A Pauson-Khand-type reaction between alkynes and olefinic aldehydes catalyzed by rhodium/cobalt heterobimetallic nanoparticles: An olefinic aldehyde as an olefin and CO source

Article abstract of DOI:10.1021/ol049765s

Co/Rh (Co:Rh = 2:2) heterobimetallic nanoparticles derived from Co ₂Rh₂(CO)₁₂ react with alkynes and α,β-unsaturated aldehydes such as acrolein, crotonaldehyde, and cinnamic aldehyde and release products resulting from [2 + 2 + 1]cycloaddition of alkyne, carbon monoxide, and alkene. α,β-Unsaturated aldehydes act as a CO and alkene source. These reactions produce 2-substituted cyclopentenones.

Full text of DOI:10.1021/ol049765s

ORGANIC
LETTERS
2004
Vol. 6, No. 7
1183-1186
A Pauson−Khand-Type Reaction
between Alkynes and Olefinic
Aldehydes Catalyzed by Rhodium/Cobalt
Heterobimetallic Nanoparticles: An
Olefinic Aldehyde as an Olefin and CO
Source
Kang Hyun Park, Il Gu Jung, and Young Keun Chung*
School of Chemistry, Seoul National UniVersity, Seoul 151-747, Korea
ykchung@plaza.snu.ac.kr
Received February 10, 2004
ABSTRACT
Co/Rh (Co:Rh ) 2:2) heterobimetallic nanoparticles derived from Co2Rh2(CO)12 react with alkynes and r,â-unsaturated aldehydes such as
acrolein, crotonaldehyde, and cinnamic aldehyde and release products resulting from [2 + 2 + 1]cycloaddition of alkyne, carbon monoxide,
and alkene. r,â-Unsaturated aldehydes act as a CO and alkene source. These reactions produce 2-substituted cyclopentenones.
The development of new processes that are simultaneously
economically sustainable and environmentally responsible
is a challenge for the twenty-first century.1 In this respect,
catalysis plays a central role in the development of envi-
ronmentally safe and clean chemical processes. Thus, the
design and development of new catalysts providing cleaner
alternative synthetic pathways has attracted a lot of attention.
The achievements of developing transition metal catalysts
for multicomponent cycloaddition reactions have been
especially remarkable.
The Pauson-Khand reaction (PKR) is a carbonylative
cycloaddition reaction involving selective incorporation of
three different molecules, i.e., an alkyne, an alkene, and
carbon monoxide. The PKR has become one of the most
convergent and versatile methods in the construction of five-
membered rings.2 However, increasing environmental aware-
ness has made the use of carbon monoxide undesirable and
created pressures to find an alternative process without using
carbon monoxide or with a substitute for carbon monoxide.
Recently, the use of decarbonylated CO from formates or
aldehydes has been utilized in the PKR3 and other transition
metal-catalyzed reactions.4 Substitution of one of the reaction
components, carbon monoxide, by an aldehyde or a formate
completely changes the reaction process. By extrapolation,
if a substance could be used instead of both carbon monoxide
and an alkene, a much simpler and cleaner process could be
(2) For recent reviews, see: (a) Gibson, S. E.; Stevenazzi, A. Angew.
Chem., Int. Ed. 2003, 42, 1800. (b) Brummond, K. M.; Kent, J. L.
Tetrahedron 2000, 56, 3263. (c) Chung, Y. K. Coord. Chem. ReV. 1999,
188, 297.
(3) (a) Morimoto, T.; Fuji, K.; Tsutsumi, K.; Kakiuchi, K. J. Am. Chem.
Soc. 2002, 124, 3806. (b) Shibata, T.; Toshida, N.; Takagi, K. Org. Lett.
2002, 4, 1619. (c) Shibata, T.; Toshida, N.; Takagi, K. J. Org. Chem. 2002,
67, 7446. (d) Park, K. H.; Son, S. U.; Chung, Y. K. Chem. Commun. 2003,
1898.
(4) (a) Buchan, C.; Hamel, N.; Woell, J. B.; Alper, H. J. Chem. Soc.,
Chem. Commun. 1986, 167. (b) Castanet, Y.; Mortreux, A.; Petit, F. J. Mol.
Catal. 1990, 63, 313. (c) Carpentier, J. P.; Castanet, Y.; Brocard, Y.;
Mortreux, A.; Petit, F. Tetrahedron Lett. 1991, 32, 4705. (d) Ko, S.; Na,
Y.; Chang, S. J. Am. Chem. Soc. 2002, 124, 750. (e) Ko, S.; Lee, C.; Choi,
M.-G.; Na, Y.; Chang, S. J. Org. Chem. 2003, 68, 1607.
(1) (a) Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and
Practice; Oxford University Press: Oxford, 1998. (b) Tundo, P.; Anastas,
P. T. Green Chemistry: Challenging PerspectiVes; Oxford University
Press: Oxford, 2000.
10.1021/ol049765s CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/06/2004

developed. Moreover, the application of cleaner heteroge-
neous catalysts with readily available starting materials would
allow the minimization of inorganic as well as organic waste
production.
Table 1. Pauson-Khand-Type Reaction Catalyzed by
Immobilized Co2Rh2 on Charcoal Using R,â-Unsaturated
Aldehydesa
Our own research interests have recently focused on the
use of transition metal nanoparticles as heterogeneous
catalysts in the PKR and related reactions.1 They provide a
clean and reusable catalytic system for the intra- and
intermolecular PKR. Our recent study of the use of Co/Rh
heterobimetallic nanoparticles as catalysts in the PKR in the
presence of an aldehyde instead of carbon monoxide6 gave
us the novel idea to use unsaturated aldehydes as a source
of CO and alkene. It has been well documented7 that the
reaction of aldehydes on metal surfaces releases hydrocar-
bons and carbon monoxide by decarbonylation. Thus, we
studied the use of R,â-unsaturated aldehydes as a source of
CO and alkene. In this paper, we report our preliminary
results. We expect that this study will provide an environ-
mentally clean, safe, and sustainable process.
Our recent study showed6 that cobalt/rhodium (Co2Rh2)
heterobimetallic nanoparticles derived from Co2Rh2(CO)12
were an excellent catalyst in the Pauson-Khand-type reac-
tion. During the present study, we also confirmed this
previous work. Thus, Co2Rh2 was our catalyst of choice.
In the beginning, we screened organic substrates that could
be easily decarbonylated by transition metals. R,â-Unsatur-
ated aldehydes were screened using Co2Rh2 as a catalyst
(Scheme 1 and Table 1).8 As expected, a PKR product was
substrate
entry
R1
R2
R3
Ph
Ph
Ph
yield (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17c
18d
19d
20d
H
H
H
H
H
H
H
H
CH3
CH3
CH3
CH3
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
H
H
H
H
H
H
Ph
Me
H
H
H
Ph
H
H
H
Ph
H
H
H
48b
49b
60
51
54
43
74
57
77
70
56
71
75
71
69
70
72
73
73
70
Bu
C5H11
TMS
Ph
Ph
Ph
Bu
TMS
Ph
Ph
Bu
TMS
Ph
Ph
Ph
Ph
H
Ph
a Isolated yields. Reaction conditions: aldehyde (15.8 mmol), alkyne
(9.1 mmol), catalyst (0.029 mmol), and THF (5 mL). b THF solution (0.32
M). c Catalyst: recovered from entry 13. d Catalyst: recovered from the
preceding entry.
giving 1,3-dienes, although some electron-deficient alkenes
can be appropriate substances in the Pauson-Khand reaction
under certain circumstances such as in the presence of a
promoter.10
Scheme 1
Thus, it is very interesting that electron-deficient alkenes
such as R,â-unsaturated aldehydes known as poor substrates
for the PKR can be used as a source of CO and alkene. R,â-
Unsaturated aldehydes such as acrolein are adsorbed in an
η4-(C,C,C,O) configuration and decarbonylate at lower
temperatures than the aliphatic analogue, propanal.7 Thus,
R,â-unsaturated aldehydes have a dual function, slowly and
continuously producing both olefin and CO in situ.
When acrolein (entries 1-8) was used as a CO and olefin
source, the reaction yields (based on the enyne used) were
moderate to high (43-74%), presumably due to the complex
decomposition of acrolein on the surface of the nanoparticles.
It is known21 that the main thermal decomposition path of
acrolein is via its decarbonylation to carbon monoxide and
ethene and that small amounts of propene and ketene are
also formed. However, a product derived from propene was
not observed. In addition to the PKR product, a coupling
product B, alkynyl aldehyde, was obtained in 7-13% yield,
presumably due to an incomplete decarbonylation of ac-
rolein.8 The yield of the coupling product varied depending
upon subtle changes in the reaction conditions. The yield of
obtained in reasonable to high yields with the concomitant
formation of a coupling product in the case of acrolein. It is
well-known9 that the PKR alkenes attached to electron-
withdrawing groups (all π-conjugating) react anomalously,
(5) (a) Kim, S.-W.; Son, S. U.; Chung, Y. K.; Hyeon, T. Chem. Commun.
2001, 2212. (b) Son, S. U.; Lee, S. I.; Chung, Y. K.; Kim, S.-W.; Hyeon,
T. Org. Lett. 2002, 4, 277. (c) Son, S. U.; Park, K. H.; Chung, Y. K. J. Am.
Chem. Soc. 2002, 124, 6838. (d) Son, S. U.; Park, K. H.; Chung, Y. K.
Org. Lett. 2002, 4, 3983. (e) Park, K H.; Son, S. U.; Chung, Y. K. Org.
Lett. 2002, 4, 4361.
(6) Park, K. H.; Kim, S. Y.; Chung, Y. K. J. Org. Chem. Submitted.
(7) (a) Bohm, D.; Hamann, J.; Kripylo, P. J. Prak. Chem. 1990, 332,
710. (b) Brown, N. F.; Barteau, M. A. J. Am. Chem. Soc. 1992, 114, 4258.
(c) Rupp, R.; Huttner, G.; Rutsch, P.; Winterhalter, U.; Barth, A.; Kircher,
P.; Zsolnai, L. Eur. J. Inorg. Chem. 2000, 523.
(8) See Supporting Information.
(9) (a) Khand, I. U.; Mahaffy, C. A. L.; Pasuon, P. L. J. Chem. Res.,
Miniprint 1978, 4454. (b) Krafft, M. E.; Romero, R. H.; Scott, I. L. J. Org.
Chem. 1992, 57, 5277.
(10) (a) Ahmar, M.; Antras, F.; Cazes, B. Tetrahedron Lett. 1999, 40,
5503. (b) Rivero, M. R.; Adrio, J.; Carretero, C. Eur. J. Org. Chem. 2002,
2881. (c) Rivero, M. R.; Carretero, J. C. J. Org. Chem. 2003, 68, 2975.
1184
Org. Lett., Vol. 6, No. 7, 2004

the PKR product (entries 1-3) is moderately dependent upon
the reaction conditions. When a 0.32 M solution of acrolein
in THF was used, the yield was 48-49%. The use of a highly
concentrated solution of acrolein in THF boosted the yield
to 60%. However, when neat acrolein was used, the reaction
was too complex to characterize. Treatment of butylacetylene
(entry 4) afforded the expected product at a 51% yield. TMS-
substituted acetylene (entry 5) gave 43% of the product, and
the cyclohexyl-substituted alkyne (entry 6) gave 54% of the
product. When diphenylacetylene (entry 7) was used, the
yield of the product was 74%. Treatment of the unsymmetric
internal alkyne (entry 8) afforded one isomer as the sole
product.
In contrast to acrolein, crotonaldehyde thermally decom-
poses to carbon monoxide and propene.12 The use of
crotonaldehyde (entries 9-12) gives the expected cyclopen-
tenones in high yields (56-77%). In most cases, the yields
were improved compared to those obtained through the use
of acrolein with acetylenes. Moreover, the reaction was quite
regioselective with respect to alkenes and alkynes. As with
the traditional PKR, terminal alkynes yielded predominantly
2-substituted ketones. It has been well-known13 that neither
terminal nor internal alkenes usually demonstrate meaningful
regioselectivity in reaction with alkynes. Thus, the high
regiocontrol is highly noteworthy.
Scheme 2
Treatment of acetylene with acrolein, crotonaldehyde, and
cinnamic aldehyde afforded the corresponding cyclopenten-
ones in 23, 25, and 17% yields, respectively (Scheme 3).8
Scheme 3
We next investigated the use of cinnamic aldehyde as a
source of CO and styrene (entries 13-16). Styrene is known
as a poor substrate in the Pauson-Khand reaction.14 Thus,
the use of styrene as an olefin substrate has been rare. To
improve the yield of the PKR, DMSO has been added as a
promoter.15 However, under our reaction conditions, the
expected PKR products were obtained in high yields (69-
75%). Particularly, the yield for TMS-substituted acetylene
was improved to 69%. Moreover, under our reaction condi-
tions, no polymers derived from free styrenes were found.
Therefore, use of these protocols might lead to slow
generation of styrene.
Recently, a rhodium-catalyzed synthesis of cyclopenten-
ones via the intramolecular trans hydroacylation of alkynals
was reported.16 Thus, there could be other reaction pathways
for our reaction. To confirm the reaction pathway, both
cinnamaldehyde and substituted styrene were used as alkenes
(Scheme 4). After workup, two Pauson-Khand products
were isolated in 32 and 20% yields, respectively. Thus, the
reaction follows the Pauson-Khand-type reaction.
When the reusability of the catalytic system was tested
for the reaction between cinnamic aldehyde and phenylacety-
lene (entries 17-20), the catalytic activity of Co2Rh2
nanoparticles was retained for at least five runs; the
maximum reusability has not been tested. Elemental analysis
(by ICP-AES) of the reaction mixture after completion of
the reaction showed that less than 0.1 ppm of cobalt and
rhodium species were present.
Scheme 4
When methacrolein was used, no reaction was observed,
presumably due to the steric hindrance of the methyl
group.
When 1,6-nonadiyne was reacted with acrolein, a double
carbonylative cycloaddition product was obtained in a 70%
yield (Scheme 2).8
We attempted to develop an intramolecular version of the
reaction (Scheme 5). However, after workup, the reactant
was recovered. Unfortunately, the catalytic system was not
effective for an intramolecular reaction. Further study will
hopefully disclose a catalytic system that will be effective
for an intramolecular reaction.
(11) (a) de Jesus, J. C.; Zaera, F. J. Mol. Catal. A: Chem. 1999, 138,
237. (b) de Jesus, J. C.; Zaera, F. Surf. Sci. 1999, 430, 99.
(12) Bock, H.; Breuer, O. Angew. Chem. 1987, 99, 492
(13) Khand, I. U.; Pauson, P. L. J. Chem. Res., Synop. 1977, 9.
(14) (a) Pauson, P. L.; Khand, I. U. Ann. N. Y. Acad. Sci. 1977, 295, 2.
(b) Khand, I. U.; Murphy, E.; Pasuon, P. L. J. Chem. Res., Synop. 1978,
350. (c) Pauson, P. L. Tetrahedron 1985, 41, 5855.
(15) Kang, Y. K.; Lee, H.-K.; Lee, S. S.; Chung, Y. K.; Carpenter, G.
B. Inorg. Chim. Acta 1997, 261, 37.
(16) Tanaka, K.; Fu, G. C. J. Am. Chem. Soc. 2001, 123, 11492 and
references therein.
Org. Lett., Vol. 6, No. 7, 2004
1185

friendly because the transformation occurs in the absence
of additives except for the catalyst, and the catalyst can be
reused semipermanently without losing catalytic activity.
Further studies are currently underway to extend the scope
of this reaction and our associated asymmetric catalysis.
Scheme 5
Acknowledgment. This work was supported by the
Ministry of Science and Technology of Korea through
Research Center for Nanocatalysis, one of the National
Science Programs for Key Nanotechnology. K.H.P. and I.G.J.
give thanks for BK21 fellowships.
Tremendous progress for the catalytic intramolecular PKR
has been reported. However, the development of an efficient
and general procedure for a catalytic intermolecular PKR
lags far behind. We believe that our study provides concep-
tually a new model for a catalytic intermolecular PKR.
In conclusion, a new catalytic protocol has been developed
for the formal [2 + 2 + 1]cycloaddition reaction of alkynes
and R,â-unsaturated aldehydes to 2-substituted cyclopenten-
ones. The procedure is characterized to be environmentally
Supporting Information Available: Detailed experi-
mental procedures and compound characterization data. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OL049765S
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Org. Lett., Vol. 6, No. 7, 2004