CuI/amino acid catalysis in coupling and cyclization of β-bromo-α,β-unsaturated carboxylic acids with terminal alkynes leading to alkylidenefuranones

Article abstract of DOI:10.1002/aoc.2963

β-Bromo-α,β-unsaturated carboxylic acids are coupled and cyclized with terminal alkynes in DMF at 110°C in the presence of a catalytic amount of CuI and amino acid along with a base to give alkylidenefuranones in good yields. Similar reaction under microw

Full text of DOI:10.1002/aoc.2963

Full Paper
Received: 14 November 2012
Revised: 5 December 2012
Accepted: 8 December 2012
Published online in Wiley Online Library
(wileyonlinelibrary.com) DOI 10.1002/aoc.2963
CuI/amino acid catalysis in coupling and
cyclization of b-bromo-a,b-unsaturated
carboxylic acids with terminal alkynes leading
to alkylidenefuranones
Son Long Hoa, Chan Sik Choa*, Heung-Jin Choia and Ho-Sang Sohnb
b-Bromo-a,b-unsaturated carboxylic acids are coupled and cyclized with terminal alkynes in DMF at 110ꢀC in the presence of
a catalytic amount of CuI and amino acid along with a base to give alkylidenefuranones in good yields. Similar reaction under
microwave irradiation also gave alkylidenefuranones in higher yields. Copyright © 2013 John Wiley & Sons, Ltd.
Keywords: alkylidenefuranones; amino acids; b-bromo-a,b-unsaturated carboxylic acids; cyclization; terminal alkynes
proceeded with regio- and stereoselective 5-exo-dig cyclization.[32]
The configuration of 3a was characterized by spectroscopic
Introduction
comparison of 1H and 13C NMR spectra and GC retention time with
the authentic sample synthesized by our recent report.[32] From
the activity of several amino acids examined employing K2CO3
as base and DMF as solvent, glycine exhibited nearly the same
catalytic activity as L-proline, and other amino acids such as
L-phenylalanine and N,N-dimethylglycine were shown to be not
effective at all (entries 2–5). With other bases such as K3PO4
and Cs2CO3 combined with L-proline in DMF, the yield of 3a
was lower than that when K2CO3 was employed (entries 6 and
7). As a result, after further tuning with several solvents (entries
8 and 9), the best result in terms of both product yield and
complete conversion of 1a was accomplished by the standard
set of reaction conditions shown in Table 1 (entries 1 and 3).
The coupling and cyclization could be applied to many
It is known that b-bromovinyl aldehydes and their derivatives,
which are readily prepared from a-methylene-containing
ketones under bromination conditions of Vilsmeier–Haack
reaction and subsequent transformation,[1,2] are used as a building
block for the construction of versatile carbo- and heterocyclic
compounds.[3–25] As part of our continuing studies directed
towards transition metal-catalyzed cyclization reactions, we have
also disclosed new synthetic methods for the synthesis of several
cyclic compounds using b-bromovinyl aldehydes and their deriva-
tives in the presence of a palladium catalyst.[26–34] Among them,
in connection with this report, b-bromo-a,b-unsaturated carboxylic
acids were found to be coupled and cyclized with terminal alkynes
in the presence of Pd/C and CuI to give alkylidenefuranones.[32] This
protocol led us to seek a cheap catalyst alternative which exhibits a
similar catalytic activity under similar reaction conditions. Recently,
Ma et al. reported that CuI combined with amino acid effectively
catalyzes cross-coupling reaction of aryl halides with terminal
alkynes in the absence of palladium and phosphine.[35–37] Under
these circumstances, this report shows a cheap CuI/amino acid-
catalyzed coupling and cyclization of b-bromo-a,b-unsaturated
carboxylic acids with terminal alkynes leading to alkylidenefuranones
under usual heating and microwave irradiation conditions.
b-bromo-a,b-unsaturated carboxylic acids
1 and terminal
alkynes 2 under the standard set of reaction conditions shown
in Table 1 (entries 1 and 3), and several representative results
are summarized in Table 2. 2-Bromocyclohex-1-enecarboxylic
acid (1a) was readily coupled and cyclized with aryl alkynes
(2a–c) having electron-donating and -withdrawing substituents
to give the corresponding benzylidenefuranones (3a–c) in the
range of 51–60% isolated yields and the product yield was not
varied significantly with the electronic nature of the substituent
on the aromatic ring of 2a–c. Lower reaction yield was observed
with alkyl alkyne 2d when compared with those of aryl alkynes
Results and Discussion
Table 1 shows several results for the attempted coupling and cycli-
zation of 2-bromocyclohex-1-enecarboxylic acid (1a)[1,2,30,32,38]
with phenylacetylene (2a), leading to (3Z)-3-benzylidene-4,5,6,
7-tetrahydroisobenzofuran-1(3H)-one (3a) under reaction variants
such as several kinds of amino acid, solvent and base. Treatment
of 1a with 1.5 equiv. of 2a in DMF at 110ꢀC for 40 h in the presence
of 10 mol% CuI and 30 mol% L-proline along with K2CO3 afforded
3a in 60% yield with concomitant formation of a small amount
of homo-coupled 1,4-diphenyl-1,3-diyne (entry 1).[35,36] As is the
case for the reaction under Pd/C and CuI, the present reaction
*
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 Materials Science and Metallurgical Engineering, Kyungpook
National University, Daegu 702-701, South Korea
Appl. Organometal. Chem. 2013, 27, 277–282
Copyright © 2013 John Wiley & Sons, Ltd.

S. L. Ho et al.
Table 1. Optimization of conditions for the reaction of 1a with 2aa
Entry
Amino acid
Base
Solvent
Yield (%)
1
2
3
4
5
6
7
8
9
L-proline
L-phenylalanine
Glycine
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K3PO4
Cs2CO3
K2CO3
K2CO3
DMF
60
0
DMF
DMF
56
28
0
Cysteine
DMF
N,N-Dimethylglycine
L-proline
DMF
DMF
19
25
Trace
28
L-proline
DMF
Glycine
DMSO
Toluene
Glycine
aReaction conditions: 1a (0.3 mmol), 2a (0.45 mmol), CuI (0.03), amino acid (0.09 mmol), base (0.6 mmol), solvent (3 ml), 110ꢀC, for 40 h.
(2a–c). From the reaction of six-membered b-bromo-a,b-unsatu-
rated carboxylic acid 1b with 2a, the corresponding benzylide-
nefuranone 3e was formed in similar yield irrespective of methyl
substituent on 1b. With cyclic b-bromo-a,b-unsaturated
carboxylic acids (1c–f) having various ring sizes, the coupled
and cyclized benzylidenefuranones (3f–i) were produced in the
range of 42–70% yields, and higher reaction yield was observed
with seven-membered b-bromo-a,b-unsaturated carboxylic acid
1d. Here again, L-proline and glycine exhibited similar catalytic
activity in the coupling and cyclization of 1c and 1e with 2a.
However, the reaction of benzo-fused b-bromo-a,b-unsaturated
carboxylic acid 1 g with 2a did not proceed at all toward coupled
and cyclized product 3j under the employed conditions, a
considerable amount of homo-coupled 1,4-diphenyl-1,3-diyne
being formed.
On the other hand, many reactions have been conducted
under microwave irradiation to speed up the reaction rate
and to obtain an acceptable yield of product in minutes.[39] As
shown in parentheses in Table 2, higher reaction rate and yield
were also observed by similar treatment of b-bromo-a,b-unsatu-
rated carboxylic acids 1 and terminal alkynes 2 under microwave
irradiation (100ꢀC, 30 min). Lower reaction temperature (70ꢀC)
resulted in lower yield of 3a (52% from 1a and 2a). In contrast
to the reaction of 1 g with 2a under usual heating conditions,
the coupling and cyclization readily took place under microwave
irradiation conditions to give (Z)- and (E)-products in 34%
and 22% yields, respectively. The configuration of isomers was
confirmed by comparing the chemical shift of vinyl proton signal
in 1H NMR. It is known that the chemical shifts of (E)-isomers
of alkylidenefuranones are shifted downfield from those of
(Z)-isomers.[40,41]
group in molecules 3a and 3j.[42–44] Thus the isomer with vinyl
proton appearing at a lower field will have Z-configuration with
the trans-carbalkoxy group. The major product of 3j showed a
vinyl proton at 6.571 ppm in the 1H NMR spectrum and the minor
product of 3j at 7.121 ppm, so the major product was tentatively
assigned as (Z)-isomer and the minor product as (E)-isomer. The
additivity rule is also agreed with a known compound (3a) which
has known Z-configuration.[32,40,41] Chemical shifts by the
additivity rule are quite confidently predicted, but steric
hindrance and the magnetic anisotropic effect need to be
considered. Thus high-level quantum chemical calculations were
performed with the general atomic and molecular electronic
structure system as implemented in the Spartan program.[45]
Hartree–Fock 6-31* calculations of chemical shifts preceded
by B3LYP 6-31* density functional calculation of geometry
resulted in chemical shifts of the concerned vinyl protons at
6.534 ppm for (Z)-3j isomer, 7.189 ppm for (E)-3j isomer,
5.874 ppm for (Z)-3a isomer and 6.981 ppm for (E)-3a isomer.
The tentatively assigned configurations for (Z)- and (E)-3j were
well matched with quantum chemical calculations, and the
Z-configuration of the known compound 3a with a vinyl proton
resonating at 5.871 ppm is also confirmed by high-level
quantum chemical calculations.
The reaction seems to proceed as shown in Scheme 1. Oxidative
addition of the carbon–bromide bond of 1a to Cu(I) species 4,
which is formed by the reaction between CuI and glycine, produces
vinyl copper complex 5.[36] Subsequent reaction of complex 5 with
2a in the presence of a base affords copper acetylide 6, which is
followed by reductive elimination to give an enyne carboxylic acid
7 with regeneration of catalyst 4. The Sonogashira coupling
product 7 triggers 5-exo-dig cyclization to afford 3a.
The configuration of (E)- and (Z)-isomers was further clarified
by substituent additivity rule at a double bond and quantum
chemical calculations. In molecules 3a and 3j, both carbalkoxy
group and conjugated vinyl substituents deshield a trans vinyl
proton to resonate at a lower field than the corresponding cis
vinyl proton, but a conjugated vinyl moiety is affected much less
than the carbalkoxy group. Thus the chemical shift of the
concerned vinyl proton is largely affected by the carbalkoxy
Conclusion
In summary, it has been shown that b-bromo-a,b-unsaturated
carboxylic acids, which are readily prepared from a-methylene-
containing ketones in two steps, undergo coupling and
cyclization with terminal alkynes in the presence of CuI and
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Appl. Organometal. Chem. 2013, 27, 277–282

CuI/amino acid catalysis in coupling and cyclization
Table 2. CuI/amino acid-catalyzed coupling and cyclization of b-bromo-a,b-unsaturated carboxylic acids with 1-alkynesab
1
2
Amino acid
3
Yieldc (%)
1a
3a
2a
L-proline
Glycine
60 (74)
56
2b
2c
2d
Glycine
Glycine
Glycine
3b
3c
3d
51
55
26
2a
Glycine
65 (79)
1b
3e
2a
2a
L-proline
Glycine
50(51)
48
1c
3f
Glycine
70(81)
1d
1e
3g
3h
2a
2a
L-proline
Glycine
42(73)
42
1f
3i
Glycine
56(71)
Appl. Organometal. Chem. 2013, 27, 277–282
Copyright © 2013 John Wiley & Sons, Ltd.
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S. L. Ho et al.
Table 2. (Continued)
1
2
Amino acid
3
Yieldc (%)
1g
2a
L-proline
3j
0 (56)d
aReaction conditions: 1 (0.3 mmol), 2 (0.45 mmol), CuI (0.03 mmol), amino acid (0.09 mmol), K2CO3 (0.6 mmol), DMF (3 ml), 110 oC, 40 h.
bReaction conditions under microwave irradiation: 1 (0.3 mmol), 2 (0.45 mmol), CuI (0.03 mmol), amino acid (0.09 mmol), K2CO3 (0.6 mmol), DMF (3
ml), 100 oC, 100 W, 30 min.
cYields under microwave irradiation are shown in parentheses.
d(E)- and (Z)-isomers were isolated in 22% and 34% yields, respectively.
Stanford Research Inc. MPA100 automated melting point
apparatus. Gas–liquid chromatographic analyses were carried
out with a Shimadzu GC-17A (FID) instrument equipped with a
CBP10-S25-050 fused-silica capillary column (0.33 mm  25 m,
0.25 mm film thickness) using N2 as carrier gas. Microwave
irradiation was conducted using the CEM Discover Microwave
System. The isolation of pure products was carried out via
thin-layer (silica gel 60 GF254, Merck) chromatography. The starting
b-bromo-a,b-unsaturated carboxylic acids were synthesized via
two steps from the corresponding ketones according to literature
procedures.[1,2,30,32,38] Commercially available organic and inorganic
compounds were used without further purification.
General Experimental Procedure for CuI/amino Acid-Catalyzed
Coupling and Cyclization of b-Bromo-a,b-Unsaturated
Scheme 1. A catalytic cycle.
Carboxylic Acids with Terminal Alkynes
L-proline (or glycine) along with K2CO3 to give alkylidenefura-
nones under usual heating or microwave irradiation conditions.
The present reaction provides a cheaper catalytic approach for
alkylidenefuranones from b-bromo-a,b-unsaturated carboxylic
acids and terminal alkynes and further study of synthetic
applications using CuI/amino acids catalytic system is currently
under investigation.
Α
mixture of b-bromo-a,b-unsaturated carboxylic acid
1
(0.3 mmol), terminal alkyne (0.45 mmol), CuI (0.006 g,
2
0.03 mmol), amino acid (0.09 mmol) and base (0.6 mmol) in
solvent (3 ml) was placed in a 5 ml screw-capped vial (Wheaton)
and the reaction mixture was allowed to react at 110ꢀC for 40 h.
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 alkylidenefuranones 3. Except
for known 3a and 3d,[30,32] all new products prepared by the
above procedure were characterized spectroscopically as shown
below.
Experimental
1H and 13C NMR (400 and 100 MHz) spectra were recorded on a
Bruker Avance Digital 400 spectrometer using tetramethylsilane
as an internal standard. Melting points were determined on a
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Appl. Organometal. Chem. 2013, 27, 277–282

CuI/amino acid catalysis in coupling and cyclization
General Experimental Procedure under Microwave
Irradiation
phenyl), 7.75–7.77 (m, 2H, ortho CH to vinyl substituent of
phenyl). 13C NMR (100 MHz, CDCl3) d 21.08 (C10) , 21.24 (C4),
28.36 (C5), 28.47 (C6), 29.87 (C7), 108.03 (C11), 126.78 (C15),
128.66 (C8), 128.87 (C13), 130.45, 133.33 (C14), 148.06 (C3),
152.55 (C9), 169.93 (C1), assignments to C5–C7 are interchangeable,
assignments to C8 and C15 are interchangeable. Anal. Calcd for
C16H16O2: C, 79.97; H, 6.71. Found: C, 79.77; H, 6.62.
Α
mixture of b-bromo-a,b-unsaturated carboxylic acid
1
(0.3 mmol), terminal alkyne (0.45 mmol), CuI (0.006 g,
2
0.03 mmol), amino acid (0.09 mmol) and K2CO3 (0.6 mmol) in
DMF (3 ml) was placed in a 10 ml microwave reaction tube and
the reaction mixture was irradiated at 100ꢀC for 30 min with
100 W of the initial power. Subsequent steps were followed by
previous usual heating procedures.
(3Z)-3-Benzylidene-5,6-dihydro-3H-cyclopenta[c]furan-1(4H)-one (3f)
(3Z)-3-(4-Methylbenzylidene)-4,5,6,7-tetrahydroisobenzofuran-1(3H)-one
(3b)
1
Solid; m.p. 96–97ꢀC. H NMR (400 MHz, CDCl3) d 2.09–2.16 (m,
2H, CH2), 2.82–2.96 (m, 4H, allylic 2CH2), 6.70 (s, 1H, vinylic CH),
7.41–7.46 (m, 3H, meta and para CH to vinyl substituent of
phenyl), 7.80–7.83 (m, 2H, ortho CH to vinyl substituent of phe-
nyl). 13C NMR (100 MHz, CDCl3) d 23.06 (C5), 29.77 (C6), 34.65
(C4), 100.76 (C9), 125.70 (C11), 125.78 (C7), 129.04 (C12), 130.53
(C13), 131.97 (C10), 159.82 (C8), 160.03 (C3), 161.46 (C1), assignments
to C3 and C8 are interchangeable. Anal. Calcd for C14H12O2: C, 79.22;
H, 5.70. Found: C, 79.11; H, 5.66.
1
Solid; m.p. 141–142ꢀC. H NMR (400 MHz, CDCl3) d 1.76–1.81
[m, 4H, -(CH2)2-], 2.34–2.36 (m, 2H, allylic CH2), 2.36 (s, 3H, CH3),
2.46–2.48 (m, 2H, allylic CH2), 5.83 (s, 1H, vinylic CH), 7.17 (d, JHH
8.1 Hz, 2H, ortho CH to CH3 substituent of phenyl), 7.66 (d, JHH
=
=
8.1 Hz, 2H, meta CH to CH3 substituent of phenyl). 13C NMR
(100 MHz, CDCl3) d 20.30 (C6), 21.31 (C5), 21.58 (C15), 21.69 (C7),
21.83 (C4), 108.11 (C10), 126.31 (C8), 129.65 (C12), 130.45 (C13),
130.55 (C11), 138.92 (C14), 147.60 (C3), 152.72 (C9), 170.22 (C1),
assignments to C4–C7 and C15 are interchangeable, assignments
to C12 and C13 are interchangeable. Anal. Calcd for C16H16O2: C,
79.97; H, 6.71. Found: C, 79.77; H, 6.63.
(3Z)-3-Benzylidene-5,6,7,8-tetrahydro-3H-cyclohepta[c]furan-1(4H)-one (3g)
(3Z)-3-(4-Fluorobenzylidene)-4,5,6,7-tetrahydroisobenzofuran-1(3H)-one (3c)
1
Solid; m.p. 112–113ꢀC. H NMR (400 MHz, CDCl3) d 1.63–1.69
(m, 2H, CH2), 1.72–1.78 (m 2H, CH2), 1.83–1.89 (m, 2H, CH2), 2.53
(t, JHH = 5.8 Hz, 2H, allylic CH2), 2.62 (t, JHH = 5.8 Hz, 2H, allylic
CH2), 6.02 (s, 1H, vinylic CH), 7.26–7.39 (m, 3H, meta and para
CH to vinyl substituent of phenyl), 7.76–7.78 (m, 2H, ortho CH to
vinyl substituent of phenyl). 13C NMR (100 MHz, CDCl3) d 25.03
(C7), 26.28 (C5), 26.72 (C8), 26.83 (C4), 30.95 (C6), 108.32 (C11),
128.68 (C15), 128.87 (C13), 129.51 (C9), 130.47 (C14), 133.48
(C12), 148.29 (C3), 154.66 (C10), 170.70 (C1), assignments to C4,
C5, C7 and C8 are interchangeable, assignments to C9 and C15
are interchangeable. Anal. Calcd for C16H16O2: C, 79.97; H, 6.71.
Found: C, 79.62; H, 6.68.
1
Solid; m.p. 156–157ꢀC. H NMR (400 MHz, CDCl3) d 1.77–1.82
[m, 4H, -(CH2)2-], 2.35–2.36 (m, 2H, allylic CH2), 2.46–2.49 (m,
2H, allylic CH2), 5.82 (s, 1H, vinylic CH), 7.03–7.07 (m, 2H, ortho
CH to F substituent of phenyl), 7.73–7.75 (m, 2H, meta CH to F
substituent of phenyl). 13C NMR (100 MHz, CDCl3) d 20.31 (C6),
21.29 (C5), 21.64 (C7), 21.78 (C4), 106.73 (C10), 115.96 (d, JCF
21.8 Hz, C13), 126.74 (C8), 129.62 (C3), 132.27 (d, JCF = 8.0 Hz,
C12), 147.81 (d, JCF = 2.9 Hz, C11), 152.67 (C9), 162.73 (d, JCF
248.5 Hz, C14), 169.99 (C1), assignments to C4–C7 are
interchangeable. Anal. Calcd for C15H13FO2: C, 73.76; H, 5.36.
Found: C, 73.58; H, 5.68.
=
=
(3Z)-3-Benzylidene-4,5,6,7,8,9-hexahydrocycloocta[c]furan-1(3H)-one (3h)
(3Z)-3-Benzylidene-4,5,6,7-tetrahydro-6-methylisobenzofuran-1(3H)-one (3e)
1
Solid; m.p. 101–102ꢀC. H NMR (400 MHz, CDCl3) d 1.52–1.57
[m, 4H, -(CH2)2-], 1.71–1.83 (m, 4H, 2CH2), 2.55 (t, JHH = 6.3 Hz,
2H, allylic CH2), 2.69 (t, JHH = 6.4 Hz, 2H, allylic CH2), 5.99 (s, 1H,
vinylic CH), 7.27–7.31 (m, 1H, para CH to vinyl substituent of
phenyl), 7.35–7.39 (m, 2H, meta CH to vinyl substituent of phe-
nyl), 7.78–7.80 (m, 2H, ortho CH to vinyl substituent of phenyl).
13C NMR (100 MHz, CDCl3) d 22.68 (C7), 23.53 (C6), 25.72 (C8),
25.84 (C5), 28.00 (C9), 28.37 (C4), 108.02 (C12), 128.04 (C16),
Solid; m.p. 154–155ꢀC. 1H NMR (400 MHz, CDCl3) d 1.08 (d,
HH = 6.3 Hz, 3H, CH3), 1.35–1.45 (m, 1H, CH2/2), 1.78–1.95 (m,
3H, CH and 2CH2/2), 2.40–2.62 (m, 3H, 3CH2/2), 5.85 (s, 1H, vinylic
CH), 7.28–7.38 (m, 3H, meta and para CH to vinyl substituent of
J
Appl. Organometal. Chem. 2013, 27, 277–282
Copyright © 2013 John Wiley & Sons, Ltd.
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S. L. Ho et al.
128.70 (C10), 128.90 (C14), 130.51 (C15), 133.46 (C13), 148.15
(C3), 153.33 (C11), 170.69 (C1), assignments to C4–C9 are
interchangeable, assignments to C10 and C16 are interchangeable.
Anal. Calcd for C17H18O2: C, 80.28; H, 7.13. Found: C, 80.09; H, 7.27.
(C11), 168.89 (C1), assignments to C6–C9 are interchangeable.
Anal. Calcd for C19H14O2: C, 83.19; H, 5.14. Found: C, 82.95; H, 5.26.
Acknowledgments
(3Z)-3-Benzylidene-4,5,6,7,8,9,10,11,12,13-decahydrocyclododeca[c]furan-
1(3H)-one (3i)
This research was supported by the Basic Science Research
Program through the National Research Foundation of Korea
(NRF) funded by the Ministry of Education, Science and Technol-
ogy (2012-0002856) and Kyungpook National University
Research Fund, 2012.
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1
Solid; m.p. 121–122ꢀC. H NMR (400 MHz, CDCl3) d 1.26–1.47
[m, 12H, -(CH2)6 -], 1.73–1.79 (m, 4H, 2CH2), 2.38 (t, JHH = 7.1 Hz,
2H, allylic CH2), 2.55 (t, JHH = 7.3 Hz, 2H, allylic CH2), 5.98 (s, 1H,
vinylic CH), 7.26–7.38 (m, 3H, meta and para CH to vinyl substituent
of phenyl), 7.76–7.78 (m, 2H, ortho CH to vinyl substituent of
phenyl). 13C NMR (100 MHz, CDCl3) d 21.50 (C8), 22.01 (C9), 22.23
(C10), 22.41 (C11), 24.47 (C7), 24.65 (C6), 25.00 (C13), 25.70 (C12),
25.72 (C5), 27.70 (C4), 108.94 (C16), 128.28 (C20), 128.58 (C14),
128.81 (C18), 130.43 (C19), 133.47 (C17), 148.47 (C3), 152.99 (C15),
170.68 (C1), assignments to C4–C13 are interchangeable, assign-
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48, 8005.
(1E)-1-Benzylidene-4,5-dihydronaphtho[1,2-c]furan-3(1H)-one [(E)-3j]
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1
Solid; m.p. 129–131ꢀC. H NMR (400 MHz, CDCl3) d 2.80–2.84
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(C9), 128.91 (C6), 129.12 (C17), 130.62 (C7), 130.84 (C13), 130.93
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1
Solid; m.p. 130–132ꢀC. H NMR (400 MHz, CDCl3) d 2.61–2.65
(m, 2H, CH2), 2.94–2.98 (m, 2H, CH2), 6.57 (s, 1H, vinylic CH),
7.32–7.43 (m, 6H, aryl CH), 7.70–7.74 (m, 1H, aryl CH), 7.86–7.88
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(C13), 128.98 (C16), 129.10 (C6), 129.27 (C7), 130.67 (C18),
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Appl. Organometal. Chem. 2013, 27, 277–282