Carboxylation of terminal alkynes at ambient CO2 pressure in ethylene carbonate

Article abstract of DOI:10.1039/c3gc40896e

The CuI-catalyzed carboxylation of terminal alkynes with CO₂ and alkyl halides using ethylene carbonate as the solvent under mild conditions was studied. DFT calculations reveal that the energy barrier for CO₂ insertion into the sp-h

Full text of DOI:10.1039/c3gc40896e

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Carboxylation of terminal alkynes at ambient CO2
pressure in ethylene carbonate†
Cite this: DOI: 10.1039/c3gc40896e
Bing Yu,a Zhen-Feng Diao,a Chun-Xiang Guo,a Chun-Lai Zhong,a Liang-Nian He,*a
Ya-Nan Zhao,a Qing-Wen Song,a An-Hua Liua and Jin-Quan Wang*b
The CuI-catalyzed carboxylation of terminal alkynes with CO2 and alkyl halides using ethylene carbonate
as the solvent under mild conditions was studied. DFT calculations reveal that the energy barrier for CO2
insertion into the sp-hybridized Cu–C bond could be reduced by employing ethylene carbonate as the
solvent. Notably, the procedure was conducted under ambient CO2 pressure without any external
ligands. A broad range of substrates with electron-withdrawing groups or electron-donating groups gave
the corresponding products in reasonable yields.
Received 14th May 2013,
Accepted 1st July 2013
DOI: 10.1039/c3gc40896e
www.rsc.org/greenchem
Carboxylic acids are found in medicinally important com-
pounds such as worldwide commercialized aspirin and ibupro-
Introduction
Carbon dioxide chemistry has drawn much attention in the fen. This makes them particularly attractive targets for the
last two decades as CO2 can be regarded as an ubiquitous, fine-chemical synthesis.6 On the other hand, the widespread
abundant, cheap, and nontoxic C1 feedstock in organic syn- availability of carboxylic acids makes them extremely promis-
thesis.1 A myriad of industrial chemicals such as polycarbo- ing raw materials for chemical synthesis as well as a versatile
nates, urea and salicylic acid can be produced from CO2.2 synthon in organic synthesis.7 Moreover, the synthesis of car-
However, further application of CO2 as a reactant is limited boxylic acids and derivatives using CO2 as the carboxylative
due to its low reactivity as a result of its high thermodynamic reagent is an attractive approach. In this context, a plethora of
stability and kinetic inertness. Consequently, vigorous nucleo- scientific efforts have been devoted to the development of
philes (like Grignard reagents and organolithium reagents), various efficient carboxylation methods.8 For example, the car-
high-energy starting materials (like small-membered ring com- boxylation of organotin,9 organozinc,10 and organoboron
pounds and organometallics) or drastic reaction conditions reagents11 has been reported. However, these methods require
are commonly required for reactions involving CO2 to perform the synthesis of expensive and sensitive prefunctionalized sub-
smoothly.3 Moreover, CO2 capture and storage/sequestration strates. From the point view of atom- and step-economical
(CCS) has been a highly intriguing research topic in recent chemistry, the most concise route to carboxylic acids is the
years.4 In some cases, captured CO2, considered an activated straightforward carboxylation of C–H with CO2.12
form of CO2, can be applied as a feedstock to produce value-
The first coupling reaction of a terminal alkyne and CO2 to
added chemicals or fuels. This leads to systems suitable for form the corresponding alkynoate was observed by the Inoue
accomplishing chemical transformations of CO2 under mild group.13 Since then, carboxylation of terminal alkynes with
conditions, getting rid of the desorption step. This concept CO2 has been well studied (Scheme 1). The research groups of
has been named as ‘CO2 capture and utilization’ (CCU) in the Zhang,14 Gooßen,15 Lu16 and Kondo17 still made significant
literature.5 Nevertheless, synthetic methods using CO2 as feed- contributions to this field. In all reported procedures, a polar
stock under low pressure (ideally at 1 atm) are still highly aprotic solvent such as DMF, DMSO, DMA (N,N-dimethylaceta-
desirable.
mide) is required for a reasonable yield. This is probably
because such solvents improve CO2 solubility18 and thus
enhance the interactions between the solvent and the
aState Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai
University, Tianjin 300071, People’s Republic of China. E-mail: heln@nankai.edu.cn
bKey Laboratory of Green Process and Engineering, Institute of Process Engineering,
Chinese Academy of Sciences, Beijing, 100190, People’s Republic of China.
E-mail: jqwang@home.ipe.ac.cn
†Electronic supplementary information (ESI) available: Characterization pro-
ducts and copies of the NMR spectra. See DOI: 10.1039/c3gc40896e
Scheme 1 Carboxylation of terminal alkynes with CO2.
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catalyst.15b However, these traditional organic solvents are
often environmentally hazardous.
Table 1 Base effect on carboxylation of phenylacetylenea
On the other hand, organic carbonates as polar solvents are
available in large amounts.19 Owing to the high solvency,
high boiling and flash points, low odor levels, and low toxi-
cities, they have been applied as an alternative reaction
media for oxidation,20 asymmetric hydrogenation,21 substi-
tution reactions,22 olefin metathesis transformations,23 and
functionalization of arene C–H bonds.24 Furthermore, organic
carbonates are prepared in industry via cycloaddition
reactions of epoxides with CO2, and subsequent transesterifi-
cation.2c In 2009, our group reported the palladium-catalyzed
Wacker oxidation using oxygen in ethylene carbonate.25
Higher alkenes and aryl alkenes were successfully transformed
to the corresponding ketone by employing this protocol. As
part of our continuous interest in carboxylation with CO2 as
the carbonylating agent and a catalysis in organic carbon-
ates,26 the carboxylation of terminal alkynes with CO2 in
organic carbonates offers significant benefits. In particular, an
organic carbonate could improve the CO2 solubility and is ben-
eficial to stabilizing the intermediate metal species in metal
catalysis.
Entry
Base
Yieldb (%)
1
2
3
4
5
6
7
8
Cs2CO3
K2CO3
TBD
>99
42
38
23
4
tBuOK
tBuOLi
CsF
3
KF
<1
<1
<1
<1
<1
NaNH2
CsOAc
KOH
9
10
11
NaOH
a Reaction conditions: phenylacetylene (0.0511 g, 0.5 mmol), CuI
(0.0095 g, 0.05 mmol), Ph3P (0.0131 g, 0.05 mmol), base (0.6 mmol),
n-BuI (0.1104 g, 0.6 mmol), EC (3 mL), CO2 (99.999%, balloon), 80 °C,
18 h. b The yields were determined by GC with biphenyl as the internal
standard.
We herein would like to disclose the carboxylation of term-
inal alkynes with ambient CO2 in ethylene carbonate using
CuI as the catalyst to give the corresponding alkyl 2-alkynoates.
It is worth noting that the procedure needs no external ligands
and terminal alkynes with electron-withdrawing groups or
electron-donating groups proceed smoothly under mild
conditions.
Table 2 Optimization of the carboxylation of phenylacetylenea
Entry
T (°C)
Time (h)
Yieldb (%)
1
80
80
80
80
80
50
18
18
18
12
12
12
>99
>99
4
13
88
61
2c
3d
4e
5
Results and discussion
The exploratory experiments started using phenylacetylene (1a)
as the model substrate, ethylene carbonate (EC) as the
solvent in the presence of n-butyl iodide (2a), CuI/Ph3P, and
Cs2CO3 as a base. The product n-butyl 2-alkynoate (3aa)
was obtained in a quantitative yield at 80 °C for 18 h (Table 1,
entry 1). The promising results encouraged us to further
investigate the effect of the base as shown in Table 1. The base
was found to have a dramatic impact on the reaction
outcome. Using K2CO3 as the base, the reaction gave 3aa in a
42% yield (entry 2). Similarly, the carboxylation could
happen in the presence of 1,5,7-triazabicyclo[4.4.0]dec-5-ene
6
a Reaction conditions: phenylacetylene (0.0511 g, 0.5 mmol), CuI
(0.0095 g, 0.05 mmol), Cs2CO3 (0.1955 g, 0.6 mmol), n-BuI (0.1104 g,
0.6 mmol), EC (3 mL), CO2 (99.999%, balloon). b The yields were
determined by GC with biphenyl as the internal standard. c Ph3P
(0.0131 g, 0.05 mmol) was added as a ligand. d Argon (1 atm) was used
to replace CO2. e Without CuI.
was observed (entry 4). Moreover, a shorter reaction time
caused a decrease in the 3aa yield to 88% (entry 5). When the
reaction was carried out at 50 °C for 12 h, the yield dropped to
61% (entry 6). Consequently, the catalytic carboxylation pro-
ceeded efficiently at 80 °C for 18 h without any additional
ligand by using EC as the solvent.
With the EC results in hand, we then examined the influ-
ence of different solvents such as DMF and other organic car-
bonates (Table 3). The carboxylation using DMF as the solvent
gave a 70% yield of 3aa (entry 1), being similar to Kondo’s
report.17 For the organic carbonates chosen as the solvents,
the cyclic carbonates, e.g. PC and EC, exhibited better perform-
ances than the acyclic carbonates, such as DMC and DEC
(entries 2–5). This is presumably because EC is helpful
t
(TBD) or BuOK, but the yields were not satisfactory (entries
t
3 and 4). Other bases, e.g. BuOLi, CsF, KF, NaNH2, CsOAc,
KOH and NaOH, were inefficient under identical conditions
(entries 5–11). In addition, several organic bases like DBU,
DBN, TMG, DABCO etc. did not work for this reaction (see
Table S1, ESI†).
Subsequently, the survey of other reaction parameters was
conducted using Cs2CO3 as the base. As summarized in
Table 2, a quantitative yield was obtained at 80 °C for 18 h
even without Ph3P as a ligand (entry 1 vs. 2). The control
experiment revealed that the carboxylation did not proceed
without CO2 (entry 3). Without CuI, only a 13% yield of 3aa
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Table 3 Influence of solvent on the carboxylation of phenylacetylenea
corresponding alkynoates in 80–96% yields (Table 5,
entries 1–6). In addition, electron-withdrawing groups
substituted at the meta- or ortho-positions on the phenylacetyl-
enes were also tolerable and gave good yields (entries 7–10).
The reaction using 2-ethynylthiophene as the substrate
was also practical, providing the corresponding product 3ka in
Entry
Solvent
Yieldb (%)
a
high yield (entry 11). The reaction with aliphatic
alkynes, such as 1-octyne and 3,3-dimethyl-1-butyne, were
also tested under the standard conditions. The desired
products were formed in 88% and 90% yields, respectively
(entries 12 and 13). Moreover, n-butyl bromide was also
suitable for in situ alkylation, affording the product in a good
yield (entry 14). In particular, we were pleased to find that
n-butyl chloride also worked well (entry 15). Likewise, the reac-
tion of 1a with CO2 could be successfully run on a gram scale
(see ESI†).
1
2
3
4
5
DMF
DMC
DEC
PC
70
15
16
73
88
EC
a Reaction conditions: phenylacetylene (0.0511 g, 0.5 mmol), CuI
(0.0095 g, 0.05 mmol), Cs2CO3 (0.1955 g, 0.6 mmol), n-BuI (0.1104 g,
0.6 mmol), solvent (3 mL), CO2 (99.999%, balloon), 80 °C, 12 h, DMC =
dimethyl carbonate, DEC
= diethyl carbonate, PC = propylene
carbonate. b The yields were determined by GC with biphenyl as the
internal standard.
To elucidate the origin of the reactivity in ethylene carbon-
ate, DFT calculations were performed based on the mechan-
ism of the carboxylation. As delineated in Scheme 2, the
catalytic cycle for the copper-catalyzed carboxylation of term-
inal alkynes with CO2 proceeds via copper acetylide as the key
intermediate,27 generated from the reaction of the terminal
alkyne and CuI with the aid of a base. Subsequently, the inser-
tion of CO2 into the sp-hybridized Cu–C bond forms the
copper propynoate intermediate. Then the product ester can
be generated using iodoalkane with regeneration of the copper
catalyst.
We explored the energetics for the CO2 insertion step as
shown in Scheme 3. Following the prevalent mechanism of the
carboxylation reactions, insertion of CO2 into the Cu–C bond
of alkynylcopper by transferring the alkynyl group to the
carbon atom of CO2 occurs via the transition states TS1, TS2
and TS3 to give the corresponding copper propynoate.28 DFT
calculations in the gas phase show that the activation energy
for the CO2 insertion without solvent is 32.9 kcal mol−1 (TS1),
whereas the activation energy is much lower with EC or DMF
as the solvent (TS2, TS3).29 The results demonstrate that using
the appropriate solvent has a dramatic impact on the reaction
outcome. Although the activation energy in EC (19.3 kcal
mol−1) is slightly higher than in DMF (18.5 kcal mol−1), we
hypothesize that ethylene carbonate could act as a proper
ligand (binding energy of about 26.86 kcal mol−1), which pre-
sumably stabilizes the reaction intermediate and thus facili-
tates the carboxylation.
Table 4 Influence of the copper salt on the carboxylation reactiona
Entry
Catalyst
Yieldb (%)
1
2
3
4
5
CuCl
CuBr
CuI
CuCN
Cu2O
26
61
88
81
46
a Reaction conditions: phenylacetylene (0.0511 g, 0.5 mmol), catalyst
(10 mol%), Cs2CO3 (0.1955 g, 0.6 mmol), n-BuI (0.1104 g, 0.6 mmol),
solvent (3 mL), CO2 (99.999%, balloon), 80 °C, 12 h. b The yields were
determined by GC with biphenyl as the internal standard.
for enhancing the stability of the intermediate, i.e. copper acet-
ylide, and facilitating interactions among the reactant species.
Therefore, ethylene carbonate was chosen as the solvent for
the carboxylation of phenylacetylene with CO2.
Furthermore, the catalytic performance of different cuprous
salts was evaluated in ethylene carbonate in the presence
of Cs2CO3, n-BuI and CO2 at 80 °C for 12 h. The results
summarized in Table 4 reveal that the reactivity decreases
in the order of CuI > CuBr > CuCl (Table 4, entries 1–3).
Additionally, CuCN and Cu2O could also promote the
carboxylation towards alkyl 2-alkynoates in yields of 81%
Conclusions
and 46%, respectively (entries
4
and 5). Thus CuI
In conclusion, we have developed an efficient CuI-catalyzed
carboxylation reaction of terminal alkynes, CO2 and alkyl
halides using ethylene carbonate as the solvent under mild
conditions without any additional ligands. A range of terminal
alkynes and various alkyl halides could undergo the coupling
reaction smoothly. In addition, the DFT calculations revealed
that the energy barrier of the CO2 insertion step could be
reduced by employing ethylene carbonate as the solvent and
was employed as the catalyst for further investigation. As a
result, the optimal reaction conditions were CuI (10 mol%) as
the catalyst, Cs2CO3 as the base, ethylene carbonate as the
solvent, and 80 °C.
The generality of this methodology was further examined as
listed in Table 5. Phenylacetylenes substituted with electron-
rich groups (e.g. Me, Et and MeO) were converted to the
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Table 5 Cu(I)-catalyzed carboxylation in ethylene carbonatea
Entry
1
R1CuCH
R2X
Product
Yieldb (%)
96
nBuI 2a
2
3
4
nBuI 2a
nBuI 2a
nBuI 2a
80
84
90
5
6
nBuI 2a
nBuI 2a
90
89
7
nBuI 2a
84
8
9
nBuI 2a
nBuI 2a
81
80
10
nBuI 2a
81
11
12
13
14
15
nBuI 2a
nBuI 2a
nBuI 2a
nBuBr 2b
nBuCl 2c
91
88
90
87
56
a Reaction conditions: terminal alkyne (1.0 mmol), CuI (0.0190 g. 0.1 mmol), Cs2CO3 (0.3910 g, 1.2 mmol), n-BuI (0.2208 g, 1.2 mmol) and
ethylene carbonate (3 mL), CO2 (99.999%, balloon), 80 °C, 18 h. b Isolated yield.
ligand. Such findings in this study may be of great interest to Studies are currently underway in our laboratory to explore
stimulate the development of novel access routes to form car- other procedures for CO2 utilization in green solvents under
boxylic acids from hydrocarbons and CO2 in a green solvent. mild conditions.
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coordinates (IRC) were examined to ensure the smooth con-
nection of reactants and products.
Compound 3aa. Colourless oil; 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.62–7.59 (m, 2H), 7.48–7.37 (m, 3H), 4.26 (t, J = 6.7 Hz,
2H), 1.72 (quint, J = 6.8 Hz, 2H), 1.51–1.41 (m, 2H), 0.98 (t, J =
7.4 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ (ppm): 154.2, 132.9,
130.5, 128.5, 119.6, 86.0, 80.7, 65.9, 30.4, 19.0, 13.6; EI-MS,
m/z (%): 129.10 (100), 201.08 (34) [M+].
Compound 3ba. Light yellow solid; 1H NMR (400 MHz,
CDCl3) δ (ppm): 7.48 (d, J = 7.5 Hz, 2H), 7.17 (d, J = 7.6 Hz,
2H), 4.23 (t, J = 6.6 Hz, 2H), 2.37 (s, 3H), 1.69 (quint, J = 7.3 Hz,
2H), 1.51–1.36 (m, 2H), 0.96 (t, J = 7.5 Hz, 3H); 13C NMR
(100 MHz, CDCl3) δ (ppm): 154.3, 141.2, 132.9, 129.3, 116.5,
86.6, 80.3, 65.8, 30.5, 21.7, 19.0, 13.6; EI-MS, m/z (%): 116.20
(100), 216.25 (13) [M+].
Scheme 2 The proposed mechanism for the carboxylation of the terminal
alkyne with CO2.
Compound 3ca. Yellow oil; 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.52–7.40 (m, 2H), 7.21–7.14 (m, 2H), 4.23 (t, J = 6.7 Hz,
2H), 2.70–2.61 (m, 2H), 1.73–1.63 (m, 2H), 1.48–1.37 (m, 2H),
1.25–1.20 (m, 3H), 0.98–0.92 (m, 3H); 13C NMR (100 MHz,
CDCl3) δ (ppm): 154.3, 147.4, 133.1, 128.1, 116.7, 86.6, 80.3,
65.8, 30.5, 28.9, 19.0, 15.1, 13.6; EI-MS, m/z (%): 130.20 (100),
230.20 (14) [M+]; HRMS (ESI): C15H18O2Na for [M + Na]+ calcu-
lated 253.1199, found 253.1196.
Compound 3da. Yellow oil; 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.50 (d, J = 8.1 Hz, 2H), 7.18 (d, J = 8.1 Hz, 2H), 4.23 (t,
J = 6.7 Hz, 2H), 2.63–2.59 (m, 2H), 1.70–1.58 (m, 4H), 1.46–1.28
(m, 6H), 0.98–0.87 (m, 6H). 13C NMR (100 MHz, CDCl3) δ
(ppm): 154.3, 146.2, 133.0, 128.6, 116.7, 86.6, 80.3, 65.8, 36.0,
31.4, 30.7, 30.5, 22.4, 19.0, 14.0, 13.6; EI-MS, m/z (%):172.25
(100), 272.30 (15) [M+]; HRMS (ESI): C18H24O2Na for [M + Na]+
calculated 295.1669, found 295.1664.
Scheme 3 Free energy profile for the step of CO2 insertion calculated by the
B3LYP/6-311++G(d,p)/LANL2DZ method. The calculated relative energies are
given in kcal mol−1
.
Experimental section
General procedure for the carboxylation of terminal alkynes in
ethylene carbonate
Compound 3ea. White solid; 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.53 (d, J = 8.8 Hz, 2H), 6.87 (d, J = 8.8 Hz, 2H), 4.22 (t,
J = 6.7 Hz, 2H), 3.82 (s, 3H), 1.69 (dt, J = 14.7, 6.8 Hz, 2H), 1.43
(dq, J = 14.7, 7.4 Hz, 2H), 0.95 (t, J = 7.4 Hz, 3H); 13C NMR
(100 MHz, CDCl3) δ (ppm): 161.4, 154.4, 134.9, 114.2, 111.4,
86.8, 80.1, 65.7, 55.3, 30.5, 19.0, 13.6; EI-MS, m/z (%): 132.15
(100), 232.20 (15) [M+].
In a 20 mL Schlenk flask, the terminal alkyne (1.0 mmol), CuI
(0.0190 g, 0.1 mmol), Cs2CO3 (0.3910 g, 1.2 mmol), n-BuI
(0.2208 g, 1.2 mmol) and ethylene carbonate (3 mL) were
added. The flask was capped with a stopper and sealed. Then
the freeze–pump–thaw method was employed for gas exchan-
ging process. The reaction mixture was stirred at 80 °C for the
desired time under an atmosphere of CO2 (99.999%, balloon).
After the reaction, the mixture was cooled to room tempera-
ture, and extracted with n-hexane. The combined organic
layers were washed with saturated NaCl solution, then dried
with anhydrous Na2SO4. The residue was purified by column
chromatography (silica gel, petroleum ether–EtOAc) to afford
the desired product 3.
1
Compound 3fa. Colourless oil; H NMR (400 MHz, CDCl3) δ
(ppm): 7.34–7.31 (m, 2H), 7.19–7.17 (m, 2H), 4.16 (t, J = 6.7 Hz,
2H), 2.27 (s, 3H), 1.66–1.55 (m, 2H), 1.41–1.32 (m, 2H), 0.89 (t,
J = 7.4 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ (ppm): 154.2,
138.3, 133.4, 131.5, 130.1, 128.4, 119.4, 86.3, 80.4, 65.9, 30.4,
21.1, 19.0, 13.6; EI-MS, m/z (%):143.15 (100), 216.20 (8) [M+];
HRMS (ESI): C14H16O2Na for [M + Na]+ calculated 239.1043,
found 239.1046.
Compound 3ga. Yellow oil; 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.57 (s, 1H), 7.47–7.41 (m, 2H), 7.33–7.29 (m, 1H), 4.24
Computational methods
The calculations were carried out by performing DFT using the (t, J = 6.6 Hz, 2H), 1.73–1.63 (m, 2H), 1.48–1.37 (m, 2H), 0.96
B3PW91 functional with the 6-311++G(d,p) (C, H, N, O) and (t, J = 7.4 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ (ppm): 153.8,
LANL2DZ (Cu) basis set implemented in the Gaussian 09 134.5, 132.6, 131.0, 130.9, 129.8, 121.4, 84.1, 81.4, 66.1, 30.4,
program package.29 All the final structures were confirmed by 19.0, 13.6; EI-MS, m/z (%):163.10 (100), 235.15 (7) [M+]; HRMS
frequency calculations to be the real minima without any ima- (ESI): C13H13O2ClNa for [M + Na]+ calculated 259.0496, found
ginary frequencies using the same level of theory. All tran- 259.0493.
sition-state (TS) geometries were characterized by the presence
of single imaginary frequency, and intrinsic reaction (ppm): 7.59–7.56 (m, 2H), 7.08–7.04 (m, 2H), 4.23 (t, J = 6.6 Hz,
Compound 3ha. Yellow oil; 1H NMR (400 MHz, CDCl3) δ
a
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2H), 1.73–1.62 (m, 2H), 1.46–1.38 (m, 2H), 0.95 (t, J = 7.8 Hz,
3H). 13C NMR (100 MHz, CDCl3) δ (ppm): 165.1, 162.6, 154.1,
135.2, 116.1, 84.9, 80.6, 65.9, 30.4, 19.0, 13.6; EI-MS,
m/z (%):147.15 (100), 220.15 (5) [M+]; HRMS (ESI): C13H13FO2Na
for [M + Na]+ calculated 243.0792, found 243.0786.
(f) L.-N. He, Z.-Z. Yang, A.-H. Liu and J. Gao, in Advances in
CO2 Conversion and Utilization, ed. Y. Hu, ACS, 2010, ch. 6,
vol. 1056, pp. 77–101; (g) M. Cokoja, C. Bruckmeier,
B. Rieger, W. A. Herrmann and F. E. Kühn, Angew. Chem.,
Int. Ed., 2011, 50, 8510–8537.
Compound 3ia. Yellow oil; 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.51 (d, J = 8.4 Hz, 2H), 7.35 (d, J = 8.5 Hz, 2H), 4.23 (t,
J = 6.7 Hz, 2H), 1.71–1.66 (m, 2H), 1.46–1.40 (m, 2H), 0.95 (t, J =
7.4 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ (ppm): 154.0, 136.9,
134.1, 129.0, 118.1, 84.7, 81.5, 66.0, 30.4, 19.0, 13.6; EI-MS, m/z
(%): 163.10 (100), 236.10 (7) [M+]; HRMS (ESI): C13H13O2ClNa
for [M + Na]+ calculated 259.0496, found 259.0494.
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Compound 3ja. Yellow oil; 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.52 (d, J = 8.5 Hz, 2H), 7.44 (d, J = 8.5 Hz, 2H), 4.23 (t,
J = 6.7 Hz, 2H), 1.73–1.66 (m, 2H), 1.48–1.38 (m, 2H), 0.95 (t,
J = 7.4 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ (ppm): 154.0,
134.2, 131.9, 125.3, 118.6, 84.7, 81.6, 66.1, 30.4, 19.0, 13.6;
EI-MS, m/z (%):180.00 (100), 280.10 (8) [M+].
Compound 3ka. Brown oil; 1H NMR (400 MHz, CDCl3) δ
(ppm): 7.48–7.45 (m, 2H), 7.04 (s, 1H), 4.23 (t, J = 6.6 Hz, 2H),
1.71–1.67 (m, 2H), 1.46–1.40 (m, 2H), 0.95 (t, J = 7.4 Hz, 3H).
13C NMR (100 MHz, CDCl3) δ (ppm): 154.0, 136.4, 131.0, 127.5,
119.4, 84.9, 80.0, 65.9, 30.4, 19.0, 13.6; EI-MS, m/z (%): 108.19
(100), 207.90 (14) [M+].
Compound 3la. Yellow oil; 1H NMR (400 MHz, CDCl3) δ
(ppm): 4.13 (t, J = 6.7 Hz, 2H), 2.30 (t, J = 7.2 Hz, 2H),
1.65–1.53 (m, 4H), 1.40–1.25 (m, 8H), 0.93–0.85 (m, 6H); 13C
NMR (100 MHz, CDCl3) δ (ppm): 154.0, 89.4, 73.1, 65.5, 31.1,
30.4, 28.5, 27.4, 22.4, 19.0, 18.6, 13.9, 13.6; EI-MS, m/z (%):
67.19 (100), 211.02 (46) [M+].
6 L. J. Gooßen, N. Rodriguez and K. Gooßen, Angew. Chem.,
Int. Ed., 2008, 47, 3100–3120.
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1
Compound 3ma. Colourless oil; H NMR (400 MHz, CDCl3)
δ (ppm): 4.14 (t, J = 6.8 Hz, 2H), 1.67–1.60 (m, 2H), 1.43–1.36
(m, 2H), 1.27 (s, 9H), 0.93 (t, J = 7.4 Hz, 3H); 13C NMR
(100 MHz, CDCl3) δ (ppm): 154.2, 96.3, 71.8, 65.6, 30.4, 29.9,
27.5, 19.0, 13.6; HRMS (ESI): C15H18O2Na for [M + Na]+ calcu-
lated 205.1199, found 205.1197.
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Acknowledgements
We are grateful to the National Natural Science Foundation of 10 (a) C. S. Yeung and V. M. Dong, J. Am. Chem. Soc., 2008,
China (no. 21172125, 21121002), the “111” Project of Ministry
of Education of China (Project no. B06005), and Tianjin Co-
Innovation Center of Chemical Science and Engineering for
financial support. We also would like to thank Prof. Ao Yu for
his constructive discussion on theoretical calculations.
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