Rh(I)-catalyzed carbonylative cyclization reactions of alkynes with 2-bromophenylboronic acids leading to indenones

Article abstract of DOI:10.1021/ja070107n

The Rh-catalyzed reaction of alkynes with 2-bromophenylboronic acids involves carbonylative cyclization to give indenones. The key steps in the reaction involve the addition of an arylrhodium(I) species to an alkyne and the oxidative addition of C-Br bond

Full text of DOI:10.1021/ja070107n

Published on Web 04/07/2007
Rh(I)-Catalyzed Carbonylative Cyclization Reactions of
Alkynes with 2-Bromophenylboronic Acids Leading to
Indenones
Yasuyuki Harada, Jun Nakanishi, Hirokazu Fujihara, Mamoru Tobisu,
Yoshiya Fukumoto, and Naoto Chatani*
Contribution from the Department of Applied Chemistry, Faculty of Engineering, Osaka
UniVersity, Suita, Osaka 565-0871, Japan
Received January 6, 2007; E-mail: chatani@chem.eng.osaka-u.ac.jp
Abstract: The Rh-catalyzed reaction of alkynes with 2-bromophenylboronic acids involves carbonylative
cyclization to give indenones. The key steps in the reaction involve the addition of an arylrhodium(I) species
to an alkyne and the oxidative addition of C-Br bonds on the adjacent phenyl ring to give vinylrhodium(I)
species II. The regioselectivity depends on both the electronic and the steric nature of the substituents on
the alkynes. A bulky group and an electron-withdrawing group favor the R-position of indenones. In the
case of silyl- or ester-substituted alkynes, the regioselectivity is extremely high. The selectivity increases
in the order SiMe3 > COOR . aryl . alkyl. The reaction of norbornene with 2-bromophenylboronic acids
under 1 atm of CO gives the corresponding indanone derivative. The reaction of alkynes with 2-bromophe-
nylboronic acids under nitrogen gives naphthalene derivatives, in which two molecules of alkynes are
incorporated. A vinylrhodium complex similar to II can also be generated by a different route by employing
2-bromophenyl(trimethylsilyl)acetylene and arylboronic acids in the presence of Rh(I) complex as the catalyst,
resulting in the formation of indenones. The reaction of 1-(2-bromophenyl)-hept-2-yn-1-one with PhB(OH)2
in the presence of Rh(I) complex also resulted in carbonylative cyclization to give an indan-1,3-dione
derivative.
Introduction
arylboronic acids catalyzed by Rh(I) complexes gives styrene
derivatives and that the reaction does not proceed via the direct
The use of organoboron reagents in transition metal-catalyzed
reactions has generated considerable interest in organic synthesis
because of their unique reactivities, the diversity of transforma-
tions that can be achieved, and the extremely high functional
group compatibility.1 A variety of reactions in which organobo-
ron reagents are used has been developed thus far as efficient
methods for the formation of carbon-carbon bonds. Among
them, the addition of arylboronic acids to alkynes, catalyzed
by Rh,2-9 Ni,10 and Pd complexes,11 has been the subject of
extensive study. Hayashi found that the reaction of alkynes with
protonation of an initially generated vinylrhodium complex, but
a 1,4-shift of the hydride in the vinylrhodium complexes takes
place prior to the direct protonation.2a In addition to protonoly-
sis,2 vinylrhodium complexes are reported to undergo nucleo-
philic attack on various intramolecular electrophiles,3 such as
aldehydes,4 ketones,4,5 esters,4a,6 nitriles,7 R,â-unsaturated esters,8
and allyl ethers.9 A 1,4-shift of a hydride not only in rhodium
complexes but also palladium and platinum complexes has been
of considerable interest in the sense of organic chemistry as
well as organometallic chemistry.12 A 1,4-shift of other func-
tional groups X, such as alkoxy, alkylthio, or halides, in II
leading to III is also interesting, which might lead to new
(1) For reviews, see: (a) Miyaura, N.; Suzuki, A. Chem. ReV. 1995, 95, 2457-
2483. (b) Fagnou, K.; Lautens, M. Chem. ReV. 2003, 103, 169-196. (c)
Hayashi, T.; Yamasaki, K. Chem. ReV. 2003, 103, 2829-2844. (d) Darses,
S.; Geneˆt, J.-P. Eur. J. Org. Chem. 2003, 4313-4327.
(2) (a) Hayashi, T.; Inoue, K.; Taniguchi, N.; Ogasawara, M. J. Am. Chem.
Soc. 2001, 123, 9918-9919. (b) Lautens, M.; Yoshida, M. Org. Lett. 2002,
4, 123-125. (c) Murakami, M.; Igawa, H. HelV. Chim. Acta 2002, 85,
4182-4188. (d) Lautens, M.; Yoshida, M. J. Org. Chem. 2003, 68, 762-
769. (e) Genin, E.; Michelet, V.; Geneˆt, J.-P. J. Organomet. Chem. 2004,
689, 3820-3830. (f) Genin, E.; Michelet, V.; Geneˆt, J.-P. Tetrahedron Lett.
2004, 45, 4157-4161.
(8) (a) Lautens, M.; Marquardt, T. J. Org. Chem. 2004, 69, 4607-4614. (b)
Shintani, R.; Tsurusaki, A.; Okamoto, K.; Hayashi, T. Angew. Chem., Int.
Ed. 2005, 44, 3909-3912. (c) Tseng, N.-W.; Mancuso, J.; Lautens, M. J.
Am. Chem. Soc. 2006, 128, 5338-5339. (d) Kurahashi, T.; Shinokubo,
H.; Osuka, A. Angew. Chem., Int. Ed. 2006, 45, 6336-6338.
(9) (a) Miura, T.; Shimada, M.; Murakami, M. J. Am. Chem. Soc. 2005, 127,
1094-1095. (b) Miura, T.; Shimada, M.; Murakami, M. Chem. Asian J.
2006, 1, 868-877.
(3) For a recent review, see: Miura, T.; Murakami, M. Chem. Commun. 2007,
217-224.
(4) (a) Shintani, R.; Okamoto, K.; Otomaru, Y.; Ueyama, K.; Hayashi, T. J.
Am. Chem. Soc. 2005, 127, 54-55. (b) Shintani, R.; Okamoto, K.; Hayashi,
T. Chem. Lett. 2005, 34, 1294-1295. (c) Matsuda, T.; Makino, M.;
Murakami, M. Chem. Lett. 2005, 34, 1416-1417.
(10) (a) Shirakawa, E.; Takahashi, G.; Tsuchimoto, T.; Kawakami, Y. Chem.
Commun. 2001, 2688-2689. (b) Takahashi, G.; Shirakawa, E.; Tsuchimoto,
T.; Kawakami, Y. AdV. Synth. Catal. 2006, 348, 837-840.
(11) (a) Oh, C. H.; Jung, H. H.; Kim, K. S.; Kim, N. Angew. Chem., Int. Ed.
2003, 42, 805-808. (b) Oh, C. H.; Ryu, J. H. Bull. Korean Chem. Soc.
2003, 24, 1563-1564. (c) Kim, N.; Kim, K. S.; Gupta, A. K.; Oh, C. H.
Chem. Commun. 2004, 618-619. (d) Satoh, T.; Ogino, S.; Miura, M.;
Nomura, M. Angew. Chem., Int. Ed. 2004, 43, 5063-5065. (e) Zhou, C.;
Larock, R. C. Org. Lett. 2005, 7, 259-262. (f) Gupta, A. K.; Kim, K. S.;
Oh, C. H. Synlett 2005, 457-460. (g) Tsukamoto, H.; Ueno, T.; Kondo,
Y. J. Am. Chem. Soc. 2006, 128, 1406-1407.
(5) (a) Miura, T.; Shimada, M.; Murakami, M. Synlett 2005, 667-669. (b)
Miura, T.; Shimada, M.; Murakami, M. Angew. Chem., Int. Ed. 2005, 44,
7598-7600.
(6) Miura, T.; Sasaki, T.; Nakazawa, H.; Murakami, M. J. Am. Chem. Soc.
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(7) (a) Miura, T.; Nakazawa, H.; Murakami, M. Chem. Commun. 2005, 2855-
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9
5766
J. AM. CHEM. SOC. 2007, 129, 5766-5771
10.1021/ja070107n CCC: $37.00 © 2007 American Chemical Society

Cyclization Reactions Leading to Indenones
A R T I C L E S
Scheme 1. A Working Hypothesis (1,4-Shift or Oxidative Addition)
Table 1. Rh(I)-Catalyzed Reaction of Alkynes with
2-Bromophenylboronic Acids (1) under COa
Scheme 2. Reaction of 4-Octyne with 1 under CO
reactions (Scheme 1). The shift would proceed via the Rh(III)
species IV, formed by the oxidative addition of C-X bonds to
the generated vinylrhodium complexes II. There have been no
reports, however, on catalytic reactions involving III or IV as
a key species, when this project was started.13 In this report,
we wish to report on some Rh(I)-catalyzed carbonylative
cyclization reactions of alkynes with 2-bromophenylboronic acid
(1), in which the oxidative addition of C-Br bonds on the
adjacent phenyl ring to the generated rhodium species II (X )
Br) leading to IV is involved as a key step. A carbonylation
reaction takes place to give indenones in a regioselective manner
under an ambient pressure of CO. In addition, we found that a
similar vinylrhodium intermediate could be generated by the
addition of arylrhodium species to 2-bromophenyl(trimethylsi-
lyl)acetylene followed by olefin isomerization, which also leads
to the formation of indenones.
a Reaction conditions: alkyne (1 mmol), 2-bromophenylboronic acid (1,
1.5 mmol), [RhCl(cod)]2 (0.05 mmol), Na2CO3 (2 mmol) in dioxane/H2O
(100/1, 2 mL) at 80 °C for 20 h under CO (1 atm of balloon). b Isolated
yields. Numbers in parentheses are the ratio of regioisomers. c [RhCl(cod)]2
(0.025 mmol) was used. d 40 h.
Na2CO3 gave the best results: Cs2CO3 (50%), KOH (20%), Cy2-
NMe (31%). Certain other rhodium complexes were also found
to be active. For example, [RhCl(CO)2]2 gave 2 in 70% yield.
Interestingly, a Rh(0) complex also shows catalytic activity.
When Rh4(CO)12 was used as the catalyst, 2 was produced in
77% yield. However, rhodium phosphine complexes, such as
RhCl(PPh3)3 and RhH(CO)(PPh3)3, were not active.
Results and Discussion
We first examined the rearrangement of the Br group, because
C-Br bonds are known to undergo oxidative addition to Ph-
Rh(I) species.14 We were pleased to discover a new carbony-
lation reaction using 2-bromophenylboronic acid (1). When
4-octyne (1 mmol) was treated with 2-bromophenylboronic acid
(1, 1.5 mmol) in the presence of [RhCl(cod)]2 (0.025 mmol)
and Na2CO3 (2 mmol) in dioxane/H2O (100/1, 2 mL) at 80 °C
under a CO atmosphere (1 atm, CO balloon) for 20 h,
2,3-dipropylinden-1-one (2) was isolated in 91% yield, along
with 1,2,3,4-tetrapropylnaphthalene (3) in 2% (Scheme 2).
Unlike other known reactions,2 the styrene derivative 4 was not
detected. Furthermore, a protonation product 5, derived from a
1,4-Br shift, was also not detected. The use of a base was
required for the reaction to proceed. Among the bases examined,
Various internal alkynes having aryl, alkyl, ester, and silyl
groups could be used to give the corresponding indenones in
high yields, as shown in Table 1. The reaction generally
proceeded in a regioselective manner, and a sterically bulky
group or an electron-withdrawing group on alkynes favored the
R-position of indenones. The steric and electronic nature of the
substituents on the phenyl ring also had an effect on the
regioselectivity of the reaction (entries 3-6). The substitution
of an electron-withdrawing group at the 4-position on the phenyl
ring increased the selectivity (entries 3-5). The substitution of
a methyl group at the 2-position on the phenyl ring also
dramatically increased the regioselectivity (entries 4 and 6). In
the case of trimethylsilylacetylene derivatives, high regioselec-
tivities were observed, and no regioisomers were detected by
GC analysis and 1H NMR measurements (entries 7 and 8). An
ester group is also a good directing group (entry 10). Silyl and
ester groups are comparable, but a silyl group is a slightly
(12) For a recent review, see: (a) Ma, S.; Gu, Z. Angew. Chem., Int. Ed. 2005,
44, 7512-7517. For recent papers, see: (b) Shintani, R.; Okamoto, K.;
Hayashi, T. J. Am. Chem. Soc. 2005, 127, 2872-2873. (c) Yamabe, H.;
Mizuno, A.; Kusama, H.; Iwasawa, N. J. Am. Chem. Soc. 2005, 127, 3248-
3249. (d) Singh, A.; Sharp, P. R. J. Am. Chem. Soc. 2006, 128, 5998-
5999.
(13) Shintani, R.; Yamagami, T.; Hayashi, T. Org. Lett. 2006, 8, 4799-4801.
(14) Ueura, K.; Satoh, T.; Miura, M. Org. Lett. 2005, 7, 2229-2231.
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A R T I C L E S
Harada et al.
Scheme 3. C-Br versus CdO
Table 2. Rh(I)-Catalyzed Reaction of Alkynes with
2-Bromoarylboronic Acids and COa
Scheme 4. Reaction of Norbornene with 1 under CO
stronger directing group (entry 11). The selectivity increases in
the order of SiMe3 > COOR . aryl . alkyl. Terminal alkynes
could not be used in this reaction.15 The result for entry 14 shows
that the generated vinylrhodium species 20 does not react with
the intramolecular ketone functionality, unlike the known
reaction (Scheme 3).4,5
The reaction of alkenes with 1 was next examined. However,
styrene and cyclopentene did not undergo carbonylative cy-
clization, but norbornene gave the corresponding ketone 21 in
high yield (Scheme 4).
Because the generation of the benzyne-Pd complex from
2-bromophenylboronic ester and Pd(0) is known to occur,16,17
we anticipated that the reaction would proceed by a [2 + 2 +
1] cycloaddition of the in situ generated benzyne, alkynes, and
CO. In fact, we previously reported the Co4(CO)12- and [RhCl-
(cod)]2-catalyzed carbonylative cycloaddition of benzyne leading
to the formation of anthraquionone and fluorenone.18 To exclude
this possibility, reactions using substituted 2-bromophenylbo-
ronic acids were performed. The reaction of 4-octyne with
2-bromo-5-methoxyphenylboronic acid (22)19 gave 23 as a
single isomer (Table 2), the formation of which clearly supports
the conclusion that the reaction does not involve benzyne as an
intermediate. Other substituted 2-bromophenylboronic acids
could be used for the carbonylation reaction, and indenones 24-
32 were obtained in good to high yields, as shown in Table 2.
Replacing 2-bromophenylboronic acid with a corresponding
chloro analogue also gave indenone 2, along with a small
amount of styrene derivative (6%) as a byproduct; the latter
would have been formed by protonation of the generated
vinylrhodium complex, related to II.
Interestingly, the course of the reaction was found to be
significantly affected by the nature of the atmosphere. Even
under 1 atm of CO, indenone 2 was formed as a major product,
and only a small amount (2%) of naphthalene derivative 3 was
detected (Scheme 2). However, naphthalene derivatives were
selectively produced when the reaction was carried out under
N2. After optimization of the reaction conditions, 1,2,3,4-
a Reaction conditions: alkyne (1 mmol), 2-bromoarylboronic acid (1.5
mmol), [RhCl(cod)]2 (0.025 mmol), Na2CO3 (2 mmol) in dioxane/H2O (100/
1, 2 mL) at 80 °C for 20 h under CO (1 atm of balloon). b Isolated yields.
c [RhCl(cod)]2 (0.05 mmol) was used.
tetrapropylnaphthalene (3) and 1,2,3,4-tetraphenynaphthalene
(35) were produced in 76% and 77% isolated yields, respec-
tively, when 4-octyne and diphenylacetylene (1 mmol) were
reacted with 1 (0.75 mmol) in the presence of [RhCl(cod)]2
(0.025 mmol) and Na2CO3 (1 mmol) in dioxane/H2O (100/1, 1
mL) at 50 °C under N2 for 20 h (Scheme 5).20
(15) Chen, Y.; Lee, C. J. Am. Chem. Soc. 2006, 128, 15598-15599.
(16) Retboll, M.; Edwards, A. J.; Rae, A. D.; Willis, A. C.; Bennett, M. A.;
Wenger, E. J. Am. Chem. Soc. 2002, 124, 8348-8360.
(17) For a review, see: Dyke, A. M.; Hester, A. J.; Lloyd-Jones, G. C. Synthesis
2006, 4093-4112.
(18) Chatani, N.; Kamitani, A.; Oshita, M.; Fukumoto, Y.; Murai, S. J. Am.
Chem. Soc. 2001, 123, 12686-12687.
(19) 2-Bromo-5-methoxyphenylboronic acid was easily prepared by bromination
of 3-methoxyphenylboronic acid. Kuivila, H. G.; Benjamin, L. E.;
Murphy, C. J.; Price, A. D.; Polevy, J. H. J. Org. Chem. 1962, 27, 825-
829. Other 2-haloarylboronic acids employed in Table 2 are commercially
available.
(20) The reaction of 1-phenylpropyne with 1 gave the corresponding naphthalene
in 77% yield as a 1:1 mixture of regioisomers.
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5768 J. AM. CHEM. SOC. VOL. 129, NO. 17, 2007

Cyclization Reactions Leading to Indenones
A R T I C L E S
Scheme 5. Reaction of Alkynes with 1 under N2
Scheme 7. An Alternative Route for Generating the
Vinylrhodium(I) Complex II
Scheme 6. Proposed Reaction Mechanism
Scheme 8. Reaction of 2-Bromophenyl(trimethylsilyl)acetylene
(42) with Phenylboronic Acid and CO
A proposed mechanism for the reaction is shown in Scheme
6. The arylrhodium(I) complex 36 is generated via the trans-
metalation of Rh-X (X ) Cl, Br, or OH) with 2-bromophe-
nylboronic acid 1. The insertion of an alkyne gives the
vinylrhodium(I) complex 37 (corresponding to II). When
unsymmetric alkynes are used, rhodium favors attachment at
the acetylenic carbon that contains a sterically bulky group or
an electron-withdrawing group. The oxidative addition of C-Br
on the adjacent phenyl ring to 37 produces the rhodium(III)
species 38.13,14 The insertion of CO in 38 followed by reductive
elimination gives indenones, with regeneration of the catalyst.
In the case where the reaction is conducted under N2, the
insertion of a second molecule of an alkyne in 37 or 38 occurs,
followed by reductive elimination to afford a naphthalene
derivative.21 The use of 2-chlorophenylboronic acid in place of
1 also gave indenones (Table 2), but styrene derivatives were
also formed (<10%), although no styrene derivatives were
obtained in the case of 2-bromophenylboronic acids. These
results clearly show that complex 37 undergoes oxidative
addition much faster than protonation (or a 1,4-H shift), as
compared to the chloro analogue.
Scheme 9
With the success of these processes, we sought to develop
new carbonylation reactions, in which the same intermediate
II could be generated by the addition of phenylrhodium species
to 2-bromophenyl(trimethylsilyl)acetylene followed by isomer-
ization, as shown in Scheme 7. The requisite substrates for
testing this hypothesis were readily prepared in one step by the
Sonogashira coupling of 2-bromoiodobenzene with silylacety-
lene, and various arylboronic acids would be expected to be
applicable to the new carbonylation reactions. However, a
critical issue for the success of the designed reaction is whether
the facile isomerization of 41 to 39 takes place. This prompted
us to examine the Rh-catalyzed reaction of 2-bromophenyl-
(trimethylsilyl)acetylene (42) with arylboronic acids.
13 as the sole product. When 42 (0.5 mmol) was treated with
phenylboronic acid (1.5 mmol) in the presence of [RhCl(cod)]2
(0.025 mmol) and Na2CO3 (1 mmol) in dioxane/H2O (100/1, 1
mL) at 80 °C under a CO atmosphere (1 atm, CO balloon) for
20 h, 3-phenyl-2-trimethylsilylinden-1-one (13) was obtained
in 86% isolated yield (Scheme 8). Because the addition of a
Ph-Rh species to an alkyne is known to take place in a cis
manner, the formation of 13 suggests that the initially generated
vinylrhodium species 41 undergoes E-Z isomerization leading
to 39, as expected. The virtue of this protocol is that no
regioisomeric indenones are formed, because the wrong isomers
43 cannot be converted to indenones even if they are formed.
The use of a dimethylphenylsilyl group in place of a
trimethylsilyl, as in 44, led to a slight decrease in the yield of
the corresponding indenone 45 (Scheme 9). The replacement
of Br by Cl also gave 13 in good yield.
To our delight, the reaction of 2-bromophenyl(trimethylsilyl)-
acetylene (42) with PhB(OH)2 and CO (1 atm) gave indenone
(21) An alternative mechanism for the formation of naphthalene derivatives
involves the [4 + 2] cycloaddition of 38 with alkyne followed by
demetalation.
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J. AM. CHEM. SOC. VOL. 129, NO. 17, 2007 5769

A R T I C L E S
Harada et al.
Scheme 10. Rh(I)-Catalyzed Reaction of
2-Bromophenyl(trimethylsilyl)acetylenes with Arylboronic Acids
under CO
Scheme 11
Scheme 12
Scheme 13. Reaction of 1-(2-Bromophenyl)-hept-2-yn-1-one (70)
with PhB(OH)2 and CO
A variety of arylboronic acid derivatives can be used in the
present carbonylation reaction, as shown in Scheme 10. Aryl-
boronic acids having a methoxy group at the ortho and para
positions on the phenyl ring gave the corresponding indenones
in quite low yields (results not shown), because a facile
protonation of the arylboronic acids took place under the
reaction conditions used. In contrast, the meta-methoxy substrate
gave the corresponding indenone 50 in 65% yield. The reaction
shows high functional group compatibility. Even nitro and
formyl groups were tolerated under the reaction conditions used
herein.
We next examined the effect of a substituent on the acetylenic
terminal carbon to determine whether the presence of a
trimethylsilyl group at the terminal acetylenic carbon is neces-
sary for E/Z isomerization, which is a crucial step for the
reaction to proceed. The replacement of a trimethylsilyl group
by a tert-butyl group, as in 61, resulted in the predominant
formation of styrene derivative 62, and the corresponding
indenone was not detected, showing that the required E/Z
isomerization did not take place, but instead protonation took
place prior to the isomerization (Scheme 11). An ester 63 and
phenyl analogue 64 also did not give the corresponding
indenones, and complex mixtures were obtained. These results
indicate that the presence of a silyl group at the terminal
acetylenic carbon is essential for the isomerization to pro-
ceed.22,23
It was found that the E/Z isomerization of vinylrhodium
complexes is a key step for the indenone synthesis. Next, the
reaction of 65 with 2-chlorophenylbononic acid and CO was
performed to examine if the isomerization is slow. If the
oxidative addition of a C-Cl bond in the initially generated
vinylrhodium complex 66 takes place, indenone 67 will be
(22) For a paper on isomerization of â-silyl-substituted vinylrhodium complexes,
see: Ojima, I.; Clos, N.; Donovan, R. J.; Ingallina, P. Organometallics
1990, 9, 3127-3133.
(23) For a paper on isomerization of R-silyl-substituted vinyllithium, see:
Negishi, E.-i.; Takahashi, T. J. Am. Chem. Soc. 1986, 108, 3402-
3408.
9
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Cyclization Reactions Leading to Indenones
A R T I C L E S
122.9, 125.1, 134.4, 149.7, 163.9, 166.2, 200.3. IR (KBr): 2989 m,
2898 m, 2833 m, 1695 s, 1597 s, 1560 s, 1475 m, 1433 m, 1408 m,
1375 s, 1338 m, 1296 s, 1250 s, 1228 s, 1190 m, 1172 s, 1126 m,
1084 s, 1041 s, 1030 s, 864 s, 841 s, 826 s, 760 m, 748 m, 711 m, 688
m, 631 s. MS, m/z (relative intensity, %): 246 (M+, 27), 232 (19), 231
(100), 188 (13), 115 (20), 75 (10). Anal. Calcd for C14H18O2Si: C,
68.25; H, 7.36; O, 12.99. Found: C, 68.19; H, 7.26.
obtained. On the other hand, isomerization of 66 to 68 takes
place prior to the oxidative addition of the C-Cl bond; the
oxidative addition of a C-Br bond in 68 occurs leading to the
formation of 69. The result obtained was the exclusive formation
of 67, and 69 was not formed, showing that the isomerization
of a vinylrhodium complex is not facile (Scheme 12).
The reaction of 1-(2-bromophenyl)-hept-2-yn-1-one (70) with
PhB(OH)2 in the presence of a Rh(I) complex also resulted in
carbonylative cyclization to give indan-1,3-dione derivative 71
in good yield (Scheme 13). In this reaction, isomerization of
the olefin is not required in the vinylrhodium complex 72.
5-Chloro-2,3-dipropylinden-1-one (33). Yellow oil. Rf 0.29 (hexane/
1
EtOAc ) 20/1). H NMR (CDCl3) δ: 0.92 (t, J ) 7.3 Hz, 3H), 1.03
(t, J ) 7.3 Hz, 3H), 1.48 (tq, J ) 7.3 Hz, 7.7 Hz, 2H), 1.62 (tq, J )
7.3 Hz, 7.6 Hz, 2H), 2.23 (t, J ) 7.7 Hz, 2H), 2.49 (t, J ) 7.6 Hz,
2H), 6.98 (s, 1H), 7.11 (d, J ) 7.8 Hz, 1H), 7.28 (d, J ) 7.8 Hz, 1H).
13C NMR (CDCl3) δ: 14.1, 14.3, 21.1, 22.4, 24.9, 28.1, 119.8, 122.5,
127.3, 129.2, 136.2, 139.2, 147.6, 156.4, 197.0. IR (neat): 2962 m,
2933 m, 2871 m, 1711 s, 1604 m, 1585 m, 1464 m, 1410 w, 1360 m,
1261 w, 1227 w, 1159 w, 1113 w, 1066 m, 1009 w, 947 w, 910 w,
874 w, 829 m, 783 w, 744 w, 596 w. MS, m/z (relative intensity, %):
250 (M+ + 2, 17), 248 (M+, 46), 221 (33), 220 (22), 219 (100), 206
(24), 205 (32), 191 (39), 179 (29), 178 (35), 177 (67), 165 (21), 149
(37), 141 (29), 139 (25), 128 (52), 127 (53), 126 (23), 115 (31), 77
(25), 75 (29), 63 (33), 55 (21), 51 (24). Anal. Calcd for C15H17ClO:
C, 72.43; H, 6.89; Cl, 14.25. Found: C, 72.20; H, 6.74; Cl, 14.51.
Conclusion
We report herein on the development of a new carbonylation
reaction of alkynes with 2-bromophenylboronic acid (1)24
leading to the formation of indenones.25 The reaction involves
the Rh-catalyzed regioselective addition of an arylrhodium(I)
species to alkynes and the oxidative addition of C-Br bonds
in the adjacent phenyl ring to the resulting vinylrhodium(I)
species as key steps. The regioselectivity is generally high and
is significantly affected by the steric and electronic factors.
Sterically bulky and electron-withdrawing groups, such as silyl,
tert-butyl, and ester groups, favor the attachment at the
R-position of indenones. Similar vinylrhodium intermediates
could be generated by the addition of arylrhodium species to
2-bromophenyl(trimethylsilyl)acetylene followed by olefin isomer-
ization, which also leads to the formation of indenones.
3-(4-Chlorophenyl)-2-trimethylsilanylinden-1-one (52). Yellow
1
solid. Rf 0.31 (hexane/EtOAc ) 20/1). H NMR (CDCl3) δ: 0.06 (s,
9H), 6.85 (d, J ) 6.4 Hz, 1H), 7.25-7.33 (c, 4H), 7.46-7.51 (c, 3H).
13C NMR (CDCl3) δ: 0.0, 120.8, 122.6, 128.9, 129.3, 129.4, 132.4,
133.2, 133.6, 135.3, 135.5, 147.1, 169.3, 201.6. IR (KBr): 2958 w,
1693 s, 1595 w, 1541 w, 1481 w, 1454 w, 1398 w, 1363 w, 1298 w,
1244 w, 1174 w, 1092 m, 1012 w, 862 m, 845 m, 795 w, 756 w, 719
w, 638 w, 611 w. MS, m/z (relative intensity, %): 314 (M+ + 1, 10),
312 (M+ - 1, 26), 299 (37), 298 (24), 297 (100), 281 (18), 277 (17),
203 (16), 202 (20), 189 (14), 176 (11), 131 (12), 75 (10), 73 (10), 62
(18). Anal. Calcd for C18H17ClOSi: C, 69.10; H, 5.48; Cl, 11.33; O,
5.11. Found: C, 68.92; H, 5.36; Cl, 11.68.
Experimental Section
A few representative examples are listed here. Experimental
procedures and spectroscopic data for new compounds can be found
in the Supporting Information.
3-(4-Formylphenyl)-2-trimethylsilanylinden-1-one (53). Yellow
solid. Rf 0.14 (hexane/EtOAc ) 20/1). H NMR (CDCl3) δ: 0.05 (s,
Typical Procedure for the Rh-Catalyzed Formation of Indenones.
A 10-mL two-necked flask was charged with sodium carbonate (212.0
mg, 2.0 mmol), 2-bromophenylboronic acid (1, 301.2 mg, 1.5 mmol),
[RhCl(cod)]2 (12.3 mg, 0.025 mmol), 4-octyne (110.2 mg, 1.0 mmol),
and 1,4-dioxane/H2O (2 mL/0.02 mL), and a three-way stopcock,
connected to a vacuum line and a balloon filled with carbon monoxide,
was attached to the flask. The system was carefully evacuated and
refilled with carbon monoxide and then filled with carbon monoxide
(1 atm). It was then immersed in an oil bath at 80 °C. After 20 h, it
was removed from the oil bath and cooled to room temperature. The
contents were transferred to a round-bottom flask, and volatiles were
removed in vacuo. The residue was subjected to column chromatog-
raphy on silica gel (eluent; hexane/EtOAc ) 50/1) to give 2,3-
dipropylinden-1-one (2) (195.0 mg, 91% yield) as a yellow oil.
5-Methoxy-3-methyl-2-trimethylsilylinden-1-one (24). Yellow solid.
1
9H), 6.81 (d, J ) 6.4 Hz, 1H), 7.26-7.32 (c, 2H), 7.52-7.55 (c, 3H),
8.01 (d, J ) 8.0 Hz, 2H), 10.10 (s, 1H). 13C NMR (CDCl3) δ: -0.2,
120.8, 122.9, 128.7, 129.6, 123.0, 132.2, 133.5, 136.3, 136.9, 141.6,
147.0, 168.9, 191.9, 201.5. IR (KBr): 2949 w, 2831 w, 2736 w, 1699
s, 1611 m, 1549 m, 1495 w, 1456 w, 1365 w, 1298 m, 1284 w, 1250
m, 1205 m, 1184 m, 1092 m, 1011 w, 870 s, 847 s, 796 m, 754 m, 714
m, 611 w. MS, m/z (relative intensity, %): 307 (M+ + 1, 11), 306
(M+, 49), 292 (25), 291 (100), 278 (10), 277 (19), 263 (25), 248 (10),
247 (39), 218 (11), 217 (35), 204 (12), 203 (27), 202 (31), 201 (14),
189 (19), 176 (11), 145 (46), 123 (21), 75 (11), 73 (13), 59 (10), 53
(11). Anal. Calcd for C19H18O2Si: C, 74.47; H, 5.92. Found: C, 74.25;
H, 5.81.
1
Acknowledgment. This work was partially supported by The
Ministry of Education, Science, Sport, and Culture, Japan. N.C.
acknowledges the Merck Research Laboratories for financial
support.
Rf 0.23 (hexane/EtOAc ) 20/1). H NMR (CDCl3) δ: 0.28 (s, 9H),
2.25 (s, 3H), 3.85 (s, 3H), 6.64 (d, J ) 7.5 Hz, 1H), 6.67 (s, 1H), 7.35
(d, J ) 7.5 Hz, 1H). 13C NMR (CDCl3) δ: 0.0, 14.5, 55.7, 107.5, 110.3,
(24) Recently, Rh(I)-catalyzed carbonylation of alkynes with PhB(OH)2 leading
to R,â-unsaturated γ-lactones was reported. Aksin, O.; Dege, N.; Artok,
L.; Tu¨rkmen, H.; Cetinkaya, B. Chem. Commun. 2006, 3187-3189.
(25) For papers on indenone synthesis, see: (a) Larock, R. C.; Doty, M. J.;
Cacchi, S. J. Org. Chem. 1993, 58, 4579-4583. (b) Kokubo, K.;
Matsumasa, K.; Miura, M.; Nomura, M. J. Org. Chem. 1996, 61, 6941-
6946. (c) Pletnev, A. A.; Tian, Q.; Larock, R. C. J. Org. Chem. 2002, 67,
9276-9287.
Supporting Information Available: Experimental procedures
and spectroscopic data for new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
JA070107N
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J. AM. CHEM. SOC. VOL. 129, NO. 17, 2007 5771