Oxidative Annulation of Arenecarboxylic and Acrylic Acids with Alkynes under Ambient Conditions Catalyzed by an Electron-Deficient Rhodium(III) Complex

Article abstract of DOI:10.1002/chem.201603499

It has been established that an electron-deficient Cp^Erhodium(III) complex catalyzes the oxidative [4+2] annulation of substituted arenecarboxylic and acrylic acids with alkynes under ambient conditions (at RT–40 °C, under air) without using excess amounts of substrates to produce the corresponding substituted isocoumarins and α-pyrones in high yields. Minor modification of reaction conditions depending on the coordination ability of alkynes realized the high efficiency.

Full text of DOI:10.1002/chem.201603499

A Journal of
Accepted Article
Title: Oxidative Annulation of Arenecarboxylic and Acrylic Acids with Alkynes Under
Ambient Conditions Catalyzed by an Electron-Deficient Rhodium(III) Complex
Authors: Eiji Kudo; Yu Shibata; Mutsumi Yamazaki; Koji Masutomi; Yuta Miyauchi;
Miho Fukui; Haruki Sugiyama; Hidehiro Uekusa; Tetsuya Satoh; Masahiro Mi-
ura; Ken Tanaka
This manuscript has been accepted after peer review and the authors have elected
to post their 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 pu-
blished 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.201603499
Link to VoR: http://dx.doi.org/10.1002/chem.201603499
Supported by

Chemistry - A European Journal
10.1002/chem.201603499
COMMUNICATION
Oxidative Annulation of Arenecarboxylic and Acrylic Acids with
Alkynes Under Ambient Conditions Catalyzed by an Electron-
Deficient Rhodium(III) Complex
Eiji Kudo,[a] Yu Shibata,*,[a] Mutsumi Yamazaki,[b] Koji Masutomi,[a] Yuta Miyauchi,[a] Miho Fukui,[a,b]
Haruki Sugiyama,[c] Hidehiro Uekusa,[c] Tetsuya Satoh,[d,e] Masahiro Miura,[d] and Ken Tanaka*,[a,b]
Abstract: It has been established that an electron-deficient CpE
rhodium(III) complex catalyzes the oxidative [4+2] annulation of
substituted arenecarboxylic and acrylic acids with alkynes under
ambient conditions (at RT–40 °C, under air) without using excess
amounts of substrates to produce the corresponding substituted
isocoumarins and α-pyrones in high yields. Minor modification of
reaction conditions depending on the coordination ability of alkynes
realized the high efficiency.
showed high catalytic activity for oxidative coupling reactions via
cleavage of sp2 C–H bonds on electron-rich aromatic rings under
ambient conditions (at RT, under air).[10,11] The observed high
catalytic activity might be induced by the strong π-metal
interaction between the electron-rich aromatic rings and the
highly electrophilic rhodium in the transition state of the C–H
bond cleavage. It was anticipated that an electron-rich benzoate
salt would show high reactivity in the CpE rhodium(III)-catalyzed
oxidative annulation with alkynes as a result of the strong π-
metal interaction. In this paper, we succeeded this
transformation under ambient conditions with the wide substrate
scope by minor modification of reaction conditions depending on
the coordination ability of alkynes (Scheme 1, bottom).
Transition-metal catalyzed oxidative annulations with alkynes
via cleavage of sp2 C–H bonds are powerful methods for the
construction of carbocycles and heterocycles.[1] For example,
the oxidative [4+2] annulation of benzoic and acrylic acids with
alkynes produces isocoumarins and α-pyrones,[2] respectively, in
a highly step- and atom-economical manner (Scheme 1, top).[3–9]
In 2007, Satoh and Miura developed the first example of the
oxidative [4+2] annulation of benzoic acids with alkynes using a
Cp* rhodium(III) complex as a catalyst, and Cu(OAc)2•H2O and
air as oxidants.[3] They subsequently reported the annulation of
acrylic acids instead of benzoic acids by using Ag2CO3 as an
oxidant.[4] Not only rhodium(III) complex[5] but also iridium(III),[6]
ruthenium(II),[7] and palladium(II)[8] complexes can catalyze this
annulation, however, these reactions required high temperature
(≥90 °C), stoichiometric metal oxidants, and/or excess amounts
of substrates. Therefore, a new catalyst system, which shows
the satisfyingly wide substrate scope under ambient conditions
without using stoichiometric metal oxidants and excess amounts
of substrates, remains a challenge. On the other hand, we
reported that electron-deficient CpE rhodium(III) complex 1[10a]
Previous work
R2
RhIII, IrIII, RuII, or PdII
catalyst
R2
R3
R1
R1
OH
+
O
R3
Satoh and Miura (benzoic acids in 2007):
cat. [Cp*RhCl2 2/Cu(OAc)2¥H2O, acid/alkyne = 1:1.2, 120 ¡C, under air
Satoh and Miura (acrylic acids in 2009):
cat. [Cp*RhCl2 2, Ag2CO3, acid/alkyne = 1:1, 120 ¡C
Ison (benzoic acids in 2013):
cat. [Cp*IrCl2 2, AgOAc, acid/alkyne = 1:1, 60 ¡C
O
O
]
]
]
Ackerm ann (benzoic acids in 2012, 2015):
cat. [RuCl2(p-cymene)]2, NaOAc, acid/alkyne = 2:1, 45 ¡C, under O2
Gogoi (acrylic acids, in 2015):
cat. [RuCl2(p-cymene)]2, Cu(OAc)2¥H2O, acid/alkyne = 1:1, 90 ¡C
Jiang (acrylic acids in 2014):
cat. Pd(OAc)2/CuBr2, Et3N, acid/alkyne = 1:1.5, 90 ¡C, under O2
This work
CO2Et
Me
Me
Cl
R h
Cl
Me
EtO 2
R3
C
R2
R1
2
R3
R2
R1
R4
[CpERhCl2
] catalyst (1)
2
OH
+
O
cat. AgNTf2
cat. Cu(OAc)2¥H2
(cat. NaOAc)
R4
O
O
O
(1.1 equiv)
RTĞ40 ¡C, under air
[a]
E. Kudo, Dr. Y. Shibata, K. Masutomi, Dr. Y. Miyauchi, M. Fukui,
Prof. Dr. K. Tanaka
Department of Chemical Science and Engineering, Tokyo Institute
of Technology, O-okayama, Meguro-ku, Tokyo 152-8550, Japan
E-mail: yshibata@apc.titech.ac.jp
Scheme 1. Transition-metal-catalyzed oxidative [4+2] annulations of benzoic
and acrylic acids with alkynes.
First we screened the reaction conditions using 1.1 equiv of
benzoic acid (2a) and 1.0 equiv of three types of alkynes,
diphenylacetylene (3a), 1-phenyl-1-propyne (3b), and 6-
dodecyne (3c). As a result, we established three reaction
conditions A–C depending on the coordination ability of alkynes
to the cationic rhodium (Table 1). When using weakly
coordinating 3a, the desired annulation proceeded in the
presence of 1 (2.5 mol %), AgNTf2 (12.5 mol %), and
Cu(OAc)2•H2O (5 mol %) in (CH2Cl)2 at RT under air to give
isocoumarin 4aa in excellent yield (conditions A, entry 1). In
sharp contrast, the use of [Cp*RhCl2]2 instead of 1 afforded only
a trace amount of 4aa (entry 2). However, the reaction of
moderately coordinating 3b afforded 4ab in low yield (entry 3)
and that of strongly coordinating 3c afforded only a trace
amount of 4ac (entry 4). On the other hand, the conditions B
E-mail: ktanaka@apc.titech.ac.jp
http://www.apc.titech.ac.jp/~ktanaka/
M. Yamazaki, M. Fukui, Prof. Dr. K. Tanaka
Department of Applied Chemistry, Graduate School of Engineering,
Tokyo University of Agriculture and Technology, Koganei, Tokyo
184-8588, Japan
[b]
[c]
[d]
[e]
H. Sugiyama, Prof. Dr. H. Uekusa
Department of Chemistry, Tokyo Institute of Technology, O-
okayama, Meguro-ku, Tokyo 152-8550, Japan
Prof. Dr. T. Satoh, Prof. Dr. M. Miura
Department of Applied Chemistry, Faculty of Engineering, Osaka
University, Suita, Osaka 565-0871, Japan
Prof. Dr. T. Satoh
Department of Chemistry, Graduate School of Science, Osaka City
University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585,
Japan
Supporting information for this article is given via a link at the end of
the document

Chemistry - A European Journal
10.1002/chem.201603499
COMMUNICATION
using moderately coordinating acetone as a solvent and an
increasing amount of Cu(OAc)2•H2O (20 mol %) at 40 °C was
found to be effective for 3b (entry 6), while a slight decrease and
modest increase of the product yield were observed for 3a and
3c, respectively (entries 5 and 7). Pleasingly, the addition of
NaOAc (20 mol %) to conditions A significantly increased the
yield of 4ac (conditions C, entry 10), while this protocol was not
effective for 3a and 3b (entries 8 and 9).
with good to perfect regioselectivities, although high catalyst
loadings were required for 3k and 3l. Highly electron-rich
diarylacetylene 3m, and dialkyl acetylenes 3c and 3n reacted
with 2a under the conditions C to give isocoumarins 4am, 4ac,
and 4an in high yields. Importantly, thus obtained electron-rich
isocoumarin 4am could be converted to -lactone 5 by oxidative
rearrangement.[12] Interestingly, the reaction of 2n with 3c
afforded oxepin 4nc’ as well as α-pyrone 4nc.
Notably, non-fused α-pyrones could also be prepared under
the conditions A by the oxidative annulation of acrylic acid
derivatives with alkynes regardless of their coordination abilities
(Scheme 2). Various 2-substituted and 2,3-disubstituted acrylic
acids 2o–r reacted with 3a to give α-pyrones 4oa–ra in good to
high yields, although high catalyst loadings were required for
2p–r. Unsymmetrical alkynes 3f and 3j could also react with 2o
to give 4of/4of’ and 4oj/4oj’ in high yields, while the
regioselectivities were low. Furthermore, highly coordinating
dialkylacetylene 3c reacted with 2o by using 20 mol % of
Cu(OAc)2 to give 4oc in high yield presumably due to possible
bidentate coordination of 2o to rhodium.
In the course of the reaction optimization, we found that the
reaction of 2a with 3a in DMF resulted in low substrate
conversion and afforded isocoumarin-coordinating rhodium(I)
complex 6 (Scheme 3a). The reaction of 2a with 3a using a
catalytic amount of 6 instead of 1 afforded 4aa in high yield
(Scheme 3b). These results indicate that 6 is the intermediate of
the present oxidative [4+2] annulation and DMF deters oxidative
decomplexation of 6. Thus, the oxidative decomplexation of 6
was examined by using various oxidants and additives (Scheme
3c). Surprisingly no reaction was observed using the copper(II)
oxidant under argon (entry 1). Instead, the reaction with NaNTf2
under air afforded 4aa in 25% yield (entry 2). The use of both
the copper(II) oxidant and NaNTf2 under argon afforded 4aa in
Table 1. Optimized conditions depending on coordination ability of alkynes 3.[a]
R1 (R2
R2 (R1
)
R1
2.5 mol % 1
12.5 mol % AgNTf2
)
OH
+
O
conditions AĞC
under air
R2
O
O
2a
(1.1 equiv)
3a (R1
3b (R1
3c (R1
=
=
=
R2
Me, R2 = Ph)
R2
n-C5H11
= Ph)
4 (4')
=
)
conditions A: 5 mol % Cu(OAc)2¥H2O, (CH2Cl)2, RT
conditions B: 20 mol % Cu(OAc)2¥H2O, acetone, 40 ¡C
conditions C: 5 mol % Cu(OAc)2¥H2O, 20 mol % NaOAc, (CH2Cl)2, RT
Entry
Conditions
3
4
Yield
[%][b]
97
2
r.s.[b]
1
2[c]
3
A (24 h)
A (24 h)
A (24 h)
A (24 h)
B (72 h)
B (72 h)
B (72 h)
C (72 h)
C (72 h)
C (72 h)
3a
3a
3b
3c
3a
3b
3c
3a
3b
3c
4aa
4aa
–
–
4ab (4ab’)
4ac
36
3
89:11
4
–
–
5
4aa
95
73
38
11
40
87
6
4ab (4ab’)
4ac
91:9
–
7
8
4aa
–
9
4ab (4ab’)
4ac
88:12
–
10
[a] Conditions A: 1 (0.0050 mmol), AgNTf2 (0.025 mmol), Cu(OAc)2•H2O
(0.010 mmol), 2 (0.22 mmol), 3 (0.20 mmol), and (CH2Cl)2 (1.0 mL) were used.
Conditions B: Cu(OAc)2•H2O (0.040 mmol) was used. Conditions C: NaOAc
(0.040 mmol) was used. [b] Determined by 1H NMR using 1,1,2,2-tetra-
chloroethane as an internal standard. [c] [Cp*RhCl2]2 was used instead of 1.
the highest yield (entry 3). These facts suggest that coordination
Wide substrate scope was realized by employing the above
protocols (Scheme 2). With respect to weakly coordinating
alkynes under the conditions A, not only 3a but also electron-
deficient diarylacetylene 3d reacted with 2a to afford 4ad in high
yield. The reactions of 2a with unsymmetrical alkynes bearing
tert-butyl (3e), cyclohexyl (3f), and chloropropyl (3g) groups
afforded 4ae–ag in high yields. In these reactions, the opposite
regioselectivities were observed between 3e and 3f,g. With
respect to benzoic acids, para, meta-, and ortho-substituted
ones 2b–g could equally participate in this reaction regardless of
their electron densities, although regioselectivities were poor
(4ea/4ea’) to moderate (4fa/4fa’). Importantly, sterically
hindered 3,5-dimethylbenzoic acid (2h) also reacted with 3a to
give 4ha in good yield. In the reaction of 2-naphthalene-
carboxylic acid (2i), the C–H bond at the 3-position was cleaved
in preference to the 1-position to give 4ia as a major product.
Not only benzoic acids but also indole-, thiophene-, and furan-
carboxylic acids 2j–m reacted with 3a under the conditions A to
give 4ja–ma in good to high yields. With respect to moderately
coordinating alkynes under the conditions B, electron-rich
diarylacetylenes 3h and 3i reacted with 2a and 2n to give 4ah,
4ai, and 4ni in good yields. With respect to unsymmetrical
alkynes, not only 1-phenyl-1-propyne (3b) but also hexyl (3j),
methoxymethyl (3k), and cyclopropyl (3l) substituted
phenylacetylenes reacted with 2a to give 4aj–l in good yields
–
of NTf2
to rhodium may accelerate the oxidative
decomplexation. Contrary to the oxidative decomplexation of an
isocoumarin-ruthenium(0) complex reported by Ackermann,[7d]
the use of acetic acid under air was ineffective (entry 4).
In order to gain mechanistic insights into the C–H bond
cleavage step using 1, we conducted the deuterium-labeling
experiments (Scheme 4). The reaction of benzoic acid-d5 (2a-
[D5]) with 3a under the conditions A furnished 4aa-[D5] (Scheme
4a). As almost no loss of deuterium from 4aa-[D5] was observed,
the metalation of the benzoic acid was found to be irreversible.
The intermolecular competition experiments between 2a and 2a-
[D5] in the presence of 3a (conditions A) or 3c (conditions C)
revealed large DKIE values of 8.1 and 6.7, respectively (Scheme
4b).[13] These facts suggest that the rate-determining step
involves the C-H bond cleavage.
A plausible mechanism for the oxidative [4+2] annulation of 2
with 3 is shown in Scheme 5. First, a cationic rhodium species A
is likely generated by the reaction of 1, AgNTf2, and Cu(OAc)2.
Next, coordination of 2 through deprotonation forms rhodium(III)
carboxylate B. Cyclometalation through cleavage of the ortho-
C–H bond furnishes rhodacycle C. Coordination and subsequent
insertion of 3 to C give rhodacycle D. When using benzoic acid
(2a), bulky substituents (R1) of alkynes reside in α-position to
rhodium in order to avoid steric repulsion to the aromatic
hydrogen in D’. On the contrary, when using methacrylic acid

Chemistry - A European Journal
10.1002/chem.201603499
COMMUNICATION
R3
R2
R1
R3
2.5 mol %
12.5 mol % AgNTf2
1
R2
R1
R4
+
OH
O
conditions AĞC
under air
O
R4
O
4 [4' (regioisomer)]
2 (1.1 equiv)
3
conditions
A
Cl
(weakly coordinating alkynes)
Ph
Ph
Ph (tBu)
tBu (Ph)
Cy (Ph)
Ph (Cy)
(CH2
)
3Cl [Ph]
Ph
Cl
Ph [(CH2
)
3Cl]
Me
Ph
O
O
O
O
O
O
O
O
O
O
O
96% (4aa, 24 h)
80% (4ad, 24 h)
86% (4ae/4ae' = 78:22[a], 24 h)
96% (4af/4af' = 74:26[a], 48 h)
82% (4ag/4ag' = 83:17[a], 24 h)
92% (4ba, 24 h)
O
Ph
Ph
Ph
(MeO) H
(H) F
Ph
Ph
Me Ph
Ph
Ph
MeO
Ph
Ph
Ph
Ph
O
O
O
O
O
O
O
Me
(H) MeO
(F) H
Me
Me
O
O
O
O
O
98% (4ca, 24 h)
97% (4da, 24 h)
90% (4ea/4ea' = 56:44,[a] 24 h)
92% (4fa/4fa' =80:20,[a] 72 h)
>99% (4ga, 24 h)
60% (4ha, 72 h)
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
O
S
+
O
O
O
O
O
O
N
S
Me
O
O
O
O
O
O
91% (4ia/4ia' = 87:13[a], 24 h)
75% (4ja, 70 h)
84% (4ka, 72 h)
74% (4la, 48 h)
52% (4m a, 72 h)
conditions
B
(m oderately coordinating alkynes)
Me
n-C5H11
n-C5H11
MeO
(Ph)
Ph
O
R
O
(Ph)
Ph (R)
Me
n-C5H11
n-C5H11
Ph
Me
N
O
O
O
O
O
O
O
76% (4al/4al' = 88:12[a], 72 h)[b]
O
conditions
73% (4ah, 72 h)
O
78% (4ai, 72 h)
O
60% (4ni, 45 h)
68% [4ab/4ab' = 91:9[a], R
=
=
Me, 72 h)
nBu, 72 h)
62% (4ak, 72 h)[b]
84% [4aj/4aj' = 87:13[a], R
C
(strongly coordinating alkynes)
OMe
MeO
Me
N
1) m CPBA (3 equiv)
CH2Cl2, RT, 24
n-C5H11
n-C5H11
nPr
nPr
n-C5H11
Me
O
OMe
h
O
n-C5H11
N
+
2) 10 mol % TsOH¥H2
CH2Cl2, RT, 1
O
O
O
O
O
O
O
O
h
OMe
O
n-C5H11
n-C5H11
O
O
5
/ 54%
50% (4nc, 72 h)[c]
O
82% (4am, 72 h)
86% (4ac, 72 h)
82% (4an, 72 h)
24% (4nc')
conditions
A
(acrylic acid derivatives)
Ph
Ph
O
Ph
Cy (Ph)
Ph (Cy)
nBu (Ph)
Ph (nBu)
n-C5H11
Ph
Me
Ph
Ph
n-C5H11
O
O
O
O
O
O
O
R
Me
Me
Me
Me
O
O
O
O
76% (4qa, 72 h)[d]
51% (4ra, 72 h)[d]
89% (4of/4of' = 56:44[a], 43 h)
89% (4oj/4oj' = 60:40[a], 43 h)
82% (4oc, 72 h)[e]
91% (4oa, R
67% (4pa, R
=
=
Me, 48 h)
Ph, 72 h)[d]
Scheme 2. Substrate scope. Conditions A–C: see Table 1. [a] Ratios of regioisomers. [b] 1 (5 mol %), AgNTf2 (25 mol %), and Cu(OAc)2•H2O (40 mol %) were
used. [c] At 40 °C. [d] 1 (5 mol %), AgNTf2 (25 mol %), and Cu(OAc)2•H2O (10 mol %) were used. [e] Cu(OAc)2•H2O (20 mol %) was used.
2.5 mol %
12.5 mol % AgNTf2
1
D
D
Ph
2.5 mol %
12.5 mol % AgNTf2
mol % Cu(OAc)2¥H2
1
CpE
Rh
Ph
D
D
D
D
D
Ph
5
mol % Cu(OAc)2¥H2O
+
(a)
5
O
O
OH
O
(a)
(CH2Cl)2, RT, 24 h
under air
+
4aa
2a
+
3a
O
DMF, RT, 24
under air
h
Ph
(1.1 equiv)
D
O
D
O
2%
Ph
Ph
2a-[D5
]
3a
<1%
H
6 / 67% based on
1
(1.1 equiv)
4aa-[D5] / 69%
5
mol %
6
Ph
Ph
12.5 mol % AgNTf2
2.5 mol %
12.5 mol % AgNTf2
1
R
5
mol % Cu(OAc)2¥H2
O
R
R
R
2a
3a
+
(b)
5
mol % Cu(OAc)2¥H2O
O
(CH2Cl)2, RT, 24 h
under air
OH
(1.1 equiv)
+
(b)
O
(CH2Cl)2, RT, 1 h
under air
H4/D4
O
H4/D4
O
O
4aa / 87%
2a/2a-[D5
]
3a (R = Ph)
n-C5H11, 20 mol % NaOAc)
4aa/4aa-[D4] = 8.1 (17% yield)
4ac/4ac-[D4] = 6.7 (9% yield)
additive
(0.55 + 0.55 equiv) 3c (R
=
6
4aa
(c)
(CH2Cl)2, RT, 16
h
Scheme 4. Deuterium-labeling experiments.
Entry
Additive
Yield [% ]
(2o), steric hindrance in D’ may be small, therefore, the
reactions of 2o with unsymmetrical alkynes resulted in low
regioselectivity. From D, C–O reductive elimination affords
rhodium(I) complex 6. This rhodium(I) complex 6 is oxidized by
copper(II) oxidant in the presence of the counteranion NTf2 to
regenerate the active rhodium(III) complex A and the resulting
1
2
3
4
Cu(OAc)2¥H2
O
(2 equiv), under Ar
<5
25
NaNTf2 (2 equiv ), under air
Cu(OAc)2¥H2 (2 equiv), NaNTf2 (2 equiv), under Ar
AcOH (50 equiv), under air
O
40
9
–
Scheme 3. (a) Isolation, (b) catalytic activity, and (c) oxidative decomplexation
of isocoumarin-coordinating CpERhI complex 6.
copper(I) is reoxidized by molecular oxygen in air.

Chemistry - A European Journal
10.1002/chem.201603499
COMMUNICATION
R2
grateful to Umicore for generous support in supplying the
rhodium complex.
R1
X
= NTf2, OAc, or OCOR
O
2
AcOH
O
1/2 O2
H
CpE
=
4
Keywords: Alkynes • Annulation • Isocoumarins • α-Pyrones •
Me
H2
O
OH
Me
EtO2
C
+
Cu(I)
Rhodium
O
2
Me
CO2Et
Rh
Cu(II)
OAcĞ, NTf2
X
Ğ
XH
A
[1]
For recent reviews, see: a) Y. Yang, K. Li, Y. Cheng, D. Wan, M. Li, J.
You, Chem. Commun. 2016, 52, 2872; b) C. G. Newton, D. Kossler, N.
Cramer, J. Am. Chem. Soc. 2016, 138, 3935; c) T. Gensch, M. N.
Hopkinson, F. Glorius, J. Wencel-Delord, Chem. Soc. Rev. 2016, 45,
2900; d) M. Miura, T. Satoh, K. Hirano, Bull. Chem. Soc. Jpn. 2014, 87,
751; e) S. I. Kozhushkov, L. Ackermann, Chem. Sci. 2013, 4, 886; f) G.
Song, F. Wang, X. Li, Chem. Soc. Rev. 2012, 41, 3651; g) P. B.
Arockiam, C. Bruneau, P. H. Dixneuf, Chem. Rev. 2012, 112, 5879; h)
J. Wencel-Delord, T. Droege, F. Liu, F. Glorius, Chem. Soc. Rev. 2011,
40, 4740; i) T. Satoh, M. Miura, Chem. Eur. J. 2010, 16, 11212.
For recent reviews, see: a) J. S. Lee, Mar. Drugs 2015, 13, 1581; b) S.
Pal, V. Chatare, M. Pal, Curr. Org. Chem. 2011, 15, 782; c) A. Goel, V.
J. Ram, Tetrahedron 2009, 65, 7865.
CpE
Rh
3
CpE
H
Rh
O
CpE
O
O
R1
Rh
R1
R2
X
R1
O
R2
R2
B
6
E
X
R2
CpE
R1
XH
Rh
Rh CpE
O
O
–
RCO2
O
[2]
RL
O
H
RS
Rh CpE
C
R2
R1
D
CpE
Rh
3
O
[3]
[4]
a) K. Ueura, T. Satoh, M. Miura, Org. Lett. 2007, 9, 1407; b) K. Ueura,
T. Satoh, M. Miura, J. Org. Chem. 2007, 72, 5362.
O2CR
O
O
D'
disfavored
O
a) S. Mochida, K. Hirano, T. Satoh, M. Miura, J. Org. Chem. 2009, 74,
6295; b) M. Itoh, M. Shimizu, K. Hirano, T. Satoh, M. Miura, J. Org.
Chem. 2013, 78, 11427.
F
estim ated coordination ability to rhodium
n-C5H11
n-C5H11
Ph
Me
Ph
O
O
[5]
a) M. Shimizu, K. Hirano, T. Satoh, M. Miura, J. Org. Chem. 2009, 74,
3478; b) Q. Li, Y. Yan, X. Wang, B. Gong, X. Tang, J. Shi, H. E. Xu, W.
Yi, RSC Adv. 2013, 3, 23402; c) Y. Unoh, K. Hirano, T. Satoh, M. Miura,
Tetrahedron 2013, 69, 4454.
O
OH
O
Me
Me
Ph
weak
strong
[6]
[7]
D. A. Frasco, C. P. Lilly, P. D. Boyle, E. A. Ison, ACS Catal. 2013, 3,
2421.
Scheme 5. Plausible mechanism for the formation of 4.
a) L. Ackermann, J. Pospech, K. Graczyk, K. Rauch, Org. Lett. 2012,
14, 930; b) R. K. Chinnagolla, M. Jeganmohan, Chem. Commun. 2012,
48, 2030; c) M. Deponti, S. I. Kozhushkov, D. S. Yufit, L. Ackermann,
Org. Biomol. Chem. 2013, 11, 142; d) S. Warratz, C. Kornhaass, A.
Cajaraville, B. Niepoetter, D. Stalke, L. Ackermann, Angew. Chem. Int.
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Shekarrao, S. Gogoi, Org. Lett. 2015, 17, 5264; f) K. S. Singh, S. G.
Sawant, P. H. Dixneuf, ChemCatChem 2016, 8, 1046.
Beneficial effects of minor modification of reaction conditions
can be explained as follows. Coordination of two molecules of
strongly coordinating alkynes to A giving inactive species E
results in low conversion of 2 under the conditions A. When
adding NaOAc (conditions C), strong coordination of in situ
generated carboxylate anion to A accelerates the reactions with
the strongly coordinating alkynes, although this carboxylate
anion may coordinate to C giving inactive species F, which
inhibits the coordination of weakly coordinating alkynes. When
using moderately coordinating alkynes, the use of moderately
[8]
[9]
Y. Yu, L. Huang, W. Wu, H. Jiang, Org. Lett. 2014, 16, 2146.
For the oxidative [4+2] annulation of benzoic acids with alkenes leading
to isocoumarins, see: a) D. Nandi, D. Ghosh, S.-J. Chen, B.-C. Kuo, N.
M. Wang, H. M. Lee, J. Org. Chem. 2013, 78, 3445; b) M. Zhang, H.-J.
Zhang, T. Han, W. Ruan, T.-B. Wen, J. Org. Chem. 2015, 80, 620.
coordinating acetone as
a
solvent at slightly elevated
[10] a) Y. Shibata, K. Tanaka, Angew. Chem. Int. Ed. 2011, 50, 10917;
Angew. Chem. 2011, 123, 11109; b) Y. Hoshino, Y. Shibata, K. Tanaka,
Adv. Synth. Catal. 2014, 356, 1577; c) M. Fukui, Y. Hoshino, T. Satoh,
M. Miura, K. Tanaka, Adv. Synth. Catal. 2014, 356, 1638; d) Y.
Takahama, Y. Shibata, K. Tanaka, Chem. Eur. J. 2015, 21, 9053; e) Y.
Takahama, Y. Shibata, K. Tanaka, Org. Lett. 2016, 18, 2934.
temperature (conditions B) facilitates ligand exchange through
equilibration between intermediates A and E, and C and F via
acetone-coordinating rhodium species.[14]
In conclusion, we have established that an electron-deficient
CpE rhodium(III) complex catalyzes the oxidative [4+2]
annulation of substituted arenecarboxylic and acrylic acids with
alkynes under ambient conditions (at RT–40 °C, under air)
without using excess amounts of substrates to produce the
corresponding substituted isocoumarins and α-pyrones in high
yields. Minor modification of reaction conditions depending on
the coordination ability of alkynes realized the high efficiency.
[11] For recent examples of sterically and electronically tuned Cp ligands in
the rhodium(III)-catalyzed C–H functionalization, see: a) R. Zeng, J. Ye,
C. Fu, S. Ma, Adv. Synth. Catal. 2013, 355, 1963; b) T. Piou, T. Rovis,
J. Am. Chem. Soc. 2014, 136, 11292; c) M. D. Wodrich, B. Ye, J. F.
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d) J. M. Neely, T. Rovis, J. Am. Chem. Soc. 2014, 136, 2735; e) F.
Romanov-Michailidis, K. F. Sedillo, J. M. Neely, T. Rovis, J. Am. Chem.
Soc. 2015, 137, 8892; f) T. Piou, T. Rovis, Nature 2015, 527, 86.
[12] a) T. Opatz, D. Ferenc, Eur. J. Org. Chem. 2005, 121; b) S. J. Eade, R.
M. Adlington, A. R. Cowley, M. W. Walter, J. E. Baldwin, Org. Lett.
2005, 7, 3705.
Acknowledgements
[13] The observed DKIE values were larger than that of the RuII-catalyzed
annulation of 2a/2a-[D5] with 3n (DKIE value = 4.5). See ref 7d.
[14] a) K. Tanaka, R. Tanaka, G. Nishida, M. Hirano, Synlett 2008, 2017; b)
Y. Otake, R. Tanaka, K. Tanaka, Eur. J. Org. Chem. 2009, 2737.
This work was supported partly by ACT-C from JST (Japan),
Grants-in-Aid for Scientific Research (Nos. 26102004 and
25105714) from MEXT (Japan), and a Grant-in-Aid for Research
Activity Start-up (No. 15H06201) from JSPS (Japan). We are

Chemistry - A European Journal
10.1002/chem.201603499
COMMUNICATION
COMMUNICATION
R3
R2
Eiji Kudo, Yu Shibata,* Mutsumi
Yamazaki, Koji Masutomi, Yuta
Miyauchi, Miho Fukui, Tetsuya Satoh,
Masahiro Miura, Haruki Sugiyama,
Hidehiro Uekusa, and Ken Tanaka*
R3
CO2Et
R2
R1
R4
[CpERhCl2]2 catalyst
Me
Me
Cl
OH
+
R1
Rh
Cl
O
Me
EtO2
cat. AgNTf2
C
R4
2
O
cat. Cu(OAc)2¥H2
O
O
[CpERhCl2]2
(cat. NaOAc)
(1.1 equiv)
51Ğ>99% yield
(35 exam ples)
RTĞ40 ¡C, under air
Page No. – Page No.
It has been established that an electron-deficient CpE rhodium(III) complex
catalyzes the oxidative [4+2] annulation of substituted arenecarboxylic and acrylic
acids with alkynes under ambient conditions (at RT–40 °C, under air) without using
excess amounts of substrates to produce the corresponding substituted
isocoumarins and α-pyrones in high yields. Minor modification of reaction conditions
depending on the coordination ability of alkynes realized the high efficiency.
Oxidative Annulation of
Arenecarboxylic and Acrylic Acids
with Alkynes Under Ambient
Conditions Catalyzed by an Electron-
Deficient Rhodium(III) Complex