Room Temperature Decarboxylative and Oxidative [2+2+2] Annulation of Benzoic Acids with Alkynes Catalyzed by an Electron-Deficient Rhodium(III) Complex

Article abstract of DOI:10.1002/chem.201703928

It has been established that an electron-deficient (η⁵-cyclopentadienyl)rhodium(III) [Cp^ERh^III] complex is capable of catalyzing the decarboxylative and oxidative [2+2+2] annulation of benzoic acids with alkynes to produce substituted naphthalenes at room temperature. The appropriate choice of the additive and the solvent is crucial for this transformation. This catalyst system allowed use of oxygen as a terminal oxidant and broadened the substrate scope including both aromatic and aliphatic alkynes. In this catalysis, the electron deficient nature of the Cp^ERh^III catalyst would cause the strong rhodium-π interaction, which accelerates the decarboxylation as well as the C?H bond cleavage.

Full text of DOI:10.1002/chem.201703928

A Journal of
Accepted Article
Title: Room Temperature Decarboxylative and Oxidative [2+2+2]
Annulation of Benzoic Acids with Alkynes Catalyzed by an
Electron-Deficient Rhodium(III) Complex
Authors: Yusaku Honjo, Yu Shibata, Eiji Kudo, Tomoya Namba, Koji
Masutomi, and Ken Tanaka
This manuscript has been accepted after peer review and appears as an
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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
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to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201703928
Link to VoR: http://dx.doi.org/10.1002/chem.201703928
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10.1002/chem.201703928
Chemistry - A European Journal
COMMUNICATION
Room Temperature Decarboxylative and Oxidative [2+2+2]
Annulation of Benzoic Acids with Alkynes Catalyzed by an
Electron-Deficient Rhodium(III) Complex
Yusaku Honjo,[a] Yu Shibata,*,[a] Eiji Kudo,[a] Tomoya Namba,[a] Koji Masutomi,[a] and Ken Tanaka*,[a]
Abstract: It has been established that an electron-deficient (η5-
cyclopentadienyl)rhodium(III) [CpERhIII] complex is capable of
catalyzing the decarboxylative and oxidative [2+2+2] annulation of
benzoic acids with alkynes to produce substituted naphthalenes at
room temperature. The appropriate choice of the additive and the
solvent is crucial for this transformation. This catalyst system
allowed use of oxygen as a terminal oxidant and broadened the
substrate scope including both aromatic and aliphatic alkynes. In this
catalysis, the electron deficient nature of the CpERhIII catalyst would
cause the strong rhodium-π interaction, which accelerates the
decarboxylation as well as the C–H bond cleavage.
applicable alkynes were largely limited to diarylacetylenes.
It is well known that the decarboxylation proceeds via β-
carbon elimination from the metal carboxylate with metal-π
interaction.[10] Therefore, there is
a
good chance that
electronically tuned catalysts facilitate the decarboxylation. As
an example of the electronically tuned catalyst, we reported the
synthesis of an electron-deficient CpERhIII complex bearing two
ester moieties on the Cp ring and its high catalytic activity
toward various C–H bond functionalization reactions.[11,12] For
example, the oxidative [4+2] annulation of benzoic acids with
alkynes catalyzed by RhIII, RuII, and IrIII complexes required high
temperature, stoichiometric amounts of metal oxidants, and/or
excess amounts of benzoic acids (Scheme 1c).[13] Pleasingly,
the use of the CpERhIII catalyst solved all the above problems
(Scheme 1c).[11g] We anticipated that this electrophilic CpERhIII
catalyst would accelerate the decarboxylation as well as the C–
H bond cleavage as a result of the strong rhodium-π interaction.
In this paper, we disclose the room temperature decarboxylative
and oxidative [2+2+2] annulation of benzoic acids with alkynes
catalyzed by the electron deficient CpERhIII complex.
Decarboxylative C–C bond forming reactions using
carboxylic acids are highly efficient and economical due to ready
availability of starting materials.[1–3] For example, the
decarboxylative in situ generation of arylmetal species from
arylcarboxylic acids and transition-metal catalysts eliminates the
synthesis of expensive arylmetal compounds (Scheme 1a).[4]
Alternatively,
the
transition-metal-catalyzed
C–H
bond
functionalization at the ortho position of the carboxyl group
followed by decarboxylation has also been developed (Scheme
1a).[2,5] By combining these two reactions, the decarboxylative
double functionalization of the neighboring C–CO2H and C–H
bonds has been developed.[6–8] For example, Satoh and Miura
reported the decarboxylative and oxidative [2+2+2] annulation of
Previous works
a) decarboxylative C–C bond formation with/without C–H bond cleavage
H
or
X
R
R'
H
R2
R1
R1
R1
or
OH
–CO2
>100 °C
R2
H
O
R2 = R or CHCHR'
b) decarboxylative and oxidative [2+2+2] annulation
(η5-
complex,
R2
benzoic acids with diarylacetylenes catalyzed by
pentamethyl-cyclopentadienyl)iridium(III)
[Cp*IrIII]
a
R2
H
R3
R3
R1
R1
+
OH
which furnished substituted naphthalenes (Scheme 1b).[6]
Loginov and Kudinov also reported that a CpRhIII complex
catalyzes the same reaction using an phenyl- and ethyl-
substituted acetylene.[7] However, in sharp contrast to the
decarboxylation of alkyl-, acyl-, β-keto-, or alkynyl-carboxylic
acids giving highly stable radical or anion species,[3] that of
arylcarboxylic acids giving the arylmetal species requires harsh
reaction conditions (>100 °C).[9] Indeed, the above transition-
metal-catalyzed decarboxylative [2+2+2] annulation reactions
–CO2, –H2O
R3
O
R2
Satoh, Miura
cat. [Cp*IrCl2]2, Ag2CO3 (2 equiv)
53–89% yields
o-xylene, 160 °C (R2 = R3 = aryl)
Loginov, Kudinov cat. [CpRhI2]2, Ag2CO3 (2 equiv)
o-xylene, reflux
81% yield
(R1 = H, R2 = Et, R3 = Ph)
48–98% yields
This work
cat. [CpERhCl2]2 (1), cat. AgOAc
or NaOAc, under O2 or air
room temperature–80 °C
c) oxidative [4+2] annulation
R2
R2
H
R3
R1
R1
+
OH
O
were conducted at 160 °C in o-xylene. Furthermore,
a
–H2O
R3
O
O
stoichiometric amount of a silver oxidant was required and
Satoh, Miura, Ackermann, etc.
our previous work
cat. [CpERhCl2]2 (1)
cat. AgNTf2, cat. Cu(OAc)2•H2O
cat. Cp*RhIII, RuII, or IrIII
high temperature,
stoichiometric metal oxidant,
and/or excess amount of benzoic acid
benzoic and acrylic acids (1.1 equiv)
under air, room temperature
Me
Me
Me
Cl
CO2Et
Me
Me
Me
[a]
Y. Honjo, Dr. Y. Shibata, E. Kudo, T. Namba, K. Masutomi, Prof.
Dr. K. Tanaka
Me
Cl
Me
Cl
Ir
Me Cl
Rh
Me Cl
Rh
EtO2C Cl
Me
Me
Me
2
2
2
Department of Chemical Science and Engineering, Tokyo Institute
of Technology
[Cp*IrCl2]2
[Cp*RhCl2]2
[CpERhCl2]2 (1)
O-okayama, Meguro-ku, Tokyo 152-8550 (Japan)
E-mail: ktanaka@apc.titech.ac.jp
E-mail: yshibata@apc.titech.ac.jp
Scheme 1. Transition-metal-catalyzed C–C bond forming reactions of benzoic
acids.
http://www.apc.titech.ac.jp/~ktanaka/
Supporting information for this article is given via a link at the end
of the document
In the course of our study on the [4+2] annulation of benzoic
acid (2a) with diphenylacetylene (3a) (Table 1, entry 1),[11g] the
use of AgOAc in place of AgNTf2 afforded not [4+2] annulation
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10.1002/chem.201703928
Chemistry - A European Journal
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product 5aa but decarboxylative [2+2+2] annulation product 4aa
as a major product, although the reaction was sluggish (entry 2).
The reaction under O2 atmosphere slightly improved the yield of
4aa (entry 3). Screening of solvents[14] revealed that the use of
aromatic solvents (toluene or chlorobenzene) improved the yield
of 4aa (entries 4 and 5). Pleasingly, reducing the amount of 2a
to a slight excess relative to 3a (0.6 equiv) further improved the
yield of 4aa (entry 6). Screening of additives revealed that
Ag2CO3 and NaOAc work as well, while the yields of 4aa
decrease somewhat (entries 7 and 8). The use of cationic salts
(SbF6, NTf2, and OTf) afforded exclusively 5aa (entries 9–11)
With optimized conditions in hand, we investigated the scope
of benzoic acids 2 (Scheme 2). With regard to the substituent at
the para position, the introduction of both electron donating (2b–
d) and withdrawing (2e,f) groups was tolerable (entries 2–7),
although the reaction of highly electron-deficient 2f required
higher catalyst loading (entry 6) or reaction temperature (entry 7).
In entry 6, the use of NaOAc instead of AgOAc slightly
decreased the yield of 4fa. When using 4-methoxybenzoic acid
(2c), not only 4ca but also a trace amount of 5-substituted
naphthalene 4ca’ was generated via the 1,3-shift of the rhodium
center.[6] Although the introduction of the substituent at the meta-
and no reaction was observed without additive (entry 12). Finally, position (2g–i) decreased the reactivity (entries 8–12), the
prolonged reaction time (48 h) furnished 4aa in the highest yield
(entry 13). Importantly, under this optimized reaction conditions,
Cp*RhIII and Cp*IrIII complexes failed to afford 4aa (entries 14
and 15). Inexpensive NaOAc could be employed instead of
AgOAc, while even longer reaction time (72 h) was required
(entry 16). Although the yield decreased, 4aa was obtained even
in the absence of the CuII oxidant (entry 17).
reactions at elevated temperature afforded the corresponding
naphthalenes in good yields (entries 9, 11, 12). Interestingly, the
reaction of 3-fluorobenzoic acid (2i) afforded 5-fluoro-substituted
naphthalene 4ia’ as a major regioisomer, as a result of the
preferred C–H bond cleavage at the ortho-position of the fluorine
atom (entry 12). 3,4-Dimethylbenzoic acid (2j) reacted with 3a at
80 °C to give the corresponding naphthalene 4ja selectively
(entry 13). 2-Methoxybenzoic acid (2k) reacted with 3a to give
rearranged product 4ca as a major regioisomer via the 1,3-shift
of the rhodium center (entry 14).[6]
Table 1. Optimization of reaction conditions.[a]
2.5 mol % Rh complex
10 mol % additive
10 mol % Cu(OAc)2•H2O
Ph
Ph
Ph
Ph
Ph
Ph
2.5 mol % 1
10 mol % AgOAc
10 mol % Cu(OAc)2•H2O
H
OH
+
Ph
+
O
solvent, RT, 24 h
under O2
R
OH
+
O
Ph
PhCl, RT, 24–92 h
under O2
Ph
O
2a
(0.6–1.1 equiv)
3a
Ph
Ph
R
Ph
O
5aa
4aa
Ph
Ph
Ph
Ph
Ph
2
3a
R
(0.6 equiv)
Entry Rh Complex
Additive
2a
Solvent
Yield [%][b]
Ph
4
4'
(equiv)
1.1
1.1
1.1
1.1
1.1
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
4aa 5aa
Entry
2
Time (h)
4 / Yield (%)
1[c]
2[c]
3
1
1
1
1
1
1
1
1
1
1
1
1
1
AgNTf2
AgOAc
AgOAc
AgOAc
AgOAc
AgOAc
(CH2Cl)2
(CH2Cl)2
(CH2Cl)2
toluene
PhCl
0
6
96
R
Ph
Ph
Ph
R
Ph
R
Ph
Ph
<1
OH
Ph
11
42
46
66
58
49
0
<3
O
Ph
1
2
2a (R = H)
2b (R = Me)
48 (72[a]
72
)
)
4aa / 81% (83%[a]
)
4
0
4ba / 98%
3
2c (R = OMe)
2d (R = OPh)
2e (R = Cl)
72
4ca+4ca' / 70% (95:5)
4da / 79%
5
<3
4
72
5
72
4ea / 77%
4fa / 63% (55%[a]
6[b]
7[c]
2f (R = CF3)
2f (R = CF3)
72 (92[a]
24
)
6
PhCl
<3[d]
<3[d]
<3[d]
28[d]
72[d]
8[d]
4fa / 88%
Ph
[e]
7
Ag2CO3
NaOAc[f]
AgSbF6
AgNTf2
AgOTf
PhCl
R
Ph
Ph
Ph
Ph
Ph
OH
8
PhCl
R
R
Ph
Ph
O
9
PhCl
8
9[c]
10[b]
11[c]
12[c]
2g (R = Me)
2g (R = Me)
2h (R = CF3)
2h (R = CF3)
2i (R = F)
72
24
72
24
24
4ba / 29% (>50:1)
4ba+4ba' / 85% (95:5)
4fa / 49% (>50:1)
4fa / 90% (>50:1)
4ia+4ia' / 71% (29:71)
Ph
10
11
12
13[g]
PhCl
0
PhCl
0
none
PhCl
0
0
Me
Me
Me
Ph
<3[d]
35[d]
0
OH
AgOAc
AgOAc
AgOAc
NaOAc[f]
NaOAc[f]
PhCl
81
0
Me
Ph
O
Ph
14[g] [Cp*RhCl2]2
15[g] [Cp*IrCl2]2
PhCl
13[c]
2j
24
92
4ja / 93%
Ph
Ph
PhCl
<1
83
74
Ph
Ph
Ph
Ph
OH
16[h]
1
1
PhCl
<3[d]
<3[d]
MeO
OMe O
OMe Ph
Ph
17[h,i]
PhCl
14
2k
4ca'+4ca / 77% (12:88)
Scheme 2. Scope of benzoic acids. 1 (0.0050 mmol), AgOAc (0.020 mmol),
Cu(OAc)2•H2O (0.020 mmol), 2a (0.120 mmol), 3a (0.200 mmol), and PhCl
(2.0 mL) were used. The structures of 4 and 4’ are shown on the left and right,
respectively. Cited yields were of the isolated products. [a] NaOAc [0.040
mmol (entry 1) or 0.080 mmol (entry 6)] was used instead of AgOAc. [b] 1
(0.010 mmol), AgOAc (0.040 mmol) were used. [c] At 80 °C.
[a] Rh complex (0.0050 mmol), additive (0.020 mmol), Cu(OAc)2•H2O (0.020
mmol), 2a (0.120–0.220 mmol), 3a (0.200 mmol), and solvent (2.0 mL) were
used. [b] Isolated yields based on 3a. [c] Under air. [d] Based on 2a. [e]
Ag2CO3 (0.010 mmol) was used. [f] NaOAc (0.040 mmol) was used. [g] For 48
h. [h] For 72 h. [i] In the absence of Cu(OAc)2•H2O.
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10.1002/chem.201703928
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COMMUNICATION
The scope of alkynes 3 was also investigated (Scheme 3).
Substituted diarylacetylenes 3b–e reacted with 2a to give the
corresponding naphthalenes 4ab–ae (entries 1–5). In the
reactions of electron-rich alkynes 3b–d, the use of toluene as a
solvent improved the product yields (entries 1–4). In the
reactions of highly electron-rich alkynes 3c and 3d, high catalyst
The present decarboxylative and oxidative [2+2+2]
annulation is useful for the synthesis of π-conjugated molecules.
For example, the Scholl reaction of the product tetraaryl
naphthalene
4ac
with
FeCl3
afforded
hemi-
hexabenzocoronene[15] 6 in 85% yield (Scheme 5a). The use of
diyne 7 afforded 7,12-diphenylbenzo[k]fluoranthene (8) in 57%
yield (Scheme 5b).
loadings improved the product yields (entries
Pleasingly, previously unusable dialkylacetylenes 3f and 3g
could be employed to give the corresponding
3 and 4).
conditions A
2.5 mol % 1
10 mol % AgOAc
10 mol % Cu(OAc)2•H2O
PhCl, RT, 72 h
under air
Ph
tetraalkylnaphthalenes 4af and 4ag in good yields (entries 6 and
7). In entry 6, the use of NaOAc instead of AgOAc afforded 4af
in moderate yield, although prolonged reaction time (72 h) was
required. Unsymmetrical alkyl-phenyl-substituted acetylenes 3h
and 3i showed low reactivity (entry 8–10), but the desired
cycloadducts were obtained in good yields with moderate
regioselectivity at 80 °C (entries 9 and 10).
Ph
Ph
Ph
OH
+
conditions B
0.25 mol % 1
1 mol % AgOAc
1 mol % Cu(OAc)2•H2O
PhCl, 80 °C, 72 h
under air
O
Ph
3a
(2 mmol)
Ph
2a
(1.2 mmol)
4aa
79% (343 mg, 0.793 mmol)
(conditions A)
78% (337 mg, 0.779 mmol)
(conditions B)
Scheme 4. Preparative scale reactions.
2.5 mol % 1
10 mol % AgOAc
10 mol % Cu(OAc)2•H2O
R2 (R3)
R2
R
R
a)
R3 (R2)
OH
+
toluene, RT, 24–72 h
under O2
R3
R
R
R
R3
O
R2
4 (4')
2a
(0.6 equiv)
FeCl3 (20 equiv)
3
CH2Cl2-MeNO2
40 °C, 40 min
Entry
Time (h)
2
4 / Yield (%)
R
R
Ar
Ar
R
R
4ac (R = n-C5H11
)
6 / 85%
Ar
b)
O
Ar
R
(Ar = 4-RC6H4)
OH
10 mol % 1
40 mol % AgOAc
40 mol % Cu(OAc)2•H2O
1
3b (R = Me)
72
72
72
72
72
4ab / 60%
4ac / 47%
4ac / 81%
4ad / 48%
4ae / 60%
2
3c (R = n-C5H13
3c (R = n-C5H13
3d (R = OMe)
3e (R = Cl)
)
)
2a (1.2 equiv)
3[a]
4[a]
5[b]
+
PhCl, RT, 48 h
under O2
R
R
R
8 / 57%
7
R
R
R
4af / 70% (42%[c]
Scheme 5. Synthetic applications.
6
7
3f (R = n-C5H11
3g (R = nBu)
)
24 (72[c]
72
)
)
4ag / 60%
To confirm the decaroboxylation step in the catalytic cycle,
the following reactions were conducted (Scheme 6a).
Isocoumarin 5aa failed to react with 3a under the standard
conditions, which revealed that 5aa was not the intermediate
leading to 4aa. The reaction of 2d in the absence of 3a under
the standard conditions did not afford decarboxylated product 9,
which revealed that the direct decarboxylation of 2d to form the
corresponding arylrhodium species can be excluded.
Furthermore, as the use of NaOAc instead of AgOAc was also
effective for this reaction, the silver-mediated decarboxylation[9]
can also be excluded. Therefore, we proposed the mechanism
shown in Scheme 6b.[6] Rhodium acetate A generated from
[CpERhCl2]2 and AgOAc reacts with 2a to give rhodium benzoate
B. Subsequent C–H bond cleavage affords rhodacycle C.
Insertion of 3 furnishes rhodacycle D, and the strong rhodium-π
interaction would accelerate the decarboxylation to generate
rhodacycle E. The second alkyne insertion affords rhodacycle F
or F’, in which at least F is operative due to the formation of 8
from 7. Reductive elimination furnishes 4 and RhI species G.
Finally, reoxidation of G by CuII regenerates catalytically active
RhIII species A. The use of cationic silver salts instead of AgOAc
might accelerate ionic reductive elimination of D to give 5
selectively. Hong suggested a similar counter anion effect in the
RuII catalysis.[16]
nBu
nBu
Ph
n-Bu
Ph
Ph
nBu
Ph
nBu
8
9[d]
3h
3h
72
24
4ah+4ah' / 27% (78:22)
4ah+4ah' / 91% (75:25)
Cy
Ph
Ph
Ph
Cy
Ph
Cy
Cy
10[d]
3i
24
4ai+4ai' / 75%[e] (75:25)
Scheme 3. Scope of alkynes.
1 (0.0050 mmol), AgOAc (0.020 mmol),
Cu(OAc)2•H2O (0.020 mmol), 2a (0.120 mmol), 3a (0.200 mmol), and toluene
(2.0 mL) were used. The structures of 4 and 4’ are shown on the left and right,
respectively. Cited yields were of the isolated products. Ratio of regioisomers
were determined by 1H NMR. [a] 1 (0.010 mmol) and AgOAc (0.040 mmol)
were used. [b] PhCl was used instead of toluene. [c] NaOAc (0.040 mmol) was
used instead of AgOAc. [d] At 80 °C. [e] Isolated with small amounts of
impurities (ca. 5%).
This naphthalene synthesis could be conducted on
a
preparative scale (Scheme 4). The reaction on a >1 mmol scale
under air proceeded to give 4aa in 79% yield, which is
comparable to the yield in a small scale under O2 (81%: Scheme
2, entry 1). The catalyst loading could be reduced to 0.25 mol %
without erosion of the product yield by conducting at 80 °C.
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10.1002/chem.201703928
Chemistry - A European Journal
COMMUNICATION
a)
5 mol % 1
20 mol % AgOAc
20 mol % Cu(OAc)2•H2O
Gooßen, Chem. Eur. J. 2016, 22, 18654; d) T. Satoh, M. Miura,
Synthesis 2010, 3395.
Ph
Ph
Ph
Ph
Ph
Ph
+
O
[3]
[4]
For recent reviews of decarboxylative coupling reactions using
photoredox catalysts, see: a) Y. Jin, H. Fu, Asian J. Org. Chem. 2017, 6,
368; b) P. Liu, G. Zhang, P. Sun, Org. Biomol. Chem. 2016, 14, 10763.
For selected examples of decarboxylative coupling reactions of
arylcarboxylic acids, see: a) A. G. Myers, D. Tanaka, M. R. Mannion, J.
Am. Chem. Soc. 2002, 124, 11250; b) L. J. Gooßen, G. Deng, L. M.
Levy, Science 2006, 313, 662; c) R. Shang, Y. Fu, Y. Wang, Q. Xu, H.-
Z. Yu, L. Liu, Angew. Chem. Int. Ed. 2009, 48, 9350; Angew. Chem.
2009, 121, 9514; d) C. Wang, I. Piel, F. Glorius, J. Am. Chem. Soc.
2009, 131, 4194; e) P. Hu, M. Zhang, X. Jie, W. Su, Angew. Chem. Int.
Ed. 2012, 51, 227; Angew. Chem. 2012, 124, 231; f) B. Song, T.
Knauber, L. J. Gooßen, Angew. Chem. Int. Ed. 2013, 52, 2954; Angew.
Chem. 2013, 125, 3026.
PhCl, RT or 80 °C, 24 h
under O2
Ph
O
5aa
Ph
3a
(2 equiv)
4aa / <5%
(>95% recovery)
1 (0.005 mmol)
AgOAc (0.02 mmol)
Cu(OAc)2•H2O (0.02 mmol)
O
O
H
CO2H
PhCl, RT or 80 °C, 24 h
under O2
9
2d
(0.12 mmol)
0% (93% recovery, RT)
0% (89% recovery, 80 °C)
CpE
CpE
Rh
b)
CpE
H
2
Rh
OAc
O
Rh
O
–AcOH
–AcOH
AcO
OAc
O
O
A
B
C
D
E
R
R
R
2 Cu(OAc)2
–2 Cu(OAc)
[5]
For selected examples of decarboxylation of arylcarboxylic acids with
directed C–H bond functionalizations, see: a) M. Shimizu, K. Hirano, T.
Satoh, M. Miura, J. Org. Chem. 2009, 74, 3478; b) S. Mochida, K.
Hirano, T. Satoh, M. Miura, Org. Lett. 2010, 12, 5776; c) J. Cornella, M.
Righi, I. Larrosa, Angew. Chem. Int. Ed. 2011, 50, 9429; Angew. Chem.
2011, 123, 9601; d) S. Mochida, K. Hirano, T. Satoh, M. Miura, J. Org.
Chem. 2011, 76, 3024; e) Y. Zhang, H. Zhao, M. Zhang, W. Su, Angew.
Chem. Int. Ed. 2015, 54, 3817; Angew. Chem. 2015, 127, 3888; f) J.
Zhang, R. Shrestha, J. F. Hartwig, P. Zhao, Nat. Chem. 2016, 8, 1144.
K. Ueura, T. Satoh, M. Miura, J. Org. Chem. 2007, 72, 5362.
a) D. A. Loginov, A. O. Belova, A. R. Kudinov, Russ. Chem. Bull. 2014,
63, 983; b) D. A. Loginov, D. V. Muratov, Y. V. Nelyubina, J. Laskova, A.
R. Kudinov, J. Mol. Catal. A: Chem. 2017, 426, 393.
3
CpE
Rh
G
R
Rh CpE
O
R
O
R
O
OH
5
–CO2
R
R
R
R
R
R
R
Rh
R
R
R
R
3
or
R
CpE
[6]
[7]
R
Rh
CpE
Rh
CpE
R
F
4
F'
Scheme 6. a) Mechanistic studies and b) plausible reaction mechanism.
[8]
[9]
a) A. A. Cant, L. Roberts, M. F. Greaney, Chem. Commun. 2010, 46,
8671; b) C. Wang, S. Rakshit, F. Glorius, J. Am. Chem. Soc. 2010, 132,
14006.
In conclusion, we have established that an electron-deficient
CpERhIII complex is capable of catalyzing the decarboxylative
and oxidative [2+2+2] annulation of benzoic acids with alkynes
to produce substituted naphthalenes at room temperature. The
appropriate choice of the additive and the solvent is crucial for
this transformation. This catalyst system allowed use of oxygen
as a terminal oxidant and broadened the substrate scope. In this
catalysis, the electron deficient nature of the CpERhIII catalyst
might account for acceleration of the decarboxylation as well as
the C–H bond cleavage as a result of the strong rhodium-π
interaction. Future works will include further application of the
CpERhIII catalyst to the decarboxylative C–C bond formations.
Although the room temperature decarboxylative coupling reactions of
arylcarboxylic acids was reported, the substrates were limited to 2,6-
dimethoxybenzoic acids and pentafluorobenzoic acid. See: A. Hossian,
S. K. Bhunia, R. Jana, J. Org. Chem. 2016, 81, 2521.
[10] For mechanistic studies of decarboxylation, see: a) S.-L. Zhang, Y. Fu,
R. Shang, Q.-X. Guo, L. Liu, J. Am. Chem. Soc. 2010, 132, 638; b) R.
Shang, Q. Xu, Y.-Y. Jiang, Y. Wang, L. Liu, Org. Lett. 2010, 12, 1000;
c) A. Fromm, C. van Wuellen, D. Hackenberger, L. J. Gooßen, J. Am.
Chem. Soc. 2014, 136, 10007.
[11]
For the C–H bond functionalization catalyzed by the CpERhIII complex,
see: a) Y. Shibata, K. Tanaka, Angew. Chem. Int. Ed. 2011, 50, 10917;
Angew. Chem. 2011, 123, 11109; b) M. Fukui, Y. Hoshino, T. Satoh, M.
Miura, K. Tanaka, Adv. Synth. Catal. 2014, 356, 1638; c) Y. Hoshino, Y.
Shibata, K. Tanaka, Adv. Synth. Catal. 2014, 356, 1577; d) Y.
Takahama, Y. Shibata, K. Tanaka, Chem. Eur. J. 2015, 21, 9053; e) M.
Fukui, Y. Shibata, Y. Hoshino, H. Sugiyama, K. Teraoka, H. Uekusa, K.
Noguchi, K. Tanaka, Chem. Asian J. 2016, 11, 2260; f) E. Kudo, Y.
Shibata, M. Yamazaki, K. Masutomi, Y. Miyauchi, M. Fukui, H.
Sugiyama, H. Uekusa, T. Satoh, M. Miura, K. Tanaka, Chem. Eur. J.
2016, 22, 14190; g) Y. Takahama, Y. Shibata, K. Tanaka, Chem. Lett.
2016, 45, 1177.
Acknowledgements
This work was supported partly by ACT-C (No.
JPMJCR1122YR) from JST (Japan), and Grants-in-Aid for
Scientific Research (No. JP26102004), Research Activity Start-
up (No. 15H06201), and Young Scientists (No. 17K14481) from
JSPS (Japan). We thank Umicore for generous support in
supplying RhCl3•nH2O.
[12] For electronical properties of the CpERhIII complex, see: T. Piou, F.
Romanov-Michailidis, M. Romanova-Michaelides, K. E. Jackson, N.
Semakul, T. D. Taggart, B. S. Newell, C. D. Rithner, R. S. Paton, T.
Rovis, J. Am. Chem. Soc. 2017, 139, 1296.
Keywords: [2+2+2] Annulation • Cyclopentadienyl Complexes •
C–H Functionalization • Decarboxylation • Rhodium
[1]
For recent general reviews of decarboxylative coupling reactions, see:
a) T. Patra, D. Maiti, Chem. Eur. J. 2017, 23, 7382; b) G. J. P. Perry, I.
Larrosa, Eur. J. Org. Chem. 2017, 2017, 3517; c) H. Li, T. Miao, M.
Wang, P. Li, L. Wang, Synlett 2016, 27, 1635; d) W. I. Dzik, P. P.
Lange, L. J. Gooßen, Chem. Sci. 2012, 3, 2671; e) N. Rodriguez, L. J.
Gooßen, Chem. Soc. Rev. 2011, 40, 5030.
[13] For selected examples of the oxidative [4+2] annulation of benzoic
acids with alkynes, see: a) K. Ueura, T. Satoh, M. Miura, Org. Lett.
2007, 9, 1407; b) D. A. Frasco, C. P. Lilly, P. D. Boyle, E. A. Ison, ACS
Catal. 2013, 3, 2421; c) Y. Yu, L. Huang, W. Wu, H. Jiang, Org. Lett.
2014, 16, 2146; d) S. Warratz, C. Kornhaaß, A. Cajaraville, B.
Niepoetter, D. Stalke, L. Ackermann, Angew. Chem. Int. Ed. 2015, 54,
5513; Angew. Chem. 2015, 127, 5604.
[2]
For recent reviews of decarboxylative coupling reactions with directed
C–H bond cleavage, see: a) Y. Wei, P. Hu, M. Zhang, W. Su, Chem.
Rev. 2017, 117, 8864; b) M. Font, J. M. Quibell, G. J. P. Perry, I.
Larrosa, Chem. Commun. 2017, 53, 5584; c) M. Pichette Drapeau, L. J.
[14] See the Supporting Information.
[15] A. K. Dutta, A. Linden, L. Zoppi, K. K. Baldridge, J. S. Siegel, Angew.
Chem. Int. Ed. 2015, 54, 10792; Angew. Chem. 2015, 127, 10942.
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10.1002/chem.201703928
Chemistry - A European Journal
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[16] J.-L. Yu, S.-Q. Zhang, X. Hong, J. Am. Chem. Soc. 2017, 139, 7224.
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10.1002/chem.201703928
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Entry for the Table of Contents (Please choose one layout)
COMMUNICATION
cat. [CpERhCl2]2
cat. AgOAc or NaOAc
cat. Cu(II)
R2
Yusaku Honjo, Yu Shibata,* Eiji Kudo,
Tomoya Namba, Koji Masutomi, and
Ken Tanaka*
R2
H
R3
R3
CO2Et
R1
Me
R1
Me
Cl
OH
+
PhCl or toluene
RT (or 80 °C)
under O2 (air)
(–CO2, –H2O)
Rh
EtO2C Cl
Me
R3
O
R2
2
[CpERhCl2]2
48–98% yields
(20 examples)
Page No. – Page No.
It has been established that an electron-deficient (η5-cyclopentadienyl)rhodium(III)
[CpERhIII] complex is capable of catalyzing the decarboxylative and oxidative
[2+2+2] annulation of benzoic acids with alkynes to produce substituted
naphthalenes at room temperature. This catalyst system allowed use of oxygen as
a terminal oxidant and broadened the substrate scope including both aromatic and
aliphatic alkynes.
Room Temperature Decarboxylative
and Oxidative [2+2+2] Annulation of
Benzoic Acids with Alkynes
Catalyzed by an Electron-Deficient
Rhodium(III) Complex
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