Cobalt-Catalyzed Oxidative Homocoupling of Arylzinc Species

Article abstract of DOI:10.1055/s-0035-1562488

A novel procedure for the synthesis of functionalized symmetrical biaryl compounds is described. The reaction proceeds via the oxidative homocoupling of arylzinc species formed by cobalt catalysis in the presence of air or p-benzoquinone depending on the nature of the functional group.

Full text of DOI:10.1055/s-0035-1562488

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2016, 48, A–E
paper
A
Y. Bourne-Branchu et al.
Paper
Synthesis
Cobalt-Catalyzed Oxidative Homocoupling of Arylzinc Species
Yann Bourne-Branchu
Aurélien Moncomble
Martin Corpet
Reductive
Process
Oxidative
Process
CoBr2, cat.
Zn
air or BQ
Ar Br
Ar Ar
Ar ZnBr
r.t.
Gregory Danoun
Corinne Gosmini*
18 examples 0–95%
Ar = aryl or heteroaryl
with FG = o-MeO, m-MeO, p-MeO, Me,
NMe2, H, Cl, COMe, CN, CF3, CO2Et
LCM, CNRS, Ecole Polytechnique, Université Paris-Saclay,
91128 Palaiseau Cedex, France
corinne.gosmini@polytechnique.edu
Dedicated to the memory of Professor Jean F. Normant;
a brilliant scientist and a great person
Received: 13.05.2016
Accepted after revision: 23.05.2016
Published online: 27.06.2016
lic compounds can be used, such as silane, tin, boron,
Grignard, lithium, manganese, and zinc derivatives with
different catalysts.5 Although Rh was one of the first metals
reported in this type of reaction, the homocoupling could
be performed with other catalysts, such as the more com-
mon Pd and Ni.6 However, some of these catalysts have
some disadvantages in terms of cost, toxicity, and the ne-
cessity for additional ligands. Nevertheless, new sustainable
catalytic systems based on iron7 or cobalt8 have been devel-
oped and, more recently, a few reactions were reported
without transition metals from aryl Grignard reagents, bo-
ronic acids, or diarylmanganese reagents using only an oxi-
dant.5i,9 Although many common organometallic reagents
(ArM; M = B, Sn, Si, Sn, Mn, and Mg) can react, arylzinc re-
agents are the best choice since they show high functional
group compatibility compared to Grignard reagents and
higher reactivity than organoboron, organotin, and organo-
silicon reagents. However, these arylzinc compounds
should be prepared directly from aryl halides to be compet-
itive with other organometallic reagents.
A few years ago, we established that cobalt catalysis al-
lowed a simple and high-yielding preparation of a broad
range of functionalized arylzinc species from readily avail-
able corresponding halides or sulfonates. These reactions
require commercially available zinc dust along with aceto-
nitrile as the solvent in the case of aryl bromides and io-
dides or with a mixture of acetonitrile/pyridine for aryl
chlorides or triflates.10 Moreover, we have already demon-
strated that cobalt salts used for the preparation of arylzinc
derivatives can be also involved in the subsequent cross-
coupling reaction.11 Although considerable effort has been
made, the development of other efficient routes to access
symmetrical biaryls would be highly desirable. Thus, with
the urgent demand for sustainable processes in the chemi-
cal industry, the development of new reactions involving
cheap and less toxic catalysts as well as green and/or inex-
DOI: 10.1055/s-0035-1562488; Art ID: ss-2016-c0348-op
Abstract A novel procedure for the synthesis of functionalized sym-
metrical biaryl compounds is described. The reaction proceeds via the
oxidative homocoupling of arylzinc species formed by cobalt catalysis in
the presence of air or p-benzoquinone depending on the nature of the
functional group.
Key words homocoupling, arylzinc, cobalt, symmetrical biaryl, oxida-
tive coupling, air, p-benzoquinone
The biaryl motif plays a considerable role in various
areas ranging from supramolecular chemistry to natural
product synthesis.1 Two classes of reactions allow their syn-
thesis: homo- and cross-coupling. Historically, the Ullmann
reaction was the first efficient process to form symmetrical
biaryls through copper-promoted coupling.2 Afterwards,
due to the harsh conditions and stoichiometric amounts of
copper required, new catalyzed processes were developed
to synthesize symmetrical biaryls using catalysts such as
palladium or nickel, starting from ArX (X = I, Br, Cl, OTf,
OMe), and in the presence of a reducing agent.3 Following
this approach, a few years ago, we reported a cobalt-
catalyzed procedure for the reductive homocoupling of aryl
halides.4 This efficient alternative involved simple and
cheap CoBr2 with Mn as a reducing agent and allowed the
synthesis of various functionalized symmetrical biaryls.
However, excess Mn was necessary and only low yields
were obtained from aryl halides bearing electron-donating
substituents.
The oxidative coupling of organometallic nucleophiles
constitutes a complementary method for the construction
of symmetrical biaryls. This other synthetic method implies
an organometallic species in conjunction with an oxidant
and a transition metal in most cases. Various organometal-
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–E

B
Y. Bourne-Branchu et al.
Paper
Synthesis
pensive oxidants has become an important research focus.
Undoubtedly, using cheap cobalt salts as catalysts com-
bined with a cheap oxidant for the synthesis of biaryls
would be a valuable alternative.
ed to an arylzinc species bearing an ortho substituent (Table
2, entry 2) or an electron-withdrawing group (Table 2, en-
tries 5–8). With the latter, the corresponding phenols were
observed in significant amounts. Interestingly, this method
allowed the dimerization of the heterocyclic zinc species
from 3-bromothiophene in moderate yield (Table 2, entry
9), whereas it was not possible with our previous cobalt-
catalyzed reductive homocoupling.
Since we have cobalt in the medium, and the oxidative
homocoupling of arylzinc species is somewhat described,
the development of a useful and mild method for the con-
struction of symmetrical biaryl backbones from arylzinc
species under aerobic conditions will possibly provide a
promising alternative. Herein, we report a versatile method
for the dimerization of functionalized arylzinc species em-
ploying a simple cobalt salt as the catalyst associated with a
simple oxidant. This simple dimerization proceeds smooth-
ly with a variety of arylzinc species including various reac-
tive groups such as esters, ketones, and nitriles.
Table 2 Cobalt-Catalyzed Homocoupling of Different ArZnBr with Air
Oxidanta
1) AllylCl (0.4 equiv)
ZnBr
MeCN, H+
"air"
FG
CoBr2 + Zn
FG
Br
FG
2)
FG
We chose to start our study with an arylzinc species
bearing an electron-donating group to access symmetrical
biaryls. Therefore, we first investigated the oxidative cou-
pling of the arylzinc compound from p-bromoanisole, gen-
erated via cobalt catalysis, in the presence of various oxi-
dants. Actually, our previous co-catalyzed reductive homo-
coupling method gave low yields with this kind of
compound. Various oxidants were tested at room tempera-
ture and the results are reported in Table 1.
Entry
FG
GC yield (%)
of ArZnBr
GC yield (%) GC yield (%)
of biarylb
of ArOHb
1
2
3
4
5
6
7
8
9
p-OMe
o-OMe
p-Me
84
86
80
81
59
81
80
78
82
84
48
80
59
61
39
58
36
63
–
–
–
H
–
p-MeCO
p-CN
12
44
20
36
–
Table 1 Cobalt-Catalyzed Homocoupling of p-MeOC6H4ZnBr with Var-
ious Oxidantsa
p-CF3
p-CO2Et
ZnBr
OMe
1) AllylCl (0.4 equiv)
MeCN, H+
3-bromothiophenec
"ox"
CoBr2 + Zn
a All reactions were carried out using CoBr2 (13 mol%), Zn (2.6 equiv), allyl
chloride (40 mol%), TFA (trace), MeCN (5 mL) followed by addition of aryl
bromide (7.5 mmol). After consumption of the starting material, air was
bubbled into the solution.
Br
2)
MeO
OMe
MeO
b Based on aryl bromide.
c Substrate.
b
Entry
Oxidant
GC yield (%) of (MeOC6H4)2
1
2
3
4
5
air
84
82
73
0c
To extend this method to aryl bromides bearing elec-
tron-withdrawing groups, a rapid screening of oxidants on
various arylzinc species was performed: p-benzoquinone
showed the largest scope. Consequently, we decided to per-
form the homocoupling reaction with various arylzinc spe-
cies bearing either an electron-donating or an electron-
withdrawing group with this oxidant (Table 3).
Generally, good to excellent yields were obtained with
an electron-donating or an electron-withdrawing group in
the meta or para position at room temperature. However, a
moderate yield was obtained with a ketone on the aromatic
cycle (Table 3, entry 8). As previously reported, a ketone
might act as a strong chelating ligand for cobalt.12 With a
functional group in the ortho position, dimerization does
not proceed correctly (Table 3, entries 2, 11, and 14), except
in the case of ortho-acylated groups, which afforded mod-
erate yields (Table 3, entries 9 and 16). In the same manner,
the organozinc compound bearing a cyano group in the
ortho position is very stable explaining the difficulty to ho-
O2
BrCH2CH2Br
N-chlorosuccinimide
p-benzoquinone
79
a All reactions were carried out using CoBr2 (13 mol%), Zn (2.6 equiv), allyl
chloride (40 mol%), TFA (trace), MeCN (5 mL) followed by addition of
p-MeOC6H4Br (7.5 mmol). After consumption of the starting material, an
oxidant (0.5 equiv) was then added.
b Based on p-MeOC6H4Br.
c The corresponding ArCl was obtained in 54% GC yield.
All tested oxidants gave similar yields except N-chloro-
succinimide, which afforded the corresponding aryl chlo-
ride in 54% GC yield. Fortunately, the most environmentally
friendly oxidant, air, gives the best result and yielded 84% of
the homocoupling product. This green oxidant was used to
dimerize a broad range of arylzinc bromides. Results are re-
ported in Table 2. Good yields were obtained with a para-
electron-donating group (Table 2, entries 1 and 3). Unfortu-
nately, the yield decreased when this reaction was extend-
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–E

C
Y. Bourne-Branchu et al.
Paper
Synthesis
Table 3 Cobalt-Catalyzed Homocoupling of Different ArZnBr with
p-Benzoquinone as Oxidanta
could be then transmetalated with two arylzincs to form
the dimer after reductive elimination. In order to check this
hypothesis, we performed the oxidative dimerization of
commercial arylzinc bromide in the presence of 0.5 equiv of
CoBr2 without any oxidant. The dimer was obtained in 73%
yield, which is comparable to our method (Table 3, entry 6).
The experiment was repeated but with a Co(I) source [0.5
equiv of CoCl(PPh3)3], only around 50% of ArZnBr was con-
sumed even after 24 h. This result is not surprising, and
could be explained by the disproportionation of Co(I) spe-
cies into Co(0) and active Co(II).
In summary, we have developed a new cobalt-catalyzed
homocoupling of arylzinc compounds, allowing the synthe-
sis of various dimers. This reaction tolerates a large number
of functional groups, and yields range from modest to ex-
cellent. The reactions involving electron-rich arylzinc bro-
mides can be achieved using a green oxidant, air, while in
other cases, p-benzoquinone is preferable. The low price of
the catalyst and the mild and bench-friendly conditions
make this homocoupling reaction an interesting alternative
to other reductive or oxidative methods. However the steric
hindrance of the arylzinc species has an influence on the
outcome of the reaction. From a mechanistic point of view,
some experimental evidence points towards the involve-
ment of Co(II) in the dimerization by transmetalation.
1) AllylCl (0.4 equiv)
MeCN, H+
ZnBr
benzoquinone
(0.5 equiv)
FG
CoBr2 + Zn
FG
Br
r.t.
FG
2)
FG
Entry
FG
GC yield (%) of
ArZnX
Isolated yield (%)
of biarylb
1
2
p-OMe
87
90
93
71
62
74
89
64
0c
71
4
o-OMe
3
m-OMe
p-Me
77
42
59
75
95
45
28
74
6d
4
5
p-NMe2
H
6
7
p-Cl
8
p-COMe
o-COMe
p-CN
9
10
11
12
13
14
15
16
17
18
79
97
82
85
91
82
73
88
71
o-CN
p-CF3
79
60
0
m-CF3
o-CF3
p-CO2Et
o-CO2Et
3-bromothiophenee
2-bromothiophenee
74
48
79
52
All reactions were carried out in air unless otherwise stated. All glass-
ware were oven-dried before use. All solvents and chemicals were ob-
tained commercially and used as received unless otherwise men-
tioned. NMR spectra were recorded on a Bruker AC-300 SY spectrom-
eter operating at 300.0 MHz for 1H, 75.0 MHz for 13C, and 282.0 MHz
for 19F and are internally referenced to residual solvents signals. IR
spectra were recorded on a Perkin Elmer using the ATR method.
UV/vis data were recorded in MeCN using a Cary 60 UV-Vis spectro-
photometer. Mass spectra were obtained from the Ecole Polytech-
nique Mass Spectral facility. Gas–liquid chromatography (GLC) was
performed on a Perichrom PR 2100 2317 Series gas chromatograph
equipped with a split-mode, capillary injection system and flame ion-
ization detectors using a SGE apolar ID-BP1 (25 m × 0.32 mm) col-
umn. Column chromatography was performed on silica gel with 60,
40–63 μm.
a All reaction were carried out using CoBr2 (13 mol%), Zn (2.6 equiv), allyl
chloride (40 mol%), TFA (trace), MeCN (5 mL) followed by addition of aryl
bromide (7.5 mmol). After consumption of the starting material, p-benzo-
quinone (0.5 equiv) was then added.
b Based on aryl bromide.
c Only homocoupled product was obtained,
d GC yield.
e Substrate.
mocouple it (Table 3, entry 11). In the case of ortho-meth-
oxy compounds, air seems to be more efficient (Table 3, en-
try 2 vs. Table 2, entry 2).
Oxidative Synthesis of Symmetrical Biaryl Using Air as Oxidant;
General Procedure
To get an explicit insight into the mechanism of this ho-
mocoupling reaction, we turned our attention towards the
cobalt species involved. First, we have shown that the pres-
ence of cobalt is required in this oxidative dimerization of
arylzinc species. The reaction of a commercial arylzinc
compound carried out without cobalt, did not lead to the
dimer even in the presence of an oxidant. As already report-
ed, Co(0) is present at the end of the formation of the aryl-
zinc.13 The cobalt species is oxidized by air or p-benzoqui-
none and reacts with the arylzinc by transmetalation to
form the dimer after reductive elimination. We hypothe-
sized that the active species was a Co(II) complex, that
To a solution of CoBr2 (220 mg, 1 mmol, 13 mol%) and zinc powder
(1.3 g, 20 mmol) in MeCN (5 mL) were successively added at r.t. allyl
chloride (250 μL, 3 mmol) and TFA (50 μL), causing an immediate rise
in temperature and color change to dark grey. After stirring the result-
ing mixture for 3 min, aryl bromide (7.5 mmol) was added. The medi-
um was then stirred at r.t. until the aryl halide was consumed. The
amount of the corresponding organozinc species was measured by re-
action with I2 and GC analysis using an internal reference (dodecane
100 μL). When the aromatic halide had been consumed, air was bub-
bled into the mixture. Then, when the organozinc had been con-
sumed, the mixture was hydrolyzed by 2 M HCl and extracted with
Et2O. The organic layer was analyzed by GC.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–E

D
Y. Bourne-Branchu et al.
Paper
Synthesis
Oxidative Synthesis of Symmetrical Biaryl Using p-Benzoquinone
Biphenyl
as Oxidant; General Procedure
[CAS Reg. No.: 92-52-4]
To a solution of CoBr2 (220 mg, 1 mmol, 13 mol%) and zinc powder
(1.3 g, 20 mmol) in MeCN (5 mL) were successively added at r.t. allyl
chloride (250 μL, 3 mmol) and TFA (50 μL), causing an immediate rise
in temperature and color change to dark grey. After stirring the re-
sulting mixture for 3 min, aryl bromide (7.5 mmol) was added. The
medium was then stirred at r.t. until the aryl halide was consumed.
The amount of the corresponding organozinc species was measured
by reaction with I2 and GC analysis using an internal reference (do-
decane 100 μL). When the aromatic halide had been consumed, p-
benzoquinone (405 mg, 3.75 mmol) was added and the mixture was
stirred overnight. The mixture was hydrolyzed by 2 M HCl and ex-
tracted with Et2O. The organic layer was dried (MgSO4). Evaporation
of solvent and purification by column chromatography (silica gel, pe-
troleum ether/Et2O) afforded the symmetrical biaryl characterized by
NMR (1H, 13C).
Yield: 434 mg (75%).
1H NMR (300 MHz, CDCl3): δ = 7.84 (d, J = 7.5 Hz, 2 H), 7.66 (dd, J = 7.5,
7.3 Hz, 3 H), 7.58 (d, J = 7.3 Hz, 1 H).
13C NMR (75 MHz, CDCl3): δ = 141.5, 129.0, 127.5, 127.4.
4,4′-Dichlorobiphenyl
[CAS Reg. No.: 2050-68-2]
Yield: 795 mg (95%).
1H NMR (300 MHz, CDCl3): δ = 7.48 (d, J = 8.6 Hz, 4 H), 7.41 (d, J = 8.6
Hz, 4 H).
13C NMR (75 MHz, CDCl3): δ = 138.4, 133.8, 129.1, 128.2.
4,4′-Diacetylbiphenyl
[CAS Reg. No.: 787-69-9]
Yield: 402 mg (45%).
1H NMR (300 MHz, CDCl3): δ = 8.04 (d, J = 8.5 Hz, 4 H), 7.70 (d, J = 8.4
Hz, 4 H), 2.63 (s, 6 H).
4,4′-Dimethoxybiphenyl
[CAS Reg. No.: 2132-80-1]
Yield: 570 mg (71%).
1H NMR (300 MHz, CDCl3): δ = 7.50 (d, J = 8.7 Hz, 4 H), 6.98 (d, J = 8.7
Hz, 4 H), 3.86 (s, 6 H).
13C NMR (75 MHz, CDCl3): δ = 197.7, 144.3, 136.5, 129.0, 127.4, 26.7.
13C NMR (75 MHz, CDCl3): δ = 158.7, 133.5, 127.7, 114.2, 55.3.
2,2′-Diacetybiphenyl
[CAS Reg. No.: 24017-95-6]
Yield: 250 mg (28%).
1H NMR (300 MHz, CDCl3): δ = 7.72 (dd, J = 7.1, 1.9 Hz, 2 H), 7.44
(quintd, J = 7.4, 1.5 Hz, 4 H), 7.15 (dd, J = 7.2, 1.5 Hz, 2 H), 2.24 (s, 6 H).
2,2′-Dimethoxybiphenyl
[CAS Reg. No.: 4877-93-4]
Yield: 32 mg (4%).
1H NMR (300 MHz, CDCl3): δ = 7.37 (ddd, J = 8.1, 7.5, 1.8 Hz, 2 H), 7.29
(dd, J = 7.4, 1.8 Hz, 2 H), 7.08–6.99 (m, 4 H), 3.81 (s, 6 H).
13C NMR (75 MHz, CDCl3): δ = 201.6, 140.7, 138.7, 131.1, 130.8, 128.6,
127.6, 29.3.
13C NMR (75 MHz, CDCl3): δ = 157.1, 131.5, 128.7, 127.9, 120.4, 111.1,
55.7.
4,4′-Biphenyldicarbonitrile
[CAS Reg. No.: 1591-30-6]
Yield: 567 mg (74%).
1H NMR (300 MHz, CDCl3): δ = 7.78 (d, J = 8.3 Hz, 4 H), 7.69 (d, J = 8.3
Hz, 4 H).
3,3′-Dimethoxybiphenyl
[CAS Reg. No.: 6161-50-8]
Yield: 619 mg (77%).
1H NMR (300 MHz, CDCl3): δ = 7.44 (t, J = 79 Hz, 2 H), 7.32–7.21 (m, 4
H), 6.99 (dd, J = 8.2, 2.4 Hz, 2 H), 3.92 (s, 6 H).
13C NMR (75 MHz, CDCl3): δ = 143.5, 132.9, 128.0, 118.5, 112.4.
13C NMR (75 MHz, CDCl3): δ = 160.1, 142.7, 129.9, 119.8, 113.1, 112.9,
55.3.
4,4′-Bis(trifluoromethyl)biphenyl
[CAS Reg. No.: 581-80-6]
Yield: 860 mg (79%).
1H NMR (300 MHz, CDCl3): δ = 7.77–7.69 (m, 8 H).
13C NMR (75 MHz, CDCl3): δ = 143.2, 130.3 (q, J = 32.5 Hz), 127.6,
125.9 (q, J = 3.7 Hz), 122.4.
4,4′-Dimethylbiphenyl
[CAS Reg. No.: 613-33-2]
Yield: 287 mg (42%).
1H NMR (300 MHz, CDCl3): δ = 7.66 (d, J = 7.2 Hz, 4 H), 7.39 (d, J = 7.8
Hz, 4 H), 2.55 (s, 6 H).
13C NMR (75 MHz, CDCl3): δ = 138.5, 136.8, 129.6, 127.0, 21.3.
3,3′-Bis(trifluoromethyl)biphenyl
[CAS Reg. No.: 580-82-5]
Yield: 653 mg (60%).
1H NMR (300 MHz, CDCl3): δ = 7.87–7.58 (m, 8 H).
13C NMR (75 MHz, CDCl3): δ = 140.5, 131.5 (q, J = 32.3 Hz), 130.4,
129.5, 124.7 (q, J = 3.8 Hz), 123.9 (q, J = 3.8 Hz), 122.3.
N,N,N′,N′-Tetramethylbenzidine
[CAS Reg. No.: 366-29-0]
Yield: 532 mg (59%).
1H NMR (300 MHz, CDCl3): δ = 7.47, (d, J = 8.8 Hz, 4 H), 6.82 (d, J = 8.8
Hz, 4 H), 2.98 (s, 12 H).
13C NMR (75 MHz, CDCl3): δ = 149.0, 127.0, 113.3, 40.9; one quaterna-
ry carbon is not visible.
Diethyl Biphenyl-4,4′-dicarboxylate
[CAS Reg. No.: 47230-38-6]
Yield: 828 mg (74%).
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–E

E
Y. Bourne-Branchu et al.
Paper
Synthesis
1H NMR (300 MHz, CDCl3): δ = 8.07 (d, J = 8.2 Hz, 4 H), 7.60 (d, J = 8.3
Hz, 4 H), 4.35 (q, J = 7.1 Hz, 4 H), 1.37 (t, J = 7.1 Hz, 6 H).
13C NMR (75 MHz, CDCl3): δ = 166.2, 144.1, 130.1, 129.9, 127.1, 61.0,
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Diethyl Biphenyl-2,2′-dicarboxylate
[CAS Reg. No.: 5807-65-8]
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Chaboche, C.; Mahuteau-Betzer, F.; Ahr, M. Org. Lett. 2005, 7,
1943. (c) Cahiez, G.; Moyeux, A.; Buendia, J.; Duplais, C. J. Am.
Chem. Soc. 2007, 129, 13788.
13C NMR (75 MHz, CDCl3): δ = 167.1, 143.3, 131.3, 130.2, 129.9, 129.9,
127.1, 60.6, 13.7.
3,3′-Bithiophene
[CAS Reg. No.: 3172-56-3]
Yield: 493 mg (79%).
1H NMR (300 MHz, CDCl3): δ = 7.42–7.39 (m, 1 H), 7.37 (d, J = 1.8 Hz, 2
H).
13C NMR (75 MHz, CDCl3): δ = 137.3, 126.4, 126.2, 119.9.
2,2′-Bithiophene
[CAS Reg. No.: 492-97-7]
Yield: 324 mg (52%).
1H NMR (300 MHz, CDCl3): δ = 7.30–7.19 (m, 2 H), 7.11–7.04 (m, 1 H).
13C NMR (75 MHz, CDCl3): δ = 137.5, 127.9, 124.5, 123.9.
Supporting Information
(8) Mayer, M.; Czaplik, W. M.; Jacobi von Wangelin, A. Synlett 2009,
2931.
(9) (a) Krasovskiy, A.; Tishkov, A.; Del Amo, V.; Mayr, H.; Knochel, P.
Angew. Chem. Int. Ed. 2006, 45, 5010. (b) Maji, M. S.; Pfeifer, T.;
Studer, A. Angew. Chem. Int. Ed. 2008, 47, 9547.
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0035-1562488.
S
u
p
p
ortioInfgrmoaitn
S
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p
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ortiInfogrmoaitn
(10) (a) Fillon, H.; Gosmini, C.; Périchon, J. J. Am. Chem. Soc. 2003,
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(11) (a) Gosmini, C.; Moncomble, A. Isr. J. Chem. 2010, 50, 568.
(b) Qian, X.; Yu, Z.; Auffrant, A.; Gosmini, C. Chem. Eur. J. 2013,
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, A–E