Transition-Metal-Free Matsuda-Heck Type Cross-Coupling and Mechanistic Evidence for a Radical Mechanism

Article abstract of DOI:10.1002/ejoc.202100032

The Matsuda-Heck reaction, usually performed with palladium catalysts, can be carried out under transition-metal-free conditions in the presence of a KOtBu/DMF couple. This system allows the selective and direct synthesis of stilbenes from aryldiazonium salts under mild temperature (20 °C). Mechanistic studies suggest a radical pathway in which the DMF acts as the initiator of the overall process.

Full text of DOI:10.1002/ejoc.202100032

Communications
doi.org/10.1002/ejoc.202100032
1
2
3
4
5
Transition-Metal-Free Matsuda-Heck Type Cross-Coupling
and Mechanistic Evidence for a Radical Mechanism
Julien Bergès,[a] Yassir Zaid,[a] Anis Tlili,[b] Jean-Marc Sotiropoulos,[c] and Marc Taillefer*[a]
6
7
8
9
The Matsuda-Heck reaction, usually performed with palladium
catalysts, can be carried out under transition-metal-free con-
ditions in the presence of a KOtBu/DMF couple. This system
allows the selective and direct synthesis of stilbenes from
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
°
aryldiazonium salts under mild temperature (20 C). Mechanistic
studies suggest a radical pathway in which the DMF acts as the
initiator of the overall process.
Scheme 1. The Matsuda-Heck reaction: traditional method with palladium
catalysts and pathway described herein with KOtBu/DMF system.
Herein, we present a new way to perform the traditionally
palladium catalysed Matsuda-Heck reaction under both ligand
and transition metal free conditions (Scheme 1).[1,2,3] The latter is
performed with an excess amount of iron[14–17] or titanium
salts,[18,19] without transition metals[20–24] or through visible-light
induced photoredox strategies, often catalyzed by Eosin Y or
ruthenium complexes (Ru(bpy)3Cl2).[25–29] However, with these
methods, when the generated aryl radical couples with an
alkene, the double bond is often not conserved, which
constitutes a great challenge.
We previously discovered that the α-arylation of enolizable
ketones, usually performed with nickel, palladium or copper
catalysts, could be carried out using a simple KOtBu/DMF
system that is able to generate aryl radicals in the initiation
process.[30f–i] Taking into account the well-known possibility of
forming aryl radicals from arene diazonium salts,[4] we assumed
that the Matsuda-Heck process could be performed with this
system to give stilbenes, which are very important intermedi-
ates and targets in the chemical, pharmaceutical, and materials
industries.[31]
a
versatile method allowing the preparation of stilbene
derivatives by selective alkene functionalization from arenedia-
zonium salts, which constitute highly attractive aryl halide
surrogates. Arenediazonium salts are easily prepared from
widely available and inexpensive anilines, are often reactive
under mild conditions, and the leaving group is inert (N2)
towards the reaction mixture.[4–7] The use of alkenes as starting
materials, some of the most widespread chemical compounds,
is another advantage of the method. However, the presence of
palladium-based catalysts for most Matsuda-Heck reactions is
not favourable, owing to the high cost and toxicity issues, and
limits the attractiveness for large-scale or industrial applications.
For the Matsuda-Heck process, the C(sp2)À C(sp2) bond formation
proceeds via the intermediate formation of a reactive cationic
palladium intermediate resulting from the initial oxidative
addition of Pd(0) at the C(sp2)À N bond of the arenediazonium
salts.[3,8] This carbon-carbon bond formation can also be
achieved by the Meerwein reaction, a long known copper-
mediated coupling between aryldiazoniums and electron-
deficient alkenes.[9,10] The method, which suffers from several
drawbacks that have limited its application in synthesis,
proceeds via reversible oxidation of copper(I) to copper(II),
associated to the initial formation of an aryl radical.[11–13] The
generation of the latter from arenediazonium has also been
We report herein that a KOtBu/DMF couple alone promotes
the direct and selective synthesis of stilbenes by a Matsuda-
Heck type-cross-coupling, performed in the absence of ligand
and palladium catalyst. We also propose a radical mechanistic
pathway based on the literature, alongside experimental and
theoretical studies (Scheme 1).
To start our investigations, we reacted 4-meth-
oxybenzenediazonium tetrafluoroborate 1a with styrene in
°
DMF (2 mL) for 18 h at 20 C in the presence of 2 equivalents of
KOtBu. In these conditions, the desired stilbene 2a (trans
isomer) was selectively obtained in 39% yield (Table 1, entry 2).
Using other bases such as KOAc or NaOtBu gave only traces of
2a (Table 1, entries 3, 4) and replacing the solvent with
acetonitrile, toluene or 1,2-dichloroethane also led to negligible
amounts of product (Table 1, entries 5–7). While increasing the
amount of KOtBu was moderately beneficial, we noticed the
crucial role of the concentration since reducing the volume of
DMF to 220 μL and 500 μL afforded 2a in 45% and 71% yields
respectively (Table 1, entries 9, 10). Finally, we obtained a very
good yield of stilbene 2a using resublimed KOtBu (purchased
[a] Dr. J. Bergès, Dr. Y. Zaid, Dr. M. Taillefer
ICGM, Univ Montpellier, CNRS, ENSCM, 34296 Montpellier, France
E-mail: marc.taillefer@enscm.fr
[b] Dr. A. Tlili
Institute of Chemistry and Biochemistry (ICBMS – UMR CNRS 5246), CNRS,
INSA, CPE-Lyon
Université Lyon 1
1 Rue victor Grignard, 69622 Villeurbanne, France
[c] Dr. J.-M. Sotiropoulos
E2S UPPA, CNRS, IPREM,
Universite de Pau et des Pays de l’Adour
Pau, France
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejoc.202100032
Eur. J. Org. Chem. 2021, 1559–1563
1559
© 2021 Wiley-VCH GmbH

Communications
doi.org/10.1002/ejoc.202100032
Table 1. Synthesis of stilbene 2a from 4-methoxybenzenediazonium
tetrafluoroborate 1a and styrene: reaction conditions.[a]
Table 2. Synthesis of stilbenes 2a–p (trans isomers) from styrenes and
1
2
arenediazonium tetrafluoroborate derivatives: scope of the method.[a]
3
4
5
y [M][b]
Yield of 2a
6
7
Entry
Base
x
Solvent
[%][c]
8
9
1
2
3
4
5
6
7
8
9
KOtBu
KOtBu
KOAc
0
2
2
2
2
2
2
5
5
5
5
5
DMF
DMF
DMF
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.055
0.125
0.125
0.125
0
39
traces
<5
traces
0
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
NaOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
DMF
MeCN
Toluene
DCE
DMF
DMF
DMF
DMF
DMF
0
52
45
10
11
12
71 (77[d]
81[d,e]
0[f]
)
[a] Reaction conditions: 4-methoxybenzenediazonium tetrafluoroborate 1a
(1 mmol), styrene (2 mmol), base (x mmol), solvent, 18 h at 20 C. [b] Molar
concentration of 1a (mol/L). [c] Yields calculated by GCMS using 1,3,5-
trimethoxybenzene as an internal standard. [d] 48 h at 20 C. [e] reaction
reformed with resublimed KOtBu purchased form Alfa Aesar (99.994%). [f]
Reaction performed with 1.0 equivalent of Galvinoxyl or TEMPO.
°
°
from Alfa Aesar À 99.994%), thus ruling out the possibility of a
reaction catalyzed by undesirable metallic contaminants (ta-
ble 1, entry 11).
We next explored the scope of the method (Table 2). With
the styrene as a coupling partner, the 4-methoxy and the
challenging hindered 2-methoxybenzenediazonium tetrafluoro-
borates lead to the expected stilbenes 2a and 2b. Arenediazo-
nium salts bearing an atom of fluorine or chlorine in the para
position also produced the corresponding stilbenes (2d, 2e)
while in the case of p-bromo and p-iodo substituents, the
reduction of the starting salts to benzene is mainly observed.
The benzenediazonium tetrafluoroborate forms the stilbene 2c
and the electron-poor p-trifluoromethylbenzene diazonium salt
provides the stilbene 2f, which is an important intermediate in
the pharmaceutical industry.[31] This procedure is also compat-
ible with a range of styrene derivatives. Thus the benzenediazo-
nium in the presence of styrenes bearing alkyl substituents (4-
Me, 4-tBu) gives the stilbenes 2g and 2h respectively, while the
meta-substituted 3-chlorostyrene leads to the expected cou-
pling product 2i. The use of benzene- or p-anisyldiazonium
tetrafluoroborates (1a) with other halogenated styrenes (4-Br,
4-Cl, 4-F) as coupling partners also produced the corresponding
stilbenes (2j–2l). The salt 1a was a suitable substrate for
styrenes with electron donating alkyl groups (4-Me, 4-tBu) in
the para positions, whilst comparatively the electron-poor 4-
cyanostyrene resulted in a poor yield (15 mol%). Finally, when
the biphenyldiazonium tetrafluoroborate was tested for cou-
pling with styrene and 2-fluorostyrene, the stilbenes 2o and 2p
were obtained respectively, both in good yields.
[a] Reaction performed with 1.0 mmol of arenediazonium tetrafluorobo-
rate, 2 mmol of styrene derivative, 5 mmol of KOtBu in 500 μL of DMF, 48 h
°
at 20 C under argon. [b] NMR yield calculated with 1,3,5 trimeth-
oxybenzene internal as standard. Isolated yield in bracket.
one equivalent of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEM-
PO) or Galvinoxyl and observed with these common radical
scavengers that the coupling of 1a with styrene was completely
inhibited (Table 1, entry 12). Furthermore, repeating the reac-
tion with limited exposure to light resulted in the formation of
the coupling product in good yield (77% of 2a), thus showing
that the reaction is self-generated by the t-BuOK/DMF system
without assistance from outside light. It should be also noted
that for all starting diazonium salts used, the formation of any
regioisomers was never observed. The functionalization on the
ipso position is only obtained, which is inconsistent with the
formation of benzyne intermediates and not in agreement with
an arynic mechanism. We could also rule out this possibility by
carrying out
a
test from styrene and 2,4,6-trimeth-
ylbenzenediazonium tetrafluoroborate which, because of its
structure, cannot give rise to reactions proceeding via an aryne
intermediate.[32] Under standard conditions we observed,
although in low yield, the formation of the expected coupling
product (20%) together with the formation of the mesitylene
We then turned our attention to the mechanism of this
method. As we assumed the reaction to proceed via radical
intermediates, we attempted the reactions in the presence of
Eur. J. Org. Chem. 2021, 1559–1563
www.eurjoc.org
1560
© 2021 Wiley-VCH GmbH

Communications
doi.org/10.1002/ejoc.202100032
due to the reduction of the corresponding arenediazonium
(Scheme 2A).
On the basis of these observations we postulated a radical
mechanism, illustrated with the benzenediazonium tetrafluor-
oborate 1c (Figure 1).
The overall process would be initiated by deprotonation of
the solvent with KOtBu resulting in the in situ formation of the
electron-rich carbamoyl anion 3, stabilized by an interaction
with tert-butanol and the associated potassium cation. In similar
reaction conditions we had previously shown the possibility for
this electron-donor active carbamoyl anion to transfer an
electron to an aryliodane to form an aryl radical.[30h,32] Taking
into account the well-known possibility of generating the latter
from arene diazonium salts,[4] we hypothesized that such a
development is also possible in the present study. The
mechanism would thus, in the presence of diazonium salt 1c
and the carbamoyl anion 3, lead to the phenyl radical 4 while
releasing N2, KBF4, t-BuOH into the reaction medium, and the
corresponding carbamoyl radical 3”. Propagation could then
follow an SRN1 pathway in which the phenyl radical 4 reacts
with the styrene, thus leading to a new radical intermediate 5.
The tert-butoxide anion then abstracts a proton from the latter,
which evolves to the formation of a new radical anion 6. A final
SET from 6 to the starting phenyldiazonium tetrafluoroborate
1c releases the expected stilbene 2c. Another possibly would
involve the abstraction of a hydrogen radical from 5 by 3”, with
the formation after radical combination of the corresponding
stilbene.
In order to assess these hypothesis the process simulation
was performed (density functional theory calculations at the
M06-2X/6-311+G(d,p) level of theory, the solvent can be taking
into account using the polarizable continuum model PCM)(see
Figure 2 and the Supporting Information).
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
From computed DFT calculations we propose in a first step
the formation of
a relatively stable complex 3’ (ΔG=
À 13.16 kcalmolÀ 1) resulting from the interaction of DMF with
KOtBu.[30h] From the latter the anionic carbamoyl adduct 3
would be formed with a quite low activation barrier (ΔGa =
11.52 kcalmolÀ 1), following the abstraction of a DMF proton by
potassium tert-butoxide. The corresponding computed transi-
tion state is located at an energy level almost similar to that of
the anionic carbamoyl 3. Subsequently, in the presence of the
diazonium salt 1c, an electron transfer would lead to the diazo
radical (4’; ΔG=À 29.48 kcalmolÀ 1) which spontaneously de-
composes into the phenyl one (4). The carbamoyl radical 3”
formed in this step is thermodynamically favorably stabilized by
interactions with KBF4 and t-BuOH. DFT calculations then show
that the reaction between the generated phenyl radical 4 and
the styrene is thermodynamically favorable (ΔG=
À 33.05 kcalmolÀ 1) and produces the radical 5. In the presence
Scheme 2. A) Reaction of 2,4,6-trimethylbenzenediazonium tetrafluoroborate
with styrene. B) Evolution of 4-methoxybenzenediazonium tetrafluoroborate
in standard conditions.
Figure 2. Energie levels (ΔG) for all steps of the reaction starting from the
ethanolate. M06-2X/6-311+G(d,p) level of theory, in DMF, is used. ΔG values
Figure 1. Proposed radical mechanism for the Matsuda-Heck reaction
promoted by the KOtBu/DMF system.
are given in KcalmolÀ 1
.
Eur. J. Org. Chem. 2021, 1559–1563
www.eurjoc.org
1561
© 2021 Wiley-VCH GmbH

Communications
doi.org/10.1002/ejoc.202100032
of an excess amount of tert-butoxide, the passage through an
Aquitain) and CINES under allocation A005080045 made by Grand
Equipement National de Calcul Intensif (GENCI) are acknowledged
for computational facilities.
1
2
3
4
5
6
7
8
9
anion radical (6) is quite conceivable, the reaction being
undeniably controlled by the high thermodynamics towards
the corresponding ethylenic 2c (ΔG=À 37.81 kcalmolÀ 1 com-
pared to 6). The formation of the stilbene via abstraction of a
hydrogen radical from 5 by 3” (ΔG=À 6.28 kcalmolÀ 1 compared Conflict of Interest
to 5) and subsequent formation of the product by radical
combination (ΔG=À 46.85 kcalmolÀ 1) is also conceivable.
It is important to note that when we carried out the reaction
from 4-methoxybenzenediazonium 1a under standard condi-
tions in the absence of styrene (Scheme 2B), we mostly
observed the reduction product (anisole) and the N,N-dimethyl-
p-anisamide. The formation of the latter could result from the
coupling between the carbamoyl radical 3’ and the arylradical
4. As this is sometimes obtained when the reactivity is low or
under very diluted conditions, it is compatible with our
hypothesis of a mechanism proceeding through radical inter-
mediates. As far as the very low reactivity noted with NaOtBu is
concerned, it may be due to the absence of proton exchange of
this base with the DMF.[30h] Comparatively, a rapid exchange of
the formamide proton takes place in a solution of KOtBu in
DMF, which is much more soluble than the NaOtBu in this
solvent.
The authors declare no conflict of interest.
Keywords: Arylation · Csp2À Csp2 bond formation · Matsuda-
Heck · Reaction mechanisms · Stilbene
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
[1] a) K. Kikukawa, T. Matsuda, Chem. Lett. 1977, 159–162; b) R. Yamashita,
K. Kikukawa, F. Wada, T. Matsuda, J. Organomet. Chem. 1980, 201, 463–
468; c) K. Kikukawa, K. Nagira, N. Terao, F. Wada, T. Matsuda, Bull. Chem.
Soc. Jpn. 1979, 52, 2609–2610; d) K. Kikukawa, K. Nagira, F. Wada, T.
Matsuda, Tetrahedron 1981, 31–36.
[2] A. Roglans, A. Pla-Quintana, M. Moreno-Manas, Chem. Rev. 2006, 106,
4622–4643.
[3] J. G. Taylor, A. V. Moro, C. R. D. Correia, Eur. J. Org. Chem. 2011, 8, 1403–
1428.
[4] a) C. Galli, Chem. Rev. 1988, 88, 765–792; b) L. Troian-Gautier, D. E.
Martínez-Tong, J. Hubert, F. Reniers, M. Sferrazza, A. Mattiuzzi, C.
Lagrost, I. Jabin, J. Phys. Chem. C. 2016, 120, 40, 22936–22945; c) E. R. M.
Habraken, A. R. Jupp, J. C. Slootweg, Synlett 2019, 30(08), 875–884.
[5] F. Mo, G. Dong, Y. Zhang, J. Wang, Org. Biomol. Chem. 2013, 11, 1582–
1593.
[6] a) F. Callonnec, E. Fouquet, F. Felpin, Org. Lett. 2011, 13, 2646–2649;
b) H. Bonin, M. Sauthier, F. X. Xavier, Adv. Synth. Catal. 2014, 356, 645–
671.
[7] a) D. Toummini, A. Tlili, J. Bergès, F. Ouazzani, M. Taillefer, Chem. Eur. J.
2014, 20, 14619–14623; b) I. Fabre, L. A. Perego, J. Bergès, I. Ciofini, L.
Grimaud, M. Taillefer, Eur. J. Org. Chem. 2016, 5887–5896.
[8] a) A. A. Sabino, A. H. L. Machado, C. R. D. Correia, M. N. Eberlin, Angew.
Chem. 2004, 116, 2568–2572; Angew. Chem. Int. Ed. 2004, 43, 2514–
2518; b) A. A. Sabino, A. H. L. Machado, C. R. D. Correia, M. N. Eberlin,
Angew. Chem. 2004, 116, 4489; Angew. Chem. Int. Ed. 2004, 43, 4389.
[9] H. Meerwein, E. B. Buchner, K. von Emster, J. Prakt. Chem. 1939, 152,
237–266.
[10] J. K. Kochi, J. Am. Chem. Soc. 1955, 77, 5090–5092.
[11] H. Brunner, C. Blüchel, M. P. Doyle, J. Organomet. Chem. 1997, 541, 89–
95.
[12] M. R. Heinrich, Chem. Eur. J. 2009, 15, 820–833.
[13] P. Mastrorilli, C. F. Nobile, N. Taccardi, Tetrahedron Lett. 2006, 4759–
4762.
[14] H. Jasch, Y Landais, M. R. Heinrich, Chem. Eur. J. 2013, 19, 8411–8416.
[15] M. R. Heinrich, O. Blank, D. Ullrich, M. Kirschstein, J. Org. Chem. 2007, 72,
9609–9616.
[16] M. K. Staples, R. L. Grange, J. A. Angus, J. Ziogas, N. P. H. Tan, M. K.
Taylor, C. H. Schiesser, Org. Bio. Chem. 2011, 9, 473–479.
[17] G. Pratsch, C. A. Anger, K. Ritter, M. R. Heinrich, Chem. Eur. J. 2011, 17,
4104–4108.
In summary, we have disclosed a new way to perform the
Matsuda-Heck reaction, which does not require the presence of
a transition metal catalyst. The costly palladium/ligand catalytic
systems traditionally used are here replaced by the KOtBu/DMF
couple which allows, from aryldiazonium salts and under mild
°
temperature conditions (20 C), the selective and direct syn-
thesis of stilbenes, which constitute highly important intermedi-
ates and targets in the chemical, pharmaceutical, and materials
industries. Mildness, low-cost, experimental simplicity and the
fact that it is not necessary to remove impurities of transition
metal from final molecules are features of our method, which
make it particularly well suited for syntheses of pharmaceuticals
where financial, environmental and toxicity issues are of greater
concern. Based on our experimental and theoretical studies we
propose a radical mechanism which proceeds through the
initial formation of a carbamoyl anion, able to initiate the
formation of an aryl radical in the presence of the diazonium
salt. The propagation phase would then follow an SRN1 pathway
leading to the formation of stilbenes through the intermediate
formation of a new radical anion. Another way could involve a
radical abstraction/recombination sequence. Efforts to expand
the utility of this system to other cross-coupling and related
reactions, along with mechanistic studies, are in progress and
will be reported in due course.
[18] C. Hultsch, O. Blank, H.-J. Wester, M. R. Heinrich Tetrahedron Lett. 2008,
49, 1881–1883.
[19] M. R. Heinrich, O. Blank, S. Wölfel, Org. Lett., 2006, 8, 3323–3325.
[20] C. Molinaro, J. Mowat, F. Gosselin, P. D. O’Shea, J.-F. Marcoux, R.
Angelaud, I. W. Davies, J. Org. Chem. 2007, 72, 1865–1858.
[21] M. Hartmann, Y. Li, A. Studer, J. Am. Chem. Soc. 2012, 134, 16516–16519.
[22] S. Kindt, K. Wicht, M. R. Heinrich, Angew. Chem. 2016, 128, 8886–8889;
Angew. Chem. Int. Ed. 2016, 55, 8744–8747.
Acknowledgements
[23] S. Shaaban, A. Jolit, D. Petkova, N. Maulide, Chem. Commun. 2015, 51,
13902–13905.
We thank Centre National de la Recherche Scientifique (CNRS),
Ecole Nationale Supérieure de Chimie de Montpellier (ENSCM), the
Agence Nationale de la Recherche (ANR) for support and the
Centre National pour la recherche Scientifique (CNRST) of
Morocco. The “Direction du Numérique” of the Université de Pau
et des Pays de l’Adour, MCIA (Mésocentre de Calcul Intensif
[24] B. Majhi, D. Kundu, B. C. Ranu, J. Org. Chem. 2015, 80, 7739–7745.
[25] D. P. Hari, B. König, Angew. Chem. 2013, 125, 4832–4842; Angew. Chem.
Int. Ed. 2013, 52, 4734–4743.
[26] P. Schroll, D. P. Hari, B. König, ChemistryOpen, 2012, 1, 130–133.
[27] L Huang, J. Zhao, RSC Adv. 2013, 3, 23377–23388.
[28] B. Sahoo, M. N. Hopkinson, F. Glorius, J. Am. Chem. Soc. 2013, 135,
5505–5508.
Eur. J. Org. Chem. 2021, 1559–1563
www.eurjoc.org
1562
© 2021 Wiley-VCH GmbH

Communications
doi.org/10.1002/ejoc.202100032
[29] X.-Z. Shu, M. Zhang, Y. He, H. Frei, F. D. Toste, J. Am. Chem. Soc. 2014,
[31] G. Likhtenshtein, in Stilbenes: Applications in Chemistry, Life Science and
Materials Science; Wiley-VCH, Verlag GmbH & Co. KGaA: Weinheim,
2010.
[32] J. P. Barham, G. Coulthard, K. J. Emery, E. Doni, F. Cumine, G. Nocera,
M. P. John, L. E. A. Berlouis, T. M. McGuire, T. Tuttle, J. A. Murphy, J. Am.
Chem. Soc. 2016, 138, 7402–7410. In this paper Murphy et al propose
that the DMF, after deprotonation in the presence of KOtBu, can also
dimerise to form an electron donnor.
1
2
3
4
5
6
7
8
9
136, 5844–5847.
[30] a) W. Liu, H. Cao, H. Zhang, H. Zhang, K. H. Chung, C. He, H. Wang, F. Y.
Kwong, A. Lei, J. Am. Chem. Soc. 2010, 132, 16737–16740; b) C.-L. Sun, H.
Li, D.-G. Yu, M. Yu, X. Zhou, X.-Y. Lu, K. Huang, S.-F. Zheng, B.-J. Li, Z.-J.
Shi, Nat. Chem. 2010, 2, 1044–1049; c) S. Yanagisawa, K. Itami,
ChemCatChem 2011, 3, 827–829; d) E. Shirakawa, X. Zhang, T. Hayashi,
Angew. Chem. 2011, 123, 4767–4770; Angew. Chem. Int. Ed. 2011, 50,
4671–4674; e) H. Zhang, R. Shi, A. Ding, L. Lu, B. Chen, A. Lei, Angew.
Chem. 2012, 124, 12710–12713; Angew. Chem. Int. Ed. 2012, 51, 12542–
12545; f) G. Danoun, A. Tlili, F. Monnier, M. Taillefer, Angew. Chem. 2012,
124, 12987–12991; Angew. Chem. Int. Ed. 2012, 51, 12815–12819; g) A.
Tlili, G. Danoun, F. Monnier, M. Taillefer, FR,2012-0055275, WO 2013–
182640; h) M. P. Drapeau, I. Fabre, L. Grimaud, I. Ciofini, T. Ollevier, M
Taillefer, Angew. Chem. 2015, 127, 10733–10737; Angew. Chem. Int. Ed.
2015, 54, 10587–10591; i) M. Pichette Drapeau, T. Ollevier, M. Taillefer,
FR, 2014–0057458, WO 2016–016414.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
Manuscript received: January 11, 2021
Revised manuscript received: January 12, 2021
Accepted manuscript online: January 22, 2021
Eur. J. Org. Chem. 2021, 1559–1563
www.eurjoc.org
1563
© 2021 Wiley-VCH GmbH