Electrochemically catalyzed synthesis of cyclic carbonates from CO 2 and propargyl alcohols

Article abstract of DOI:10.1016/j.tet.2010.10.039

A convenient and efficient electrochemical method has been developed for the synthesis of the α-alkylidene cyclic carbonates from carbon dioxide (CO₂) and propargyl alcohols at room temperature. The electrosynthesis was successfully carried out with a copper anode and a nickel cathode in an undivided cell containing n-Bu₄NBr-MeCN electrolyte with a constant current under 3 MPa pressure of CO₂, and the α-alkylidene cyclic carbonates were obtained in good to excellent isolated yields in the secondary and tertiary terminal propargylic alcohols cases. The experimental results show that the electrogenerated Cu⁺ ions and strong bases in situ could efficiently catalyze or promote the coupling reaction under the cooperation of electrolytic medium MeCN and supporting electrolyte n-Bu₄NBr. The plausible mechanism of the coupling reaction was also discussed briefly.

Full text of DOI:10.1016/j.tet.2010.10.039

Tetrahedron 66 (2010) 9981e9985
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Electrochemically catalyzed synthesis of cyclic carbonates from CO2 and propargyl
alcohols
*
Gao-Qing Yuan , Guo-Jun Zhu, Xiao-Ying Chang, Chao-Rong Qi, Huan-Feng Jiang
School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou 510640, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 August 2010
Received in revised form 7 September 2010
Accepted 15 October 2010
Available online 17 November 2010
A convenient and efficient electrochemical method has been developed for the synthesis of the
a
-alkylidene cyclic carbonates from carbon dioxide (CO2) and propargyl alcohols at room temperature.
The electrosynthesis was successfully carried out with a copper anode and a nickel cathode in an un-
divided cell containing n-Bu4NBreMeCN electrolyte with a constant current under 3 MPa pressure of
CO2, and the a-alkylidene cyclic carbonates were obtained in good to excellent isolated yields in the
secondary and tertiary terminal propargylic alcohols cases. The experimental results show that the
electrogenerated Cuþ ions and strong bases in situ could efficiently catalyze or promote the coupling
reaction under the cooperation of electrolytic medium MeCN and supporting electrolyte n-Bu4NBr. The
plausible mechanism of the coupling reaction was also discussed briefly.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
Al or Mg as a sacrificial anode was widely used in almost all the
investigations,11e29,31e35 including our previous work,36,37 on the
The direct introduction of carbon dioxide, harmless, abundant,
and recyclable source of carbon, into organic substrates may be
considered as an attractive goal in organic synthesis. In recent years,
considerable attention has been focused on the fixation of carbon
dioxide (CO2) to organic substrates.1,2 Among these investigations,
the coupling reaction of CO2 with propargyl alcohols is one of in-
teresting topics because it can afford valuable cyclic carbonates,
which are used as polar solvents, electrolytes in secondary batteries
and as useful intermediates for the synthesis of functional carba-
mates, esters or oxazolidinone compounds, and polymers.3 Up to
now, various metal salts and organic compounds have been used to
catalyze the coupling reaction of CO2 with propargyl alcohols, such
as copper,4,5 silver,6 phosphanes,7 tri-n-butylphosphine,8 N-hetero-
cyclic carbine,9 and iodine of tert-butyl hypoiodite (t-BuOI).10 Most
of these catalytic systems often required harsh reaction conditions,
such as a high reaction temperature, because CO2 is very stable
molecule. In fact, CO2 can react with some organic compounds
through an electrochemical route at mild conditions. The electro-
chemical method has become one of the efficient routes of the fix-
ation of CO2 to various organic compounds, including alkenes,11e15
alkynes,16,17 ketones,18e21 halides,22e29 imines,30 epoxides,31e33
and heterocyclic compounds.34,29,35 However, to our knowledge,
the incorporation of CO2 into propargyl alcohols via an electro-
chemical route has not ever been reported.
electrocarboxylations of CO2 with organic substrates. Here, we fur-
ther investigated the possibility of electrochemically coupling re-
action of CO2 with propargyl alcohols. We found that the
electrochemical route with Al as a sacrificial anode was unsuccessful
for the coupling reaction of CO2 with propargyl alcohols. In this
paper, we demonstrate a new and efficient electrochemical route
(i.e., with copper as a sacrificial anode and Ni as cathode, and n-
Bu4NBreMeCN as electrolyte) for the coupling reaction. It was found
that the electrogenerated Cuþ ions and strong bases in situ could
efficiently catalyze the coupling reaction under the cooperation of
solvent MeCN, and the target product a-alkylidene cyclic carbonates
could be obtained in good to excellent yields at room temperature.
2. Results and discussion
The electrochemical synthesis of cyclic carbonates from prop-
argyl alcohols and CO2 follows the principle as shown in Scheme 1.
With 2-phenylbut-3-yn-2-ol (1a) as a model compound, the
O
0.1 mol L-1 n-Bu4NBr-solvent,
HO
constant current, rt.
O
O
Ni
Cu
CO2
2a
Scheme 1. Electrosynthesis of cyclic carbonates from propargylic alcohols and CO2.
1a
* Corresponding author. E-mail address: gqyuan@scut.edu.cn (G.-Q. Yuan).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.10.039

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G.-Q. Yuan et al. / Tetrahedron 66 (2010) 9981e9985
influence of the electrolytic conditions (solvents, electrode mate-
rials, conducting salts, and CO2 pressure, substrate concentration,
and electricity) was first investigated. Then the electrochemical
reactions of other propargyl alcohols with CO2 were further ex-
amined under the optimized conditions.
2.2. Influence of electricity and substrate concentrations as
well as CO2 pressure
Table 2 shows the influence of electricity, substrate concentra-
tions, and CO2 pressure on the electrosynthesis of cyclic carbonates
from propargyl alcohol and CO2. As shown in Table 2, the yield of
the target product strongly depends on the electricity (Q) supplied
to the electrodes. When the electricity passed the cell increased
from 1 to 4 F molꢀ1, the yield of the product increased rapidly from
38% to 88% (Table 2, entries 1e4). Further increasing the electricity,
the yield of the target product increased slightly (Table 2, entry 5).
2.1. Influence of electrode materials and solvents
In our previous investigations,36 the electrocarboxylations of
aryl-substituted alkenes with CO2 could be successfully carried out
in n-Bu4NBreDMF solution with Ni as the cathode and Al or Zn as
a sacrificial anode, affording the corresponding 2-arylsuccinic acids
in moderate to good yields (50e87%). Based on our previous results,
the coupling reaction of CO2 with propargyl alcohols was examined
under the same conditions. Unfortunately, the results are un-
expected, and the corresponding cyclic carbonate (2a) could not be
obtained (Table 1, entries 1 and 2). When Al was replaced by Cu as
a sacrificial anode, the target product 2a could be obtained in 30%
yield (Table 1, entry 3). Although the yield is very low, this indicates
the possibility of electrochemically coupling reaction of CO2 with
propargyl alcohols at room temperature. Inspired by the successful
result, we try to improve the yield of 2a through changing elec-
trolytic parameters (such as electrolytic media). When THF (tetra-
hydrofuran) or MeCN (acetonitrile) was chosen as electrolytic
medium, the yield of 2a rapidly increased to 76% and 86%, re-
spectively (Table 1, entries 4 and 5). The experimental results mean
that the Cu ions resulting from the oxidation of Cu anode and
electrolytic medium MeCN or THF play an important role in the
coupling reaction of CO2 with propargyl alcohols. The excellent
yield of the desired product could be obtained with MeCN or THF as
solvent. The reason may be that the Cu ions generated at Cu anode
could form complexes with MeCN38 or THF,39 which could effi-
ciently catalyze the cyclic reaction. The detailed mechanism of in-
fluence of the solvent and anode materials would be further
discussed in Section 3.4.
Table 2
Influence of electricity, substrate concentration and CO2 pressure on the electro-
a
chemical cyclization of propargyl alcohols with CO2
Entry
Electricity/(F molꢀ1
)
c(1a)/(mol Lꢀ1
)
P(CO2)/(MPa)
Yieldb (%)
1
2
3
4
5
6
7
8
1
2
3
4
5
4
4
4
4
4
4
0.1
0.1
0.1
0.1
0.1
0.2
0.4
0.1
0.1
0.1
0.1
4
4
4
4
4
4
4
1
2
3
5
38
50
67
88
89
92
83
29
52
86
88
9
10
11
a
Electrolytic conditions: room temperature, Ni cathode, Cu anode, MeCN (35 mL),
n-Bu4NBr (3.5 mmol), current density 10 mA cmꢀ2
.
b
Isolated yield based on the starting propargyl alcohols.
The yield of 2a increases from 88% to 92% upon increasing in the
initial concentration of the substrate from 0.1 to 0.2 mol Lꢀ1 (Table 2,
entries 4 and 6). However, when the electrolysis was conducted
with a higher concentrated solution of propargyl alcohols, it led to
the decrease of yield of the target product (83%, Table 2, entry 7). The
further increase of concentration of propargyl alcohols may bring
a negative effect, such as the increase of byproduct allyl alcohol.
As the CO2 pressure increased from 1 to 3 MPa, the yield of the
target product increased (Table 2, entries 8e10). Higher CO2 pres-
sure favors to the electrochemical cyclization reaction with prop-
argyl alcohols and CO2, which may be related to the solubility of
CO2 in MeCN solvent. Practically, the amount of CO2 at 3 MPa dis-
solved in MeCN solvent may greatly exceed that of propargyl al-
cohol. In order to confirm this point, the relevant experiment was
carried out. CO2 was charged into the cell to reach 3 MPa. Then, the
quantity of CO2 was determined via weighting after superfluous
CO2 was discharged from the cell. The result indicates that the
amount of CO2 dissolved in MeCN solvent is about 10 times as much
as that of propargyl alcohol. So the influence of CO2 pressure further
increasing from 3 to 5 MPa becomes negligible (Table 2, entries 4,
10, and 11). Based on the experimental results, 3 MPa of CO2
pressure appears to be more suitable for the electrosynthesis.
Table 1
Influence of electrode materials and solvent on the electrochemical cyclization of
a
propargyl alcohols with CO2
Entry
Cathode
Anode
Solvent
Yieldb (%)
1
2
3
4
5
6
7
8
9
Ni
Ni
Ni
Ni
Ni
Zn
Al
Al
DMF
DMF
DMF
THF
MeCN
MeCN
MeCN
MeCN
MeCN
0
0
Zn
Cu
Cu
Cu
Cu
Cu
Cu
Cu
30
76
86
45
50
59
80
Cu
Ag
a
Electrolytic conditions: room temperature, propargyl alcohol 0.1 mol Lꢀ1, sol-
vent (35 mL), n-Bu4NBr (3.5 mmol), current density 10 mA cmꢀ1, CO2 3 MPa and
electricity 4 F molꢀ1
.
b
Isolated yield based on the starting propargyl alcohols (3.5 mmol).
In addition, the influence of different cathodes (Zn, Al, Cu, and Ag)
was carefully studied, under the same experimental conditions (Cu
anode, 35 mL of MeCN, 2.5 mmol of n-Bu4NBr, 0.1 mol Lꢀ1 of prop-
argyl alcohols, 10 mA cmꢀ2 of current density, 3 MPa of CO2, and
4 F molꢀ1 of electricity, room temperature), and the results are
summarized in Table 1. Indeed, the nature of cathode materials has
a great impact on the yield of 2a. The use of Zn, Al, and Cu cathodes
gave 2a in moderate yields (45%, 50%, and 59%, respectively, Table 1,
entries 6e8), together with the formation of byproduct allyl alcohol
(20e30%). Among the examined cathodes, Ni and Ag cathodes ex-
hibit better results (86% and 80%, respectively, Table 1, entries 5 and
9), only the trace of byproduct allyl alcohol detected by GCeMS. The
nature of cathode materials may affect the reduction of propargyl
alcohols.
2.3. Electrochemical cyclization of other propargyl alcohols
with CO2
Based on the above investigations, the optimal conditions of the
electrochemical cyclization for propargyl alcohols with CO2 are
summarized as follows: Ni as the cathode and Cu as the anode, n-
Bu4NBreMeCN as the electrolyte, concentration of substrate
0.2 mol Lꢀ1, CO2 pressure at 3 MPa, and electricity at 4 F molꢀ1
.
Under the optimized reaction conditions, the electrochemical
route is extended to examine the cyclization reaction of other
propargyl alcohols (1bei) with CO2. The obtained results were col-
lected in Table 3. When tertiary propargyl alcohols (1beg) were
employed as substrates, such as aliphatic-substituted alcohols,

G.-Q. Yuan et al. / Tetrahedron 66 (2010) 9981e9985
9983
2-methylbut-3-yn-2-ol, 3-methylpent-1-yn-3-ol, 3,5-dimethylhex-
1-yn-3-ol, 3-methylnon-1-yn-3-ol or five- or six-member-ring-
substituted propargyl alcohols, the corresponding cyclic carbonates
could be obtained in excellent yields (85e93%, Table 3, entries 1e7).
The electrolysis with secondary propargylic alcohols 1h in contrast
to the tertiary propargyl alcohols gave the corresponding cyclic
carbonate products 2h in slightly decreasing yield (75%, Table 3,
entry 8). It should be noted that when primary propargylic alcohol
was used as substrate, the target product was not formed (Table 3,
entry 9), and the internal propargyl alcohols afforded the corre-
sponding products only in low yields (5e20%, Table 3, entries 10 and
11). The results suggest that the present electrochemical route could
be specific to secondary and tertiary terminal propargylic alcohols.
Table 3
a
Electrochemical cyclization of propargyl alcohols with CO2
Entry
Substrate
Product
Yieldb (%)
O
HO
O
O
1
92
Ph
1a
2a
O
O
2
3
92
93
O
OH
1b
2b
2.4. Electrochemical reaction mechanism
O
OH
According to the mentioned above results, Al or Zn as the sac-
rificial anode is not feasible at all for the cyclization process of
propargyl alcohols with CO2 (Table 1, entries 1 and 2). Only when
Cu was used as the sacrificial anode, the cyclization process could
be smoothly carried out. We deduced that the Cu metal ions gen-
erated at the anode may act as the catalytic role for the cyclization
process. It is well known that Cu as the sacrificial anode is able to
produce Cu2þ or Cuþ ions (i.e., Cu/Cu2þþ2eꢀ or Cu/Cuþþeꢀ). In
the present system, which Cu metal ions can promote the cycliza-
tion reaction, Cu2þ or Cuþ ions? In order to better understand the
electrocatalyzed cyclization process of propargyl alcohols with CO2,
we further examined the reaction with CuBr or CuBr2 as additive,
and the obtained results are listed in the Table 4. Moreover, an inert
carbon electrode was chosen as the anode to replace Cu electrode in
order to avoid the interference from the metal ions electro-
generated at anode. When the CuBr (copper(I) salt) was added into
the electrolytic system, the cyclic carbonate could be obtained
(Table 4, entry 1). However, the addition of CuBr2 (copper(II) salt)
does not activate the cyclization reaction at all (Table 4, entry 2).
Thus, it could be inferred that the Cuþ ions generated at the Cu
anode catalyzed the cyclization reaction instead of Cu2þ ions in the
present electrolytic system. Besides, in contrast to the solvent DMF
(Table 1, entry 3), it could be deduced that the high activity of the
Cu(I) ion generated in situ is most probably due to the complex
effect of the copper(I) cations with solvent MeCN38 or THF.39
O
O
1c
2c
O
O
O
4
5
6
90
88
85
86
OH
1d
2d
O
OH
O
O
4
1e
4
2e
O
HO
O
O
O
1f
2f
O
HO
O
7
8
1g
2g
O
OH
Table 4
O
O
75
3
Influence of other parameters on the electrochemical cyclization of propargyl
a
alcohols with CO2
3
1h
2h
Entry
Anode
Additive
Conducting salt
Yieldb (%)
O
1
2
3
4
5
6
C
C
d
Cu
Cu
d
CuBr
CuBr2
CuBr
d
n-Bu4NBr
n-Bu4NBr
n-Bu4NBr
KBr
LiClO4
d
14
0
O
OH
0c
0
O
9
0
1i
d
0
2i
CuBr, Bu3N
27d
O
a
Electrolytic conditions: room temperature, Ni cathode, propargyl alcohols
0.1 mol Lꢀ1, MeCN (35 mL), conducting salt (3.5 mmol), additive (4 equiv), current
O
10
20c
Py
N
O
OH
OH
density 10 mA cmꢀ2, CO2 3 MPa and electricity 4 F molꢀ1
.
1j
b
2j
Determined by GCeMS.
Without electric current passing through the cell.
Without electric current passing through the cell.
c
O
d
O
11
5d
Ph
O
1k
2k
The formation of Cu(I) ions during the electrolysis is supported
by the literature and our experimental results. For example, in the
electrolytic system containing halogen ions (Clꢀ, Brꢀ, and Iꢀ), the
oxidation of Cu anode could produce cuprous precipitates or
complexes.40 In our experiments, it was observed that a red deposit
was formed when the distilled water was added to the solution
after electrolyzed. The red deposit was proved to be metal copper,
a
Electrolytic conditions: room temperature, Ni cathode, Cu anode, propargyl al-
cohols 0.2 mol Lꢀ1
, MeCN (35 mL), n-Bu4NBr (3.5 mmol), current density
10 mA cmꢀ2, CO2 3 MPa and electricity 4 F molꢀ1
.
b
Isolated yield based on the starting propargyl alcohols (7.0 mmol).
Determined by GCeMS.
c
d
Determined by GCeMS.

9984
G.-Q. Yuan et al. / Tetrahedron 66 (2010) 9981e9985
which resulted from the disproportionation of Cu(I) ions in the
aqueous solution (i.e., Cuþ/CuþCu2þ). The experimental result
confirms the existence of Cu(I) ions in the present electrolytic
system.
produce a carbamate anion intermediate B. Simultaneously the
sacrificial copper anode is continuously oxidized to form complexes
of copper(I) with MeCN tentatively represented as [Cu(MeCN)4]
Br,38 which could activate a intramolecular ring-closing reaction
taking place on the alkyne, to afford the corresponding cyclic car-
bonate with the release of the Cu(I) catalyst.
It was worthy to note that the cyclization reaction did not take
place without electric current passing through the cell even in the
presence of CuBr catalyst (Table 4, entry 3). This result indicates
that the electrochemical activation is necessary for the cyclization
reaction under the present conditions. In addition, if LiClO4 or KBr
(instead of a R4Nþ salt) was used as supporting electrolyte, the
electrolysis could also not afford the corresponding products
(Table 4, entries 4 and 5). The result shows that n-Bu4NBr not only
conduces to the electric conduction but also promotes the forma-
tion of the corresponding cyclic carbonate. Based on the published
work,41e43 the electrochemical reduction of tetraalkylammonium
cations R4Nþ at the cathode can generate a trialkylamine R3N and
alkyl radical Rꢁ (R4Nþþeꢀ/R4Nꢁ, R4Nꢁ/RꢁþR3N). In the present
system, since the Brꢀ ions of Bu4NBr could react with the Cu(I) ions
generated at the anode to form CuBr precipitates or complexes, the
reduction of the corresponding Bu4Nþ ions becomes feasible. Our
experimental results (GCeMS analysis) have confirmed the for-
mation of Bu3N. The formed Bu3N could activate propargyl alcohols,
then could react with carbon dioxide to generate a carbonate in-
termediate.5,6 In addition, it should be noted that the cyclization
reaction could only afford the cyclic carbonate in 27% yield (Table 4,
entry 6) without electric current although the addition amount of
CuBr and Bu3N reached four equivalence of propargyl alcohol. This
means that another key factor should further be considered for the
activation of propargyl alcohols. As proposed in the literatures,41e43
the alkyl radical Rꢁ resulted from the electrochemical reduction of
R4Nþ cations could further be electroreduced to an alkyl anion Rꢀ
(R$þeꢀ/Rꢀ). Compared with Bu3N, Rꢀ alkyl anions have higher
reactivity and stronger basicity. Thus, Rꢀ alkyl anions more easily
deprotonate the OH group of propargyl alcohol to give an active
intermediate. The Rꢀ alkyl anions may play a key role in the acti-
vation of propargyl alcohols. Since the concentration of the elec-
trogenerated Rꢀ alkyl anions is affected by the electricity supplied
to the electrodes, the yield of cyclic carbonate (2a) increases with
increasing electricity (Table 2, entries 1e4).
3. Experimental section for electrosynthesis of cyclic
carbonates from propargyl alcohols and CO2
3.1. General methods
The electrolytic cell is the same as that reported previously.36
Before the electrosynthesis, the anode and cathode were cleaned
with detergent and diluted hydrochloric acid, followed by washing
with distilled water, and then dried. In a typical experiment, dried
acetonitrile solvent (35 mL), propargyl alcohols (3.5 mmol), and n-
Bu4NBr (3.5 mmol) were added to the cell in turn, followed by
charging of CO2 into the desired pressure. The electrosynthesis was
carried out in the high-pressure stainless-steel undivided cell fitted
with a nickel sheet cathode (wet surface area 6 cm2) and a copper
sheet anode (wet surface area 6 cm2) at a suitable constant current,
under a continuously stirring condition. The electrolysis was ended
after electricity 4 F molꢀ1 of starting substrate was passed through
the cell at room temperature. The electrolyte solution was mixed
with distilled water (35 mL) and then extracted with (25 mLꢂ4)
diethyl ether. The ether phase was washed three times with dis-
tilled water, and dried over anhydrous MgSO4. After evaporation of
ether, the obtained yellow crude product was dried in vacuum oven
at 40 ꢃC and purified by chromatography on a silica gel column
using light petroleum ethereethyl acetate as eluent.
The obtained products were characterized by FTIR, 1H NMR, and
mass spectra. FTIR spectra were measured by a TENSOR27 spec-
trometer. NMR spectra were recorded with a Bruker DRX-400
spectrometer using CDCl3 as the solvent and TMS as the internal
standard. Mass spectra were recorded with a Shimadzu GC-MS-
QP5050A spectrometer.
3.1.1. 4-Methyl-5-methylene-4-phenyl-1,3-dioxolan-2-one (2a). IR
(neat): 1820 (C]O), 1684 (C]C) cmꢀ1. 1H NMR (CDCl3, 400 MHz):
Based on the above-mentioned experimental results and anal-
yses as well as literatures,5,6 a plausible mechanism for the elec-
trochemical incorporation of carbon dioxide into propargylic
alcohols is outlined in Scheme 2. During the electrolysis, tetrabu-
tylammonium cations R4Nþ on the surface of a nickel cathode first
gets electrons to form tributylamine R3N and the alkyl radical Rꢁ.
Then, the alkyl radical Rꢁ further gets electrons to form alkyl anion
Rꢀ. R3N, especially alkyl anion Rꢀ, has enough strong basicity to
deprotonate the OH group of propargyl alcohol to generate an in-
termediate A, followed by the reaction with carbon dioxide to
d
7.475e7.366 (m, 5H), 4.93 (d, J¼4 Hz,1H), 4.45 (d, J¼4 Hz,1H), 1.95
(d, J¼4 Hz, 3H). GCeMS: m/z (%)¼190 (2) (Mþ), 146 (6), 131 (14), 117
(100), 103 (36), 51 (15).
3.1.2. 4,4-Dimethyl-5-methylene-1,3-dioxolan-2-one (2b). IR(neat):
1837 (C]O),1640 (C]C) cmꢀ1. 1H NMR (CDCl3, 400 MHz):
d¼4.78
(d, J¼4 Hz, 1H), 4.31 (d, J¼4 Hz, 1H), 1.61 (s, 6H). GCeMS: m/z (%)¼
128 (4) (Mþ), 84 (27), 56 (72), 41 (100).
3.1.3. 4-Ethyl-4-methyl-5-methylene-1,3-dioxolan-2-one
(2c). IR
(neat): 1832 (C]O),1687 (C]C) cmꢀ1. 1H NMR (CDCl3, 400 MHz):
R2
d
¼4.82 (s, 1H), 4.27 (s, 1H), 1.94e1.89 (m, 1H), 1.79e1.74 (m, 1H),
O
R1
1.59 (s, 3H), 0.99 (t, J¼7.2, 3H). 13C NMR (CDCl3, 100 MHz):
d 157.5,
O
H
O
151.6, 87.6, 85.6, 33.4, 26.0, 7.4. GCeMS: m/z (%)¼142 (1) (Mþ), 97
protonolysis
O
R2
O
O
R1
H
(2), 70 (6), 56 (100).
R4N+
O
H
O
Cu
- e-
O
R2
R1
Cu(I)
+ e-
R
3.1.4. 4-Isobutyl-4-methyl-5-methylene-1,3-dioxolan-2-one (2d). IR
(neat): 1831 (C]O),1685 (C]C) cmꢀ1. 1H NMR (CDCl3, 400 MHz):
+ e-
R
a
Cu(I)
d
¼4.76 (d, J¼4 Hz, 1H), 4.25 (d, J¼4 Hz, 1H), 1.82e1.75 (m, 2H),
MeCN
Br-
R3N
+
R1
O
R2
A
Cu
R1
R2
O
C O
1.66e1.61 (m, 1H), 1.54 (s, 3H), 0.95e0.92 (m, 6H). GCeMS: m/z
(%)¼171 (2) (Mþ), 126 (5), 111 (28), 84 (47), 69 (100), 43 (41).
a
b
O
B
Cu
Ni
3.1.5. 4-Hexyl-4-methyl-5-methylene-1,3-dioxolan-2-one
(2e). IR
R1
OH
R2
(neat): 1830 (C]O),1685 (C]C) cmꢀ1. 1H NMR (400 MHz, CDCl3):
b:
a:
CO2
d
¼4.79 (s, 1H), 4.28 (s, 1H), 1.89e1.83 (m, 1H), 1.74e1.67 (m, 1H),
1.58 (s, 3H), 1.39e1.28 (m, 8H), 0.87 (d, J¼6.4 Hz, 3H). 13C NMR
Scheme 2. Proposed mechanism for CO2 incorporation into propargylic alcohols.

G.-Q. Yuan et al. / Tetrahedron 66 (2010) 9981e9985
9985
(CDCl3, 100 MHz):
d
157.9, 151.5, 87.2, 85.2, 40.6, 31.4, 29.0, 26.3,
References and notes
22.9, 22.4, 13.8. GCeMS: m/z (%)¼199 (2) (Mþ), 155 (6), 111 (49), 83
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ꢀ
~
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~
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In conclusion, with nickel as the cathode and Cu as the anode
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Acknowledgements
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The authors thank National Natural Science Foundation of China
(No. 20332030, 20572027, 20625205, and20772034)andtheScience
& Technology planning Project Foundation of Guangdong Province
(Grant 2007B010600041) for the financial support of this work
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Supplementary data
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Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.tet.2010.10.039.