Res. 2017, 50, 2853-
2860; e) K. M. Engle, D.-H. Wang, J.-Q. Yu, J. Am. Chem. Soc. 2010,
132, 14137-14151.
Keywords: Arenes • C–H Activation • Fujiwara-Moritani
Reaction • Olefination • Palladium
[1]
For selected reviews focusing on the application of C–H
functionalizations in a synthetic context, see: a) L. McMurray, F. O'Hara,
M. J. Gaunt, Chem. Soc. Rev. 2011, 40, 1885-1898; b) J. Yamaguchi, A.
D. Yamaguchi, K. Itami, Angew. Chem. 2012, 124, 9092-9142; Angew.
Chem. Int. Ed. 2012, 51, 8960-9009; c) T. Cernak, K. D. Dykstra, S.
Tyagarajan, P. Vachal, S. W. Krska, Chem. Soc. Rev. 2016, 45, 546-
576; d) J. F. Hartwig, J. Am. Chem. Soc. 2016, 138, 2-24; e) J. Wencel-
Delord, F. Glorius, Nature Chem. 2013, 5, 369-375.
[11] For selected studies on template-mediated meta and para selective C–
H functionalizations, see: a) D. Leow, G. Li, T.-S. Mei, J.-Q. Yu, Nature
2012, 486, 518-522; b) H.-X. Dai, G. Li, X.-G. Zhang, A. F. Stepan, J.-Q.
Yu, J. Am. Chem. Soc. 2013, 135, 7567-7571; c) S. Lee, H. Lee, K. L.
Tan, J. Am. Chem. Soc. 2013, 135, 18778-18781; d) L. Wan, N.
Dastbaravardeh, G. Li, J.-Q. Yu, J. Am. Chem. Soc. 2013, 135, 18056-
18059; e) M. Bera, A. Modak, T. Patra, A. Maji, D. Maiti, Org. Lett. 2014,
16, 5760-5763; f) R.-Y. Tang, G. Li, J.-Q. Yu, Nature 2014, 507, 215-220;
g) Y. Deng, J.-Q. Yu, Angew. Chem. 2015, 127, 902-905, Angew. Chem.
Int. Ed. 2015, 54, 888-891; h) S. Li, L. Cai, H. Ji, L. Yang, G. Li, Nature
Commun. 2016, 7; i) A. Maji, B. Bhaskararao, S. Singha, R. B. Sunoj, D.
Maiti, Chem. Sci. 2016, 7, 3147-3153; j) T. Patra, S. Bag, R. Kancherla,
A. Mondal, A. Dey, S. Pimparkar, S. Agasti, A. Modak, D. Maiti, Angew.
Chem. 2016, 128, 7882-7886, Angew. Chem. Int. Ed. 2016, 55, 7751-
7755; k) S. Bag, R. Jayarajan, R. Mondal, D. Maiti, Angew. Chem. 2017,
129, 3230-3234, Angew. Chem. Int. Ed. 2017, 56, 3182-3186; l) Z. Jin,
L. Zhang, C. Zhao, Y. Liu, J. Xu, X. Xu, Angew. Chem. 2017, 129, 12413-
12417, Angew. Chem. Int. Ed. 2017, 56, 12245-12249; m) S. Bag, R.
Jayarajan, U. Dutta, R. Chowdhury, R. Mondal, D. Maiti, Angew. Chem.
2017, 129, 12712-12716, Angew. Chem. Int. Ed. 2017, 56, 12538-12542;
n) U. Dutta, A. Modak, B. Bhaskararao, M. Bera, S. Bag, A. Mondal, D.
W. Lupton, R. B. Sunoj, D. Maiti, ACS Catal. 2017, 3162-3168; o) H.-J.
Xu, Y. Lu, M. E. Farmer, H.-W. Wang, D. Zhao, Y.-S. Kang, W.-Y. Sun,
J.-Q. Yu, J. Am. Chem. Soc. 2017.
[2]
For selected reviews highlighting the different strategies pursued in
arene C–H functionalization and the use of directing groups, see: a) M.
C. Whisler, S. MacNeil, V. Snieckus, P. Beak, Angew. Chem. 2004, 116,
2256-2276; Angew. Chem. Int. Ed. 2004, 43, 2206-2225; b) A. R. Dick,
M. S. Sanford, Tetrahedron 2006, 62, 2439-2463; c) X. Chen, K. M.
Engle, D.-H. Wang, J.-Q. Yu, Angew. Chem. 2009, 121, 5196-5217;
Angew. Chem. Int. Ed. 2009, 48, 5094-5115; d) O. Daugulis, H.-Q. Do,
D. Shabashov, Acc. Chem. Res. 2009, 42, 1074-1086; e) D. A. Colby, R.
G. Bergman, J. A. Ellman, Chem. Rev. 2010, 110, 624-655; f) T. W.
Lyons, M. S. Sanford, Chem. Rev. 2010, 110, 1147-1169; g) L.
Ackermann, Chem. Rev. 2011, 111, 1315-1345; h) J. Wencel-Delord, T.
Droge, F. Liu, F. Glorius, Chem. Soc. Rev. 2011, 40, 4740-4761; i) C. S.
Yeung, V. M. Dong, Chem. Rev. 2011, 111, 1215-1292; j) T. Brückl, R.
D. Baxter, Y. Ishihara, P. S. Baran, Acc. Chem. Res. 2012, 45, 826-839;
k) K. M. Engle, T.-S. Mei, M. Wasa, J.-Q. Yu, Acc. Chem. Res. 2012, 45,
788-802; l) G. Rouquet, N. Chatani, Angew. Chem. 2013, 125, 11942-
11959; Angew. Chem. Int. Ed. 2013, 52, 11726-11743; m) Z. Chen, B.
Wang, J. Zhang, W. Yu, Z. Liu, Y. Zhang, Org. Chem. Front. 2015, 2,
1107-1295; n) H. Davis, R. J. Phipps, Chem. Sci. 2016, 8, 864-877; o) A.
Dey, S. Agasti, D. Maiti, Org. Biomol. Chem. 2016, 14, 5440-5453; p) T.
Gensch, M. N. Hopkinson, F. Glorius, J. Wencel-Delord, Chem. Soc.
Rev. 2016, 45, 2900-2936.
[12] During the preparation of this manuscript, a different catalytic system
achieving the same target has been reported by the Yu group: P. Wang,
P. Verma, G. Xia, J. Shi, J. X. Qiao, S. Tao, P. T. W. Cheng, M. A. Poss,
M. E. Farmer, K.-S. Yeung, J.-Q. Yu, Nature 2017, 551, 489-494.
[13] For details regarding the optimization studies, see the Supporting
Information.
[3]
[4]
For selected reviews on non-directed C–H activation, see: a) N. Kuhl, M.
N. Hopkinson, J. Wencel-Delord, F. Glorius, Angew. Chem. 2012, 124,
10382-10401; Angew. Chem. Int. Ed. 2012, 51, 10236-10254; b) S. R.
Neufeldt, M. S. Sanford, Acc. Chem. Res. 2012, 45, 936-946; c) J. F.
Hartwig, M. A. Larsen, ACS Cent. Sci. 2016, 2, 281-292;
[14] During our optimization studies we monitored the ortho:meta:para ratio
over the course of the reaction using substrates 1a and 1i and found that
the ratio essentially remains constant over time.
[15] G. Li, L. Wan, G. Zhang, D. Leow, J. Spangler, J.-Q. Yu, J. Am. Chem.
Soc. 2015, 137, 4391-4397.
For seminal studies on the non-directed Ir-catalyzed borylation of arenes,
see: a) J.-Y. Cho, M. K. Tse, D. Holmes, R. E. Maleczka, M. R. Smith,
Science 2002, 295, 305-308; b) T. Ishiyama, J. Takagi, K. Ishida, N.
Miyaura, N. R. Anastasi, J. Hartwig, J. Am. Chem. Soc. 2002, 124, 390-
391.
[16] Compared to the contemporary study by the Yu group (Ref 9), a different
major isomer was observed in some instances (products 3a, 3b, 3j, 3r,
and 3t). Although no comprehensive rationalization can be given at this
stage, we hypothesize that a different sensitivity of the two catalytic
systems towards competing steric and electronic effects may cause this
effect.
[5]
[6]
For a Rh-catalyzed non-directed arene C–H olefination, see: H. U. Vora,
A. P. Silvestri, C. J. Engelin, J.-Q. Yu, Angew. Chem. 2014, 126, 2721-
2724; Angew. Chem. Int. Ed. 2014, 53, 2683-2686.
a) Y. Fujiwara, I. Moritani, S. Danno, R. Asano, S. Teranishi, J. Am.
Chem. Soc. 1969, 91, 7166-7169; b) Y. Fujiwara, R. Asano, I. Moritani,
S. Teranishi, J. Org. Chem. 1976, 41, 1681-1683; c) C. Jia, W. Lu, T.
Kitamura, Y. Fujiwara, Org. Lett. 1999, 1, 2097-2100; d) L. Zhou, W. Lu,
Chem. Eur. J. 2014, 20, 634-642.
[7]
a) D. L. Davies, S. M. A. Donald, S. A. Macgregor, J. Am. Chem. Soc.
2005, 127, 13754-13755; b) D. Lapointe, K. Fagnou, Chem. Lett. 2010,
39, 1118-1126; c) S. Zhang, L. Shi, Y. Ding, J. Am. Chem. Soc. 2011,
133, 20218-20229.
This article is protected by copyright. All rights reserved.