Cyclohydrocarbonylation of substituted alkynes and tandem cyclohydrocarbonylation-CO insertion of α-keto alkynes catalyzed by immobilized Co-Rh heterobimetallic nanoparticles

Article abstract of DOI:10.1039/b416657d

The use of cobalt-rhodium (Co₂Rh₂) heterobimetallic nanoparticles in the cyclohydrocarbonylation of substituted alkynes and tandem cyclohydrocarbonylation-CO insertion of α-keto alkynes to give 2(3H)- or 2(5/7)-furanones is described

Full text of DOI:10.1039/b416657d

View Article Online / Journal Homepage / Table of Contents for this issue
C O M M U N I C A T I O N
Cyclohydrocarbonylation of substituted alkynes and tandem
cyclohydrocarbonylation–CO insertion of a-keto alkynes catalyzed
by immobilized Co–Rh heterobimetallic nanoparticles
Kang Hyun Park, So Yeon Kim and Young Keun Chung*
School of Chemistry, College of Natural Sciences, Seoul National University, Seoul, 151-747,
Korea. E-mail: ykchung@plaza.snu.ac.kr; Fax: 82 2 889 0310; Tel: 82 2 880 6662
Received 2nd November 2004, Accepted 23rd November 2004
First published as an Advance Article on the web 17th December 2004
The use of cobalt–rhodium (Co2Rh2) heterobimetallic
nanoparticles in the cyclohydrocarbonylation of substituted
alkynes and tandem cyclohydrocarbonylation–CO inser-
tion of a-keto alkynes to give 2(3H)- or 2(5H)-furanones
is described.
furanones. In our catalytic system, neither phosphite nor hydro-
gen is needed for the catalysis and no hydrogenated byproducts
are generated. Furthermore, the Co2Rh2 heterogeneous catalysts
are easily recovered and reused without loss of catalytic activity.
Transition metal complex-catalyzed carbonylation has been
proven to be a useful method for the direct introduction of
a carbonyl group into an organic molecule via the insertion
of carbon monoxide into a carbon–metal bond.1 Important
variants of carbonylation are cyclocarbonylation and cyclohy-
drocarbonylation. Both reactions allow the introduction of a
carbonyl group along with ring closure. Thus, they are expected
to provide a novel tool for the construction of cyclic systems.
Transition metal-catalyzed cyclocarbonylation reactions have
been extensively studied and established as excellent methods for
direct synthesis of cyclic carbonyl compounds such as ketones,
aldehydes, acrylic acid, esters, lactones, furanones, indenones,
and indanones.2 However, transition metal-catalyzed cyclohy-
drocarbonylation reactions have been relatively undeveloped.
Only a handful of studies have been reported by Takahashi,3
Ojima,4 and Alper5 and their coworkers in the syntheses of
furanones and pyrrolinones.
Recently, the chemistry of transition-metal nanoparticles
has developed rapidly6 and their use has widened to include
many catalytic reactions such as oxidation,7 hydrogenation,8
coupling,9 and photocatalytic reactions.10 In the context of our
studies on the use of transition metal nanoparticles in organic re-
actions, we have reported many useful catalytic reactions such as
allylic alkylation, the Pauson–Khand reaction, and the reductive
Pauson–Khand reaction.11 Very recently, we found that cobalt–
rhodium nanoparticles (Co2Rh2) derived from Co2Rh2(CO)12
were quite useful catalysts in Pauson–Khand-type reactions
and silylcarbocyclization.12 While we were investigating the
use of Co2Rh2, we found that Co2Rh2 catalyzed carbonylative
coupling reactions. Here we report the use of immobilized
cobalt–rhodium heterobimetallic nanoparticles in the presence
of CO and H2O for the cyclohydrocarbonylation of substi-
tuted acetylenes and the tandem cyclohydrocarbonylation–CO
insertion reaction of a-keto alkynes to give 2(3H)- or 2(5H)-
(1)
Diphenylacetylene (1a) was reacted with carbon monoxide
(10 atm) and water in the presence of triethylamine and a
catalytic amount of Co2Rh2 in THF at 120 ◦C (eqn. 1).
The reaction proceeded smoothly and gave 3,4-diphenylfuran-
2(5H)-one (2a) in 26% yield; the products were identified by
1
instrumental analytical techniques such as H NMR, IR, and
mass spectroscopy. Judging from the structure, furanone 2a
is constructed by the combination of 1a with one molecule
of hydrogen and two molecules of carbon monoxide. The
hydrogen atoms were from water. The presence of the amine
is necessary for the selective syntheses of furanone. In order to
establish optimized reaction conditions, we screened the reaction
temperature and pressure of CO (Table 1). As shown in Table 1,
the yield was highly dependent upon the reaction temperature,
the pressure of CO, and the reaction time. The best yield was
87% and the optimized reaction conditions were established
as follows: 30 atm of CO, 100 ◦C, and 18 h. To check the
recyclability, Co2Rh2 was separated and reused several times.
The results shown in Table 1 confirm that the catalyst maintained
its high activity even after being recycled five times. In order to
recycle the catalyst, it was filtered from the reaction mixture
and dried in vacuo. It could then be reused for further catalytic
reactions.
Furanones have been of interest for many years due to their
biological activity.13 Thus, a variety of transition metal-catalyzed
methods have been utilized for the preparation of furanones.14
The first rhodium-catalyzed carbonylation of acetylenes under
water–gas shift reaction conditions to furanones was reported
by Takahashi et al. They used rhodium carbonyl clusters
such as Rh4(CO)12 and Rh6(CO)16 as catalysts in the presence
of water and triethylamine under 100 atm of CO. Recently,
3
Table 1 Optimization of the reaction conditions
Entry
Catalyst
Pressure/atm
Temp./◦C
Time/h
Yield (%)a
1
2
3
4
5
6
7
8
9
Co2Rh2
Co2Rh2
Co2Rh2
Co2Rh2
10
20
20
30
30
30
30
30
30
120
120
100
100
100
100
100
100
100
18
18
18
6
18
18
18
18
18
26
53
19
12
87
88
85
86
87
Co2Rh2
Recovered from #6
Recovered from #7
Recovered from #8
Recovered from #9
a Isolated yields, acetylene (0.864 g, 4.85 mmol), Co2Rh2 (0.01 g, 0.029 mmol), Et3N (2 ml), H2O (1 ml), THF (10 ml).
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 9 5 – 3 9 8
3 9 5
©

View Article Online
Table 2 Cyclohydrocarbonylation of acetylenes
the isomers were easily separated by column chromatography,
the isomer ratio was based on the isolated yields. Table 2 shows
that the isomer ratio is affected by both the steric and electronic
nature of the substituents of the acetylenes. In the case of R2 =
a phenyl group, as the steric bulkiness of the R1 increased, the
yield of 2 decreased but the yield of 3 increased. In the case of
R1 = an ester group, as the steric bulkiness of R2 decreased, the
yield of 3 increased, but there was not an apparent tendency in
the yield of 2.
Substrate
Yield(%)
Entry
Compound
R1
R2
2
3
Next we investigated the use of a-keto alkynes as substrates
instead of acetylenes. We screened the reaction conditions
using 4-methyl-1-phenyl-1-pentyn-3-one (4a) as a substrate.
Interestingly, the reaction pathway is highly dependent upon the
reaction temperature and pressure. Thus, depending upon the
reaction conditions, three distinctive pathways were found and
four different cyclohydrocarbonylation products were obtained
(Scheme 1). Surprisingly, this phenomenon was quite general.
Thus, the reaction can be applied to other substrates (Table 3).
Under the same conditions (30 atm, 100 ◦C, and 18 h) as the
cyclohydrocarbonylation of acetylene derivatives, the tandem
cyclohydrocarbonylation–CO insertion reaction products, 5
and 6, were obtained in various ratios depending upon the
substituents. The total yields of 5 and 6 were also highly
variable depending upon the substrates: high yields (83–85%)
were obtained for substrates 4a–4c, but poor to moderate yields
(24–59%) were obtained for 4d–4f. A similar reaction of a-iminio
1
2
3
4
5
6
7
8
1a
1b
1c
1d
1e
1f
Ph
Et
H
Me
Ph
Et
87
89
40
61
72
23
30
17
Ph
Ph
Ph
Ph
Me
H
53
31
18
14
54
68
Et
EtO2C
EtO2C
EtO2C
1g
1h
a Isolated yields. Reaction conditions: acetylene (0.864 g, 4.85 mmol),
Co2Rh2 (0.01 g, 0.029 mmol), Et3N (2 ml), H2O (1 ml), THF (10 ml),
30 atm CO, 100 ◦C, and 18 h.
6
5c
Alper et al. reported a zwitterionic rhodium complex (g -
C6H5BPh3)Rh(cod) (2 mol%) catalyzed formation of furanones
using a-keto alkynes in the presence of a considerable amount
(32 mol%) of P(OPh)3 under 38.5 atm CO and 3.5 atm H2 at 90 ◦C
for 24 h. In addition to furanones, a hydrogenated alkynone was
obtained as a byproduct.
In order to examine the scope of the present reaction and
to obtain further information on the reaction mechanism,
cyclohydrocarbonylation of various acetylenes was carried out.
The results are summarized in Table 2, which shows that
furan-2-(5H)-ones, 2 and 3, were obtained in satisfactory
yields for internal acetylenes bearing alkyl, aryl, and ester aryl
substituents.
5b
alkynes was reported by Alper et al. They obtained the tandem
cyclohydrocarbonylation–CO insertion reaction products of a-
iminio alkynes by employing a total pressure of 21 atm to 42
atm of CO and H2, catalytic quantities of zwitterionic rhodium
6
complex (g -C6H5BPh3)Rh(1,5-COD)+, and P(OPh)3. In our
case, water was used as a hydrogen source instead of hydrogen
gas and no additives such as triphenylphosphite were required.
When the pressure of CO was lowered to 1 atm, two
different products were obtained in reasonable to high yields
depending upon the reaction temperature: 7 at 60 ◦C and 8
at 100 ◦C, respectively. The yields were dependent upon the
substituents. Compared to the alkyl substituent, a substrate
For monosubstituted acetylenes such as phenylacetylene, two
structural isomeric furanones 2 and 3 were obtained in 72% and
18% yields, respectively, under the adopted reaction conditions.
The two isomers were easily separated. When Rh4(CO)12 was
5c
containing a phenyl group gave a higher yield. Alper et al.
3f
also observed the formation of 7 and 8 in their rhodium-
catalyzed cyclohydrocarbon reaction of a-keto alkynes. They
suggested that structural and electronic properties present in the
starting materials mediate the chemo- and regioselectivity of the
reaction. For example, having an aromatic ring adjacent to the
triple bond appears to favor the formation of the unsaturated
c-lacones.
used as a catalyst, the ratio of 2 to 3 was approximately 1 : 1.
Asymmetrically substituted acetylenes afforded two struc-
tural isomers 2 and 3, the ratio of which varied depending on the
steric and electronic nature of the substituents of the acetylenes.
Takahashi et al. obtained a similar isomer ratio (73 : 27) to that
obtained by us (72 : 18) for 2d and 3d. However, the same authors
reported that the ratio of 2 : 3 was ca. 1 : 1 for phenylacetylene
derivatives independent of the electronic and steric nature of
the substituents on the phenyl ring of aromatic acetylenes. As
3d
3f
3f
Takahashi et al. proposed a mononuclear anionic rhodium
complex species stabilized by coordination of an alkyne
Scheme 1
3 9 6
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 9 5 – 3 9 8

View Article Online
Table 3 Cyclohydrocarbonylation of a-keto alkynes
was needed for our process. Good chemo- and regioselectivity
were observed for a variety of a-keto alkynes to produce 2(3H)-,
or 2(5H)-furanone as the dominant product. The three different
reaction pathways can be controlled simply by variation of the
reaction conditions, i.e., the reaction temperature and the pres-
sure of CO. Furthermore, the Co2Rh2 catalyst is recyclable and
no hydrogenated byproduct was obtained. Current efforts in our
laboratory are directed towards acquiring a deeper understand-
ing of the mechanism responsible for this new type of reaction.
Yield (%)a
Entry
1
Substrate
5
6
7
8
26
57
55b
70
2
3
4
5
6
30
17
11
12
31
54
68
13
25
28
23
22
48
73
80
43
42
62c
84
78
Acknowledgements
This work was supported by the Ministry of Science and Tech-
nology of Korea through the Research Center for Nanocatalysis,
one of the National Science Programs for Key Nanotechnology
and by grant No. (R02-2004-000-10005-0(2004)) from the
Basic Research Program of the Korea Science & Engineering
Foundation. KHP and SYK thank the Ministry of Education
for the Brain Korea 21 Fellowship.
References
1 Recent papers, see: (a) T. Shiba, D. Y. Zhou, K. Onitsuka and S.
Takahashi, Tetrahedron Lett., 2004, 45, 3211; (b) D. Y. Zhou, S. W.
Zhang, K. Onitsuka and S. Takahashi, Chem. Lett., 2004, 33, 70;
(c) K. Kumar, A. Zapf, D. Michalik, A. Tillack, T. Heinrich, H.
Bo¨ttcher, M. Arlt and M. Beller, Org. Lett., 2004, 6, 7; (d) S. M.
Kulkarni, M. R. Didgikar and R. V. Chaudhari, J. Mol. Catal
A: Chem., 2004, 207, 97; (e) T. Takahashi, S. Kusaka, T. Doi, T.
¯
Sunazuka and S. Omura, Angew. Chem., Int. Ed., 2003, 42, 5230;
(f) H. Y. Xu and L. Jia, Org. Lett., 2003, 5, 1575; (g) A. Kamitani, N.
Chatani and S. Murai, Angew. Chem., Int. Ed., 2003, 42, 1397.
2 Recent papers, see: (a) C. Granito, L. Troisi and L. Ronzini,
Heterocycles, 2004, 63, 1027; (b) G. Lenoble, C. Lacaze-Dufaure,
M. Urruitigo¨ıty, C. Mijoule and P. Kalck, Eur. J. Inorg. Chem., 2004,
791; (c) C. Dong and H. Alper, Tetrahedron: Asymmetry, 2004, 15,
35; (d) S. Ma, B. Wu and S. Zhao, Org. Lett., 2003, 5, 4429; (e) A.
Kamitani, N. Chatani and S. Murai, Angew. Chem., Int. Ed., 2003,
42, 1397.
3 (a) K. Doyama, T. Joh, S. Takahashi and T. Shiohara, Tetrahedron
Lett., 1986, 4497; (b) K. Doyama, T. Joh, T. Shiohara and S. Taka-
hatihi, Bull. Chem. Soc. Jpn., 1988, 61, 4353; (c) T. Joh, K. Doyama,
K. Fujiwara, K. Maeshima and S. Takahashi, Organometallics, 1991,
10, 508; (d) T. Joh, K. Doyama, K. Onitsuka, T. Shiohara and S.
Takahashi, Organometallics, 1991, 10, 2493; (e) T. Joh, H. Nagata
and S. Takahashi, Chem. Lett., 1992, 1305; (f) T. Joh, H. Nagata and
S. Takahashi, Inorg. Chim. Acta, 1994, 220, 45.
4 (a) N. Mizutani, W. H. Chiou and I. Ojima, Org. Lett., 2002, 4, 4575;
(b) I. Ojima, A. C. Moralee and V. C. Vassar, Topics Catal., 2002,
19, 89; (c) I. Ojima, Pure Appl. Chem., 2002, 74, 159; (d) I. Ojima
and E. S. Vidal, J. Org. Chem., 1998, 63, 7999; (e) I. Ojima, D. M.
Iula and M. Tzamarioudaki, Tetrahedron Lett., 1998, 39, 4599; (f) I.
Ojima, M. Tzamarioudaki and M. Eguchi, J. Org. Chem., 1995, 60,
7078.
5 (a) B. G. Van den Hoven and H. Alper, J. Am. Chem. Soc., 2001,
123, 1017; (b) B. G. Van den Hoven and H. Alper, J. Am. Chem. Soc.,
2001, 123, 10214; (c) B. G. Van den Hoven, B. El Ali and H. Alper,
J. Org. Chem., 2000, 65, 4131.
6 (a) A. Roucoux, J. Schulz and H. Patin, Chem. Rev., 2002, 102, 3757–
3778; (b) M. Kra´lik and A. Biffis, J. Mol. Catal. A: Chem., 2001,
177, 113–138; (c) J. M. Thomas and R. Raja, Chem. Record, 2001,
1, 448–466; (d) C. N. R. Rao and A. K. Cheetham, J. Mater. Chem.,
2001, 11, 2887–2894; (e) P. L. Gai, R. Roper and M. G. White, Curr.
Opin. Solid St. Mater. Sci., 2002, 6, 401–406.
a Isolated yields, a-keto alkynes (0.5 g, 2.42 mmol), Co2Rh2 (0.01 g,
0.029 mmol), Et3N (2 ml), H2O (1 ml), THF (10 ml). b 5-Isopropyl-3-
1
phenyl-3H-furan-2-one (7a): H NMR (CDCl3, 300 MHz): d 7.54–7.50
(m, 2H), 7.40–7.30 (m, 3H), 5.19 (d, J = 5.10 Hz, 1H), 2.92–2.80 (m,
1H), 2.16–2.14 (m, 1H), 1.23 (d, J = 2.11 Hz, 3H), 1.19 (d, J = 2.09 Hz,
3H); 13C NMR (CDCl3, 75 MHz): d 194.6, 133.3, 131.0, 128.9, 71.8,
53.1, 30.1, 21.7, 18.9, 17.9; HRMS for C13H14O2: calcd. 202.0994, obsd.
202.0996. c 5-Isopropyl-3-phenyl-3H-furan-2-one (7a): 1H NMR (CDCl3,
300 MHz): d 7.54–7.50 (m, 2H), 7.40–7.30 (m, 3H), 5.19 (d, J = 5.10 Hz,
1H), 2.92–2.80 (m, 1H), 2.16–2.14 (m, 1H), 1.23 (d, J = 2.11 Hz, 3H),
1.19 (d, J = 2.09 Hz, 3H); 13C NMR (CDCl3, 75 MHz): d 194.6, 133.3,
131.0, 128.9, 71.8, 53.1, 30.1, 21.7, 18.9, 17.9; HRMS for C13H14O2:
calcd. 202.0994, obsd. 202.0996.
molecule as the active species in the cyclohydrocarbonylation
7 (a) K.-M. Choi, T. Mizugaki, K. Ebitani and K. Kaneda, Chem.
Lett., 2003, 32, 180–181; (b) K. Mallick, M. J. Witcomb and M. S.
Scurrell, Appl. Catal. A: Gen., 2004, 259, 163–168; (c) S. Carrettin, P.
McMorn, P. Johnston, K. Griffin, C. J. Kiely, G. A. Attard and G. J.
Hutchings, Topics Catal., 2004, 27, 131–136; (d) S. Arrii, F. Morfin,
A. J. Renouprez and J. L. Rousset, J. Am. Chem. Soc., 2004, 126,
1199–1205; (e) Y.-C. Kim, N.-C. Park, J.-S. Shin, S. R. Lee, Y. J. Lee
and D. J. Moon, Catal. Today, 2003, 87, 153–162; (f) C.-M. Yang, M.
Kalwei, F. Schu¨th and K.-J. Chao, Appl. Catal. A: Gen., 2003, 254,
289–296; (g) H. Lang, R. A. May, B. L. Iversen and B. D. Chandler,
J. Am. Chem. Soc., 2003, 125, 14832–14836.
of acetylenes. In the cyclohydrocarbonylation of a-keto alkynes,
Alper et al. proposed a rhodium hydride as the active species.
5c
The reaction was initiated by the binding of the rhodium hydride
complex to the triple bond of the alkynone with possible weak
H-bonding interactions to the ketone functionality. However,
the precise mechanism of Co2Rh2 catalysis has not yet been
revealed, but it is likely to be distinct from those proposed by
the Takahashi and Alper groups.
In conclusion, we have demonstrated that the cyclohydrocar-
bonylation of acetylenes was readily accomplished by Co2Rh2
heterobimetallic nanoparticles in the presence of CO, water, and
triethylamine. Neither a toxic phosphite nor expensive hydrogen
8 (a) V. Chechik and R. M. Crooks, J. Am. Chem. Soc., 2000, 122,
1243–1244; (b) P. Lu, T. Teranishi, K. Asakura, M. Miyake and N.
Toshima, J. Phys. Chem. B, 1999, 103, 9673–9682; (c) J. Dupont, G. S.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 9 5 – 3 9 8
3 9 7

View Article Online
Fonseca, A. P. Umpierre, P. F. P. Fichtner and S. R. Teixeira, J. Am.
Chem. Soc., 2002, 124, 4228–4229; (d) G. S. Fonseca, A. P. Umpierre,
P. F. P. Fichtner, S. R. Teixeira and J. Dupont, Chem. Eur. J., 2003, 9,
3263–3269; (e) J. W. Yoo, D. Hathcock and M. A. El-Sayed, J. Phys.
Chem. A, 2002, 106, 2049–2054; (f) M. Adlim, M. Abu Bakar, K. Y.
Liew and J. Ismail, J. Mol. Catal. A: Chem., 2004, 212, 141–149; (g) S.
Kidambi, J. Dai, J. Li and M. L. Bruening, J. Am. Chem. Soc., 2004,
126, 2658–2659.
Park and Y. K. Chung, Org. Lett., 2002, 4, 3983; (d) K. H. Park, S. U.
Son and Y. K. Chung, Org. Lett., 2002, 4, 4361; (e) S. U. Son, K. H.
Park and Y. K. Chung, J. Am. Chem. Soc., 2002, 124, 6838–6839;
(f) K. H. Park, S. U. Son and Y. K. Chung, Chem. Commun., 2003,
1898.
12 (a) K. H. Park, I. G. Jung and Y. K. Chung, Org. Lett., 2004, 6, 1183;
(b) K. H. Park, I. G. Jung, S.-Y. Kim and Y. K. Chung, Org. Lett.,
2003, 5, 4967; (c) K. H. Park and Y. K. Chung, Adv. Synth. Catal.,
2004, submitted.
9 (a) Y. Liu, C. Khemtong and J. Hu, Chem. Commun., 2004, 398–399;
(b) Y. Na, S. Park, S. B. Han, H. Han, S. Ko and S. Chang, J. Am.
Chem. Soc., 2004, 126, 250–258; (c) K. R. Gopidas, J. K. Whitesell
and M. A. Fox, Nano Lett., 2003, 3, 1757–1760; (d) M. Pittelkow,
K. Moth-Poulsen, U. Boas and J. B. Christensen, Langmuir, 2003,
19, 7682–7684; (e) R. Narayanan and M. A. El-Sayed, J. Am.
Chem. Soc., 2003, 125, 8340–8347; (f) L. Strimbu, J. Liu and A. E.
Kaifer, Langmuir, 2003, 19, 483–485; (g) V. Kogan, Z. Aizenshtat,
R. Popovitz-Biro and R. Neumann, Org. Lett., 2002, 4, 3529–3532.
10 (a) H. M. Sung-Suh, J. R. Choi, H. J. Hah, S. M. Koo and Y. C. J.
Bae, Photochem. Photobiol. A: Chem., 2004, 163, 37–44; (b) H. Wei,
Y. Wu, N. Lun and F. Zhao, J. Mater. Sci., 2004, 39, 1305–1308;
(c) A. Orlov, D. A. Jefferson, N. Macleod and R. M. Lambert, Catal.
Lett., 2004, 92, 41–47; (d) S.-S. Hong, M. S. Lee, S. S. Park and G.-D.
Lee, Catal. Today, 2003, 87, 99–105; (e) T. Hirai, M. Nanba and I.
Komasawa, J. Colloid Interf. Sci., 2003, 268, 394–399; (f) H. Yoshida,
J.-I. Nishimoto, Y. Miyashita, C. Ooka, S.-I. Komai, A. Satsuma and
T. Hattori, Chem. Lett., 2003, 32, 1030–1031; (g) L. Zhang, J. C. Yu,
H. Y. Yip, Q. Li, K. W. Kwong, A.-W. Xu and P. K. Wong, Langmuir,
2003, 19, 10372–10380.
13 (a) Y. S. Rao, Chem. Rev., 1976, 76, 625; (b) D. W. Knight, Contemp.
Org. Synth., 1994, 1, 287; (c) C. L. Gibson and S. Handa, Tetrahedron:
Asymmetry, 1996, 7, 1281; (d) A. A. Freer, G. W. Kirby, G. V. Rao
and R. B. Cain, J. Chem. Soc., Perkin Trans. 1, 1996, 2111; (e) H. van
der Deen, A. D. Cuiper, R. P. Hof, A. van Oeveren, B. L. Feringa
and R. M. Kellogg, J. Am. Chem. Soc., 1996, 118, 3801; (f) D.
Barton, K. Nakanishi, O. Meth-Cohn, in Comprehensive Natural
Products Chemistry, Elsevier Science Ltd., Oxford, 1999, vol. 8, pp
378–385; (g) F. Bellina, C. Anselmi, S. Viel, L. Mannina and R. Rossi,
Tetrahedron, 2001, 57, 9997; (h) A. Zarghi, P. N. P. Rao and E. E.
Knaus, Bioorg. Med. Chem. Lett., 2004, 14, 1957; (i) R. Cheˆnevert, D.
Duguay, F. Touraille and D. Caron, Tetrahedron: Asymmetry, 2004,
15, 863; (j) N. Ghoshal and P. K. Mukherjee, Bioorg. Med. Chem.
Lett., 2004, 14, 103.
14 (a) A. Cowell and J. K. Stille, Tetrahedron Lett., 1979, 20, 133; (b) H.
Alper and D. Leonard, Tetrahedron Lett., 1985, 26, 5639; (c) Y. Inoue,
M. Taniguchi, H. Hashimoto, K. Ohuchi and S. Imaizumi, Chem.
Lett., 1988, 81; (d) B. El Ali, K. Okuro, G. Vaspollo and H. Alper,
J. Am. Chem. Soc., 1996, 118, 4264; (e) R. Rossi, F. Bellina, M.
Biagetti and L. Mannina, Tetrahedron Lett., 1998, 39, 7599; (f) P. Cao
and X. Zhang, J. Am. Chem. Soc., 1999, 121, 7708; (g) Y. Fukuta, I.
Matsuda and K. Itoh, Tetrahedron Lett., 2001, 42, 1301.
11 (a) S.-W. Kim, S. U. Son, Y. K. Chung and T. Hyeon, Chem.
Commun., 2001, 2212; (b) S. U. Son, S. I. Lee, Y. K. Chung, S.-
W. Kim and T. Hyeon, Org. Lett., 2002, 4, 277; (c) S. U. Son, K. H.
3 9 8
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 9 5 – 3 9 8