Oxidative Homocoupling of Diheteroaryl- or Diarylmanganese Reagents Generated via Directed Manganation Using TMP2Mn

Article abstract of DOI:10.1055/s-0034-1380424

We report an oxidative homocoupling of diheteroaryl or diarylmanganese reagents prepared by directed manganation using TMP₂Mn·2MgCl₂·4LiCl. The resulting diorganomanganese reagents can efficiently undergo an oxidative dimerization leading to the homocoupling products in good yields. Remarkably, a number of functional groups, as well as sensitive heterocycles are tolerated using this metalation-dimerization procedure.

Full text of DOI:10.1055/s-0034-1380424

SYNLETT
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©
Georg Thieme Verlag Stuttgart · New York
2015, 26, 1515–1519
1515
letter
Synlett
D. Haas et al.
Letter
Oxidative Homocoupling of Diheteroaryl- or Diarylmanganese
Reagents Generated via Directed Manganation Using TMP Mn
2
Diana Haasa,1
Jeffrey M. Hammanna,1
Alban Moyeuxb,c
Gérard Cahiezb
NC
Cl
N
1
) TMP2Mn•2MgCl2•4LiCl (0.6 equiv)
CN
Cl
0 °C, 1 h
N
2) chloranil (1.0 equiv)
N
–40 °C, 0.5 h
Cl
CN
4% yield
Paul Knochel*a
7
a
Department of Chemistry, Ludwig-Maximilians-Universität München,
Butenandtstr. 5–13, 81377 Munich, Germany
Paul.Knochel@cup.uni-muenchen.de
Institut de Recherche de Chimie Paris, CNRS - Chimie ParisTech,
b
1
1 Rue Pierre et Marie Curie, 75005 Paris, France
c
Université Paris 13, Sorbonne Paris Cité, 74 Rue Marcel Cachin,
3017 Bobigny, France
9
Received: 15.04.2015
Accepted after Revision: 25.05.2015
Published online: 11.06.2015
metalation
using
the
sterically
hindered
base
9
TMP Mn·2MgCl ·4LiCl (1, Scheme 1; TMP = 2,2,6,6-te-
2
2
DOI: 10.1055/s-0034-1380424; Art ID: st-2015-b0255-l
tramethylpiperidyl).
Abstract We report an oxidative homocoupling of diheteroaryl or dia-
rylmanganese reagents prepared by directed manganation using
TMP Mn·2MgCl ·4LiCl. The resulting diorganomanganese reagents can
efficiently undergo an oxidative dimerization leading to the homocou-
pling products in good yields. Remarkably, a number of functional
groups, as well as sensitive heterocycles are tolerated using this metala-
tion–dimerization procedure.
MnCl2•2LiCl
1.0 equiv)
(
2
2
2
N
MgCl•LiCl
N Mn•2MgCl2•4LiCl
2
0–25 °C, 2 h
1
95%; 0.4 M in THF
Scheme 1 Preparation of TMP Mn·2MgCl ·4LiCl
2
2
Key words homocoupling, manganese, metalation, dimerization, oxi-
dation
In preliminary experiments, we have examined the oxi-
dative homocoupling of various mono- or diheteroaryl-
metal species 3 generated via a direct metalation of benzox-
azole (2) followed by an oxidative dimerization using chlo-
The biaryl motif can be found in a broad array of natural
products, pharmaceuticals, agrochemicals, and materials.2
Thus, an increasing number of methods for their synthesis
have been described. Homo- and cross-coupling reactions
are most commonly used to construct these biaryl struc-
tures. Many symmetrical biaryls can be obtained by the
10
ranil (Table 1). First experiments metalating with n-Bu-
11
Li, or metalating with n-BuLi followed by a transmetala-
tion with either ZnCl (0.5 equiv) or MgCl (0.5 equiv) and
2
2
subsequent oxidation using chloranil (1.0 equiv) only gave
poor results (Table 1, entries 1–3). An improvement was
achieved when transmetalating the aryllithium species
3
4
palladium- or nickel-catalyzed homocoupling of ArX (X =
I, Br, Cl, OTf) in the presence of an oxidizing agent. However,
metal catalysts together with the ligands are often expen-
with MnCl ·2LiCl (0.5 equiv), which led to the desired prod-
2
5
sive or toxic. Oxidative homocoupling of aryl-metal re-
uct 4 in 47% yield after oxidation (Table 1, entry 4).
agents displays another efficient synthetic method for the
construction of symmetrical biaryls.6 Although many or-
ganometallic reagents (ArMet; Met = Mg, Zn, Mn) can be
used for this reaction, Grignard reagents remain the most
convenient choice for large-scale preparations due to their
economical preparation directly from the corresponding
The C–H zincation of benzoxazole (2) with either
12
13
TMPZnCl·LiCl or TMP Zn·2MgCl ·2LiCl followed by oxi-
2
2
dation with chloranil at –20 °C did not lead to any product
formation (Table 1, entries 5 and 6). Switching to the mag-
nesium bases TMPMgCl·LiCl14 or TMP Mg·2LiCl at –20 °C
15
2
also did not improve the result (Table 1, entries 7 and 8). Fi-
nally, it was found that the directed manganation of 2 using
TMP Mn·2MgCl ·4LiCl (1, 0.6 equiv, –20 °C, 1 h) followed by
7
aryl halides. So far, only few metalation–dimerization pro-
8
cedures have been described. Herein, we report a conve-
2
2
nient oxidative homocoupling of various diheteroaryl- or
diaryl-manganese reagents prepared by a directed C–H
an oxidation with chloranil (1.0 equiv, –20 °C) gave the best
results leading to the heterobiaryl 4 in 79% isolated yield
(
Table 1, entry 9).15
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Table 1 Homocoupling of Benzoxazole (2)
chloranil
(1.0 equiv)
N
O
N
O
N
O
O
N
MetBase
2Met
THF
20 °C, 1 h
THF
–20 °C, 0.5 h
–
2
3
4
Entry
MetBasea
Additiveb
–
GC yield of 4 (%)c
1
2
3
4
5
6
7
8
n-BuLi
n-BuLi
n-BuLi
n-BuLi
0
ZnCl
2
0
MgCl
2
traces
MnCl
2
·2LiCl
47
TMPZnCl·LiCl
TMP Zn·2MgCl
TMPMgCl·LiCl
–
–
–
–
–
–
2
2
·2LiCl
–
–
TMP
2
Mg·2LiCl
Mn·2MgCl
–
9
TMP
2
2
·4LiCl
84 (79)d
a
Conditions: 1.1 equiv of the metallic base was used, however, in entries 6, 8, and 9 only 0.6 equiv were used.
Conditions: 0.5 equiv were used.
b
c
Tetradecane (C14
Isolated yield.
H30) was used as an internal standard.
d
With these optimized conditions in hand, we applied
nese reagent 5j, which undergoes oxidative dimerization
leading to the expected product 6j in 81% yield (Table 2, en-
try 12).
this method to the dimerization of a broad range of hetero-
cycles. The reaction scope proved to be general, and various
substituted heterocycles could efficiently be homocoupled
in 61–81% yield (Table 2). Remarkably, 2,3- and 3,6-disubti-
tuted pyridines were smoothly dimerized to furnish the ex-
pected products 6a–e in up to 74% yield.
Table 2 Oxidative Homocoupling of Diheteroarylmanganese Reagents
Entry
Manganese reagenta
Yield of product 6 (%)b
Noteworthy is the metalation of 2-chloro-3-cyanopyri-
dine, as its direct magnesiation or lithiation is difficult
Cl
CN
N
Mn
using other bases, such as TMPLi, TMP Mg·2LiCl, or
2
2
NC
TMPMgCl·LiCl and usually only leads to decomposition of
the starting material. However, its manganation using
TMP Mn·2MgCl ·4LiCl (1, 0.6 equiv) proceeded smoothly
1
N
Cl
N
2
2
NC
5
a
within four hours at 0 °C and afforded the corresponding
diorganomanganese 5a. Oxidative dimerization using chlo-
ranil (1.0 equiv, –40 °C) furnished the desired bipyridine
Cl
6
a 74
Cl
16
6a
in 74% yield (Table 2, entry 1). Additionally, various
CF3
Mn
N
electron-withdrawing groups, such as CF , F, and Cl, were
3
2
F3C
Cl
tolerated under these reaction conditions, leading to the
corresponding products 6b–e in 61–71% yield (Table 2, en-
tries 2–5). 3,6-Disubstituted pyridazines were also smooth-
ly metalated using 1 (0 °C, 1 h) and gave the desired biaryls
2
N
N
F3C
b 71
5
b
Cl
6
16
6
f,g) in 61–67% yield after oxidation of the corresponding
F
manganese species 5f,g (Table 2, entries 6 and 7). The meta-
lation of benzofuran or benzothiophene using
TMP Mn·2MgCl ·4LiCl (1, 0.6 equiv) was complete within
F
Cl
N
3
N
Cl
2
2
Mn
N
Cl
2
five hours at 0 °C, providing the corresponding manganese
reagents 5h,i, that smoothly underwent the oxidative di-
merization using chloranil (1.0 equiv, –40 °C) leading to the
homocoupling products 6h,i in 74–77% yield (Table 2, en-
tries 8 and 9). Similarly, 1-methyl-benzimidazole was man-
ganated using 1 (0.6 equiv, 0 °C, 6 h) to afford the manga-
5
c
F
6c 64
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Table 2 (continued)
Table 3 Oxidative Homocoupling of Arylmanganese Reagents
Entry
4
Manganese reagenta
Yield of product 6 (%)b
Cl
Entry
Manganese reagenta
Yield of product 8 (%)b
Cl
Cl
MeO2C
MeO2C
Cl
N
N
Cl
Cl
Mn
Mn
N
Cl
1
2
2
5
d
Cl
CO2Me
Cl
6
d 63
Cl
7
7
7
7
a
b
c
8
a 76
F3C
F3C
F
EtO2C
EtO2C
Cl
N
5
6
7
N
Mn
Mn 2
N
Cl
2
3
4
5
6
7
2
5
e
CF3
CO Et
2
F
6
e 61
F
8
b 97
N
OMe
N
OMe
N
Cl
EtO2C
N
EtO2C
OMe
Mn
MeO
MeO
Mn
2
2
N
5
f
MeO
N
CO2Et
Cl
Cl
6
f 67
8
c 70
N
Cl
N
NC
N
Cl
2
MeO C
EtO2C
N
Cl
Mn
Cl
Cl
Mn
2
2
N
5
g
Cl
N
O
CO2Et
CN
6
g 61
CN
d
8
d 87
CO2Et
Mn
8
9
CO Et
2
2
O
S
O
Br
5
5
h
i
6h 74
6i 77
Br
Br
Mn
2
S
7
e
EtO2C
F
Mn
Mn
8e 53
2
S
F
F
F
Me
Mn
N
N
N
N
N
2
2
F
10
F
F
N
7
7
f
Me
8f 51
5
j
Me
6
j 81
NC
F
a
2
MgCl and LiCl are omitted for the sake of clarity.
Isolated yield.
Mn
b
2
F
CN
CN
CN
g
8
g 82
Additionally, a range of polyfunctional arenes have been
F
dimerized in 51–97% yield using this method (Table 3).
Thus, the directed manganation of methyl 3-chlorobenzo-
ate with TMP Mn·2MgCl ·4LiCl (1, 0.6 equiv, 0 °C, 6 h) and
subsequent oxidation of the resulting manganese reagent
a using chloranil (1.0 equiv) at –40 °C gave the desired bis-
arene 8a in 76% yield (Table 3, entry 1). Similarly, 3-substi-
tuted ethyl benzoates were deprotonated and dimerized to
afford the desired products 8b–d in up to 97% yield, while
tolerating various functionalities such as F, Cl, and sensitive
cyano groups (Table 3, entries 2–4). The manganation of
ethyl 4-bromobenzoate also proceeded smoothly leading to
F
CN
Mn
2
2
8
7
2
NC
8h 81
7
h
F
16
a
MgCl2 and LiCl are omitted for the sake of clarity.
Isolated yield.
b
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Letter
the manganese reagent 7e which can dimerize to give 8e in
3% yield (Table 3, entry 5). The metalation of 1,3-difluoro-
benzene using 1 (0.6 equiv, 0 °C, 6 h) followed by the oxida-
tion of the manganese reagent 7f using chloranil (1.0 equiv,
1997, 62, 261. (c) Jhaveri, S. B.; Carter, K. R. Chem. Eur. J. 2008,
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(
5) (a) Handbook on the Toxicology of Metals; Friberg, L.; Nordberg,
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(6) For recent examples of transition-metal-catalyzed homocou-
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S.; Rothenberg, G.; Gitis, D.; Sasson, Y. Org. Lett. 2000, 2, 211.
–40 °C, 0.5 h) gave the polyfluorinated product 8f in 51%
yield (Table 3, entry 6). Additionally, 3-fluorobenzonitrile
and 2-fluorobenzonitrile could be manganated efficiently
using TMP Mn·2MgCl ·4LiCl (1, 0.6 equiv, 0 °C, 6 h).
2
2
The subsequent homocoupling with chloranil (1.0 equiv) at
40 °C gave the fluorobenzonitriles 8g,h in up to 82% yield
(
1
(
b) Mathews, C. J.; Smith, P. J.; Welton, T. Chem. Commun. 2000,
249. (c) Lee, H. M.; Nolan, S. P. Org. Lett. 2000, 2, 2053.
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–
(Table 3, entries 7 and 8).
In summary, we have reported a convenient directed
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manganation–dimerization procedure for various polyfunc-
tional arenes and heterocycles. This oxidative homocou-
pling using chloranil tolerates various functional groups,
such as esters, halides, and nitriles, and proceeds at conve-
nient temperatures (–20 to –40 °C). Thus, various function-
alized diaryl- and diheteroaryl-manganese reagents have
been used successfully to prepare polyfunctionalized biaryl
and biheteroaryl compounds. Further application towards
the synthesis of natural products is under way in our labo-
ratories.
5, 5003. (j) Cahiez, G.; Chaboche, C.; Mahuteau-Betzer, F.; Ahr,
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Acknowledgment
(7) (a) Krasovskiy, A.; Knochel, P. Angew. Chem. Int. Ed. 2004, 43,
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This work was supported by the CNRS and Chimie ParisTech (Paris,
France), as well as by the Ludwig-Maximilians-University (Munich,
Germany) in the frame work of the International Associated Laborato-
ry IrMaCaR between the research groups of P. Knochel and G. Cahiez.
We also thank BASF SE (Ludwigshafen, Germany) and Rockwood Lith-
ium GmbH (Hoechst, Germany) for the generous gift of chemicals.
Int. Ed. 2006, 45, 159. (c) Cahiez, G.; Moyeux, A.; Buendia, J.;
Duplais, C. J. Am. Chem. Soc. 2007, 129, 13788. (d) Piller, F. M.;
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Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0034-1380424.
S
u
p
p
ortioIgnfrm oaitn
S
u
p
p
ortioIgnfrm oaitn
(
9) (a) Wunderlich, S. H.; Kienle, M.; Knochel, P. Angew. Chem. Int.
Ed. 2007, 48, 7256. (b) Preparation of TMP Mn·2MgCl ·4LiCl
2
2
(
1) A dry and argon-flushed Schlenk flask is charged with TMP-
References and Notes
MgCl·LiCl (348 mL, 400 mmol) and cooled to 0 °C. A solution of
MnCl ·2LiCl (1.0 N in THF, 200 mL, 200 mmol) is added over a
period of 15 min. After 2 h at 0 °C, the obtained solution of
2
(
(
1) These authors contributed equally to this work.
2) (a) Thomson, R. H. The Chemistry of Natural Products 1985.
b) Hassan, J.; Sevignon, M.; Cozzi, C.; Schulz, E.; Lemaire, M.
TMP Mn·2MgCl ·4LiCl (1) is titrated with benzoic acid using 4-
2
2
(
(phenylazo)diphenylamine as indicator prior to use showing a
Chem. Rev. 2002, 102, 1359. (c) Corbet, J.-P.; Mignani, G. Chem.
Rev. 2006, 106, 2651.
concentration of 0.40 M. The reagent is stirred and stored under
aluminum foil excluded from light.
(3) For representative examples of palladium-catalyzed homocou-
(
10) Using other oxidants such as 1,2-dichloroethane, 1,2-dibro-
moethane, or oxygen only gave poor results.
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(
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(
12) (a) Wunderlich, S.; Knochel, P. Chem. Commun. 2008, 6387.
(
(b) Mosrin, M.; Knochel, P. Org. Lett. 2009, 11, 1837. (c) Mosrin,
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3
615. (d) Mosrin, M.; Bresser, T.; Knochel, P. Org. Lett. 2009, 11,
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Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1515–1519

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Syn tl eh tet sis
D. Haas et al.
Letter
Chem. 2010, 75, 4686. (f) Bresser, T.; Monzon, G.; Mosrin, M.;
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Characterization of Typical Homocoupling Products 2,2′-
Dichloro-[4,4′-bipyridine]-3,3′-dicarbonitrile (6a)
White solid; yield 74%, 102 mg; mp 197–199 °C. 1H NMR (400
(
13) (a) Wunderlich, S.; Knochel, P. Angew. Chem. Int. Ed. 2007, 46,
MHz, CDCl ): δ = 8.79 (d, J = 5.0 Hz, 2 H), 7.49 (d, J = 5.0 Hz, 2 H)
3
13
7685. (b) Mosrin, M.; Knochel, P. Chem. Eur. J. 2009, 15, 1468.
ppm. C NMR (100 MHz, CDCl ): δ = 154.6, 153.0, 148.6, 122.2,
3
(
c) Wunderlich, S.; Rohbogner, C. J.; Unsinn, A.; Knochel, P. Org.
112.8, 109.5 ppm. FT-IR (ATR): ν = 2253, 1565, 1545, 1525,
–1
Process Res. Dev. 2010, 14, 339.
1470, 1440, 1369, 1209, 1090, 904, 840, 807, 725, 690 cm
.
+
(
14) (a) Mosrin, M.; Knochel, P. Org. Lett. 2008, 10, 2497. (b) Dunst,
C.; Knochel, P. J. Org. Chem. 2011, 76, 6972.
HRMS (EI): m/z [M] calcd for C12H Cl N : 273.9813; found:
4
2
4
273.9809.
3,3′,6,6′-Tetramethoxy-4,4′-bipyridazine (6f)
Off-white solid; yield 67%, 95 mg; mp 230–232 °C. H NMR (400
(
15) (a) Krasovskiy, A.; Krasovskaya, V.; Knochel, P. Angew. Chem. Int.
Ed. 2006, 45, 2958. (b) Clososki, G. C.; Rohbogner, C. J.;
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Roman, D. S.; León, T.; Knochel, P. Org. Lett. 2014, 16, 123.
16) General Procedure for the Metalation and Homocoupling of
1
MHz, CDCl ): δ = 7.02 (s, 2 H), 4.09 (s, 6 H), 4.04 (s, 6 H) ppm.
3
13
C NMR (100 MHz, CDCl ): δ = 161.9, 158.7, 126.5, 121.1, 55.0,
3
(
54.8 ppm. FT-IR (ATR): ν = 3020, 2999, 2958, 1690, 1679, 1608,
1569, 1526, 1469, 1452, 1390, 1363, 1341, 1264, 1244, 1206,
1183, 1176, 1130, 1109, 1008, 999, 907, 899, 887, 828, 768, 756,
(
Hetero)arenes
A dried and argon-flushed Schlenk tube is charged with the cor-
responding substrate (1.0 mmol, 1.0 equiv) and dissolved in THF
-1
+
712, 676, 662 cm . HRMS (EI): m/z [M] calcd for C12H14N O :
4
4
(
1.0 mL). TMP Mn·2MgCl ·4LiCl (1.5 mL, 0.6 mmol, 0.6 equiv,
278.1015; found: 278.1010.
2
2
0
.40 M solution in THF) is added dropwise at the given tem-
Diethyl 6,6′-Dicyano-[1,1′-biphenyl]-2,2′-dicarboxylate (8d)
perature and stirred until a reaction aliquot quenched with
iodine in THF showed full consumption of the starting material.
Then, the reaction mixture is cooled to the given temperature,
and chloranil (1.0 mmol, 1.0 equiv) dissolved in THF (4.0 mL) is
added dropwise. The reaction is stirred for 0.5 h and is then
quenched with sat. aq NH Cl solution and extracted with CH Cl
Yellowish solid; yield 87%, 153 mg; mp 180–182 °C. 1H NMR
(600 MHz, CDCl ): δ = 8.38 (dd, J= 8.0, 1.3 Hz, 2 H), 7.93 (dd, J=
3
7.8, 1.3 Hz, 2 H), 7.66 (t, J= 7.9 Hz, 2 H), 4.11 (q, J = 7.1 Hz, 4 H),
13
1.08 (t, J = 7.2 Hz, 6 H) ppm. C NMR (150 MHz, CDCl ): δ =
3
164.3, 143.4, 136.0, 134.7, 130.5, 129.1, 116.3, 114.3, 61.6, 13.7
ppm. FT-IR (ATR): ν = 2985, 2255, 2231, 1717, 1578, 1477, 1447,
1428, 1393, 1368, 1288, 1273, 1182, 1148, 1103, 1020, 905,
4
2
2
(3 × 25 mL). The crude product is purified by column chroma-
–1
+
tography on silica to yield the corresponding title compound.
865, 829, 763, 727 cm . HRMS (EI): m/z [M] calcd for
C20H16N O : 348.1110; found: 348.1102.
2
4
©
Georg Thieme Verlag Stuttgart · New York — Synlett 2015, 26, 1515–1519