Palladium-catalyzed carbonylative cyclization of 1-bromoallyl bromides with anilines leading to 1-aryl-1H-pyrrol-2(5H)-ones

Article abstract of DOI:10.1002/aoc.2887

1-Bromoallyl bromides are carbonylatively cyclized with anilines under carbon monoxide pressure in DMF in the presence of a catalytic amount of a palladium catalyst along with a base to give the corresponding 1-aryl-1H-pyrrol-2(5H)-ones in moderate to goo

Full text of DOI:10.1002/aoc.2887

Full Paper
Received: 22 March 2012
Revised: 20 April 2012
Accepted: 21 April 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.2887
Palladium-catalyzed carbonylative cyclization
of 1-bromoallyl bromides with anilines
leading to 1-aryl-1H-pyrrol-2(5H)-ones
Chan Sik Choa*, Jong Ik Sona and Nam Sik Yoonb
1-Bromoallyl bromides are carbonylatively cyclized with anilines under carbon monoxide pressure in DMF in the presence of a
catalytic amount of a palladium catalyst along with a base to give the corresponding 1-aryl-1H-pyrrol-2(5H)-ones in moderate
to good yield. Copyright © 2012 John Wiley & Sons, Ltd.
Keywords: anilines; 1-aryl-1H-pyrrol-2(5H)-ones; 1-bromoallyl bromides; carbonylative cyclization; palladium catalyst
and 5a in DMF in the presence of a catalytic amount of PdCl2
(PPh3)2 (4 mol%) along with K2CO3 under carbon monoxide
Introduction
Transition metal-catalyzed carbonylation followed by cyclization
(carbonylative cyclization) has been widely explored and used as
a promising synthetic tool for the construction of the structural core
of many pharmacologically and biologically active lactones and
lactams.[1–6] In connection with this report, it is known that
b-bromo-a,b-unsaturated aldehydes and their derivatives, which
are readily prepared from the corresponding ketones by Vilsmeier–
Haack reaction[7,8] and subsequent transformation, are used as
a building block for the construction of versatile cyclic com-
pounds.[9–31] As part of our continuing studies directed towards
palladium-catalyzed cyclization reactions using b-bromo-a,b-
unsaturated aldehydes and their derivatives,[32–35] we reported on
the synthesis of several heterocycles via such a carbonylative cycliza-
tion.[36–39] Among them, 2-bromocyclohex-1-enecarbaldehydes
were found to be carbonylatively cyclized with anilines in the
presence of a palladium catalyst under carbon monoxide pressure
to give hydroisoindol-1-ones (Scheme 1).[38] However, unfortunately,
the carbonylative cyclization did not take place at all with other
cyclic b-bromovinyl aldehydes except for six-membered ones under
the employed conditions. This led us to seek for a synthetic method
for such heterocycles using other starting compounds under
similar palladium-catalyzed carbonylative cyclization conditions. This
report shows a palladium-catalyzed carbonylative cyclization of
1-bromoallyl bromides with anilines leading to 1-aryl-1H-pyrrol-2
(5H)-ones.[40]
pressure (10 atm) afforded 2-phenyl-2,3,4,5,6,7-hexahydro-1H-
isoindol-1-one (6a) in 48% isolated yield with concomitant
formation of nucleophilic substitution product 7 (entry 1). Higher
carbon monoxide pressure did not affect the product yield and
distribution (entry 2). Performing the reaction under either higher
reaction temperature for 40 h or changing the molar ratio of
[5a]/[4a] gave no significant change to 6a yield, whereas 7 was
produced in a considerably increased yield (entries 3 and 4).
Among bases examined, NaOtBu was not effective at all toward
the formation of 6a (entry 5). With other bases such as NaOAc
and Bu3N, the yield of 6a was lower than that when K2CO3 was
employed (entries 6 and 7).
Based on reaction conditions of Table 1, various 1-bromoallyl
bromides 4 were subjected to the reaction with anilines 5 in
order to investigate the reaction scope, and several representative
results are summarized in Table 2. With cyclic 1-bromoallyl
bromides (4a–d) having various ring sizes, the carbonylative
cyclized products (6a–h) were formed in the range of 24–64% yield
and the product yield was considerably affected by the ring size of
4a–d. The product yield gradually decreases with increase in the
ring size of 4a–d. In the reaction with 4c and 4d, a higher reaction
temperature was needed for the allowable yield of products.
Judging from the reaction of 4b with anilines 5a–e, the position
and electronic nature of the substituent on the aromatic ring of
5a–e had no relevance to the product yield. To test for the
effect of the position of bromide and bromomethyl group on
1-bromoallyl bromides, 4e and 4f were employed. The carbonylative
cyclization readily took place with 4e, whereas the reaction with
4f did not proceed toward the desired carbonylative cyclization
Results and Discussion
The starting 1-bromoallyl bromides 4 were synthesized by initial
conversion of the corresponding a-methylene containing
ketones 1 into b-bromovinyl aldehydes 2 under bromination
conditions of the Vilsmeier–Haack reaction (PBr3/DMF/CHCl3)
(Scheme 2).[7,8] Allyl alcohols 3 prepared by treating 2 with
NaBH4/MeOH were easily brominated to 4 under PBr3 in CCl4.[26]
The results of several attempted carbonylative cyclizations of
1-bromo-2-(bromomethyl)cyclohex-1-ene (4a) with aniline (5a)
are listed in Table 1. Treatment of equimolar amounts of 4a
*
Correspondence to: Chan Sik Cho, Department of Applied Chemistry, Kyungpook
National University, Daegu 702–701, South Korea. E-mail: cscho@knu.ac.kr
a Department of Applied Chemistry, Kyungpook National University, Daegu 702-
701, South Korea
b Department of Textile System Engineering, Kyungpook National University,
Daegu 702-701, South Korea
Appl. Organometal. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.

C. S. Cho et al.
Conclusion
In summary, 1-bromoallyl bromides, which are readily prepared
from ketones by three steps, are carbonylatively cyclized with
anilines under carbon monoxide pressure in the presence of a
catalytic amount of PdCl2(PPh3)2 along with K2CO3 to give 1-aryl-
1H-pyrrol-2(5H)-ones. The present reaction provides a promising
route for 1-aryl-1H-pyrrol-2(5H)-ones from readily available starting
ketones. Further study of synthetic applications to heterocycles by
using this ketone as starting compound is in progress.
Scheme 1. Palladium-catalyzed carbonylative cyclization leading to
hydroisoindol-1-ones
Experimental
1H and 13C NMR (400 and 100 MHz) spectra were recorded on a
Bruker Avance Digital 400 spectrometer using tetramethylsilane
(TMS) as an internal standard. Melting points were determined on
a Standford Research Inc. MPA100 automated melting point
apparatus. Gas–liquid chromatographic analyses were carried out
with a Shimadzu GC-17A (FID) equipped with CBP10-S25-050
column (Shimadzu, silica fused capillary column, 0.33 mm 25 m,
0.25 mm film thickness) using N2 as carrier gas. The isolation of pure
products was carried out via thin-layer chromatography (silica gel
60 GF254, Merck). 1-Bromoallyl bromides 4 were synthesized in
Scheme 2. Synthesis of 1-bromoallyl bromides
under the same reaction conditions. Performing the reaction with
4f under the conditions of 150ꢀC and 40 h, as is the case for the
reaction with 4d, afforded 6j in only 25% yield. Similar reactivity
was observed by our recent report: palladium-catalyzed carbonylative
cyclization of 2-bromocyclohex-1-enecarbaldehydes with anilines
leading to hydroisoindol-1-ones.[38] Similar treatment of acyclic
1,3-dibromoprop-1-ene 4g under the employed conditions also
afforded the carbonylative cyclized product 6k; however, the
yield was lower than that when previously described cyclic
1,3-dibromoprop- 1-enes were used except for 4d and 4f.
[7,8]
three steps, initial treatment of ketones 1 with PBr3/DMF/CHCl3
to produce b-bromovinyl aldehydes 2, followed by reduction of 2
to allyl alcohols 3 using NaBH4 and bromination using PBr3.[20]
Commercially available organic and inorganic compounds were
used without further purification.
A plausible reaction pathway is presented in Scheme 3. Oxidative
addition of the carbon–bromide bond of allyl amine 7, initially
formed in situ between 4a and 5a, to palladium(0), produces a
vinylpalladium(II) complex 8, where carbon monoxide coordination
to palladium and then vinyl migration from palladium to the
carbon of carbon monoxide occurs to give an acylpalladium(II)
intermediate 9. Intermediate 9 reacts with a base to produce a
palladacycle intermediate 10 which can reductively eliminate to
give 6a. We confirmed in a separate experiment that treatment of
7 under the employed conditions afforded 6a in 8% yield.
General Experimental Procedure for Palladium-Catalyzed
Carbonylative Cyclization of 1-Bromoallyl Bromides with
Anilines
To a 50 ml stainless steel autoclave were added 1-bromoallyl
bromide 4 (0.5mmol), aniline 5 (0.5 mmol), PdCl2(PPh3)2 (0.014 g,
0.02 mmol), K2CO3 (0.138 g, 1 mmol) and DMF (10 ml). After the
system was flushed and then pressurized with carbon monoxide,
the reaction mixture was allowed to react under appropriate
Table 1. Palladium-catalyzed carbonylative cyclization of 4a with 5aa
Ph
N
PdCl2(PPh3)2
DMF, CO
Br
N
Ph
H2N Ph
+
+
H
Br
4a
Br
O
5a
6a
7
Entry
Base
Temp. (ꢀC)
Pressure (atm)
Time (h)
Yield (%)
6a
48
7
1
K2CO3
K2CO3
K2CO3
K2CO3
NaOtBu
NaOAc
Bu3N
100
100
120
130
100
100
100
10
20
10
10
10
10
10
20
20
40
20
20
20
20
25
2
49
55
48
1
31
44
47
45
32
29
3
4b
5
6
41
38
7
aReaction conditions: 4a (0.5 mmol), 5a (0.5 mmol), PdCl2(PPh3)2 (0.02 mmol), base (1 mmol), DMF (10 ml).
b5a (1 mmol).
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Copyright © 2012 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. (2012)

Palladium-catalyzed carbonylative cyclization
Table 2. Palladium-catalyzed carbonylative cyclization of 1,3-dibromopropenes 4 with anilines 5 leading to 1-aryl-1H-pyrrol-2(5H)-ones 6a
N
Br
PdCl2(PPh3)2, K2CO3
CO (10 atm), DMF
H2N
+
R
R
Br
O
6
5a R =H
4
5b R = 4-Me
5c R = 3-Me
5d R = 2-Me
5e R = 4-Cl
1,3-Dibromopropenes 4
Anilines 2
Conditions
1-Aryl-1H-pyrrol-2(5H)-ones 6
Yield (%)
Br
Br
N
O
4a
5a
100 ꢀC, 20 h
120 ꢀC, 40 h
6a
48
55
Br
Br
N
R
O
4b
5a
100 ꢀC, 20 h
100 ꢀC, 40 h
100 ꢀC, 20 h
100 ꢀC, 20 h
100 ꢀC, 20 h
100 ꢀC, 40 h
6b
51
64
52
44
50
45
5b
5c
5d
5e
6c
6d
6e
6f
Br
Br
N
O
4c
5a
5a
100 ꢀC, 20 h
150 ꢀC, 40 h
6g
25
56
Br
Br
N
O
4d
100 ꢀC, 20 h
150 ꢀC, 20 h
6h
0
24
Br
Br
N
Me
O
4e
5d
5a
100 ꢀC, 20 h
6i
6j
71
Br
Br
N
O
4f
100 ꢀC, 20 h
150 ꢀC, 40 h
0
25
Br
Br
N
O
4g
5a
100 ꢀC, 20 h
6k
30
aReaction conditions: 4 (0.5 mmol), 5 (0.5 mmol), PdCl2(PPh3)2 (0.02 mmol), K2CO3 (1 mmol), DMF (10 ml), CO (10 atm).
Appl. Organometal. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.
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C. S. Cho et al.
Scheme 3. A catalytic cycle
reaction temperature and time. The reaction mixture was filtered
through a short silica gel column (ethyl acetate–hexane mixture)
to eliminate inorganic salts. Removal of the solvent left a crude
mixture, which was separated by thin-layer chromatography (silica
gel, ethyl acetate-hexane mixture) to give 1-aryl-1H-pyrrol-2(5H)-
ones 6. Except for 6a and 6i, which were characterized by
gas–liquid chromatography and spectroscopic comparison with
authentic samples synthesized by our recent report,[38] all products
prepared by the above procedure were characterized spectroscop-
ically as shown below.
Anal. Calcd for C15H17NO: C, 79.63; H, 7.94; N, 5.80. Found: C,
79.56; H, 7.89; N, 5.75.
2-(2-Methylphenyl)-2,3,5,6,7,8-hexahydrocyclohepta[c]pyrrol-1(4H)-one (6e)
Solid; m.p. 113–114ꢀC (from hexane–ethyl acetate). 1H NMR (CDCl3)
d 1.63–1.75 (m, 4H, 2CH2), 1.81–1.87 (m, 2H, CH2), 2.22 (s, 3H, CH3),
2.44–2.49 (m, 4H, 2CH2), 4.08 (s, 2H, CH2-N), 7.12–7.15 (m, 1H, CH),
7.19–7.24 (m, 2H, 2CH), 7.26–7.28 (m, 1H, CH). 13C NMR (CDCl3) d
18.51 (CH3), 25.41 (CH2), 27.42 (CH2), 27.46 (CH2), 30.02 (CH2),
31.31 (CH2), 56.53 (CH2-N), 126.79 (aromatic C), 127.55 (aromatic
C), 127.78 (aromatic C), 131.26 (aromatic C), 134.82 (vinyl C),
136.49 (aromatic C), 137.56 (aromatic C), 153.21 (vinyl C), 177.77
(C-O). Anal. Calcd for C15H17NO: C, 79.63; H, 7.94; N, 5.80. Found:
C, 79.50; H, 7.88; N, 5.70.
2-Phenyl-2,3,5,6,7,8-hexahydrocyclohepta[c]pyrrol-1(4H)-one (6b)
Solid; m.p. 126–127ꢀC (from hexane–ethyl acetate). 1H NMR (CDCl3)
d 1.62–1.74 (m, 4H, 2CH2), 1.80–1.86 (m, 2H, CH2), 2.45–2.48 (m, 4H,
2CH2), 4.19 (s, 2H, CH2-N), 7.07–7.11 (m, 1H, CH), 7.33–7.37
(m, 2H, 2CH), 7.72–7.74 (m, 2H, 2CH). 13C NMR (CDCl3) d 25.11
(CH2), 27.33 (CH2), 27.39 (CH2), 29.92 (CH2), 31.22 (CH2), 54.05
(CH2-N), 118.42 (aromatic C), 123.59 (aromatic C), 129.22 (aromatic
C), 135.92 (vinyl C), 139.84 (aromatic C), 152.16 (vinyl C), 171.51
(C-O). Anal. Calcd for C15H17NO: C, 79.26; H, 7.54; N, 6.16. Found:
C, 79.25; H, 7.47; N, 6.14.
2-(4-Chlorophenyl)-2,3,5,6,7,8-hexahydrocyclohepta[c]pyrrol-1(4H)-one (6f)
Solid; m.p. 165–168ꢀC (from hexane–ethyl acetate). 1H NMR (CDCl3)
d 1.61–1.74 (m, 4H, 2CH2), 1.80–1.86 (m, 2H, CH2), 2.45–2.48 (m, 4H,
2CH2), 4.16 (s, 2H, CH2-N), 7.27–7.32 (m, 2H, 2CH), 7.67–7.70
(m, 2H, 2CH). 13C NMR (CDCl3) d 25.08 (CH2), 27.28 (CH2), 27.34
(CH2), 29.74 (CH2), 31.17 (CH2), 53.97 (CH2-N), 119.44 (aromatic
C), 128.51 (aromatic C), 129.19 (aromatic C), 135.91 (vinyl C),
138.43 (aromatic C), 152.34 (vinyl C), 171.47 (C-O). Anal. Calcd
for C15H16ClNO: C, 68.83; H, 6.16; N, 5.35. Found: C, 68.67; H,
6.10; N, 5.32.
2-(4-Methylphenyl)-2,3,5,6,7,8-hexahydrocyclohepta[c]pyrrol-1(4H)-one (6c)
Solid; m.p. 120–121ꢀC (from hexane–CH2Cl2). 1H NMR (CDCl3) d
1.61–1.73 (m, 4H, 2CH2), 1.79–1.85 (m, 2H, CH2), 2.32 (s, 3H, CH3),
2.44–2.46 (m, 4H, 2CH2), 4.15 (s, 2H, CH2-N), 7.15 (d, JHH = 8.5 Hz,
2H, 2CH), 7.59 (d, JHH = 8.5Hz, 2H, 2CH). 13C NMR (CDCl3) d 20.97
(CH3), 25.11 (CH2), 27.34 (CH2), 27.40 (CH2), 29.89 (CH2), 31.21
(CH2), 54.18 (CH2-N), 118.57 (aromatic C), 129.70 (aromatic C),
133.14 (aromatic C), 135.86 (vinyl C), 137.35 (aromatic C), 151.89
(vinyl C), 171.36 (C-O). Anal. Calcd for C16H19NO: C, 79.63; H,
7.94; N, 5.80. Found: C, 79.54; H, 7.85; N, 5.73.
2-Phenyl-2,3,4,5,6,7,8,9-octahydro-1H-cycloocta[c]pyrrol-1-one (6g)
Solid; m.p. 110–111ꢀC (from hexane–ethyl acetate). 1H NMR (CDCl3)
d 1.54–1.56 (m, 4H, 2CH2), 1.67–1.73 (m, 2H, CH2), 1.76–1.82 (m, 2H,
CH2), 2.50–2.56 (m, 4H, 2CH2), 4.21 (s, 2H, CH2-N), 7.07–7.11 (m, 1H,
CH), 7.33–7.38 (m, 2H, 2CH), 7.74–7.77 (m, 2H, 2CH). 13C NMR (CDCl3)
d 22.22 (CH2), 25.83 (CH2), 26.12 (CH2), 26.90 (CH2), 27.72 (CH2),
27.75 (CH2), 53.36 (CH2-N), 118.23 (aromatic C), 123.54 (aromatic
C), 129.23 (aromatic C), 134.13 (vinyl C), 139.91 (aromatic C),
150.78 (vinyl C), 171.35 (C-O). Anal. Calcd for C16H19NO: C, 79.63;
H, 7.94; N, 5.80. Found: C, 79.59; H, 7.84; N, 5.62.
2-(3-Methylphenyl)-2,3,5,6,7,8-hexahydrocyclohepta[c]pyrrol-1(4H)-one (6d)
Solid; m.p. 81–83ꢀC (from hexane–CH2Cl2). 1H NMR (CDCl3) d
1.61–1.73 (m, 4H, 2CH2), 1.78–1.85 (m, 2H, CH2), 2.36 (s, 3H,
CH3), 2.45–2.47 (m, 4H, 2CH2), 4.17 (s, 2H, CH2-N), 6.91 (d, JHH = 7.8
Hz, 1H, CH), 7.49 (d, JHH = 7.8 Hz, 1H, CH), 7.59 (s, 1H, CH), 7.23
(t, JHH = 7.8 Hz, 1H, CH). 13C NMR (CDCl3) d 21.89 (CH3), 25.11
(CH2), 27.33 (CH2), 27.40 (CH2), 29.91 (CH2), 31.20 (CH2), 54.20
(CH2-N), 115.60 (aromatic C), 119.29 (aromatic C), 124.46
(aromatic C), 129.01 (aromatic C), 135.89 (vinyl C), 139.03
(aromatic C), 139.76 (aromatic C), 152.07 (vinyl C), 171.48 (C-O).
2-Phenyl-2,3,4,5,6,7,8,9,10,11,12,13-dodecahydro-1H-cyclododeca[c]pyrrol-1-
one (6h)
Solid; m.p. 99–101ꢀC (from hexane–CH2Cl2). 1H NMR (CDCl3) d
1.35–1.46 (m, 12H, 6CH2), 1.64–1.77 (m, 4H, 2CH2), 2.87 (t, JHH = 6.7
Hz, 2H, CH2), 2.47 (t, JHH = 7.3 Hz, 2H, CH2), 4.20 (s, 2H, CH2-N),
7.06–7.09 (m, 1H, CH), 7.33–7.37 (m, 2H, 2CH), 7.74–7.76 (m, 2H,
2CH). 13C NMR (CDCl3) d 21.25 (CH2), 21.95 (CH2), 22.86 (CH2),
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Palladium-catalyzed carbonylative cyclization
[3] E. Negishi (Ed.), Handbook of Organopalladium Chemistry for
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[4] L. Kollár (Ed), Modern Carbonylation Methods, Wiley-VCH, Weinheim,
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48, 4114.
23.80 (CH2), 24.62 (CH2), 24.83 (CH2), 25.22 (CH2), 25.24 (CH2), 25.63
(CH2), 26.20 (CH2), 52.67 (CH2-N), 118.23 (aromatic C), 123.54 (aro-
matic C), 129.17 (aromatic C), 133.93 (vinyl C), 139.83 (aromatic C),
150.82 (vinyl C), 171.46 (C-O). Anal. Calcd for C20H27NO: C, 80.76;
H, 9.15; N, 4.71. Found: C, 80.55; H, 9.09; N, 4.68.
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5, 2497.
2-Phenyl-4,5-dihydro-1H>-benzo[e]isoindol-3(2H)-one (6j)
Solid; m.p. 130–131ꢀC (from hexane–CH2Cl2). 1H NMR (CDCl3) d
2.61–2.66 (m, 2H, CH2), 3.00 (t, JHH = 8.3Hz, 2H, CH2), 4.65 (t, JHH = 2.3
Hz, 2H, CH2-N), 7.11–7.15 (m, 1H, CH), 7.21–7.31 (m, 4H, 4CH),
7.38–7.42 (m, 2H, 2CH), 7.79–7.82 (m, 2H, 2CH). 13C NMR (CDCl3) d
18.65 (CH2), 28.09 (CH2), 50.06 (CH2-N), 118.72 (aromatic C), 122.99
(aromatic C), 123.96 (vinyl C), 127.09 (aromatic C), 128.77
(aromatic C), 129.32 (aromatic C), 129.48 (aromatic C), 130.00
(aromatic C), 132.93 (aromatic C), 137.38 (aromatic C), 139.88
(aromatic C), 146.01 (vinyl C), 170.20 (C-O). Anal. Calcd for
C18H15NO: C, 82.73; H, 5.79; N, 5.36. Found: C, 82.66; H, 5.70; N, 5.32.
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51, 4132.
1,3,4-Triphenyl-1H-pyrrol-2(5H)-one (6k)
Solid; m.p. 187–189ꢀC (from hexane–ethyl acetate). 1H NMR (CDCl3)
d 4.75 (s, 2H, CH2-N), 7.13–7.17 (m, 1H, CH), 7.29–7.46 (m, 12H,
12CH), 7.84–7.86 (m, 2H, 2CH). 13C NMR (CDCl3) d 52.82 (CH2-N),
118.70 (aromatic C), 124.26 (vinyl C), 127.90 (aromatic C), 128.50
(aromatic C), 128.67 (aromatic C), 129.00 (aromatic C), 129.35
(aromatic C), 129.73 (aromatic C), 129.83 (aromatic C), 131.74
(aromatic C), 132.87 (aromatic C), 133.62 (aromatic C), 139.54
(aromatic C), 147.09 (vinyl C), 169.69 (C-O). Anal. Calcd for
C22H17NO: C, 84.86; H, 5.50; N, 4.50. Found: C, 84.67; H, 5.47; N, 4.51.
[29] N. Yasmin, J. K. Ray, Synlett 2010, 924.
Acknowledgments
[30] N. Yasmin, J. K. Ray, Tetrahedron Lett. 2010, 51, 4759.
[31] S. Paul, T. Gorai, A. Koley, J. K. Ray, Tetrahedron Lett. 2011, 52, 4051.
[32] C. S. Cho, D. B. Patel, S. C. Shim, Tetrahedron 2005, 61, 9490.
[33] C. S. Cho, D. B. Patel, Tetrahedron 2006, 62, 6388.
[34] C. S. Cho, H. B. Kim, W. X. Ren, N. S. Yoon, Appl. Organomet. Chem.
2010, 24, 817.
This research was supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF)
funded by the Ministry of Education, Science and Technology
(2012–0002856).
[35] C. S. Cho, H. B. Kim, J. Organomet. Chem. 2011, 696, 3264.
[36] C. S. Cho, H. S. Shim, Tetrahedron Lett. 2006, 47, 3835.
[37] C. S. Cho, J. U. Kim, H.-J. Choi, J. Organomet. Chem. 2008, 693, 3677.
[38] C. S. Cho, H. B. Kim, S. Y. Lee, J. Organomet. Chem. 2010, 695, 1744.
[39] C. S. Cho, H. B. Kim, Catal. Lett. 2010, 140, 116.
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Appl. Organometal. Chem. (2012)
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